Fix charset conversion from utf16.

CHANGES.md

@@ -3,6 +3,7 @@
 - Add support for FLAC.
 - id3v2: use "bpm" instead of "tempo".
 - id3v2: convert "tlen" to "duration".
+- Fix charset conversion from utf16.
 
 0.1.0 (2023-02-08)
 =====

src/metadataCharEncoding.ml

@@ -8,26 +8,22 @@ end
 module Naive : T = struct
   let convert ?source s =
     let source = match source with None -> `UTF_8 | Some x -> x in
-    let endianness = ref `BE in
+    let endianness = ref (if source = `UTF_16LE then `LE else `BE) in
     let buf = Buffer.create 10 in
     match source with
-      | (`UTF_16 | `UTF_16LE | `UTF_16BE) as source ->
-          let get_char =
-            match source with
-              | `UTF_16LE -> String.get_utf_16le_uchar
-              | `UTF_16BE -> String.get_utf_16be_uchar
-              | `UTF_16 -> (
-                  match !endianness with
-                    | `LE -> String.get_utf_16le_uchar
-                    | `BE -> String.get_utf_16be_uchar)
-          in
+      | `UTF_16 | `UTF_16LE | `UTF_16BE ->
           let len = String.length s in
           let rec f pos =
+            let get_char =
+              match !endianness with
+              | `LE -> String.get_utf_16le_uchar
+              | `BE -> String.get_utf_16be_uchar
+            in
             if pos = len then Buffer.contents buf
-            else if pos + 2 <= len && s.[pos] = '\xfe' && s.[pos] = '\xff' then (
+            else if pos + 2 <= len && s.[pos] = '\xfe' && s.[pos+1] = '\xff' then (
               endianness := `BE;
               f (pos + 2))
-            else if pos + 2 <= len && s.[pos] = '\xff' && s.[pos] = '\xfe' then (
+            else if pos + 2 <= len && s.[pos] = '\xff' && s.[pos+1] = '\xfe' then (
               endianness := `LE;
               f (pos + 2))
             else (

src/metadataID3v2.ml

@@ -38,15 +38,20 @@ let next_substring encoding ?(offset = 0) s =
   let ans = ref 0 in
   let utf16 = encoding = 1 || encoding = 2 in
   try
-    for i = offset to String.length s - if utf16 then 2 else 1 do
-      if utf16 then (
-        if s.[i] = '\000' && s.[i + 1] = '\000' then (
-          ans := i + 2;
-          raise Exit))
-      else if s.[i] = '\000' then (
-        ans := i + 1;
-        raise Exit)
-    done;
+    if utf16 then
+      for i = offset to String.length s / 2 - 1 do
+        if s.[2*i] = '\000' && s.[2*i+1] = '\000' then (
+          ans := 2*i+2;
+          raise Exit
+        )
+      done
+    else
+      for i = offset to String.length s - 1 do
+        if s.[i] = '\000' then (
+          ans := i + 1;
+          raise Exit
+        )
+      done;
     raise Not_found
   with Exit -> !ans
 
@@ -78,19 +83,7 @@ let make_recode recode =
   in
   let recode : int -> string -> string = function
     | 0 -> recode ~source:`ISO_8859_1
-    | 1 -> (
-        fun s ->
-          match String.length s with
-            (* Probably invalid string *)
-            | n when n < 2 -> s
-            | n -> (
-                match String.sub s 0 2 with
-                  | "\255\254" | "\255\246" ->
-                      recode ~source:`UTF_16LE (String.sub s 2 (n - 2))
-                  | "\254\255" | "\246\255" ->
-                      recode ~source:`UTF_16BE (String.sub s 2 (n - 2))
-                  (* Probably invalid string *)
-                  | _ -> recode ~source:`UTF_16 s))
+    | 1 -> recode ~source:`UTF_16
     | 2 -> recode ~source:`UTF_16
     | 3 -> recode ~source:`UTF_8
     (* Invalid encoding. *)

test/test

@@ -0,0 +1,2 @@
+#!/bin/sh
+dune exec --no-print-directory ./test.exe -- $@

test/test.ml

@@ -1,2 +1,8 @@
 let () =
-  assert (Metadata.ID3v2.unterminate 2 "\000ab\000de\000\000" = "\000ab\000de")
+  assert (Metadata.ID3v2.unterminate 2 "\000ab\000de\000\000" = "\000ab\000de");
+  (* Little endian. *)
+  assert (Metadata.CharEncoding.Naive.convert ~source:`UTF_16LE "a\x00b\x00c\x00" = "abc");
+  assert (Metadata.CharEncoding.Naive.convert ~source:`UTF_16 "\xff\xfea\x00b\x00c\x00" = "abc");
+  (* Big endian. *)
+  assert (Metadata.CharEncoding.Naive.convert ~source:`UTF_16BE "\x00a\x00b\x00c" = "abc");
+  assert (Metadata.CharEncoding.Naive.convert ~source:`UTF_16 "\xfe\xff\x00a\x00b\x00c" = "abc")