From d07b5e537e64b1784db7faf4a39350cddb1c0a40 Mon Sep 17 00:00:00 2001
From: Matti Airas <matti.airas@hatlabs.fi>
Date: Thu, 19 Sep 2024 23:38:49 +0300
Subject: [PATCH 1/7] Rename signalk_position to signalk_types

Implement ENUVector and AttitudeVector and provide serializers for them.
---
 src/sensesp/signalk/signalk_position.cpp | 30 ----------------
 src/sensesp/signalk/signalk_position.h   | 18 ----------
 src/sensesp/signalk/signalk_types.cpp    | 46 ++++++++++++++++++++++++
 src/sensesp/signalk/signalk_types.h      | 26 ++++++++++++++
 4 files changed, 72 insertions(+), 48 deletions(-)
 delete mode 100644 src/sensesp/signalk/signalk_position.cpp
 delete mode 100644 src/sensesp/signalk/signalk_position.h
 create mode 100644 src/sensesp/signalk/signalk_types.cpp
 create mode 100644 src/sensesp/signalk/signalk_types.h

diff --git a/src/sensesp/signalk/signalk_position.cpp b/src/sensesp/signalk/signalk_position.cpp
deleted file mode 100644
index 498cf6123..000000000
--- a/src/sensesp/signalk/signalk_position.cpp
+++ /dev/null
@@ -1,30 +0,0 @@
-
-#include "signalk_position.h"
-
-namespace sensesp {
-
-/**
- * @brief Template specialization for SKOutputPosition::as_signalk()
- *
- * This specialization allows `Position` objects to be output as Signal K
- * deltas.
- *
- * @tparam
- * @return String
- */
-template <>
-String SKOutput<Position>::as_signalk() {
-  JsonDocument json_doc;
-  String json;
-  json_doc["path"] = this->get_sk_path();
-  JsonObject value = json_doc["value"].to<JsonObject>();
-  value["latitude"] = output.latitude;
-  value["longitude"] = output.longitude;
-  if (output.altitude != kPositionInvalidAltitude) {
-    value["altitude"] = output.altitude;
-  }
-  serializeJson(json_doc, json);
-  return json;
-}
-
-}  // namespace sensesp
diff --git a/src/sensesp/signalk/signalk_position.h b/src/sensesp/signalk/signalk_position.h
deleted file mode 100644
index 0cc9312a3..000000000
--- a/src/sensesp/signalk/signalk_position.h
+++ /dev/null
@@ -1,18 +0,0 @@
-#ifndef SENSESP_SRC_SENSESP_SIGNALK_SIGNALK_POSITION_H_
-#define SENSESP_SRC_SENSESP_SIGNALK_SIGNALK_POSITION_H_
-
-#include <set>
-
-#include "sensesp/signalk/signalk_output.h"
-#include "sensesp/types/position.h"
-
-namespace sensesp {
-
-template <>
-String SKOutput<Position>::as_signalk();
-
-typedef SKOutput<Position> SKOutputPosition;
-
-}  // namespace sensesp
-
-#endif
diff --git a/src/sensesp/signalk/signalk_types.cpp b/src/sensesp/signalk/signalk_types.cpp
new file mode 100644
index 000000000..69f4bd3da
--- /dev/null
+++ b/src/sensesp/signalk/signalk_types.cpp
@@ -0,0 +1,46 @@
+
+#include "signalk_types.h"
+
+namespace sensesp {
+
+/**
+ * @brief Template specialization for SKOutputPosition::as_signalk_json()
+ *
+ * This specialization allows `Position` objects to be output as Signal K
+ * deltas.
+ *
+ * @tparam
+ * @return String
+ */
+template <>
+void SKOutput<Position>::as_signalk_json(JsonDocument& doc) {
+  doc["path"] = this->get_sk_path();
+  JsonObject value = doc["value"].to<JsonObject>();
+  value["latitude"] = output.latitude;
+  value["longitude"] = output.longitude;
+  if (output.altitude != kPositionInvalidAltitude) {
+    value["altitude"] = output.altitude;
+  }
+}
+
+template <>
+void SKOutput<ENUVector>::as_signalk_json(JsonDocument& doc) {
+  doc["path"] = this->get_sk_path();
+  JsonObject value = doc["value"].to<JsonObject>();
+  value["east"] = output.east;
+  value["north"] = output.north;
+  if (output.up != kPositionInvalidAltitude) {
+    value["up"] = output.up;
+  }
+}
+
+template <>
+void SKOutput<AttitudeVector>::as_signalk_json(JsonDocument& doc) {
+  doc["path"] = this->get_sk_path();
+  JsonObject value = doc["value"].to<JsonObject>();
+  value["roll"] = output.roll;
+  value["pitch"] = output.pitch;
+  value["yaw"] = output.yaw;
+}
+
+}  // namespace sensesp
diff --git a/src/sensesp/signalk/signalk_types.h b/src/sensesp/signalk/signalk_types.h
new file mode 100644
index 000000000..c41ad9218
--- /dev/null
+++ b/src/sensesp/signalk/signalk_types.h
@@ -0,0 +1,26 @@
+#ifndef SENSESP_SRC_SENSESP_SIGNALK_SIGNALK_TYPES_H_
+#define SENSESP_SRC_SENSESP_SIGNALK_SIGNALK_TYPES_H_
+
+#include <vector>
+
+#include "sensesp/signalk/signalk_output.h"
+#include "sensesp/types/position.h"
+
+namespace sensesp {
+
+template <>
+void SKOutput<Position>::as_signalk_json(JsonDocument& doc);
+
+template <>
+void SKOutput<ENUVector>::as_signalk_json(JsonDocument& doc);
+
+template <>
+void SKOutput<AttitudeVector>::as_signalk_json(JsonDocument& doc);
+
+typedef SKOutput<Position> SKOutputPosition;
+typedef SKOutput<ENUVector> SKOutputENUVector;
+typedef SKOutput<AttitudeVector> SKOutputAttitudeVector;
+
+}  // namespace sensesp
+
+#endif

From 3428f73e646ecb29c6dbe079205d5053cbfea65f Mon Sep 17 00:00:00 2001
From: Matti Airas <matti.airas@hatlabs.fi>
Date: Thu, 19 Sep 2024 23:36:32 +0300
Subject: [PATCH 2/7] Output free memory in system status screen.

---
 src/sensesp_app.h | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/src/sensesp_app.h b/src/sensesp_app.h
index b498d2208..21142507c 100644
--- a/src/sensesp_app.h
+++ b/src/sensesp_app.h
@@ -146,8 +146,11 @@ class SensESPApp : public SensESPBaseApp {
       new UIOutput<String>("MAC Address", WiFi.macAddress(), "Network", 1100);
   UILambdaOutput<String>* wifi_ssid_ui_output_ = new UILambdaOutput<String>(
       "SSID", [this]() { return WiFi.SSID(); }, "Network", 1200);
+  UILambdaOutput<String>* free_memory_ui_output_ = new UILambdaOutput<String>(
+      "Free memory (bytes)", []() { return String(ESP.getFreeHeap()); }, "System",
+      1250);
   UILambdaOutput<int8_t>* wifi_rssi_ui_output_ = new UILambdaOutput<int8_t>(
-      "WiFi signal strength", [this]() { return WiFi.RSSI(); }, "Network",
+      "WiFi signal strength (dB)", [this]() { return WiFi.RSSI(); }, "Network",
       1300);
   UILambdaOutput<String>* sk_server_address_ui_output_ =
       new UILambdaOutput<String>(

From 632d276bbdc987555821a202c768eaeeaf81b2b3 Mon Sep 17 00:00:00 2001
From: Matti Airas <matti.airas@hatlabs.fi>
Date: Thu, 19 Sep 2024 23:38:07 +0300
Subject: [PATCH 3/7] Remove last remaining ReactESP singleton refs

---
 src/sensesp/system/async_response_handler.h | 22 +++++-----
 src/sensesp/system/stream_producer.h        | 47 +++++++++++----------
 src/sensesp/transforms/repeat.h             | 12 +++---
 3 files changed, 43 insertions(+), 38 deletions(-)

diff --git a/src/sensesp/system/async_response_handler.h b/src/sensesp/system/async_response_handler.h
index 2f2ad142c..bffb59976 100644
--- a/src/sensesp/system/async_response_handler.h
+++ b/src/sensesp/system/async_response_handler.h
@@ -6,6 +6,7 @@
 #include <Arduino.h>
 #include <elapsedMillis.h>
 
+#include "sensesp_base_app.h"
 #include "valueproducer.h"
 
 namespace sensesp {
@@ -49,17 +50,18 @@ class AsyncResponseHandler : public ValueConsumer<bool>,
     this->emit(status_);
 
     if (timeout_event_ != nullptr) {
-      reactesp::EventLoop::app->remove(timeout_event_);
+      SensESPBaseApp::get_event_loop()->remove(timeout_event_);
       timeout_event_ = nullptr;
     }
-    timeout_event_ = reactesp::EventLoop::app->onDelay(timeout_, [this]() {
-      if (status_ == AsyncResponseStatus::kPending) {
-        ESP_LOGV("AsyncResponseHandler", "Timeout");
-        status_ = AsyncResponseStatus::kTimeout;
-        this->emit(status_);
-      }
-      this->timeout_event_ = nullptr;
-    });
+    timeout_event_ =
+        SensESPBaseApp::get_event_loop()->onDelay(timeout_, [this]() {
+          if (status_ == AsyncResponseStatus::kPending) {
+            ESP_LOGV("AsyncResponseHandler", "Timeout");
+            status_ = AsyncResponseStatus::kTimeout;
+            this->emit(status_);
+          }
+          this->timeout_event_ = nullptr;
+        });
   }
 
   void set(const bool& success) override {
@@ -72,7 +74,7 @@ class AsyncResponseHandler : public ValueConsumer<bool>,
 
     // Clear the timeout event
     if (timeout_event_ != nullptr) {
-      reactesp::EventLoop::app->remove(timeout_event_);
+      SensESPBaseApp::get_event_loop()->remove(timeout_event_);
       timeout_event_ = nullptr;
     }
 
diff --git a/src/sensesp/system/stream_producer.h b/src/sensesp/system/stream_producer.h
index e9bbac6b4..f600a9a01 100644
--- a/src/sensesp/system/stream_producer.h
+++ b/src/sensesp/system/stream_producer.h
@@ -5,6 +5,7 @@
 
 #include "ReactESP.h"
 #include "sensesp/system/valueproducer.h"
+#include "sensesp_base_app.h"
 
 namespace sensesp {
 
@@ -14,12 +15,13 @@ namespace sensesp {
 class StreamCharProducer : public ValueProducer<char> {
  public:
   StreamCharProducer(Stream* stream) : stream_{stream} {
-    read_event_ = reactesp::EventLoop::app->onAvailable(*stream_, [this]() {
-      while (stream_->available()) {
-        char c = stream_->read();
-        this->emit(c);
-      }
-    });
+    read_event_ =
+        SensESPBaseApp::get_event_loop()->onAvailable(*stream_, [this]() {
+          while (stream_->available()) {
+            char c = stream_->read();
+            this->emit(c);
+          }
+        });
   }
 
  protected:
@@ -36,23 +38,24 @@ class StreamLineProducer : public ValueProducer<String> {
       : stream_{stream}, max_line_length_{max_line_length} {
     static int buf_pos = 0;
     buf_ = new char[max_line_length_ + 1];
-    read_event_ = reactesp::EventLoop::app->onAvailable(*stream_, [this]() {
-      while (stream_->available()) {
-        char c = stream_->read();
-        if (c == '\n') {
-          // Include the newline character in the output
-          buf_[buf_pos++] = c;
-          buf_[buf_pos] = '\0';
-          this->emit(buf_);
-          buf_pos = 0;
-        } else {
-          buf_[buf_pos++] = c;
-          if (buf_pos >= max_line_length_ - 1) {
-            buf_pos = 0;
+    read_event_ =
+        SensESPBaseApp::get_event_loop()->onAvailable(*stream_, [this]() {
+          while (stream_->available()) {
+            char c = stream_->read();
+            if (c == '\n') {
+              // Include the newline character in the output
+              buf_[buf_pos++] = c;
+              buf_[buf_pos] = '\0';
+              this->emit(buf_);
+              buf_pos = 0;
+            } else {
+              buf_[buf_pos++] = c;
+              if (buf_pos >= max_line_length_ - 1) {
+                buf_pos = 0;
+              }
+            }
           }
-        }
-      }
-    });
+        });
   }
 
  protected:
diff --git a/src/sensesp/transforms/repeat.h b/src/sensesp/transforms/repeat.h
index 585ddbf4d..2e7504b27 100644
--- a/src/sensesp/transforms/repeat.h
+++ b/src/sensesp/transforms/repeat.h
@@ -33,7 +33,7 @@ class Repeat : public SymmetricTransform<T> {
       // Delete the old repeat event
       repeat_event_->remove();
     }
-    repeat_event_ = reactesp::EventLoop::app->onRepeat(
+    repeat_event_ = SensESPBaseApp::get_event_loop()->onRepeat(
         interval_, [this]() { this->notify(); });
   }
 
@@ -63,7 +63,7 @@ class RepeatStopping : public Repeat<T> {
       // Delete the old repeat event
       this->repeat_event_->remove();
     }
-    this->repeat_event_ = reactesp::EventLoop::app->onRepeat(
+    this->repeat_event_ = SensESPBaseApp::get_event_loop()->onRepeat(
         this->interval_, [this]() { this->repeat_function(); });
   }
 
@@ -74,7 +74,7 @@ class RepeatStopping : public Repeat<T> {
       // Delete the old repeat event
       this->repeat_event_->remove();
     }
-    this->repeat_event_ = reactesp::EventLoop::app->onRepeat(
+    this->repeat_event_ = SensESPBaseApp::get_event_loop()->onRepeat(
         this->interval_, [this]() { this->repeat_function(); });
   }
 
@@ -113,7 +113,7 @@ class RepeatExpiring : public Repeat<T> {
       // Delete the old repeat event
       this->repeat_event_->remove();
     }
-    this->repeat_event_ = reactesp::EventLoop::app->onRepeat(
+    this->repeat_event_ = SensESPBaseApp::get_event_loop()->onRepeat(
         this->interval_, [this]() { this->repeat_function(); });
   }
 
@@ -124,7 +124,7 @@ class RepeatExpiring : public Repeat<T> {
       // Delete the old repeat event
       this->repeat_event_->remove();
     }
-    this->repeat_event_ = reactesp::EventLoop::app->onRepeat(
+    this->repeat_event_ = SensESPBaseApp::get_event_loop()->onRepeat(
         this->interval_, [this]() { this->repeat_function(); });
   }
 
@@ -166,7 +166,7 @@ class RepeatConstantRate : public RepeatExpiring<T> {
       this->repeat_event_->remove();
     }
 
-    this->repeat_event_ = reactesp::EventLoop::app->onRepeat(
+    this->repeat_event_ = SensESPBaseApp::get_event_loop()->onRepeat(
         interval, [this]() { this->repeat_function(); });
   }
 

From d9ef15d5d993353f0b25b98807f7c4dc3b9bb435 Mon Sep 17 00:00:00 2001
From: Matti Airas <matti.airas@hatlabs.fi>
Date: Thu, 19 Sep 2024 23:36:04 +0300
Subject: [PATCH 4/7] Utilize ArduinoJson's automatic serialization

Provide serializers and deserializers for key classes.
---
 README.md                                   |  4 +++-
 src/sensesp/signalk/signalk_delta_queue.cpp |  9 +++++++--
 src/sensesp/signalk/signalk_emitter.h       |  8 ++++++--
 src/sensesp/signalk/signalk_output.h        | 20 ++++++--------------
 src/sensesp/signalk/signalk_time.cpp        | 10 +++-------
 src/sensesp/signalk/signalk_time.h          |  2 +-
 6 files changed, 26 insertions(+), 27 deletions(-)

diff --git a/README.md b/README.md
index 79254bda8..64c464b43 100644
--- a/README.md
+++ b/README.md
@@ -48,7 +48,9 @@
 
 - Implement stream producers that emit characters or lines from a stream
   (e.g., a serial port)
--
+- SKEmitter::as_signalk() has been renamed to SKEmitter::as_signalk_json().
+  It now writes its output to a JsonDocument reference instead
+  of returning a String.
 
 ### Migrating Existing Projects
 
diff --git a/src/sensesp/signalk/signalk_delta_queue.cpp b/src/sensesp/signalk/signalk_delta_queue.cpp
index 604a3f91c..b8a850265 100644
--- a/src/sensesp/signalk/signalk_delta_queue.cpp
+++ b/src/sensesp/signalk/signalk_delta_queue.cpp
@@ -39,8 +39,13 @@ void SKDeltaQueue::append(const String& val) {
 void SKDeltaQueue::connect_emitters() {
   for (auto const& sk_source : SKEmitter::get_sources()) {
     if (sk_source->get_sk_path() != "") {
-      sk_source->attach(
-          [sk_source, this]() { this->append(sk_source->as_signalk()); });
+      sk_source->attach([sk_source, this]() {
+        String output;
+        JsonDocument doc;
+        sk_source->as_signalk_json(doc);
+        serializeJson(doc, output);
+        this->append(output);
+      });
     }
   }
 }
diff --git a/src/sensesp/signalk/signalk_emitter.h b/src/sensesp/signalk/signalk_emitter.h
index 431ade2d4..ed5e05ae0 100644
--- a/src/sensesp/signalk/signalk_emitter.h
+++ b/src/sensesp/signalk/signalk_emitter.h
@@ -29,9 +29,13 @@ class SKEmitter : virtual public Observable {
 
   /**
    * Returns the data to be reported to the server as
-   * a Signal K json string.
+   * a Signal K json object.
    */
-  virtual String as_signalk() { return "not implemented"; }
+  virtual void as_signalk_json(JsonDocument& doc) {
+    ESP_LOGE("SKEmitter", "as_signalk_json() not implemented");
+    JsonVariant obj = doc.as<JsonVariant>();
+    obj.set("ERROR! Not implemented");
+  }
 
   /**
    * Returns a Metadata structure that describes the sk_path this SKEmitter
diff --git a/src/sensesp/signalk/signalk_output.h b/src/sensesp/signalk/signalk_output.h
index c095ef8b2..247705deb 100644
--- a/src/sensesp/signalk/signalk_output.h
+++ b/src/sensesp/signalk/signalk_output.h
@@ -46,13 +46,9 @@ class SKOutput : public SKEmitter, public SymmetricTransform<T> {
     this->ValueProducer<T>::emit(new_value);
   }
 
-  virtual String as_signalk() override {
-    JsonDocument json_doc;
-    String json;
-    json_doc["path"] = this->get_sk_path();
-    json_doc["value"] = ValueProducer<T>::output;
-    serializeJson(json_doc, json);
-    return json;
+  virtual void as_signalk_json(JsonDocument& doc) override {
+    doc["path"] = this->get_sk_path();
+    doc["value"] = ValueProducer<T>::output;
   }
 
   virtual void get_configuration(JsonObject& root) override {
@@ -92,13 +88,9 @@ class SKOutputRawJson : public SKOutput<String> {
                   SKMetadata* meta = NULL)
       : SKOutput<String>(sk_path, config_path, meta) {}
 
-  virtual String as_signalk() override {
-    JsonDocument json_doc;
-    String json;
-    json_doc["path"] = this->get_sk_path();
-    json_doc["value"] = serialized(ValueProducer<String>::output);
-    serializeJson(json_doc, json);
-    return json;
+  virtual void as_signalk_json(JsonDocument& doc) override {
+    doc["path"] = this->get_sk_path();
+    doc["value"] = serialized(ValueProducer<String>::output);
   }
 };
 
diff --git a/src/sensesp/signalk/signalk_time.cpp b/src/sensesp/signalk/signalk_time.cpp
index 95dae64ff..cbfda878f 100644
--- a/src/sensesp/signalk/signalk_time.cpp
+++ b/src/sensesp/signalk/signalk_time.cpp
@@ -8,13 +8,9 @@ SKOutputTime::SKOutputTime(const String& sk_path, const String& config_path)
   load_configuration();
 }
 
-String SKOutputTime::as_signalk() {
-  JsonDocument json_doc;
-  String json;
-  json_doc["path"] = this->sk_path_;
-  json_doc["value"] = output;
-  serializeJson(json_doc, json);
-  return json;
+void SKOutputTime::as_signalk_json(JsonDocument& doc){
+  doc["path"] = this->sk_path_;
+  doc["value"] = output;
 }
 
 void SKOutputTime::get_configuration(JsonObject& doc) {
diff --git a/src/sensesp/signalk/signalk_time.h b/src/sensesp/signalk/signalk_time.h
index dda0e32a5..90fd021c0 100644
--- a/src/sensesp/signalk/signalk_time.h
+++ b/src/sensesp/signalk/signalk_time.h
@@ -9,7 +9,7 @@ namespace sensesp {
 class SKOutputTime : public TimeString, public SKEmitter {
  public:
   SKOutputTime(const String& sk_path, const String& config_path = "");
-  virtual String as_signalk() override;
+  virtual void as_signalk_json(JsonDocument& doc) override;
   virtual void get_configuration(JsonObject& doc) override;
   virtual bool set_configuration(const JsonObject& config) override;
   virtual String get_config_schema() override;

From 9dfa98b02ae18048d6e1841ce7a97cbad5c522e8 Mon Sep 17 00:00:00 2001
From: Matti Airas <matti.airas@hatlabs.fi>
Date: Thu, 19 Sep 2024 23:39:23 +0300
Subject: [PATCH 5/7] Implement serializers for std::vector and position types

---
 src/sensesp/types/json.h       | 31 ++++++++++++++++++++
 src/sensesp/types/position.cpp | 52 ++++++++++++++++++++++++++++++++++
 src/sensesp/types/position.h   | 38 ++++++++++++++++++++++++-
 3 files changed, 120 insertions(+), 1 deletion(-)
 create mode 100644 src/sensesp/types/json.h

diff --git a/src/sensesp/types/json.h b/src/sensesp/types/json.h
new file mode 100644
index 000000000..131a66159
--- /dev/null
+++ b/src/sensesp/types/json.h
@@ -0,0 +1,31 @@
+#ifndef SENSESP_SRC_SENSESP_TYPES_JSON_H_
+#define SENSESP_SRC_SENSESP_TYPES_JSON_H_
+
+#include <vector>
+
+#include "ArduinoJson.h"
+
+namespace ArduinoJson {
+template <typename T>
+struct Converter<std::vector<T> > {
+  static void toJson(const std::vector<T>& src, JsonVariant dst) {
+    JsonArray array = dst.to<JsonArray>();
+    for (T item : src) array.add(item);
+  }
+
+  static std::vector<T> fromJson(JsonVariantConst src) {
+    std::vector<T> dst;
+    for (T item : src.as<JsonArrayConst>()) dst.push_back(item);
+    return dst;
+  }
+
+  static bool checkJson(JsonVariantConst src) {
+    JsonArrayConst array = src;
+    bool result = array;
+    for (JsonVariantConst item : array) result &= item.is<T>();
+    return result;
+  }
+};
+}  // namespace ARDUINOJSON_NAMESPACE
+
+#endif  // SENSESP_SRC_SENSESP_TYPES_JSON_H_
diff --git a/src/sensesp/types/position.cpp b/src/sensesp/types/position.cpp
index 873f5a5bc..16df87fac 100644
--- a/src/sensesp/types/position.cpp
+++ b/src/sensesp/types/position.cpp
@@ -13,8 +13,60 @@ void convertFromJson(JsonVariantConst src, Position &dst) {
   }
 }
 
+void convertFromJson(JsonVariantConst src, ENUVector &dst) {
+  dst.east = src["east"].as<float>();
+  dst.north = src["north"].as<float>();
+
+  if (src.containsKey("up")) {
+    dst.up = src["up"].as<float>();
+  }
+}
+
+void convertFromJson(JsonVariantConst src, AttitudeVector &dst) {
+  dst.roll = src["roll"].as<float>();
+  dst.pitch = src["pitch"].as<float>();
+  dst.yaw = src["yaw"].as<float>();
+}
+
 bool canConvertFromJson(JsonVariantConst src, const Position & /*position*/) {
   return src.containsKey("latitude") && src.containsKey("longitude");
 }
 
+bool canConvertFromJson(JsonVariantConst src, const ENUVector & /*enu*/) {
+  return src.containsKey("east") && src.containsKey("north");
+}
+
+bool canConvertFromJson(JsonVariantConst src,
+                        const AttitudeVector & /*attitude*/) {
+  return src.containsKey("roll") && src.containsKey("pitch") &&
+         src.containsKey("yaw");
+}
+
+void convertToJson(const Position &src, JsonVariant dst) {
+  JsonObject obj = dst.to<JsonObject>();
+  obj["latitude"] = src.latitude;
+  obj["longitude"] = src.longitude;
+
+  if (src.altitude != kPositionInvalidAltitude) {
+    obj["altitude"] = src.altitude;
+  }
+}
+
+void convertToJson(const ENUVector &src, JsonVariant dst) {
+  JsonObject obj = dst.to<JsonObject>();
+  obj["east"] = src.east;
+  obj["north"] = src.north;
+
+  if (src.up != kPositionInvalidAltitude) {
+    obj["up"] = src.up;
+  }
+}
+
+void convertToJson(const AttitudeVector &src, JsonVariant dst) {
+  JsonObject obj = dst.to<JsonObject>();
+  obj["roll"] = src.roll;
+  obj["pitch"] = src.pitch;
+  obj["yaw"] = src.yaw;
+}
+
 }  // namespace sensesp
diff --git a/src/sensesp/types/position.h b/src/sensesp/types/position.h
index 88a27e737..28af88e96 100644
--- a/src/sensesp/types/position.h
+++ b/src/sensesp/types/position.h
@@ -7,6 +7,7 @@
 namespace sensesp {
 
 /// Value used to indicate an invalid or missing altitude
+constexpr double kInvalidDouble = std::numeric_limits<double>::lowest();
 constexpr float kPositionInvalidAltitude = std::numeric_limits<float>::lowest();
 
 /**
@@ -20,6 +21,11 @@ struct Position {
   double latitude;
   double longitude;
   float altitude = kPositionInvalidAltitude;
+
+  Position() : latitude(kInvalidDouble), longitude(kInvalidDouble) {}
+  Position(double latitude, double longitude,
+           float altitude = kPositionInvalidAltitude)
+      : latitude(latitude), longitude(longitude), altitude(altitude) {}
 };
 
 /**
@@ -33,13 +39,35 @@ struct ENUVector {
   float east;
   float north;
   float up = kPositionInvalidAltitude;
+
+  ENUVector() : east(kInvalidDouble), north(kInvalidDouble) {}
+  ENUVector(float east, float north, float up = kPositionInvalidAltitude)
+      : east(east), north(north), up(up) {}
+};
+
+/**
+ * @brief Container for attitude data.
+ *
+ * Roll, pitch, and yaw (heading) angles, in radians.
+ *
+ */
+struct AttitudeVector {
+  // Ordering chosen to match the order of fields in Signal K
+  float roll;
+  float pitch;
+  float yaw;  // heading
+
+  AttitudeVector()
+      : roll(kInvalidDouble), pitch(kInvalidDouble), yaw(kInvalidDouble) {}
+  AttitudeVector(float roll, float pitch, float yaw)
+      : roll(roll), pitch(pitch), yaw(yaw) {}
 };
 
 /**
  * @brief Adds support in ArduinoJson to deserialize Position type data.
  *
  * This is an ArduinoJson custom converter to convert position type data from
- * JSON into a Postion struct. The JSON data must at least contain "latitude"
+ * JSON into a Position struct. The JSON data must at least contain "latitude"
  * and "longitude", "altitude" is optional. ArduinoJson will automatically
  * call this function whenever it has to convert a JSON to a Position struct.
  * More info here: https://arduinojson.org/news/2021/05/04/version-6-18-0/
@@ -48,6 +76,8 @@ struct ENUVector {
  * @param dst The address to a Position struct to write the data to
  */
 void convertFromJson(JsonVariantConst src, Position &dst);
+void convertFromJson(JsonVariantConst src, ENUVector &dst);
+void convertFromJson(JsonVariantConst src, AttitudeVector &dst);
 
 /**
  * @brief Tells ArduinoJson whether the given JSON is a Position or not
@@ -61,6 +91,12 @@ void convertFromJson(JsonVariantConst src, Position &dst);
  * keys
  */
 bool canConvertFromJson(JsonVariantConst src, const Position &);
+bool canConvertFromJson(JsonVariantConst src, const ENUVector &);
+bool canConvertFromJson(JsonVariantConst src, const AttitudeVector &);
+
+void convertToJson(const Position &src, JsonVariant dst);
+void convertToJson(const ENUVector &src, JsonVariant dst);
+void convertToJson(const AttitudeVector &src, JsonVariant dst);
 
 }  // namespace sensesp
 

From 0b56948f316f89208dce6a128bd1a5940b5fbcde Mon Sep 17 00:00:00 2001
From: Matti Airas <matti.airas@hatlabs.fi>
Date: Thu, 19 Sep 2024 23:39:56 +0300
Subject: [PATCH 6/7] Implement a nullable class for types that hold a special
 "invalid" value

---
 src/sensesp/types/nullable.cpp | 14 +++++++
 src/sensesp/types/nullable.h   | 76 ++++++++++++++++++++++++++++++++++
 2 files changed, 90 insertions(+)
 create mode 100644 src/sensesp/types/nullable.cpp
 create mode 100644 src/sensesp/types/nullable.h

diff --git a/src/sensesp/types/nullable.cpp b/src/sensesp/types/nullable.cpp
new file mode 100644
index 000000000..0da4a40a4
--- /dev/null
+++ b/src/sensesp/types/nullable.cpp
@@ -0,0 +1,14 @@
+#include "nullable.h"
+
+#include <limits>
+#include <cstdint>
+
+namespace sensesp {
+
+template <typename T> T Nullable<T>::invalid_value_ = T{};
+template <> int Nullable<int>::invalid_value_ = std::numeric_limits<int>::lowest();
+template <> float Nullable<float>::invalid_value_ = std::numeric_limits<float>::lowest();
+template <> double Nullable<double>::invalid_value_ = std::numeric_limits<double>::lowest();
+template <> char Nullable<char>::invalid_value_ = 255;
+
+}  // namespace sensesp
diff --git a/src/sensesp/types/nullable.h b/src/sensesp/types/nullable.h
new file mode 100644
index 000000000..dbb422cf0
--- /dev/null
+++ b/src/sensesp/types/nullable.h
@@ -0,0 +1,76 @@
+#ifndef SENSESP_SRC_SENSESP_TYPES_NULLABLE_H_
+#define SENSESP_SRC_SENSESP_TYPES_NULLABLE_H_
+
+#include "ArduinoJson.h"
+
+namespace sensesp {
+
+/**
+ * @brief Template class that supports a special invalid magic value for a type.
+ *
+ * The invalid value is always provided by the type's default constructor.
+ *
+ */
+template <typename T>
+class Nullable {
+  public:
+    Nullable() : value_{} {}
+    Nullable(T value) : value_{value} {}
+    Nullable<T>& operator=(T& value) {
+      value_ = value;
+      return *this;
+    }
+    Nullable<T>& operator=(const Nullable<T>& other) {
+      value_ = other.value_;
+      return *this;
+    }
+    operator T() const {
+      return value_;
+    }
+
+    bool is_valid() const {
+      return value_ != invalid_value_;
+    }
+
+    T* ptr() {
+      return &value_;
+    }
+
+    static T invalid() {
+      return invalid_value_;
+    }
+
+    T value() const {
+      return value_;
+    }
+
+  private:
+    T value_;
+    static T invalid_value_;
+};
+
+typedef Nullable<int> NullableInt;
+typedef Nullable<float> NullableFloat;
+typedef Nullable<double> NullableDouble;
+
+template <typename T>
+void convertFromJson(JsonVariantConst src, Nullable<T> &dst) {
+  if (src.isNull()) {
+    dst = NullableInt::invalid();
+  } else {
+    dst = src.as<T>();
+  }
+}
+
+template <typename T>
+void convertToJson(const Nullable<T> &src, JsonVariant dst) {
+  if (src.is_valid()) {
+    dst.set(src.value());
+  } else {
+    dst.clear();
+  }
+}
+
+}  // namespace sensesp
+
+#endif  // SENSESP_SRC_SENSESP_TYPES_NULLABLE_H_

From 9eae6292ab93fd70734ac9957d967aed7cf76da7 Mon Sep 17 00:00:00 2001
From: Matti Airas <matti.airas@hatlabs.fi>
Date: Thu, 19 Sep 2024 23:41:51 +0300
Subject: [PATCH 7/7] Make repeat transforms return nullable values

---
 src/sensesp/transforms/repeat.h | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/src/sensesp/transforms/repeat.h b/src/sensesp/transforms/repeat.h
index 2e7504b27..0fe0f592a 100644
--- a/src/sensesp/transforms/repeat.h
+++ b/src/sensesp/transforms/repeat.h
@@ -3,6 +3,7 @@
 
 #include <elapsedMillis.h>
 
+#include "sensesp/types/nullable.h"
 #include "transform.h"
 
 namespace sensesp {
@@ -103,10 +104,10 @@ class RepeatStopping : public Repeat<T> {
  * @tparam T
  */
 template <typename T>
-class RepeatExpiring : public Repeat<T> {
+class RepeatExpiring : public Repeat<Nullable<T>> {
  public:
-  RepeatExpiring(long interval, long max_age, T expired_value)
-      : Repeat<T>(interval), max_age_{max_age}, expired_value_{expired_value} {
+  RepeatExpiring(long interval, long max_age)
+      : Repeat<T>(interval), max_age_{max_age} {
     age_ = max_age;
 
     if (this->repeat_event_ != nullptr) {
@@ -131,7 +132,6 @@ class RepeatExpiring : public Repeat<T> {
  protected:
   elapsedMillis age_;
   long max_age_;
-  T expired_value_;
 
  protected:
   void repeat_function() {
@@ -140,7 +140,7 @@ class RepeatExpiring : public Repeat<T> {
     if (age_ < max_age_) {
       this->notify();
     } else {
-      this->emit(expired_value_);
+      this->emit(Nullable::invalid());
     }
   };
 };
@@ -159,8 +159,8 @@ class RepeatExpiring : public Repeat<T> {
 template <typename T>
 class RepeatConstantRate : public RepeatExpiring<T> {
  public:
-  RepeatConstantRate(long interval, long max_age, T expired_value)
-      : RepeatExpiring<T>(interval, max_age, expired_value) {
+  RepeatConstantRate(long interval, long max_age)
+      : RepeatExpiring<T>(interval, max_age) {
     if (this->repeat_event_ != nullptr) {
       // Delete the old repeat event
       this->repeat_event_->remove();