From 4577e7e29728c7ff98b9f88dc7ec7928da1132b9 Mon Sep 17 00:00:00 2001
From: Markus Gasser <markus.gasser@mailbox.org>
Date: Sun, 27 Aug 2023 18:52:33 +0200
Subject: [PATCH 01/24] Add api for UserLanguage

Include example showing basic usage
---
 axum-extra/src/extract/mod.rs       |  6 ++++-
 axum-extra/src/extract/user_lang.rs | 40 +++++++++++++++++++++++++++++
 examples/user-language/Cargo.toml   | 10 ++++++++
 examples/user-language/src/main.rs  | 37 ++++++++++++++++++++++++++
 4 files changed, 92 insertions(+), 1 deletion(-)
 create mode 100644 axum-extra/src/extract/user_lang.rs
 create mode 100644 examples/user-language/Cargo.toml
 create mode 100644 examples/user-language/src/main.rs

diff --git a/axum-extra/src/extract/mod.rs b/axum-extra/src/extract/mod.rs
index c7946413a8..9d47a19276 100644
--- a/axum-extra/src/extract/mod.rs
+++ b/axum-extra/src/extract/mod.rs
@@ -2,6 +2,7 @@
 
 mod cached;
 mod optional_path;
+mod user_lang;
 mod with_rejection;
 
 #[cfg(feature = "form")]
@@ -16,7 +17,10 @@ mod query;
 #[cfg(feature = "multipart")]
 pub mod multipart;
 
-pub use self::{cached::Cached, optional_path::OptionalPath, with_rejection::WithRejection};
+pub use self::{
+    cached::Cached, optional_path::OptionalPath, user_lang::UserLanguage,
+    with_rejection::WithRejection,
+};
 
 #[cfg(feature = "cookie")]
 pub use self::cookie::CookieJar;
diff --git a/axum-extra/src/extract/user_lang.rs b/axum-extra/src/extract/user_lang.rs
new file mode 100644
index 0000000000..bfb8145e4d
--- /dev/null
+++ b/axum-extra/src/extract/user_lang.rs
@@ -0,0 +1,40 @@
+use axum::{async_trait, extract::FromRequestParts};
+use http::request::Parts;
+
+/// TBD
+#[derive(Debug, Clone)]
+pub struct UserLanguage {
+    preferred_languages: Vec<String>,
+    fallback_language: String,
+}
+
+impl UserLanguage {
+    /// TBD
+    pub fn preferred_language(&self) -> &str {
+        self.preferred_languages
+            .first()
+            .unwrap_or(&self.fallback_language)
+    }
+
+    /// TBD
+    pub fn preferred_languages(&self) -> &[String] {
+        self.preferred_languages.as_slice()
+    }
+
+    /// TBD
+    pub fn fallback_language(&self) -> &str {
+        &self.fallback_language
+    }
+}
+
+#[async_trait]
+impl<S> FromRequestParts<S> for UserLanguage
+where
+    S: Send + Sync,
+{
+    type Rejection = ();
+
+    async fn from_request_parts(_parts: &mut Parts, _state: &S) -> Result<Self, Self::Rejection> {
+        todo!()
+    }
+}
diff --git a/examples/user-language/Cargo.toml b/examples/user-language/Cargo.toml
new file mode 100644
index 0000000000..000e3604fd
--- /dev/null
+++ b/examples/user-language/Cargo.toml
@@ -0,0 +1,10 @@
+[package]
+name = "example-user-language"
+version = "0.1.0"
+edition = "2021"
+publish = false
+
+[dependencies]
+axum = { path = "../../axum" }
+axum-extra = { path = "../../axum-extra" }
+tokio = { version = "1.0", features = ["full"] }
diff --git a/examples/user-language/src/main.rs b/examples/user-language/src/main.rs
new file mode 100644
index 0000000000..65542b0c39
--- /dev/null
+++ b/examples/user-language/src/main.rs
@@ -0,0 +1,37 @@
+//! Run with
+//!
+//! ```not_rust
+//! cargo run -p example-user-language
+//! ```
+
+use axum::{response::Html, routing::get, Router};
+use axum_extra::extract::UserLanguage;
+
+#[tokio::main]
+async fn main() {
+    // build our application with a route
+    let app = Router::new()
+        .route("/", get(handler))
+        .route("/:lang", get(handler));
+
+    // run it
+    let listener = tokio::net::TcpListener::bind("127.0.0.1:3000")
+        .await
+        .unwrap();
+    println!("listening on {}", listener.local_addr().unwrap());
+    axum::serve(listener, app).await.unwrap();
+}
+
+async fn handler(lang: UserLanguage) -> Html<&'static str> {
+    println!(
+        "User prefers content in the following languages (in order): {:?}",
+        lang.preferred_languages()
+    );
+
+    match lang.preferred_language() {
+        "de" => Html("<h1>Hallo, Welt!</h1>"),
+        "es" => Html("<h1>Hola, Mundo!</h1>"),
+        "fr" => Html("<h1>Bonjour, le monde!</h1>"),
+        _ => Html("<h1>Hello, World!</h1>"),
+    }
+}

From 2eb08a17afe8fca6655a1a6cd6e216c486162fba Mon Sep 17 00:00:00 2001
From: Markus Gasser <markus.gasser@mailbox.org>
Date: Sun, 27 Aug 2023 19:07:26 +0000
Subject: [PATCH 02/24] Add a first implementation to read user language

---
 axum-extra/src/extract/user_lang.rs | 67 +++++++++++++++++++++++++++--
 1 file changed, 63 insertions(+), 4 deletions(-)

diff --git a/axum-extra/src/extract/user_lang.rs b/axum-extra/src/extract/user_lang.rs
index bfb8145e4d..ca17944fdb 100644
--- a/axum-extra/src/extract/user_lang.rs
+++ b/axum-extra/src/extract/user_lang.rs
@@ -1,5 +1,10 @@
-use axum::{async_trait, extract::FromRequestParts};
+use axum::{
+    async_trait,
+    extract::{FromRequestParts, Path, Query},
+    RequestPartsExt,
+};
 use http::request::Parts;
+use std::{cmp::Ordering, collections::HashMap, convert::Infallible};
 
 /// TBD
 #[derive(Debug, Clone)]
@@ -32,9 +37,63 @@ impl<S> FromRequestParts<S> for UserLanguage
 where
     S: Send + Sync,
 {
-    type Rejection = ();
+    type Rejection = Infallible;
 
-    async fn from_request_parts(_parts: &mut Parts, _state: &S) -> Result<Self, Self::Rejection> {
-        todo!()
+    async fn from_request_parts(parts: &mut Parts, _state: &S) -> Result<Self, Self::Rejection> {
+        let mut preferred_languages = Vec::<String>::new();
+
+        // First try to get the language from the query string
+        if let Ok(query) = parts.extract::<Query<HashMap<String, String>>>().await {
+            if let Some(lang) = query.get("lang") {
+                preferred_languages.push(lang.to_string());
+            }
+        };
+
+        // Then try to get the language from the path
+        if let Ok(path) = parts.extract::<Path<HashMap<String, String>>>().await {
+            if let Some(lang) = path.get("lang") {
+                preferred_languages.push(lang.to_string());
+            }
+        };
+
+        // Then try to get the language from the Accept-Language header
+        if let Some(accept_language) = parts.headers.get("Accept-Language") {
+            if let Ok(accept_language) = accept_language.to_str() {
+                for (lang, _) in parse_quality_values(accept_language) {
+                    preferred_languages.push(lang.to_string());
+                }
+            }
+        }
+
+        Ok(UserLanguage {
+            preferred_languages,
+            fallback_language: "en".to_string(),
+        })
+    }
+}
+
+fn parse_quality_values(values: &str) -> Vec<(&str, f32)> {
+    let mut values = values.split(',');
+    let mut quality_values = Vec::new();
+
+    while let Some(value) = values.next() {
+        let mut value = value.trim().split(';');
+        let (value, quality) = (value.next(), value.next());
+
+        let Some(value) = value else {
+            // empty quality value entry
+            continue;
+        };
+
+        let quality = if let Some(quality) = quality.and_then(|q| q.strip_prefix("q=")) {
+            quality.parse::<f32>().unwrap_or(0.0)
+        } else {
+            1.0
+        };
+
+        quality_values.push((value, quality));
     }
+
+    quality_values.sort_by(|a, b| b.1.partial_cmp(&a.1).unwrap_or(Ordering::Equal));
+    quality_values
 }

From ca79cfba21400191e865c41debd69ad524a8174f Mon Sep 17 00:00:00 2001
From: Markus Gasser <markus.gasser@mailbox.org>
Date: Sun, 27 Aug 2023 19:43:34 +0000
Subject: [PATCH 03/24] Extract user lang sources

---
 axum-extra/src/extract/mod.rs                 |  4 +-
 axum-extra/src/extract/user_lang.rs           | 99 -------------------
 axum-extra/src/extract/user_lang/lang.rs      | 69 +++++++++++++
 axum-extra/src/extract/user_lang/mod.rs       |  8 ++
 axum-extra/src/extract/user_lang/source.rs    |  9 ++
 .../src/extract/user_lang/sources/header.rs   | 56 +++++++++++
 .../src/extract/user_lang/sources/mod.rs      |  7 ++
 .../src/extract/user_lang/sources/path.rs     | 36 +++++++
 .../src/extract/user_lang/sources/query.rs    | 36 +++++++
 9 files changed, 224 insertions(+), 100 deletions(-)
 delete mode 100644 axum-extra/src/extract/user_lang.rs
 create mode 100644 axum-extra/src/extract/user_lang/lang.rs
 create mode 100644 axum-extra/src/extract/user_lang/mod.rs
 create mode 100644 axum-extra/src/extract/user_lang/source.rs
 create mode 100644 axum-extra/src/extract/user_lang/sources/header.rs
 create mode 100644 axum-extra/src/extract/user_lang/sources/mod.rs
 create mode 100644 axum-extra/src/extract/user_lang/sources/path.rs
 create mode 100644 axum-extra/src/extract/user_lang/sources/query.rs

diff --git a/axum-extra/src/extract/mod.rs b/axum-extra/src/extract/mod.rs
index 9d47a19276..0889517dba 100644
--- a/axum-extra/src/extract/mod.rs
+++ b/axum-extra/src/extract/mod.rs
@@ -18,7 +18,9 @@ mod query;
 pub mod multipart;
 
 pub use self::{
-    cached::Cached, optional_path::OptionalPath, user_lang::UserLanguage,
+    cached::Cached,
+    optional_path::OptionalPath,
+    user_lang::{sources, UserLanguage, UserLanguageSource},
     with_rejection::WithRejection,
 };
 
diff --git a/axum-extra/src/extract/user_lang.rs b/axum-extra/src/extract/user_lang.rs
deleted file mode 100644
index ca17944fdb..0000000000
--- a/axum-extra/src/extract/user_lang.rs
+++ /dev/null
@@ -1,99 +0,0 @@
-use axum::{
-    async_trait,
-    extract::{FromRequestParts, Path, Query},
-    RequestPartsExt,
-};
-use http::request::Parts;
-use std::{cmp::Ordering, collections::HashMap, convert::Infallible};
-
-/// TBD
-#[derive(Debug, Clone)]
-pub struct UserLanguage {
-    preferred_languages: Vec<String>,
-    fallback_language: String,
-}
-
-impl UserLanguage {
-    /// TBD
-    pub fn preferred_language(&self) -> &str {
-        self.preferred_languages
-            .first()
-            .unwrap_or(&self.fallback_language)
-    }
-
-    /// TBD
-    pub fn preferred_languages(&self) -> &[String] {
-        self.preferred_languages.as_slice()
-    }
-
-    /// TBD
-    pub fn fallback_language(&self) -> &str {
-        &self.fallback_language
-    }
-}
-
-#[async_trait]
-impl<S> FromRequestParts<S> for UserLanguage
-where
-    S: Send + Sync,
-{
-    type Rejection = Infallible;
-
-    async fn from_request_parts(parts: &mut Parts, _state: &S) -> Result<Self, Self::Rejection> {
-        let mut preferred_languages = Vec::<String>::new();
-
-        // First try to get the language from the query string
-        if let Ok(query) = parts.extract::<Query<HashMap<String, String>>>().await {
-            if let Some(lang) = query.get("lang") {
-                preferred_languages.push(lang.to_string());
-            }
-        };
-
-        // Then try to get the language from the path
-        if let Ok(path) = parts.extract::<Path<HashMap<String, String>>>().await {
-            if let Some(lang) = path.get("lang") {
-                preferred_languages.push(lang.to_string());
-            }
-        };
-
-        // Then try to get the language from the Accept-Language header
-        if let Some(accept_language) = parts.headers.get("Accept-Language") {
-            if let Ok(accept_language) = accept_language.to_str() {
-                for (lang, _) in parse_quality_values(accept_language) {
-                    preferred_languages.push(lang.to_string());
-                }
-            }
-        }
-
-        Ok(UserLanguage {
-            preferred_languages,
-            fallback_language: "en".to_string(),
-        })
-    }
-}
-
-fn parse_quality_values(values: &str) -> Vec<(&str, f32)> {
-    let mut values = values.split(',');
-    let mut quality_values = Vec::new();
-
-    while let Some(value) = values.next() {
-        let mut value = value.trim().split(';');
-        let (value, quality) = (value.next(), value.next());
-
-        let Some(value) = value else {
-            // empty quality value entry
-            continue;
-        };
-
-        let quality = if let Some(quality) = quality.and_then(|q| q.strip_prefix("q=")) {
-            quality.parse::<f32>().unwrap_or(0.0)
-        } else {
-            1.0
-        };
-
-        quality_values.push((value, quality));
-    }
-
-    quality_values.sort_by(|a, b| b.1.partial_cmp(&a.1).unwrap_or(Ordering::Equal));
-    quality_values
-}
diff --git a/axum-extra/src/extract/user_lang/lang.rs b/axum-extra/src/extract/user_lang/lang.rs
new file mode 100644
index 0000000000..d3d8952b18
--- /dev/null
+++ b/axum-extra/src/extract/user_lang/lang.rs
@@ -0,0 +1,69 @@
+use super::{
+    sources::{AcceptLanguageSource, PathSource, QuerySource},
+    UserLanguageSource,
+};
+use axum::{async_trait, extract::FromRequestParts};
+use http::request::Parts;
+use std::convert::Infallible;
+
+/// TBD
+#[derive(Debug, Clone)]
+pub struct UserLanguage {
+    preferred_languages: Vec<String>,
+    fallback_language: String,
+}
+
+impl UserLanguage {
+    /// TBD
+    pub fn default_sources<S>() -> Vec<Box<dyn UserLanguageSource<S>>>
+    where
+        S: Send + Sync,
+    {
+        vec![
+            Box::new(QuerySource::new("lang")),
+            Box::new(PathSource::new("lang")),
+            Box::new(AcceptLanguageSource),
+        ]
+    }
+
+    /// TBD
+    pub fn preferred_language(&self) -> &str {
+        self.preferred_languages
+            .first()
+            .unwrap_or(&self.fallback_language)
+    }
+
+    /// TBD
+    pub fn preferred_languages(&self) -> &[String] {
+        self.preferred_languages.as_slice()
+    }
+
+    /// TBD
+    pub fn fallback_language(&self) -> &str {
+        &self.fallback_language
+    }
+}
+
+#[async_trait]
+impl<S> FromRequestParts<S> for UserLanguage
+where
+    S: Send + Sync,
+{
+    type Rejection = Infallible;
+
+    async fn from_request_parts(parts: &mut Parts, state: &S) -> Result<Self, Self::Rejection> {
+        let sources = Self::default_sources::<S>();
+
+        let mut preferred_languages = Vec::<String>::new();
+
+        for source in sources {
+            let languages = source.languages_from_parts(parts, state).await;
+            preferred_languages.extend(languages);
+        }
+
+        Ok(UserLanguage {
+            preferred_languages,
+            fallback_language: "en".to_string(),
+        })
+    }
+}
diff --git a/axum-extra/src/extract/user_lang/mod.rs b/axum-extra/src/extract/user_lang/mod.rs
new file mode 100644
index 0000000000..1343006d05
--- /dev/null
+++ b/axum-extra/src/extract/user_lang/mod.rs
@@ -0,0 +1,8 @@
+mod lang;
+mod source;
+
+/// TBD
+pub mod sources;
+
+pub use lang::*;
+pub use source::*;
diff --git a/axum-extra/src/extract/user_lang/source.rs b/axum-extra/src/extract/user_lang/source.rs
new file mode 100644
index 0000000000..adee1f6e3f
--- /dev/null
+++ b/axum-extra/src/extract/user_lang/source.rs
@@ -0,0 +1,9 @@
+use axum::async_trait;
+use http::request::Parts;
+
+/// TBD
+#[async_trait]
+pub trait UserLanguageSource<S>: Send + Sync {
+    /// TBD
+    async fn languages_from_parts(&self, parts: &mut Parts, state: &S) -> Vec<String>;
+}
diff --git a/axum-extra/src/extract/user_lang/sources/header.rs b/axum-extra/src/extract/user_lang/sources/header.rs
new file mode 100644
index 0000000000..1ce5a504ea
--- /dev/null
+++ b/axum-extra/src/extract/user_lang/sources/header.rs
@@ -0,0 +1,56 @@
+use std::cmp::Ordering;
+
+use crate::extract::UserLanguageSource;
+use axum::async_trait;
+
+/// TBD
+#[derive(Debug, Clone)]
+pub struct AcceptLanguageSource;
+
+#[async_trait]
+impl<S> UserLanguageSource<S> for AcceptLanguageSource {
+    async fn languages_from_parts(
+        &self,
+        parts: &mut http::request::Parts,
+        _state: &S,
+    ) -> Vec<String> {
+        let Some(accept_language) = parts.headers.get("Accept-Language") else {
+            return vec![];
+        };
+
+        let Ok(accept_language) = accept_language.to_str() else {
+            return vec![];
+        };
+
+        parse_quality_values(accept_language)
+            .into_iter()
+            .map(|(lang, _)| lang.to_string())
+            .collect()
+    }
+}
+
+fn parse_quality_values(values: &str) -> Vec<(&str, f32)> {
+    let mut values = values.split(',');
+    let mut quality_values = Vec::new();
+
+    while let Some(value) = values.next() {
+        let mut value = value.trim().split(';');
+        let (value, quality) = (value.next(), value.next());
+
+        let Some(value) = value else {
+            // empty quality value entry
+            continue;
+        };
+
+        let quality = if let Some(quality) = quality.and_then(|q| q.strip_prefix("q=")) {
+            quality.parse::<f32>().unwrap_or(0.0)
+        } else {
+            1.0
+        };
+
+        quality_values.push((value, quality));
+    }
+
+    quality_values.sort_by(|a, b| b.1.partial_cmp(&a.1).unwrap_or(Ordering::Equal));
+    quality_values
+}
diff --git a/axum-extra/src/extract/user_lang/sources/mod.rs b/axum-extra/src/extract/user_lang/sources/mod.rs
new file mode 100644
index 0000000000..b166f9a738
--- /dev/null
+++ b/axum-extra/src/extract/user_lang/sources/mod.rs
@@ -0,0 +1,7 @@
+mod header;
+mod path;
+mod query;
+
+pub use header::*;
+pub use path::*;
+pub use query::*;
diff --git a/axum-extra/src/extract/user_lang/sources/path.rs b/axum-extra/src/extract/user_lang/sources/path.rs
new file mode 100644
index 0000000000..7e751a677d
--- /dev/null
+++ b/axum-extra/src/extract/user_lang/sources/path.rs
@@ -0,0 +1,36 @@
+use crate::extract::UserLanguageSource;
+use axum::{async_trait, extract::Path, RequestPartsExt};
+use std::collections::HashMap;
+
+/// TBD
+#[derive(Debug, Clone)]
+pub struct PathSource {
+    /// TBD
+    name: String,
+}
+
+impl PathSource {
+    /// TBD
+    pub fn new(name: impl Into<String>) -> Self {
+        Self { name: name.into() }
+    }
+}
+
+#[async_trait]
+impl<S> UserLanguageSource<S> for PathSource {
+    async fn languages_from_parts(
+        &self,
+        parts: &mut http::request::Parts,
+        _state: &S,
+    ) -> Vec<String> {
+        let Ok(path) = parts.extract::<Path<HashMap<String, String>>>().await else {
+            return vec![];
+        };
+
+        let Some(lang) = path.get(self.name.as_str()) else {
+            return vec![];
+        };
+
+        vec![lang.to_string()]
+    }
+}
diff --git a/axum-extra/src/extract/user_lang/sources/query.rs b/axum-extra/src/extract/user_lang/sources/query.rs
new file mode 100644
index 0000000000..e74c119394
--- /dev/null
+++ b/axum-extra/src/extract/user_lang/sources/query.rs
@@ -0,0 +1,36 @@
+use crate::extract::UserLanguageSource;
+use axum::{async_trait, extract::Query, RequestPartsExt};
+use std::collections::HashMap;
+
+/// TBD
+#[derive(Debug, Clone)]
+pub struct QuerySource {
+    /// TBD
+    name: String,
+}
+
+impl QuerySource {
+    /// TBD
+    pub fn new(name: impl Into<String>) -> Self {
+        Self { name: name.into() }
+    }
+}
+
+#[async_trait]
+impl<S> UserLanguageSource<S> for QuerySource {
+    async fn languages_from_parts(
+        &self,
+        parts: &mut http::request::Parts,
+        _state: &S,
+    ) -> Vec<String> {
+        let Ok(query) = parts.extract::<Query<HashMap<String, String>>>().await else {
+            return vec![];
+        };
+
+        let Some(lang) = query.get(self.name.as_str()) else {
+            return vec![];
+        };
+
+        vec![lang.to_string()]
+    }
+}

From e2c538b5955e42cd960301c14313736c6b18a9ec Mon Sep 17 00:00:00 2001
From: Markus Gasser <markus.gasser@mailbox.org>
Date: Sun, 27 Aug 2023 20:30:46 +0000
Subject: [PATCH 04/24] Add possibility to configure

---
 axum-extra/src/extract/mod.rs                 |  2 +-
 axum-extra/src/extract/user_lang/config.rs    | 52 +++++++++++++++++++
 axum-extra/src/extract/user_lang/lang.rs      | 43 +++++++++------
 axum-extra/src/extract/user_lang/mod.rs       |  2 +
 axum-extra/src/extract/user_lang/source.rs    |  5 +-
 .../src/extract/user_lang/sources/header.rs   |  8 +--
 .../src/extract/user_lang/sources/path.rs     |  8 +--
 .../src/extract/user_lang/sources/query.rs    |  8 +--
 examples/user-language/src/main.rs            | 11 ++--
 9 files changed, 99 insertions(+), 40 deletions(-)
 create mode 100644 axum-extra/src/extract/user_lang/config.rs

diff --git a/axum-extra/src/extract/mod.rs b/axum-extra/src/extract/mod.rs
index 0889517dba..cdde256e19 100644
--- a/axum-extra/src/extract/mod.rs
+++ b/axum-extra/src/extract/mod.rs
@@ -20,7 +20,7 @@ pub mod multipart;
 pub use self::{
     cached::Cached,
     optional_path::OptionalPath,
-    user_lang::{sources, UserLanguage, UserLanguageSource},
+    user_lang::{sources, UserLanguage, UserLanguageConfig, UserLanguageSource},
     with_rejection::WithRejection,
 };
 
diff --git a/axum-extra/src/extract/user_lang/config.rs b/axum-extra/src/extract/user_lang/config.rs
new file mode 100644
index 0000000000..43e0e3980d
--- /dev/null
+++ b/axum-extra/src/extract/user_lang/config.rs
@@ -0,0 +1,52 @@
+use std::sync::Arc;
+
+use super::{UserLanguage, UserLanguageSource};
+
+/// TBD
+#[derive(Debug, Clone)]
+pub struct UserLanguageConfig {
+    /// TBD
+    pub fallback_language: String,
+
+    /// TBD
+    pub sources: Vec<Arc<dyn UserLanguageSource>>,
+}
+
+#[derive(Debug, Clone)]
+pub struct UserLanguageConfigBuilder {
+    fallback_language: String,
+    sources: Vec<Arc<dyn UserLanguageSource>>,
+}
+
+impl UserLanguageConfigBuilder {
+    pub fn fallback_language(mut self, fallback_language: impl Into<String>) -> Self {
+        self.fallback_language = fallback_language.into();
+        self
+    }
+
+    pub fn add_source(mut self, source: impl UserLanguageSource + 'static) -> Self {
+        self.sources.push(Arc::new(source));
+        self
+    }
+
+    pub fn build(self) -> UserLanguageConfig {
+        UserLanguageConfig {
+            fallback_language: self.fallback_language,
+            sources: if !self.sources.is_empty() {
+                self.sources
+            } else {
+                UserLanguage::default_sources().clone()
+            },
+        }
+    }
+}
+
+impl UserLanguage {
+    /// TBD
+    pub fn config() -> UserLanguageConfigBuilder {
+        UserLanguageConfigBuilder {
+            fallback_language: "en".to_string(),
+            sources: vec![],
+        }
+    }
+}
diff --git a/axum-extra/src/extract/user_lang/lang.rs b/axum-extra/src/extract/user_lang/lang.rs
index d3d8952b18..aeaeb3ad84 100644
--- a/axum-extra/src/extract/user_lang/lang.rs
+++ b/axum-extra/src/extract/user_lang/lang.rs
@@ -1,10 +1,13 @@
 use super::{
     sources::{AcceptLanguageSource, PathSource, QuerySource},
-    UserLanguageSource,
+    UserLanguageConfig, UserLanguageSource,
 };
-use axum::{async_trait, extract::FromRequestParts};
+use axum::{async_trait, extract::FromRequestParts, Extension, RequestPartsExt};
 use http::request::Parts;
-use std::convert::Infallible;
+use std::{
+    convert::Infallible,
+    sync::{Arc, OnceLock},
+};
 
 /// TBD
 #[derive(Debug, Clone)]
@@ -15,15 +18,16 @@ pub struct UserLanguage {
 
 impl UserLanguage {
     /// TBD
-    pub fn default_sources<S>() -> Vec<Box<dyn UserLanguageSource<S>>>
-    where
-        S: Send + Sync,
-    {
-        vec![
-            Box::new(QuerySource::new("lang")),
-            Box::new(PathSource::new("lang")),
-            Box::new(AcceptLanguageSource),
-        ]
+    pub fn default_sources() -> &'static Vec<Arc<dyn UserLanguageSource>> {
+        static DEFAULT_SOURCES: OnceLock<Vec<Arc<dyn UserLanguageSource>>> = OnceLock::new();
+
+        DEFAULT_SOURCES.get_or_init(|| {
+            vec![
+                Arc::new(QuerySource::new("lang")),
+                Arc::new(PathSource::new("lang")),
+                Arc::new(AcceptLanguageSource),
+            ]
+        })
     }
 
     /// TBD
@@ -51,19 +55,26 @@ where
 {
     type Rejection = Infallible;
 
-    async fn from_request_parts(parts: &mut Parts, state: &S) -> Result<Self, Self::Rejection> {
-        let sources = Self::default_sources::<S>();
+    async fn from_request_parts(parts: &mut Parts, _state: &S) -> Result<Self, Self::Rejection> {
+        let (sources, fallback_language) =
+            match parts.extract::<Extension<UserLanguageConfig>>().await {
+                Ok(Extension(config)) => (Some(config.sources), Some(config.fallback_language)),
+                Err(_) => (None, None),
+            };
+
+        let sources = sources.as_ref().unwrap_or(Self::default_sources());
+        let fallback_language = fallback_language.unwrap_or_else(|| "en".to_string());
 
         let mut preferred_languages = Vec::<String>::new();
 
         for source in sources {
-            let languages = source.languages_from_parts(parts, state).await;
+            let languages = source.languages_from_parts(parts).await;
             preferred_languages.extend(languages);
         }
 
         Ok(UserLanguage {
             preferred_languages,
-            fallback_language: "en".to_string(),
+            fallback_language,
         })
     }
 }
diff --git a/axum-extra/src/extract/user_lang/mod.rs b/axum-extra/src/extract/user_lang/mod.rs
index 1343006d05..db62a41306 100644
--- a/axum-extra/src/extract/user_lang/mod.rs
+++ b/axum-extra/src/extract/user_lang/mod.rs
@@ -1,8 +1,10 @@
+mod config;
 mod lang;
 mod source;
 
 /// TBD
 pub mod sources;
 
+pub use config::*;
 pub use lang::*;
 pub use source::*;
diff --git a/axum-extra/src/extract/user_lang/source.rs b/axum-extra/src/extract/user_lang/source.rs
index adee1f6e3f..32594fb9ca 100644
--- a/axum-extra/src/extract/user_lang/source.rs
+++ b/axum-extra/src/extract/user_lang/source.rs
@@ -1,9 +1,10 @@
 use axum::async_trait;
 use http::request::Parts;
+use std::fmt::Debug;
 
 /// TBD
 #[async_trait]
-pub trait UserLanguageSource<S>: Send + Sync {
+pub trait UserLanguageSource: Send + Sync + Debug {
     /// TBD
-    async fn languages_from_parts(&self, parts: &mut Parts, state: &S) -> Vec<String>;
+    async fn languages_from_parts(&self, parts: &mut Parts) -> Vec<String>;
 }
diff --git a/axum-extra/src/extract/user_lang/sources/header.rs b/axum-extra/src/extract/user_lang/sources/header.rs
index 1ce5a504ea..d623b264b6 100644
--- a/axum-extra/src/extract/user_lang/sources/header.rs
+++ b/axum-extra/src/extract/user_lang/sources/header.rs
@@ -8,12 +8,8 @@ use axum::async_trait;
 pub struct AcceptLanguageSource;
 
 #[async_trait]
-impl<S> UserLanguageSource<S> for AcceptLanguageSource {
-    async fn languages_from_parts(
-        &self,
-        parts: &mut http::request::Parts,
-        _state: &S,
-    ) -> Vec<String> {
+impl UserLanguageSource for AcceptLanguageSource {
+    async fn languages_from_parts(&self, parts: &mut http::request::Parts) -> Vec<String> {
         let Some(accept_language) = parts.headers.get("Accept-Language") else {
             return vec![];
         };
diff --git a/axum-extra/src/extract/user_lang/sources/path.rs b/axum-extra/src/extract/user_lang/sources/path.rs
index 7e751a677d..d8904432c5 100644
--- a/axum-extra/src/extract/user_lang/sources/path.rs
+++ b/axum-extra/src/extract/user_lang/sources/path.rs
@@ -17,12 +17,8 @@ impl PathSource {
 }
 
 #[async_trait]
-impl<S> UserLanguageSource<S> for PathSource {
-    async fn languages_from_parts(
-        &self,
-        parts: &mut http::request::Parts,
-        _state: &S,
-    ) -> Vec<String> {
+impl UserLanguageSource for PathSource {
+    async fn languages_from_parts(&self, parts: &mut http::request::Parts) -> Vec<String> {
         let Ok(path) = parts.extract::<Path<HashMap<String, String>>>().await else {
             return vec![];
         };
diff --git a/axum-extra/src/extract/user_lang/sources/query.rs b/axum-extra/src/extract/user_lang/sources/query.rs
index e74c119394..b46a168a5e 100644
--- a/axum-extra/src/extract/user_lang/sources/query.rs
+++ b/axum-extra/src/extract/user_lang/sources/query.rs
@@ -17,12 +17,8 @@ impl QuerySource {
 }
 
 #[async_trait]
-impl<S> UserLanguageSource<S> for QuerySource {
-    async fn languages_from_parts(
-        &self,
-        parts: &mut http::request::Parts,
-        _state: &S,
-    ) -> Vec<String> {
+impl UserLanguageSource for QuerySource {
+    async fn languages_from_parts(&self, parts: &mut http::request::Parts) -> Vec<String> {
         let Ok(query) = parts.extract::<Query<HashMap<String, String>>>().await else {
             return vec![];
         };
diff --git a/examples/user-language/src/main.rs b/examples/user-language/src/main.rs
index 65542b0c39..62dffe5a0a 100644
--- a/examples/user-language/src/main.rs
+++ b/examples/user-language/src/main.rs
@@ -4,15 +4,20 @@
 //! cargo run -p example-user-language
 //! ```
 
-use axum::{response::Html, routing::get, Router};
-use axum_extra::extract::UserLanguage;
+use axum::{response::Html, routing::get, Extension, Router};
+use axum_extra::extract::{sources::QuerySource, UserLanguage};
 
 #[tokio::main]
 async fn main() {
     // build our application with a route
     let app = Router::new()
         .route("/", get(handler))
-        .route("/:lang", get(handler));
+        .route("/:lang", get(handler))
+        .layer(Extension(
+            UserLanguage::config()
+                .add_source(QuerySource::new("lang"))
+                .build(),
+        ));
 
     // run it
     let listener = tokio::net::TcpListener::bind("127.0.0.1:3000")

From 55232bd870431863e063382d714f8752bc022d8f Mon Sep 17 00:00:00 2001
From: Markus Gasser <markus.gasser@mailbox.org>
Date: Sun, 27 Aug 2023 22:33:31 +0200
Subject: [PATCH 05/24] Improve UserLanguage example a bit

---
 examples/user-language/src/main.rs | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/examples/user-language/src/main.rs b/examples/user-language/src/main.rs
index 62dffe5a0a..6f6de7820a 100644
--- a/examples/user-language/src/main.rs
+++ b/examples/user-language/src/main.rs
@@ -5,7 +5,10 @@
 //! ```
 
 use axum::{response::Html, routing::get, Extension, Router};
-use axum_extra::extract::{sources::QuerySource, UserLanguage};
+use axum_extra::extract::{
+    sources::{PathSource, QuerySource},
+    UserLanguage,
+};
 
 #[tokio::main]
 async fn main() {
@@ -16,6 +19,7 @@ async fn main() {
         .layer(Extension(
             UserLanguage::config()
                 .add_source(QuerySource::new("lang"))
+                .add_source(PathSource::new("lang"))
                 .build(),
         ));
 
@@ -37,6 +41,6 @@ async fn handler(lang: UserLanguage) -> Html<&'static str> {
         "de" => Html("<h1>Hallo, Welt!</h1>"),
         "es" => Html("<h1>Hola, Mundo!</h1>"),
         "fr" => Html("<h1>Bonjour, le monde!</h1>"),
-        _ => Html("<h1>Hello, World!</h1>"),
+        "en" | _ => Html("<h1>Hello, World!</h1>"),
     }
 }

From d4ce66b67f3938113b00dfce7de64dc124b2a1fc Mon Sep 17 00:00:00 2001
From: Markus Gasser <markus.gasser@mailbox.org>
Date: Sun, 27 Aug 2023 20:49:48 +0000
Subject: [PATCH 06/24] Reorganize user_lang modules

---
 axum-extra/src/extract/mod.rs                          | 10 +++-------
 axum-extra/src/lib.rs                                  |  1 +
 axum-extra/src/{extract => }/user_lang/config.rs       |  7 +++++--
 axum-extra/src/{extract => }/user_lang/lang.rs         |  0
 axum-extra/src/{extract => }/user_lang/mod.rs          |  7 ++++---
 axum-extra/src/{extract => }/user_lang/source.rs       |  0
 .../src/{extract => }/user_lang/sources/header.rs      |  5 ++---
 axum-extra/src/{extract => }/user_lang/sources/mod.rs  |  0
 axum-extra/src/{extract => }/user_lang/sources/path.rs |  2 +-
 .../src/{extract => }/user_lang/sources/query.rs       |  2 +-
 examples/user-language/src/main.rs                     |  6 +++---
 11 files changed, 20 insertions(+), 20 deletions(-)
 rename axum-extra/src/{extract => }/user_lang/config.rs (92%)
 rename axum-extra/src/{extract => }/user_lang/lang.rs (100%)
 rename axum-extra/src/{extract => }/user_lang/mod.rs (68%)
 rename axum-extra/src/{extract => }/user_lang/source.rs (100%)
 rename axum-extra/src/{extract => }/user_lang/sources/header.rs (97%)
 rename axum-extra/src/{extract => }/user_lang/sources/mod.rs (100%)
 rename axum-extra/src/{extract => }/user_lang/sources/path.rs (94%)
 rename axum-extra/src/{extract => }/user_lang/sources/query.rs (94%)

diff --git a/axum-extra/src/extract/mod.rs b/axum-extra/src/extract/mod.rs
index cdde256e19..812cf698fd 100644
--- a/axum-extra/src/extract/mod.rs
+++ b/axum-extra/src/extract/mod.rs
@@ -2,7 +2,6 @@
 
 mod cached;
 mod optional_path;
-mod user_lang;
 mod with_rejection;
 
 #[cfg(feature = "form")]
@@ -17,12 +16,7 @@ mod query;
 #[cfg(feature = "multipart")]
 pub mod multipart;
 
-pub use self::{
-    cached::Cached,
-    optional_path::OptionalPath,
-    user_lang::{sources, UserLanguage, UserLanguageConfig, UserLanguageSource},
-    with_rejection::WithRejection,
-};
+pub use self::{cached::Cached, optional_path::OptionalPath, with_rejection::WithRejection};
 
 #[cfg(feature = "cookie")]
 pub use self::cookie::CookieJar;
@@ -49,3 +43,5 @@ pub use crate::json_lines::JsonLines;
 #[cfg(feature = "typed-header")]
 #[doc(no_inline)]
 pub use crate::typed_header::TypedHeader;
+
+pub use crate::user_lang::UserLanguage;
diff --git a/axum-extra/src/lib.rs b/axum-extra/src/lib.rs
index e6f9e87981..0f11110743 100644
--- a/axum-extra/src/lib.rs
+++ b/axum-extra/src/lib.rs
@@ -77,6 +77,7 @@ pub mod handler;
 pub mod middleware;
 pub mod response;
 pub mod routing;
+pub mod user_lang;
 
 #[cfg(feature = "json-lines")]
 pub mod json_lines;
diff --git a/axum-extra/src/extract/user_lang/config.rs b/axum-extra/src/user_lang/config.rs
similarity index 92%
rename from axum-extra/src/extract/user_lang/config.rs
rename to axum-extra/src/user_lang/config.rs
index 43e0e3980d..ade0484a43 100644
--- a/axum-extra/src/extract/user_lang/config.rs
+++ b/axum-extra/src/user_lang/config.rs
@@ -1,7 +1,6 @@
+use crate::user_lang::{UserLanguage, UserLanguageSource};
 use std::sync::Arc;
 
-use super::{UserLanguage, UserLanguageSource};
-
 /// TBD
 #[derive(Debug, Clone)]
 pub struct UserLanguageConfig {
@@ -12,6 +11,7 @@ pub struct UserLanguageConfig {
     pub sources: Vec<Arc<dyn UserLanguageSource>>,
 }
 
+/// TBD
 #[derive(Debug, Clone)]
 pub struct UserLanguageConfigBuilder {
     fallback_language: String,
@@ -19,16 +19,19 @@ pub struct UserLanguageConfigBuilder {
 }
 
 impl UserLanguageConfigBuilder {
+    /// TBD
     pub fn fallback_language(mut self, fallback_language: impl Into<String>) -> Self {
         self.fallback_language = fallback_language.into();
         self
     }
 
+    /// TBD
     pub fn add_source(mut self, source: impl UserLanguageSource + 'static) -> Self {
         self.sources.push(Arc::new(source));
         self
     }
 
+    /// TBD
     pub fn build(self) -> UserLanguageConfig {
         UserLanguageConfig {
             fallback_language: self.fallback_language,
diff --git a/axum-extra/src/extract/user_lang/lang.rs b/axum-extra/src/user_lang/lang.rs
similarity index 100%
rename from axum-extra/src/extract/user_lang/lang.rs
rename to axum-extra/src/user_lang/lang.rs
diff --git a/axum-extra/src/extract/user_lang/mod.rs b/axum-extra/src/user_lang/mod.rs
similarity index 68%
rename from axum-extra/src/extract/user_lang/mod.rs
rename to axum-extra/src/user_lang/mod.rs
index db62a41306..dfe04427e2 100644
--- a/axum-extra/src/extract/user_lang/mod.rs
+++ b/axum-extra/src/user_lang/mod.rs
@@ -1,10 +1,11 @@
+//! TBD
+
 mod config;
 mod lang;
 mod source;
-
-/// TBD
-pub mod sources;
+mod sources;
 
 pub use config::*;
 pub use lang::*;
 pub use source::*;
+pub use sources::*;
diff --git a/axum-extra/src/extract/user_lang/source.rs b/axum-extra/src/user_lang/source.rs
similarity index 100%
rename from axum-extra/src/extract/user_lang/source.rs
rename to axum-extra/src/user_lang/source.rs
diff --git a/axum-extra/src/extract/user_lang/sources/header.rs b/axum-extra/src/user_lang/sources/header.rs
similarity index 97%
rename from axum-extra/src/extract/user_lang/sources/header.rs
rename to axum-extra/src/user_lang/sources/header.rs
index d623b264b6..e6c7492039 100644
--- a/axum-extra/src/extract/user_lang/sources/header.rs
+++ b/axum-extra/src/user_lang/sources/header.rs
@@ -1,7 +1,6 @@
-use std::cmp::Ordering;
-
-use crate::extract::UserLanguageSource;
+use crate::user_lang::UserLanguageSource;
 use axum::async_trait;
+use std::cmp::Ordering;
 
 /// TBD
 #[derive(Debug, Clone)]
diff --git a/axum-extra/src/extract/user_lang/sources/mod.rs b/axum-extra/src/user_lang/sources/mod.rs
similarity index 100%
rename from axum-extra/src/extract/user_lang/sources/mod.rs
rename to axum-extra/src/user_lang/sources/mod.rs
diff --git a/axum-extra/src/extract/user_lang/sources/path.rs b/axum-extra/src/user_lang/sources/path.rs
similarity index 94%
rename from axum-extra/src/extract/user_lang/sources/path.rs
rename to axum-extra/src/user_lang/sources/path.rs
index d8904432c5..1a80064260 100644
--- a/axum-extra/src/extract/user_lang/sources/path.rs
+++ b/axum-extra/src/user_lang/sources/path.rs
@@ -1,4 +1,4 @@
-use crate::extract::UserLanguageSource;
+use crate::user_lang::UserLanguageSource;
 use axum::{async_trait, extract::Path, RequestPartsExt};
 use std::collections::HashMap;
 
diff --git a/axum-extra/src/extract/user_lang/sources/query.rs b/axum-extra/src/user_lang/sources/query.rs
similarity index 94%
rename from axum-extra/src/extract/user_lang/sources/query.rs
rename to axum-extra/src/user_lang/sources/query.rs
index b46a168a5e..5588454334 100644
--- a/axum-extra/src/extract/user_lang/sources/query.rs
+++ b/axum-extra/src/user_lang/sources/query.rs
@@ -1,4 +1,4 @@
-use crate::extract::UserLanguageSource;
+use crate::user_lang::UserLanguageSource;
 use axum::{async_trait, extract::Query, RequestPartsExt};
 use std::collections::HashMap;
 
diff --git a/examples/user-language/src/main.rs b/examples/user-language/src/main.rs
index 6f6de7820a..58793aedba 100644
--- a/examples/user-language/src/main.rs
+++ b/examples/user-language/src/main.rs
@@ -5,9 +5,9 @@
 //! ```
 
 use axum::{response::Html, routing::get, Extension, Router};
-use axum_extra::extract::{
-    sources::{PathSource, QuerySource},
-    UserLanguage,
+use axum_extra::{
+    extract::UserLanguage,
+    user_lang::{PathSource, QuerySource},
 };
 
 #[tokio::main]

From c40f4bf0360acb5b22490720c2c3446e8c229f61 Mon Sep 17 00:00:00 2001
From: Markus Gasser <markus.gasser@mailbox.org>
Date: Thu, 28 Sep 2023 19:00:40 +0000
Subject: [PATCH 07/24] Move modules to be more consistent with the rest

---
 .devcontainer/devcontainer.json               | 34 +++++++++++++++++++
 .vscode/settings.json                         |  4 +++
 axum-extra/src/extract/mod.rs                 |  6 ++--
 .../src/{ => extract}/user_lang/config.rs     |  3 +-
 .../src/{ => extract}/user_lang/lang.rs       | 24 ++++++++++++-
 axum-extra/src/{ => extract}/user_lang/mod.rs |  2 +-
 .../src/{ => extract}/user_lang/source.rs     |  0
 .../{ => extract}/user_lang/sources/header.rs |  3 +-
 .../{ => extract}/user_lang/sources/mod.rs    |  0
 .../{ => extract}/user_lang/sources/path.rs   |  3 +-
 .../{ => extract}/user_lang/sources/query.rs  |  3 +-
 axum-extra/src/lib.rs                         |  1 -
 examples/user-language/src/main.rs            |  7 +++-
 13 files changed, 80 insertions(+), 10 deletions(-)
 create mode 100644 .devcontainer/devcontainer.json
 create mode 100644 .vscode/settings.json
 rename axum-extra/src/{ => extract}/user_lang/config.rs (94%)
 rename axum-extra/src/{ => extract}/user_lang/lang.rs (77%)
 rename axum-extra/src/{ => extract}/user_lang/mod.rs (81%)
 rename axum-extra/src/{ => extract}/user_lang/source.rs (100%)
 rename axum-extra/src/{ => extract}/user_lang/sources/header.rs (96%)
 rename axum-extra/src/{ => extract}/user_lang/sources/mod.rs (100%)
 rename axum-extra/src/{ => extract}/user_lang/sources/path.rs (93%)
 rename axum-extra/src/{ => extract}/user_lang/sources/query.rs (93%)

diff --git a/.devcontainer/devcontainer.json b/.devcontainer/devcontainer.json
new file mode 100644
index 0000000000..60c7aa4105
--- /dev/null
+++ b/.devcontainer/devcontainer.json
@@ -0,0 +1,34 @@
+// For format details, see https://aka.ms/devcontainer.json. For config options, see the
+// README at: https://github.com/devcontainers/templates/tree/main/src/rust
+{
+	"name": "Rust",
+	// Or use a Dockerfile or Docker Compose file. More info: https://containers.dev/guide/dockerfile
+	"image": "mcr.microsoft.com/devcontainers/rust:1-1-bullseye",
+	"features": {
+		"ghcr.io/devcontainers-contrib/features/fish-apt-get:1": {}
+	}
+
+	// Use 'mounts' to make the cargo cache persistent in a Docker Volume.
+	// "mounts": [
+	// 	{
+	// 		"source": "devcontainer-cargo-cache-${devcontainerId}",
+	// 		"target": "/usr/local/cargo",
+	// 		"type": "volume"
+	// 	}
+	// ]
+
+	// Features to add to the dev container. More info: https://containers.dev/features.
+	// "features": {},
+
+	// Use 'forwardPorts' to make a list of ports inside the container available locally.
+	// "forwardPorts": [],
+
+	// Use 'postCreateCommand' to run commands after the container is created.
+	// "postCreateCommand": "rustc --version",
+
+	// Configure tool-specific properties.
+	// "customizations": {},
+
+	// Uncomment to connect as root instead. More info: https://aka.ms/dev-containers-non-root.
+	// "remoteUser": "root"
+}
diff --git a/.vscode/settings.json b/.vscode/settings.json
new file mode 100644
index 0000000000..4bc45ade3d
--- /dev/null
+++ b/.vscode/settings.json
@@ -0,0 +1,4 @@
+{
+    "rust-analyzer.showUnlinkedFileNotification": false,
+    "rust-analyzer.cargo.features": "all"
+}
\ No newline at end of file
diff --git a/axum-extra/src/extract/mod.rs b/axum-extra/src/extract/mod.rs
index 812cf698fd..d8b09d6526 100644
--- a/axum-extra/src/extract/mod.rs
+++ b/axum-extra/src/extract/mod.rs
@@ -16,6 +16,8 @@ mod query;
 #[cfg(feature = "multipart")]
 pub mod multipart;
 
+pub mod user_lang;
+
 pub use self::{cached::Cached, optional_path::OptionalPath, with_rejection::WithRejection};
 
 #[cfg(feature = "cookie")]
@@ -36,6 +38,8 @@ pub use self::query::{Query, QueryRejection};
 #[cfg(feature = "multipart")]
 pub use self::multipart::Multipart;
 
+pub use self::user_lang::UserLanguage;
+
 #[cfg(feature = "json-lines")]
 #[doc(no_inline)]
 pub use crate::json_lines::JsonLines;
@@ -43,5 +47,3 @@ pub use crate::json_lines::JsonLines;
 #[cfg(feature = "typed-header")]
 #[doc(no_inline)]
 pub use crate::typed_header::TypedHeader;
-
-pub use crate::user_lang::UserLanguage;
diff --git a/axum-extra/src/user_lang/config.rs b/axum-extra/src/extract/user_lang/config.rs
similarity index 94%
rename from axum-extra/src/user_lang/config.rs
rename to axum-extra/src/extract/user_lang/config.rs
index ade0484a43..81bf387b72 100644
--- a/axum-extra/src/user_lang/config.rs
+++ b/axum-extra/src/extract/user_lang/config.rs
@@ -1,6 +1,7 @@
-use crate::user_lang::{UserLanguage, UserLanguageSource};
 use std::sync::Arc;
 
+use crate::extract::user_lang::{UserLanguage, UserLanguageSource};
+
 /// TBD
 #[derive(Debug, Clone)]
 pub struct UserLanguageConfig {
diff --git a/axum-extra/src/user_lang/lang.rs b/axum-extra/src/extract/user_lang/lang.rs
similarity index 77%
rename from axum-extra/src/user_lang/lang.rs
rename to axum-extra/src/extract/user_lang/lang.rs
index aeaeb3ad84..bdc7eab567 100644
--- a/axum-extra/src/user_lang/lang.rs
+++ b/axum-extra/src/extract/user_lang/lang.rs
@@ -9,7 +9,29 @@ use std::{
     sync::{Arc, OnceLock},
 };
 
-/// TBD
+/// The users preferred languages, read from the request.
+///
+/// This extractor reads the users preferred languages from a
+/// configurable list of sources.
+/// 
+/// By default it will try to read from the following sources:
+///   * The query parameter `lang`
+///   * The path segment `:lang`
+///   * The `Accept-Language` header
+/// 
+/// # Configuration
+/// 
+/// To configure the sources see [`UserLanguage::config`] for details.
+/// 
+/// # Example
+/// 
+/// ```rust
+/// use axum_extra::extract::UserLanguage;
+///
+/// async fn handler(UserLanguage(lang): UserLanguage) {
+///     println!("Preferred languages: {:?}", lang.preferred_languages());
+/// }
+/// ```
 #[derive(Debug, Clone)]
 pub struct UserLanguage {
     preferred_languages: Vec<String>,
diff --git a/axum-extra/src/user_lang/mod.rs b/axum-extra/src/extract/user_lang/mod.rs
similarity index 81%
rename from axum-extra/src/user_lang/mod.rs
rename to axum-extra/src/extract/user_lang/mod.rs
index dfe04427e2..b1876f6d46 100644
--- a/axum-extra/src/user_lang/mod.rs
+++ b/axum-extra/src/extract/user_lang/mod.rs
@@ -1,4 +1,4 @@
-//! TBD
+//! User language extractor.
 
 mod config;
 mod lang;
diff --git a/axum-extra/src/user_lang/source.rs b/axum-extra/src/extract/user_lang/source.rs
similarity index 100%
rename from axum-extra/src/user_lang/source.rs
rename to axum-extra/src/extract/user_lang/source.rs
diff --git a/axum-extra/src/user_lang/sources/header.rs b/axum-extra/src/extract/user_lang/sources/header.rs
similarity index 96%
rename from axum-extra/src/user_lang/sources/header.rs
rename to axum-extra/src/extract/user_lang/sources/header.rs
index e6c7492039..65dfe4a71d 100644
--- a/axum-extra/src/user_lang/sources/header.rs
+++ b/axum-extra/src/extract/user_lang/sources/header.rs
@@ -1,7 +1,8 @@
-use crate::user_lang::UserLanguageSource;
 use axum::async_trait;
 use std::cmp::Ordering;
 
+use crate::extract::user_lang::UserLanguageSource;
+
 /// TBD
 #[derive(Debug, Clone)]
 pub struct AcceptLanguageSource;
diff --git a/axum-extra/src/user_lang/sources/mod.rs b/axum-extra/src/extract/user_lang/sources/mod.rs
similarity index 100%
rename from axum-extra/src/user_lang/sources/mod.rs
rename to axum-extra/src/extract/user_lang/sources/mod.rs
diff --git a/axum-extra/src/user_lang/sources/path.rs b/axum-extra/src/extract/user_lang/sources/path.rs
similarity index 93%
rename from axum-extra/src/user_lang/sources/path.rs
rename to axum-extra/src/extract/user_lang/sources/path.rs
index 1a80064260..45a042ffc3 100644
--- a/axum-extra/src/user_lang/sources/path.rs
+++ b/axum-extra/src/extract/user_lang/sources/path.rs
@@ -1,7 +1,8 @@
-use crate::user_lang::UserLanguageSource;
 use axum::{async_trait, extract::Path, RequestPartsExt};
 use std::collections::HashMap;
 
+use crate::extract::user_lang::UserLanguageSource;
+
 /// TBD
 #[derive(Debug, Clone)]
 pub struct PathSource {
diff --git a/axum-extra/src/user_lang/sources/query.rs b/axum-extra/src/extract/user_lang/sources/query.rs
similarity index 93%
rename from axum-extra/src/user_lang/sources/query.rs
rename to axum-extra/src/extract/user_lang/sources/query.rs
index 5588454334..50d0b0efc4 100644
--- a/axum-extra/src/user_lang/sources/query.rs
+++ b/axum-extra/src/extract/user_lang/sources/query.rs
@@ -1,7 +1,8 @@
-use crate::user_lang::UserLanguageSource;
 use axum::{async_trait, extract::Query, RequestPartsExt};
 use std::collections::HashMap;
 
+use crate::extract::user_lang::UserLanguageSource;
+
 /// TBD
 #[derive(Debug, Clone)]
 pub struct QuerySource {
diff --git a/axum-extra/src/lib.rs b/axum-extra/src/lib.rs
index 0f11110743..e6f9e87981 100644
--- a/axum-extra/src/lib.rs
+++ b/axum-extra/src/lib.rs
@@ -77,7 +77,6 @@ pub mod handler;
 pub mod middleware;
 pub mod response;
 pub mod routing;
-pub mod user_lang;
 
 #[cfg(feature = "json-lines")]
 pub mod json_lines;
diff --git a/examples/user-language/src/main.rs b/examples/user-language/src/main.rs
index 58793aedba..afcb96afb4 100644
--- a/examples/user-language/src/main.rs
+++ b/examples/user-language/src/main.rs
@@ -12,13 +12,18 @@ use axum_extra::{
 
 #[tokio::main]
 async fn main() {
-    // build our application with a route
+    // build our application with some routes
     let app = Router::new()
         .route("/", get(handler))
         .route("/:lang", get(handler))
+        // Add configuration for the `UserLanguage` extractor.
+        // This step is optional, if omitted the default
+        // configuration will be used.
         .layer(Extension(
             UserLanguage::config()
+                // read the language from the `lang` query parameter
                 .add_source(QuerySource::new("lang"))
+                // read the language from the `:lang` segment of the path
                 .add_source(PathSource::new("lang"))
                 .build(),
         ));

From 4e75f789d1c679f09d8314384c1f16d5a62d3f90 Mon Sep 17 00:00:00 2001
From: Markus Gasser <markus.gasser@mailbox.org>
Date: Thu, 28 Sep 2023 19:12:17 +0000
Subject: [PATCH 08/24] Add documentation to the lang module

---
 axum-extra/src/extract/user_lang/lang.rs | 38 ++++++++++++++++++------
 axum-extra/src/extract/user_lang/mod.rs  |  2 +-
 2 files changed, 30 insertions(+), 10 deletions(-)

diff --git a/axum-extra/src/extract/user_lang/lang.rs b/axum-extra/src/extract/user_lang/lang.rs
index bdc7eab567..a84c22e72e 100644
--- a/axum-extra/src/extract/user_lang/lang.rs
+++ b/axum-extra/src/extract/user_lang/lang.rs
@@ -15,20 +15,22 @@ use std::{
 /// configurable list of sources.
 /// 
 /// By default it will try to read from the following sources:
-///   * The query parameter `lang`
-///   * The path segment `:lang`
-///   * The `Accept-Language` header
+///  * The query parameter `lang`
+///  * The path segment `:lang`
+///  * The `Accept-Language` header
 /// 
 /// # Configuration
 /// 
-/// To configure the sources see [`UserLanguage::config`] for details.
+/// To configure the sources for the languages see [`UserLanguage::config`].
+/// You can also create a custom source. See [`UserLanguageSource`] on how to
+/// implement one.
 /// 
 /// # Example
 /// 
 /// ```rust
 /// use axum_extra::extract::UserLanguage;
 ///
-/// async fn handler(UserLanguage(lang): UserLanguage) {
+/// async fn handler(lang: UserLanguage) {
 ///     println!("Preferred languages: {:?}", lang.preferred_languages());
 /// }
 /// ```
@@ -39,7 +41,13 @@ pub struct UserLanguage {
 }
 
 impl UserLanguage {
-    /// TBD
+    /// The default sources for the preferred languages.
+    /// 
+    /// If you do not add a configuration for the [`UserLanguage`] extractor,
+    /// these sources will be used by default. They are in order:
+    ///  * The query parameter `lang`
+    ///  * The path segment `:lang`
+    ///  * The `Accept-Language` header
     pub fn default_sources() -> &'static Vec<Arc<dyn UserLanguageSource>> {
         static DEFAULT_SOURCES: OnceLock<Vec<Arc<dyn UserLanguageSource>>> = OnceLock::new();
 
@@ -52,19 +60,31 @@ impl UserLanguage {
         })
     }
 
-    /// TBD
+    /// The users most preferred language as read from the request.
+    /// 
+    /// This is the first language in the list of [`preferred_languages`].
+    /// If no language could be read from the request, the fallback language
+    /// will be returned.
     pub fn preferred_language(&self) -> &str {
         self.preferred_languages
             .first()
             .unwrap_or(&self.fallback_language)
     }
 
-    /// TBD
+    /// The users preferred languages in order of preference.
+    /// 
+    /// Preference is first determined by the order of the sources.
+    /// Within each source the languages are ordered by the users preference,
+    /// if applicable for the source. For example the `Accept-Language` header
+    /// source will order the languages by the `q` parameter.
+    /// 
+    /// This list may be empty if no language could be read from the request.
     pub fn preferred_languages(&self) -> &[String] {
         self.preferred_languages.as_slice()
     }
 
-    /// TBD
+    /// The language that will be used as a fallback if no language could be
+    /// read from the request.
     pub fn fallback_language(&self) -> &str {
         &self.fallback_language
     }
diff --git a/axum-extra/src/extract/user_lang/mod.rs b/axum-extra/src/extract/user_lang/mod.rs
index b1876f6d46..cd03355ca4 100644
--- a/axum-extra/src/extract/user_lang/mod.rs
+++ b/axum-extra/src/extract/user_lang/mod.rs
@@ -1,4 +1,4 @@
-//! User language extractor.
+//! Extractor that retrieves the preferred languages of the user.
 
 mod config;
 mod lang;

From d659285954251a3b00c044c3da69af72767688dc Mon Sep 17 00:00:00 2001
From: Markus Gasser <markus.gasser@mailbox.org>
Date: Thu, 28 Sep 2023 19:40:11 +0000
Subject: [PATCH 09/24] Add documentation for the config module

---
 axum-extra/src/extract/user_lang/config.rs | 66 ++++++++++++++++++----
 axum-extra/src/extract/user_lang/lang.rs   |  3 +
 examples/user-language/src/main.rs         |  5 +-
 3 files changed, 59 insertions(+), 15 deletions(-)

diff --git a/axum-extra/src/extract/user_lang/config.rs b/axum-extra/src/extract/user_lang/config.rs
index 81bf387b72..0c8e00837b 100644
--- a/axum-extra/src/extract/user_lang/config.rs
+++ b/axum-extra/src/extract/user_lang/config.rs
@@ -2,17 +2,61 @@ use std::sync::Arc;
 
 use crate::extract::user_lang::{UserLanguage, UserLanguageSource};
 
-/// TBD
+/// Configuration for the [`UserLanguage`] extractor.
+/// 
+/// By default the [`UserLanguage`] extractor will try to read the
+/// languages from the sources returned by [`UserLanguage::default_sources`].
+/// 
+/// You can override the default behaviour by adding a [`UserLanguageConfig`]
+/// extension to your routes.
+/// 
+/// You can add sources and specify a fallback language.
+/// 
+/// # Example
+/// 
+/// ```rust
+/// use axum::{routing::get, Extension, Router};
+/// use axum_extra::extract::user_lang::{PathSource, QuerySource, UserLanguage};
+/// 
+/// # fn main() {
+/// let app = Router::new()
+///     .route("/:lang", get(handler))
+///     .layer(Extension(
+///         UserLanguage::config()
+///             .add_source(QuerySource::new("lang"))
+///             .add_source(PathSource::new("lang"))
+///             .build(),
+///     ));
+/// # let _: Router = app;
+/// # }
+/// # async fn handler() {}
+/// ```
+///
 #[derive(Debug, Clone)]
 pub struct UserLanguageConfig {
-    /// TBD
-    pub fallback_language: String,
-
-    /// TBD
-    pub sources: Vec<Arc<dyn UserLanguageSource>>,
+    pub(crate) fallback_language: String,
+    pub(crate) sources: Vec<Arc<dyn UserLanguageSource>>,
 }
 
-/// TBD
+/// Builder for [`UserLanguageConfig`].
+/// 
+/// Allows you to declaratively create a [`UserLanguageConfig`].
+/// You can create a [`UserLanguageConfigBuilder`] by calling
+/// [`UserLanguage::config`].
+/// 
+/// # Example
+/// 
+/// ```rust
+/// use axum_extra::extract::user_lang::{QuerySource, UserLanguage};
+/// 
+/// # fn main() {
+/// let config = UserLanguage::config()
+///     .add_source(QuerySource::new("lang"))
+///     .fallback_language("es")
+///     .build();
+/// # let _ = config;
+/// # }
+/// ```
 #[derive(Debug, Clone)]
 pub struct UserLanguageConfigBuilder {
     fallback_language: String,
@@ -20,19 +64,19 @@ pub struct UserLanguageConfigBuilder {
 }
 
 impl UserLanguageConfigBuilder {
-    /// TBD
+    /// Set the fallback language.
     pub fn fallback_language(mut self, fallback_language: impl Into<String>) -> Self {
         self.fallback_language = fallback_language.into();
         self
     }
 
-    /// TBD
+    /// Add a [`UserLanguageSource`].
     pub fn add_source(mut self, source: impl UserLanguageSource + 'static) -> Self {
         self.sources.push(Arc::new(source));
         self
     }
 
-    /// TBD
+    /// Create a [`UserLanguageConfig`] from this builder.
     pub fn build(self) -> UserLanguageConfig {
         UserLanguageConfig {
             fallback_language: self.fallback_language,
@@ -46,7 +90,7 @@ impl UserLanguageConfigBuilder {
 }
 
 impl UserLanguage {
-    /// TBD
+    /// Returns a builder for [`UserLanguageConfig`].
     pub fn config() -> UserLanguageConfigBuilder {
         UserLanguageConfigBuilder {
             fallback_language: "en".to_string(),
diff --git a/axum-extra/src/extract/user_lang/lang.rs b/axum-extra/src/extract/user_lang/lang.rs
index a84c22e72e..d8dd1b1735 100644
--- a/axum-extra/src/extract/user_lang/lang.rs
+++ b/axum-extra/src/extract/user_lang/lang.rs
@@ -19,6 +19,9 @@ use std::{
 ///  * The path segment `:lang`
 ///  * The `Accept-Language` header
 /// 
+/// If no language could be read from the request, the fallback language
+/// is "en".
+/// 
 /// # Configuration
 /// 
 /// To configure the sources for the languages see [`UserLanguage::config`].
diff --git a/examples/user-language/src/main.rs b/examples/user-language/src/main.rs
index afcb96afb4..ff3962b1fa 100644
--- a/examples/user-language/src/main.rs
+++ b/examples/user-language/src/main.rs
@@ -5,10 +5,7 @@
 //! ```
 
 use axum::{response::Html, routing::get, Extension, Router};
-use axum_extra::{
-    extract::UserLanguage,
-    user_lang::{PathSource, QuerySource},
-};
+use axum_extra::extract::user_lang::{PathSource, QuerySource, UserLanguage};
 
 #[tokio::main]
 async fn main() {

From 2ccc8ac5bd7ca9c01e06097976d214167f91e6c7 Mon Sep 17 00:00:00 2001
From: Markus Gasser <markus.gasser@mailbox.org>
Date: Thu, 28 Sep 2023 19:43:57 +0000
Subject: [PATCH 10/24] Rename UserLanguageConfig/Builder

---
 axum-extra/src/extract/user_lang/config.rs | 26 +++++++++++-----------
 axum-extra/src/extract/user_lang/lang.rs   |  6 ++---
 2 files changed, 16 insertions(+), 16 deletions(-)

diff --git a/axum-extra/src/extract/user_lang/config.rs b/axum-extra/src/extract/user_lang/config.rs
index 0c8e00837b..91a81db275 100644
--- a/axum-extra/src/extract/user_lang/config.rs
+++ b/axum-extra/src/extract/user_lang/config.rs
@@ -7,7 +7,7 @@ use crate::extract::user_lang::{UserLanguage, UserLanguageSource};
 /// By default the [`UserLanguage`] extractor will try to read the
 /// languages from the sources returned by [`UserLanguage::default_sources`].
 /// 
-/// You can override the default behaviour by adding a [`UserLanguageConfig`]
+/// You can override the default behaviour by adding a [`Config`]
 /// extension to your routes.
 /// 
 /// You can add sources and specify a fallback language.
@@ -33,15 +33,15 @@ use crate::extract::user_lang::{UserLanguage, UserLanguageSource};
 /// ```
 ///
 #[derive(Debug, Clone)]
-pub struct UserLanguageConfig {
+pub struct Config {
     pub(crate) fallback_language: String,
     pub(crate) sources: Vec<Arc<dyn UserLanguageSource>>,
 }
 
-/// Builder for [`UserLanguageConfig`].
+/// Builder to create a [`Config`] for the [`UserLanguage`] extractor.
 /// 
-/// Allows you to declaratively create a [`UserLanguageConfig`].
-/// You can create a [`UserLanguageConfigBuilder`] by calling
+/// Allows you to declaratively create a [`Config`].
+/// You can create a [`ConfigBuilder`] by calling
 /// [`UserLanguage::config`].
 /// 
 /// # Example
@@ -58,12 +58,12 @@ pub struct UserLanguageConfig {
 /// # }
 /// ```
 #[derive(Debug, Clone)]
-pub struct UserLanguageConfigBuilder {
+pub struct ConfigBuilder {
     fallback_language: String,
     sources: Vec<Arc<dyn UserLanguageSource>>,
 }
 
-impl UserLanguageConfigBuilder {
+impl ConfigBuilder {
     /// Set the fallback language.
     pub fn fallback_language(mut self, fallback_language: impl Into<String>) -> Self {
         self.fallback_language = fallback_language.into();
@@ -76,9 +76,9 @@ impl UserLanguageConfigBuilder {
         self
     }
 
-    /// Create a [`UserLanguageConfig`] from this builder.
-    pub fn build(self) -> UserLanguageConfig {
-        UserLanguageConfig {
+    /// Create a [`Config`] from this builder.
+    pub fn build(self) -> Config {
+        Config {
             fallback_language: self.fallback_language,
             sources: if !self.sources.is_empty() {
                 self.sources
@@ -90,9 +90,9 @@ impl UserLanguageConfigBuilder {
 }
 
 impl UserLanguage {
-    /// Returns a builder for [`UserLanguageConfig`].
-    pub fn config() -> UserLanguageConfigBuilder {
-        UserLanguageConfigBuilder {
+    /// Returns a builder for [`Config`].
+    pub fn config() -> ConfigBuilder {
+        ConfigBuilder {
             fallback_language: "en".to_string(),
             sources: vec![],
         }
diff --git a/axum-extra/src/extract/user_lang/lang.rs b/axum-extra/src/extract/user_lang/lang.rs
index d8dd1b1735..a23d58edb5 100644
--- a/axum-extra/src/extract/user_lang/lang.rs
+++ b/axum-extra/src/extract/user_lang/lang.rs
@@ -1,6 +1,6 @@
 use super::{
     sources::{AcceptLanguageSource, PathSource, QuerySource},
-    UserLanguageConfig, UserLanguageSource,
+    Config, UserLanguageSource,
 };
 use axum::{async_trait, extract::FromRequestParts, Extension, RequestPartsExt};
 use http::request::Parts;
@@ -65,7 +65,7 @@ impl UserLanguage {
 
     /// The users most preferred language as read from the request.
     /// 
-    /// This is the first language in the list of [`preferred_languages`].
+    /// This is the first language in the list of [`UserLanguage::preferred_languages`].
     /// If no language could be read from the request, the fallback language
     /// will be returned.
     pub fn preferred_language(&self) -> &str {
@@ -102,7 +102,7 @@ where
 
     async fn from_request_parts(parts: &mut Parts, _state: &S) -> Result<Self, Self::Rejection> {
         let (sources, fallback_language) =
-            match parts.extract::<Extension<UserLanguageConfig>>().await {
+            match parts.extract::<Extension<Config>>().await {
                 Ok(Extension(config)) => (Some(config.sources), Some(config.fallback_language)),
                 Err(_) => (None, None),
             };

From 02b1f96f7bfdb345e2980e2725af303eb188551e Mon Sep 17 00:00:00 2001
From: Markus Gasser <markus.gasser@mailbox.org>
Date: Thu, 28 Sep 2023 19:55:17 +0000
Subject: [PATCH 11/24] Add docs for UserLanguageSource

---
 axum-extra/src/extract/user_lang/source.rs | 38 ++++++++++++++++++++--
 1 file changed, 36 insertions(+), 2 deletions(-)

diff --git a/axum-extra/src/extract/user_lang/source.rs b/axum-extra/src/extract/user_lang/source.rs
index 32594fb9ca..2debd55cb2 100644
--- a/axum-extra/src/extract/user_lang/source.rs
+++ b/axum-extra/src/extract/user_lang/source.rs
@@ -2,9 +2,43 @@ use axum::async_trait;
 use http::request::Parts;
 use std::fmt::Debug;
 
-/// TBD
+/// A source for the users preferred languages.
+///
+/// # Implementing a custom source
+///
+/// The following is an example of how to read the language from the query.
+///
+/// ```rust
+/// use std::collections::HashMap;
+/// use axum::{extract::Query, RequestPartsExt};
+/// use axum_extra::extract::user_lang::UserLanguageSource;
+///
+/// #[derive(Debug)]
+/// pub struct QuerySource;
+///
+/// #[axum::async_trait]
+/// impl UserLanguageSource for QuerySource {
+///     async fn languages_from_parts(&self, parts: &mut http::request::Parts) -> Vec<String> {
+///         let Ok(query) = parts.extract::<Query<HashMap<String, String>>>().await else {
+///             return vec![];
+///         };
+///
+///         let Some(lang) = query.get("lang") else {
+///             return vec![];
+///         };
+///
+///         vec![lang.to_string()]
+///     }
+/// }
+/// ```
 #[async_trait]
 pub trait UserLanguageSource: Send + Sync + Debug {
-    /// TBD
+    /// Extract a list of user languages from the request parts.
+    ///
+    /// The multiple languages are returned, they should be in
+    /// order of preference of the user, if possible.
+    ///
+    /// If no languages could be read from the request, return
+    /// an empty vec.
     async fn languages_from_parts(&self, parts: &mut Parts) -> Vec<String>;
 }

From b640fa884ebcd0ad7d70dcc4545837e2496009b6 Mon Sep 17 00:00:00 2001
From: Markus Gasser <markus.gasser@mailbox.org>
Date: Thu, 28 Sep 2023 20:16:56 +0000
Subject: [PATCH 12/24] Add docs for PathSource

---
 axum-extra/src/extract/user_lang/lang.rs      | 14 ++++---
 .../src/extract/user_lang/sources/path.rs     | 37 +++++++++++++++++--
 2 files changed, 43 insertions(+), 8 deletions(-)

diff --git a/axum-extra/src/extract/user_lang/lang.rs b/axum-extra/src/extract/user_lang/lang.rs
index a23d58edb5..bf64764b8b 100644
--- a/axum-extra/src/extract/user_lang/lang.rs
+++ b/axum-extra/src/extract/user_lang/lang.rs
@@ -19,14 +19,18 @@ use std::{
 ///  * The path segment `:lang`
 ///  * The `Accept-Language` header
 /// 
-/// If no language could be read from the request, the fallback language
-/// is "en".
+/// This extractor never fails. If no language could be read from the request,
+/// the fallback language will be used. By default the fallback is `en`, but
+/// this can be configured.
 /// 
 /// # Configuration
 /// 
-/// To configure the sources for the languages see [`UserLanguage::config`].
-/// You can also create a custom source. See [`UserLanguageSource`] on how to
-/// implement one.
+/// To configure the sources for the languages or the fallback language, see [`UserLanguage::config`].
+/// 
+/// # Custom Sources
+/// 
+/// You can create custom user langauge sources. See
+/// [`UserLanguageSource`] for details.
 /// 
 /// # Example
 /// 
diff --git a/axum-extra/src/extract/user_lang/sources/path.rs b/axum-extra/src/extract/user_lang/sources/path.rs
index 45a042ffc3..c46399d4cc 100644
--- a/axum-extra/src/extract/user_lang/sources/path.rs
+++ b/axum-extra/src/extract/user_lang/sources/path.rs
@@ -3,15 +3,46 @@ use std::collections::HashMap;
 
 use crate::extract::user_lang::UserLanguageSource;
 
-/// TBD
+/// A source that reads the user language from the request path.
+///
+/// When creating this source you specify the name of the path
+/// segment to read the language from. The routes you want to extract
+/// the language from must include a path segment with the configured
+/// name for this source to be able to read the language.
+///
+/// # Example
+///
+/// The following example will read the language from
+/// the path segment `lang_id`. Your routes need to include
+/// a `:lang_id` path segment that will contain the language.
+///
+/// ```rust
+/// # use axum::{Router, extract::Extension, routing::get};
+/// # use axum_extra::extract::user_lang::{UserLanguage, PathSource};
+/// #
+/// // The path segment name is `lang_id`.
+/// let source = PathSource::new("lang_id");
+///
+/// // The routes need to include a `:lang_id` path segment.
+/// let app = Router::new()
+///    .route("/home/:lang_id", get(handler))
+///    .layer(
+///        Extension(
+///            UserLanguage::config()
+///                .add_source(source)
+///                .build(),
+///    ));
+///
+/// # let _: Router = app;  
+/// # async fn handler() {}
+/// ```
 #[derive(Debug, Clone)]
 pub struct PathSource {
-    /// TBD
     name: String,
 }
 
 impl PathSource {
-    /// TBD
+    /// Create a new path source with a given path segment name.
     pub fn new(name: impl Into<String>) -> Self {
         Self { name: name.into() }
     }

From 0004c64a5aa290e1af2ac164709c1411eb5a727e Mon Sep 17 00:00:00 2001
From: Markus Gasser <markus.gasser@mailbox.org>
Date: Fri, 29 Sep 2023 06:49:52 +0000
Subject: [PATCH 13/24] Add docs for query and accept header sources

---
 .../src/extract/user_lang/sources/header.rs   | 27 +++++++++++++-
 .../src/extract/user_lang/sources/query.rs    | 35 +++++++++++++++++--
 2 files changed, 58 insertions(+), 4 deletions(-)

diff --git a/axum-extra/src/extract/user_lang/sources/header.rs b/axum-extra/src/extract/user_lang/sources/header.rs
index 65dfe4a71d..cb738c7216 100644
--- a/axum-extra/src/extract/user_lang/sources/header.rs
+++ b/axum-extra/src/extract/user_lang/sources/header.rs
@@ -3,7 +3,31 @@ use std::cmp::Ordering;
 
 use crate::extract::user_lang::UserLanguageSource;
 
-/// TBD
+/// A [`UserLanguageSource`] that reads languages from the `Accept-Language` header.
+/// 
+/// This source may return multiple languages. Languages are returned in order of their
+/// quality values.
+/// 
+/// # Example
+/// 
+/// ```rust
+/// # use axum::{Router, extract::Extension, routing::get};
+/// # use axum_extra::extract::user_lang::{UserLanguage, AcceptLanguageSource};
+/// #
+/// let source = AcceptLanguageSource;
+///
+/// let app = Router::new()
+///    .route("/home", get(handler))
+///    .layer(
+///        Extension(
+///            UserLanguage::config()
+///                .add_source(source)
+///                .build(),
+///    ));
+///
+/// # let _: Router = app;  
+/// # async fn handler() {}
+/// ```
 #[derive(Debug, Clone)]
 pub struct AcceptLanguageSource;
 
@@ -25,6 +49,7 @@ impl UserLanguageSource for AcceptLanguageSource {
     }
 }
 
+/// Parse quality values from the `Accept-Language` header.
 fn parse_quality_values(values: &str) -> Vec<(&str, f32)> {
     let mut values = values.split(',');
     let mut quality_values = Vec::new();
diff --git a/axum-extra/src/extract/user_lang/sources/query.rs b/axum-extra/src/extract/user_lang/sources/query.rs
index 50d0b0efc4..9db20f0810 100644
--- a/axum-extra/src/extract/user_lang/sources/query.rs
+++ b/axum-extra/src/extract/user_lang/sources/query.rs
@@ -3,15 +3,44 @@ use std::collections::HashMap;
 
 use crate::extract::user_lang::UserLanguageSource;
 
-/// TBD
+/// A [`UserLanguageSource`] that reads the language from a field in the
+/// query string.
+///
+/// When creating this source you specify the name of the query
+/// field to read the language from. You can add multiple `QuerySource`
+/// instances to read from different fields.
+///
+/// # Example
+///
+/// The following example will read the language from
+/// the query field `lang_id`.
+///
+/// ```rust
+/// # use axum::{Router, extract::Extension, routing::get};
+/// # use axum_extra::extract::user_lang::{UserLanguage, QuerySource};
+/// #
+/// // The query field name is `lang_id`.
+/// let source = QuerySource::new("lang_id");
+///
+/// let app = Router::new()
+///    .route("/home", get(handler))
+///    .layer(
+///        Extension(
+///            UserLanguage::config()
+///                .add_source(source)
+///                .build(),
+///    ));
+///
+/// # let _: Router = app;  
+/// # async fn handler() {}
+/// ```
 #[derive(Debug, Clone)]
 pub struct QuerySource {
-    /// TBD
     name: String,
 }
 
 impl QuerySource {
-    /// TBD
+    /// Create a new query source with a given query field name.
     pub fn new(name: impl Into<String>) -> Self {
         Self { name: name.into() }
     }

From 0d68fff9dff1d0c228f9fb6cc9b8ffe03a062d9a Mon Sep 17 00:00:00 2001
From: Markus Gasser <markus.gasser@mailbox.org>
Date: Fri, 29 Sep 2023 08:10:13 +0000
Subject: [PATCH 14/24] Add some tests for user language extractor

---
 axum-extra/src/extract/user_lang/lang.rs | 120 +++++++++++++++++++----
 1 file changed, 103 insertions(+), 17 deletions(-)

diff --git a/axum-extra/src/extract/user_lang/lang.rs b/axum-extra/src/extract/user_lang/lang.rs
index bf64764b8b..91433b3608 100644
--- a/axum-extra/src/extract/user_lang/lang.rs
+++ b/axum-extra/src/extract/user_lang/lang.rs
@@ -13,27 +13,27 @@ use std::{
 ///
 /// This extractor reads the users preferred languages from a
 /// configurable list of sources.
-/// 
+///
 /// By default it will try to read from the following sources:
 ///  * The query parameter `lang`
 ///  * The path segment `:lang`
 ///  * The `Accept-Language` header
-/// 
+///
 /// This extractor never fails. If no language could be read from the request,
 /// the fallback language will be used. By default the fallback is `en`, but
 /// this can be configured.
-/// 
+///
 /// # Configuration
-/// 
+///
 /// To configure the sources for the languages or the fallback language, see [`UserLanguage::config`].
-/// 
+///
 /// # Custom Sources
-/// 
+///
 /// You can create custom user langauge sources. See
 /// [`UserLanguageSource`] for details.
-/// 
+///
 /// # Example
-/// 
+///
 /// ```rust
 /// use axum_extra::extract::UserLanguage;
 ///
@@ -49,7 +49,7 @@ pub struct UserLanguage {
 
 impl UserLanguage {
     /// The default sources for the preferred languages.
-    /// 
+    ///
     /// If you do not add a configuration for the [`UserLanguage`] extractor,
     /// these sources will be used by default. They are in order:
     ///  * The query parameter `lang`
@@ -68,7 +68,7 @@ impl UserLanguage {
     }
 
     /// The users most preferred language as read from the request.
-    /// 
+    ///
     /// This is the first language in the list of [`UserLanguage::preferred_languages`].
     /// If no language could be read from the request, the fallback language
     /// will be returned.
@@ -79,12 +79,12 @@ impl UserLanguage {
     }
 
     /// The users preferred languages in order of preference.
-    /// 
+    ///
     /// Preference is first determined by the order of the sources.
     /// Within each source the languages are ordered by the users preference,
     /// if applicable for the source. For example the `Accept-Language` header
     /// source will order the languages by the `q` parameter.
-    /// 
+    ///
     /// This list may be empty if no language could be read from the request.
     pub fn preferred_languages(&self) -> &[String] {
         self.preferred_languages.as_slice()
@@ -105,11 +105,10 @@ where
     type Rejection = Infallible;
 
     async fn from_request_parts(parts: &mut Parts, _state: &S) -> Result<Self, Self::Rejection> {
-        let (sources, fallback_language) =
-            match parts.extract::<Extension<Config>>().await {
-                Ok(Extension(config)) => (Some(config.sources), Some(config.fallback_language)),
-                Err(_) => (None, None),
-            };
+        let (sources, fallback_language) = match parts.extract::<Extension<Config>>().await {
+            Ok(Extension(config)) => (Some(config.sources), Some(config.fallback_language)),
+            Err(_) => (None, None),
+        };
 
         let sources = sources.as_ref().unwrap_or(Self::default_sources());
         let fallback_language = fallback_language.unwrap_or_else(|| "en".to_string());
@@ -127,3 +126,90 @@ where
         })
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::test_helpers::*;
+    use axum::{routing::get, Router};
+    use http::{header::ACCEPT_LANGUAGE, StatusCode};
+
+    #[derive(Debug)]
+    struct TestSource(Vec<String>);
+
+    #[async_trait]
+    impl UserLanguageSource for TestSource {
+        async fn languages_from_parts(&self, _parts: &mut Parts) -> Vec<String> {
+            self.0.clone()
+        }
+    }
+
+    #[tokio::test]
+    async fn reads_from_configured_sources_in_specified_order() {
+        let app = Router::new()
+            .route("/", get(return_all_langs))
+            .layer(Extension(
+                UserLanguage::config()
+                    .add_source(TestSource(vec!["s1.1".to_string(), "s1.2".to_string()]))
+                    .add_source(TestSource(vec!["s2.1".to_string(), "s2.2".to_string()]))
+                    .build(),
+            ));
+
+        let client = TestClient::new(app);
+
+        let res = client.get("/").send().await;
+
+        assert_eq!(res.status(), StatusCode::OK);
+        assert_eq!(res.text().await, "s1.1,s1.2,s2.1,s2.2");
+    }
+
+    #[tokio::test]
+    async fn reads_languages_from_default_sources() {
+        let app = Router::new().route("/:lang", get(return_all_langs));
+
+        let client = TestClient::new(app);
+
+        let res = client
+            .get("/de?lang=fr")
+            .header(ACCEPT_LANGUAGE, "en;q=0.9,es;q=0.8")
+            .send()
+            .await;
+
+        assert_eq!(res.status(), StatusCode::OK);
+        assert_eq!(res.text().await, "fr,de,en,es");
+    }
+
+    #[tokio::test]
+    async fn falls_back_to_configured_language() {
+        let app = Router::new().route("/", get(return_lang)).layer(Extension(
+            UserLanguage::config().fallback_language("fallback").build(),
+        ));
+
+        let client = TestClient::new(app);
+
+        let res = client.get("/").send().await;
+
+        assert_eq!(res.status(), StatusCode::OK);
+        assert_eq!(res.text().await, "fallback");
+    }
+
+    #[tokio::test]
+    async fn falls_back_to_default_language() {
+        let app = Router::new().route("/", get(return_lang));
+
+        let client = TestClient::new(app);
+
+        let res = client.get("/").send().await;
+
+        assert_eq!(res.status(), StatusCode::OK);
+        assert_eq!(res.text().await, "en");
+    }
+
+    async fn return_lang(lang: UserLanguage) -> String {
+        lang.preferred_language().to_owned()
+    }
+
+    async fn return_all_langs(lang: UserLanguage) -> String {
+        lang.preferred_languages().join(",")
+    }
+}

From a89879af736a4aba50103f054f1e5516b4e72d52 Mon Sep 17 00:00:00 2001
From: Markus Gasser <markus.gasser@mailbox.org>
Date: Fri, 29 Sep 2023 08:45:42 +0000
Subject: [PATCH 15/24] Add tests for query and path source

---
 .../src/extract/user_lang/sources/path.rs     | 36 ++++++++++++++++---
 .../src/extract/user_lang/sources/query.rs    | 22 ++++++++++++
 2 files changed, 54 insertions(+), 4 deletions(-)

diff --git a/axum-extra/src/extract/user_lang/sources/path.rs b/axum-extra/src/extract/user_lang/sources/path.rs
index c46399d4cc..5dff56b800 100644
--- a/axum-extra/src/extract/user_lang/sources/path.rs
+++ b/axum-extra/src/extract/user_lang/sources/path.rs
@@ -46,6 +46,14 @@ impl PathSource {
     pub fn new(name: impl Into<String>) -> Self {
         Self { name: name.into() }
     }
+
+    fn languages_from_path(&self, path: Path<HashMap<String, String>>) -> Vec<String> {
+        let Some(lang) = path.get(self.name.as_str()) else {
+            return vec![];
+        };
+
+        vec![lang.to_string()]
+    }
 }
 
 #[async_trait]
@@ -55,10 +63,30 @@ impl UserLanguageSource for PathSource {
             return vec![];
         };
 
-        let Some(lang) = path.get(self.name.as_str()) else {
-            return vec![];
-        };
+        self.languages_from_path(path)
+    }
+}
 
-        vec![lang.to_string()]
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[tokio::test]
+    async fn reads_language_from_path() {
+        let source = PathSource::new("lang");
+
+        // We cannot setup the Path extractor here, as it requires
+        // UrlParams in the request extensions, which is private to axum.
+        //
+        // Instead we test loading from the extracted path directly.
+        let path = Path({
+            let mut path_matches = HashMap::new();
+            path_matches.insert("lang".to_string(), "it".to_string());
+            path_matches
+        });
+
+        let languages = source.languages_from_path(path);
+
+        assert_eq!(languages, vec!["it".to_string()]);
     }
 }
diff --git a/axum-extra/src/extract/user_lang/sources/query.rs b/axum-extra/src/extract/user_lang/sources/query.rs
index 9db20f0810..4cdce33340 100644
--- a/axum-extra/src/extract/user_lang/sources/query.rs
+++ b/axum-extra/src/extract/user_lang/sources/query.rs
@@ -60,3 +60,25 @@ impl UserLanguageSource for QuerySource {
         vec![lang.to_string()]
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use http::{Request, Uri};
+
+    #[tokio::test]
+    async fn reads_language_from_query() {
+        let source = QuerySource::new("lang");
+
+        let request: Request<()> = Request::builder()
+            .uri(Uri::builder().path_and_query("/?lang=de").build().unwrap())
+            .body(())
+            .unwrap();
+
+        let (mut parts, _) = request.into_parts();
+
+        let languages = source.languages_from_parts(&mut parts).await;
+
+        assert_eq!(languages, vec!["de".to_string()]);
+    }
+}

From a1fe1fd598ec3aa2fd0da346beebd80b0d4dd36d Mon Sep 17 00:00:00 2001
From: Markus Gasser <markus.gasser@mailbox.org>
Date: Fri, 29 Sep 2023 09:05:08 +0000
Subject: [PATCH 16/24] Add test for header source

---
 .../src/extract/user_lang/sources/header.rs   | 63 ++++++++++++++++++-
 1 file changed, 60 insertions(+), 3 deletions(-)

diff --git a/axum-extra/src/extract/user_lang/sources/header.rs b/axum-extra/src/extract/user_lang/sources/header.rs
index cb738c7216..30c1c1a04d 100644
--- a/axum-extra/src/extract/user_lang/sources/header.rs
+++ b/axum-extra/src/extract/user_lang/sources/header.rs
@@ -4,12 +4,12 @@ use std::cmp::Ordering;
 use crate::extract::user_lang::UserLanguageSource;
 
 /// A [`UserLanguageSource`] that reads languages from the `Accept-Language` header.
-/// 
+///
 /// This source may return multiple languages. Languages are returned in order of their
 /// quality values.
-/// 
+///
 /// # Example
-/// 
+///
 /// ```rust
 /// # use axum::{Router, extract::Extension, routing::get};
 /// # use axum_extra::extract::user_lang::{UserLanguage, AcceptLanguageSource};
@@ -63,6 +63,11 @@ fn parse_quality_values(values: &str) -> Vec<(&str, f32)> {
             continue;
         };
 
+        if value.is_empty() {
+            // empty quality value entry
+            continue;
+        }
+
         let quality = if let Some(quality) = quality.and_then(|q| q.strip_prefix("q=")) {
             quality.parse::<f32>().unwrap_or(0.0)
         } else {
@@ -75,3 +80,55 @@ fn parse_quality_values(values: &str) -> Vec<(&str, f32)> {
     quality_values.sort_by(|a, b| b.1.partial_cmp(&a.1).unwrap_or(Ordering::Equal));
     quality_values
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use http::{header::ACCEPT_LANGUAGE, Request};
+
+    #[tokio::test]
+    async fn reads_language_from_accept_header() {
+        let source = AcceptLanguageSource;
+
+        let request: Request<()> = Request::builder()
+            .header(ACCEPT_LANGUAGE, "fr,de;q=0.8,en;q=0.9")
+            .body(())
+            .unwrap();
+
+        let (mut parts, _) = request.into_parts();
+
+        let languages = source.languages_from_parts(&mut parts).await;
+
+        assert_eq!(
+            languages,
+            vec!["fr".to_string(), "en".to_string(), "de".to_string()]
+        );
+    }
+
+    #[test]
+    fn parsing_quality_values() {
+        let values = "fr-CH, fr;q=0.9, en;q=0.8, de;q=0.7, *;q=0.5";
+
+        let parsed = parse_quality_values(values);
+
+        assert_eq!(
+            parsed,
+            vec![
+                ("fr-CH", 1.0),
+                ("fr", 0.9),
+                ("en", 0.8),
+                ("de", 0.7),
+                ("*", 0.5),
+            ]
+        );
+    }
+
+    #[test]
+    fn empty_quality_values() {
+        let values = "";
+
+        let parsed = parse_quality_values(values);
+
+        assert_eq!(parsed, vec![]);
+    }
+}

From f247202e6855f1400e6ce3655c5c841b5199f9ef Mon Sep 17 00:00:00 2001
From: Markus Gasser <markus.gasser@mailbox.org>
Date: Fri, 29 Sep 2023 09:07:28 +0000
Subject: [PATCH 17/24] Remove unintentionally checked-in files

---
 .devcontainer/devcontainer.json | 34 ---------------------------------
 .vscode/settings.json           |  4 ----
 2 files changed, 38 deletions(-)
 delete mode 100644 .devcontainer/devcontainer.json
 delete mode 100644 .vscode/settings.json

diff --git a/.devcontainer/devcontainer.json b/.devcontainer/devcontainer.json
deleted file mode 100644
index 60c7aa4105..0000000000
--- a/.devcontainer/devcontainer.json
+++ /dev/null
@@ -1,34 +0,0 @@
-// For format details, see https://aka.ms/devcontainer.json. For config options, see the
-// README at: https://github.com/devcontainers/templates/tree/main/src/rust
-{
-	"name": "Rust",
-	// Or use a Dockerfile or Docker Compose file. More info: https://containers.dev/guide/dockerfile
-	"image": "mcr.microsoft.com/devcontainers/rust:1-1-bullseye",
-	"features": {
-		"ghcr.io/devcontainers-contrib/features/fish-apt-get:1": {}
-	}
-
-	// Use 'mounts' to make the cargo cache persistent in a Docker Volume.
-	// "mounts": [
-	// 	{
-	// 		"source": "devcontainer-cargo-cache-${devcontainerId}",
-	// 		"target": "/usr/local/cargo",
-	// 		"type": "volume"
-	// 	}
-	// ]
-
-	// Features to add to the dev container. More info: https://containers.dev/features.
-	// "features": {},
-
-	// Use 'forwardPorts' to make a list of ports inside the container available locally.
-	// "forwardPorts": [],
-
-	// Use 'postCreateCommand' to run commands after the container is created.
-	// "postCreateCommand": "rustc --version",
-
-	// Configure tool-specific properties.
-	// "customizations": {},
-
-	// Uncomment to connect as root instead. More info: https://aka.ms/dev-containers-non-root.
-	// "remoteUser": "root"
-}
diff --git a/.vscode/settings.json b/.vscode/settings.json
deleted file mode 100644
index 4bc45ade3d..0000000000
--- a/.vscode/settings.json
+++ /dev/null
@@ -1,4 +0,0 @@
-{
-    "rust-analyzer.showUnlinkedFileNotification": false,
-    "rust-analyzer.cargo.features": "all"
-}
\ No newline at end of file

From 49bcd596657b1604d969b309882025d210434ceb Mon Sep 17 00:00:00 2001
From: Markus Gasser <markus.gasser@mailbox.org>
Date: Fri, 29 Sep 2023 12:32:02 +0000
Subject: [PATCH 18/24] Ignore wildcard language in accept source

---
 .../src/extract/user_lang/sources/header.rs     | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/axum-extra/src/extract/user_lang/sources/header.rs b/axum-extra/src/extract/user_lang/sources/header.rs
index 30c1c1a04d..4cc7c449f5 100644
--- a/axum-extra/src/extract/user_lang/sources/header.rs
+++ b/axum-extra/src/extract/user_lang/sources/header.rs
@@ -44,6 +44,7 @@ impl UserLanguageSource for AcceptLanguageSource {
 
         parse_quality_values(accept_language)
             .into_iter()
+            .filter(|(lang, _)| *lang != "*")
             .map(|(lang, _)| lang.to_string())
             .collect()
     }
@@ -105,6 +106,22 @@ mod tests {
         );
     }
 
+    #[tokio::test]
+    async fn ignores_wildcard_lang() {
+        let source = AcceptLanguageSource;
+
+        let request: Request<()> = Request::builder()
+            .header(ACCEPT_LANGUAGE, "fr,de;q=0.8,*;q=0.9")
+            .body(())
+            .unwrap();
+
+        let (mut parts, _) = request.into_parts();
+
+        let languages = source.languages_from_parts(&mut parts).await;
+
+        assert_eq!(languages, vec!["fr".to_string(), "de".to_string()]);
+    }
+
     #[test]
     fn parsing_quality_values() {
         let values = "fr-CH, fr;q=0.9, en;q=0.8, de;q=0.7, *;q=0.5";

From cfed2b4f9b8de12068e7dfef9250e5d233ee2be1 Mon Sep 17 00:00:00 2001
From: Markus Gasser <markus.gasser@mailbox.org>
Date: Sun, 7 Jan 2024 21:44:38 +0100
Subject: [PATCH 19/24] Fix CI issues

---
 axum-extra/src/extract/user_lang/lang.rs        | 2 +-
 axum-extra/src/extract/user_lang/sources/mod.rs | 4 ++++
 2 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/axum-extra/src/extract/user_lang/lang.rs b/axum-extra/src/extract/user_lang/lang.rs
index 91433b3608..679ff94640 100644
--- a/axum-extra/src/extract/user_lang/lang.rs
+++ b/axum-extra/src/extract/user_lang/lang.rs
@@ -29,7 +29,7 @@ use std::{
 ///
 /// # Custom Sources
 ///
-/// You can create custom user langauge sources. See
+/// You can create custom user language sources. See
 /// [`UserLanguageSource`] for details.
 ///
 /// # Example
diff --git a/axum-extra/src/extract/user_lang/sources/mod.rs b/axum-extra/src/extract/user_lang/sources/mod.rs
index b166f9a738..33b9483be7 100644
--- a/axum-extra/src/extract/user_lang/sources/mod.rs
+++ b/axum-extra/src/extract/user_lang/sources/mod.rs
@@ -1,7 +1,11 @@
 mod header;
 mod path;
+
+#[cfg(feature = "query")]
 mod query;
 
 pub use header::*;
 pub use path::*;
+
+#[cfg(feature = "query")]
 pub use query::*;

From fc60aa60d8abbc79b991a94c6d7dbae759ff5b9b Mon Sep 17 00:00:00 2001
From: Markus Gasser <markus.gasser@mailbox.org>
Date: Sun, 7 Jan 2024 21:58:18 +0100
Subject: [PATCH 20/24] Replace usages of (&str).to_string() with to_owned()

---
 axum-extra/src/extract/user_lang/sources/header.rs | 6 +++---
 axum-extra/src/extract/user_lang/sources/path.rs   | 6 +++---
 axum-extra/src/extract/user_lang/sources/query.rs  | 4 ++--
 3 files changed, 8 insertions(+), 8 deletions(-)

diff --git a/axum-extra/src/extract/user_lang/sources/header.rs b/axum-extra/src/extract/user_lang/sources/header.rs
index 4cc7c449f5..7d29b0074c 100644
--- a/axum-extra/src/extract/user_lang/sources/header.rs
+++ b/axum-extra/src/extract/user_lang/sources/header.rs
@@ -45,7 +45,7 @@ impl UserLanguageSource for AcceptLanguageSource {
         parse_quality_values(accept_language)
             .into_iter()
             .filter(|(lang, _)| *lang != "*")
-            .map(|(lang, _)| lang.to_string())
+            .map(|(lang, _)| lang.to_owned())
             .collect()
     }
 }
@@ -102,7 +102,7 @@ mod tests {
 
         assert_eq!(
             languages,
-            vec!["fr".to_string(), "en".to_string(), "de".to_string()]
+            vec!["fr".to_owned(), "en".to_owned(), "de".to_owned()]
         );
     }
 
@@ -119,7 +119,7 @@ mod tests {
 
         let languages = source.languages_from_parts(&mut parts).await;
 
-        assert_eq!(languages, vec!["fr".to_string(), "de".to_string()]);
+        assert_eq!(languages, vec!["fr".to_owned(), "de".to_owned()]);
     }
 
     #[test]
diff --git a/axum-extra/src/extract/user_lang/sources/path.rs b/axum-extra/src/extract/user_lang/sources/path.rs
index 5dff56b800..996412f202 100644
--- a/axum-extra/src/extract/user_lang/sources/path.rs
+++ b/axum-extra/src/extract/user_lang/sources/path.rs
@@ -52,7 +52,7 @@ impl PathSource {
             return vec![];
         };
 
-        vec![lang.to_string()]
+        vec![lang.to_owned()]
     }
 }
 
@@ -81,12 +81,12 @@ mod tests {
         // Instead we test loading from the extracted path directly.
         let path = Path({
             let mut path_matches = HashMap::new();
-            path_matches.insert("lang".to_string(), "it".to_string());
+            path_matches.insert("lang".to_owned(), "it".to_owned());
             path_matches
         });
 
         let languages = source.languages_from_path(path);
 
-        assert_eq!(languages, vec!["it".to_string()]);
+        assert_eq!(languages, vec!["it".to_owned()]);
     }
 }
diff --git a/axum-extra/src/extract/user_lang/sources/query.rs b/axum-extra/src/extract/user_lang/sources/query.rs
index 4cdce33340..f9add43f6a 100644
--- a/axum-extra/src/extract/user_lang/sources/query.rs
+++ b/axum-extra/src/extract/user_lang/sources/query.rs
@@ -57,7 +57,7 @@ impl UserLanguageSource for QuerySource {
             return vec![];
         };
 
-        vec![lang.to_string()]
+        vec![lang.to_owned()]
     }
 }
 
@@ -79,6 +79,6 @@ mod tests {
 
         let languages = source.languages_from_parts(&mut parts).await;
 
-        assert_eq!(languages, vec!["de".to_string()]);
+        assert_eq!(languages, vec!["de".to_owned()]);
     }
 }

From 604c25ec2c87d59aed8d0046c9b973be0a410cc9 Mon Sep 17 00:00:00 2001
From: Markus Gasser <markus.gasser@mailbox.org>
Date: Sun, 7 Jan 2024 22:02:41 +0100
Subject: [PATCH 21/24] Use query source conditionally based on feature flag

---
 axum-extra/src/extract/user_lang/lang.rs | 14 +++++++++-----
 1 file changed, 9 insertions(+), 5 deletions(-)

diff --git a/axum-extra/src/extract/user_lang/lang.rs b/axum-extra/src/extract/user_lang/lang.rs
index 679ff94640..06cf560bd7 100644
--- a/axum-extra/src/extract/user_lang/lang.rs
+++ b/axum-extra/src/extract/user_lang/lang.rs
@@ -1,5 +1,5 @@
 use super::{
-    sources::{AcceptLanguageSource, PathSource, QuerySource},
+    sources::{AcceptLanguageSource, PathSource},
     Config, UserLanguageSource,
 };
 use axum::{async_trait, extract::FromRequestParts, Extension, RequestPartsExt};
@@ -9,6 +9,9 @@ use std::{
     sync::{Arc, OnceLock},
 };
 
+#[cfg(feature = "query")]
+use super::sources::QuerySource;
+
 /// The users preferred languages, read from the request.
 ///
 /// This extractor reads the users preferred languages from a
@@ -52,7 +55,7 @@ impl UserLanguage {
     ///
     /// If you do not add a configuration for the [`UserLanguage`] extractor,
     /// these sources will be used by default. They are in order:
-    ///  * The query parameter `lang`
+    ///  * The query parameter `lang` (if feature `query` is enabled)
     ///  * The path segment `:lang`
     ///  * The `Accept-Language` header
     pub fn default_sources() -> &'static Vec<Arc<dyn UserLanguageSource>> {
@@ -60,6 +63,7 @@ impl UserLanguage {
 
         DEFAULT_SOURCES.get_or_init(|| {
             vec![
+                #[cfg(feature = "query")]
                 Arc::new(QuerySource::new("lang")),
                 Arc::new(PathSource::new("lang")),
                 Arc::new(AcceptLanguageSource),
@@ -111,7 +115,7 @@ where
         };
 
         let sources = sources.as_ref().unwrap_or(Self::default_sources());
-        let fallback_language = fallback_language.unwrap_or_else(|| "en".to_string());
+        let fallback_language = fallback_language.unwrap_or_else(|| "en".to_owned());
 
         let mut preferred_languages = Vec::<String>::new();
 
@@ -150,8 +154,8 @@ mod tests {
             .route("/", get(return_all_langs))
             .layer(Extension(
                 UserLanguage::config()
-                    .add_source(TestSource(vec!["s1.1".to_string(), "s1.2".to_string()]))
-                    .add_source(TestSource(vec!["s2.1".to_string(), "s2.2".to_string()]))
+                    .add_source(TestSource(vec!["s1.1".to_owned(), "s1.2".to_owned()]))
+                    .add_source(TestSource(vec!["s2.1".to_owned(), "s2.2".to_owned()]))
                     .build(),
             ));
 

From b51c6727444b6310b93bb4f4028034fc176d60a5 Mon Sep 17 00:00:00 2001
From: Markus Gasser <markus.gasser@mailbox.org>
Date: Sun, 7 Jan 2024 22:06:26 +0100
Subject: [PATCH 22/24] Address more clippy issues

---
 axum-extra/src/extract/user_lang/config.rs         | 2 +-
 axum-extra/src/extract/user_lang/source.rs         | 2 +-
 axum-extra/src/extract/user_lang/sources/header.rs | 4 ++--
 3 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/axum-extra/src/extract/user_lang/config.rs b/axum-extra/src/extract/user_lang/config.rs
index 91a81db275..1c2861d1a6 100644
--- a/axum-extra/src/extract/user_lang/config.rs
+++ b/axum-extra/src/extract/user_lang/config.rs
@@ -93,7 +93,7 @@ impl UserLanguage {
     /// Returns a builder for [`Config`].
     pub fn config() -> ConfigBuilder {
         ConfigBuilder {
-            fallback_language: "en".to_string(),
+            fallback_language: "en".to_owned(),
             sources: vec![],
         }
     }
diff --git a/axum-extra/src/extract/user_lang/source.rs b/axum-extra/src/extract/user_lang/source.rs
index 2debd55cb2..5071d238d3 100644
--- a/axum-extra/src/extract/user_lang/source.rs
+++ b/axum-extra/src/extract/user_lang/source.rs
@@ -27,7 +27,7 @@ use std::fmt::Debug;
 ///             return vec![];
 ///         };
 ///
-///         vec![lang.to_string()]
+///         vec![lang.to_owned()]
 ///     }
 /// }
 /// ```
diff --git a/axum-extra/src/extract/user_lang/sources/header.rs b/axum-extra/src/extract/user_lang/sources/header.rs
index 7d29b0074c..1dfe6df3de 100644
--- a/axum-extra/src/extract/user_lang/sources/header.rs
+++ b/axum-extra/src/extract/user_lang/sources/header.rs
@@ -52,10 +52,10 @@ impl UserLanguageSource for AcceptLanguageSource {
 
 /// Parse quality values from the `Accept-Language` header.
 fn parse_quality_values(values: &str) -> Vec<(&str, f32)> {
-    let mut values = values.split(',');
+    let values = values.split(',');
     let mut quality_values = Vec::new();
 
-    while let Some(value) = values.next() {
+    for value in values {
         let mut value = value.trim().split(';');
         let (value, quality) = (value.next(), value.next());
 

From c596e0df3e1e923ed973e0031e37e7b5883c7f16 Mon Sep 17 00:00:00 2001
From: Markus Gasser <markus.gasser@mailbox.org>
Date: Sun, 7 Jan 2024 22:16:56 +0100
Subject: [PATCH 23/24] Use crate export insted of re-export

---
 axum-extra/src/extract/user_lang/sources/query.rs | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/axum-extra/src/extract/user_lang/sources/query.rs b/axum-extra/src/extract/user_lang/sources/query.rs
index f9add43f6a..31b3333256 100644
--- a/axum-extra/src/extract/user_lang/sources/query.rs
+++ b/axum-extra/src/extract/user_lang/sources/query.rs
@@ -1,7 +1,7 @@
-use axum::{async_trait, extract::Query, RequestPartsExt};
+use axum::{async_trait, RequestPartsExt};
 use std::collections::HashMap;
 
-use crate::extract::user_lang::UserLanguageSource;
+use crate::extract::{Query, user_lang::UserLanguageSource};
 
 /// A [`UserLanguageSource`] that reads the language from a field in the
 /// query string.

From cdf9a72c50bf2c9dcd821713bc63b4c38d03bfc2 Mon Sep 17 00:00:00 2001
From: Markus Gasser <markus.gasser@mailbox.org>
Date: Sun, 7 Jan 2024 22:17:56 +0100
Subject: [PATCH 24/24] Fix clippy hint in example

---
 examples/user-language/src/main.rs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/examples/user-language/src/main.rs b/examples/user-language/src/main.rs
index ff3962b1fa..0f88a46d3b 100644
--- a/examples/user-language/src/main.rs
+++ b/examples/user-language/src/main.rs
@@ -43,6 +43,6 @@ async fn handler(lang: UserLanguage) -> Html<&'static str> {
         "de" => Html("<h1>Hallo, Welt!</h1>"),
         "es" => Html("<h1>Hola, Mundo!</h1>"),
         "fr" => Html("<h1>Bonjour, le monde!</h1>"),
-        "en" | _ => Html("<h1>Hello, World!</h1>"),
+        _ => Html("<h1>Hello, World!</h1>"),
     }
 }