Use ref charset and language for charset detection

app/src/main/java/eu/faircode/email/ActivityEML.java

@@ -437,7 +437,6 @@ public class ActivityEML extends ActivityBase {
                         Object content = part.getContent();
                         if (content instanceof String) {
                             String text = (String) content;
-                            Charset detected = CharsetHelper.detect(text);
 
                             String charset;
                             try {
@@ -450,6 +449,7 @@ public class ActivityEML extends ActivityBase {
                                 charset = StandardCharsets.ISO_8859_1.name();
 
                             Charset cs = Charset.forName(charset);
+                            Charset detected = CharsetHelper.detect(text, cs);
                             boolean isUtf8 = CharsetHelper.isUTF8(text.getBytes(cs));
                             boolean isW1252 = !Objects.equals(text, CharsetHelper.utf8toW1252(text));
 

app/src/main/java/eu/faircode/email/CharsetHelper.java

@@ -57,7 +57,7 @@ public class CharsetHelper {
         }
     }
 
-    private static native DetectResult jni_detect_charset(byte[] octets);
+    private static native DetectResult jni_detect_charset(byte[] octets, String ref, String lang);
 
     static boolean isUTF8(String text) {
         // Get extended ASCII characters
@@ -159,7 +159,10 @@ public class CharsetHelper {
         }
     }
 
-    public static Charset detect(String text) {
+    public static Charset detect(String text, Charset ref) {
+        if (text == null)
+            return null;
+
         try {
             byte[] octets = text.getBytes(StandardCharsets.ISO_8859_1);
 
@@ -172,7 +175,9 @@ public class CharsetHelper {
             }
 
             Log.i("compact_enc_det sample=" + sample.length);
-            DetectResult detected = jni_detect_charset(sample);
+            DetectResult detected = jni_detect_charset(sample,
+                    ref == null ? null : ref.name(),
+                    Locale.getDefault().getLanguage());
 
             if (TextUtils.isEmpty(detected.charset)) {
                 Log.e("compact_enc_det result=" + detected);
@@ -185,7 +190,7 @@ public class CharsetHelper {
                 Log.e("compact_enc_det result=" + detected + " chinese=" + chinese);
                 if (!chinese)
                     return null;
-            } else // GBK, Big5, ISO-2022-JP, HZ-GB-2312, Shift_JIS
+            } else // GBK, Big5, ISO-2022-JP, HZ-GB-2312, Shift_JIS, x-binaryenc
                 Log.e("compact_enc_det result=" + detected);
 
             return Charset.forName(detected.charset);

app/src/main/java/eu/faircode/email/MessageHelper.java

@@ -1840,7 +1840,7 @@ public class MessageHelper {
         if (header.trim().startsWith("=?"))
             return header;
 
-        Charset detected = CharsetHelper.detect(header);
+        Charset detected = CharsetHelper.detect(header, StandardCharsets.ISO_8859_1);
         if (detected == null && CharsetHelper.isUTF8(header))
             detected = StandardCharsets.UTF_8;
         if (detected == null ||
@@ -2928,7 +2928,7 @@ public class MessageHelper {
                             Log.i("Charset upgrade=UTF8");
                             result = new String(result.getBytes(StandardCharsets.ISO_8859_1), StandardCharsets.UTF_8);
                         } else {
-                            Charset detected = CharsetHelper.detect(result);
+                            Charset detected = CharsetHelper.detect(result, StandardCharsets.ISO_8859_1);
                             if (detected == null) {
                                 if (CharsetHelper.isUTF8(result)) {
                                     Log.i("Charset plain=UTF8");
@@ -2984,7 +2984,7 @@ public class MessageHelper {
                     // Fix incorrect UTF16
                     try {
                         if (CHARSET16.contains(cs)) {
-                            Charset detected = CharsetHelper.detect(result);
+                            Charset detected = CharsetHelper.detect(result, cs);
                             if (!CHARSET16.contains(detected))
                                 Log.w(new Throwable("Charset=" + cs + " detected=" + detected));
                             if (StandardCharsets.US_ASCII.equals(detected) ||
@@ -3034,7 +3034,7 @@ public class MessageHelper {
                                         break;
                                     }
 
-                                    Charset detected = CharsetHelper.detect(result);
+                                    Charset detected = CharsetHelper.detect(result, c);
                                     if (c.equals(detected))
                                         break;
 

app/src/main/jni/fairemail.cc

@@ -24,11 +24,21 @@ void log_android(int prio, const char *fmt, ...) {
 
 extern "C"
 JNIEXPORT jobject JNICALL
+
 Java_eu_faircode_email_CharsetHelper_jni_1detect_1charset(
         JNIEnv *env, jclass type,
-        jbyteArray _octets) {
+        jbyteArray _octets, jstring _ref, jstring _lang) {
     int len = env->GetArrayLength(_octets);
     jbyte *octets = env->GetByteArrayElements(_octets, nullptr);
+    const char *ref = env->GetStringUTFChars(_ref, 0);
+    const char *lang = env->GetStringUTFChars(_lang, 0);
+
+    // ISO-8859-1 is unknown
+    Encoding encoding_hint;
+    EncodingFromName(ref, &encoding_hint);
+
+    Language language_hint;
+    LanguageFromCode(lang, &language_hint);
 
     // https://github.com/google/compact_enc_det
 
@@ -38,19 +48,25 @@ Java_eu_faircode_email_CharsetHelper_jni_1detect_1charset(
     Encoding encoding = CompactEncDet::DetectEncoding(
             (const char *) octets, len,
             nullptr, nullptr, nullptr,
-            UNKNOWN_ENCODING,
-            UNKNOWN_LANGUAGE,
+            encoding_hint,
+            language_hint,
             CompactEncDet::EMAIL_CORPUS,
             false,
             &bytes_consumed,
             &is_reliable);
+    // TODO: PreferredWebOutputEncoding?
     const char *name = MimeEncodingName(encoding);
 
-    log_android(ANDROID_LOG_DEBUG, "detect=%d/%s bytes=%d reliable=%d",
-                encoding, name, bytes_consumed, is_reliable);
+    log_android(ANDROID_LOG_DEBUG,
+                "MMM detect=%d/%s bytes=%d reliable=%d"
+                " ref=%s/%s lang=%s/%s",
+                encoding, name, bytes_consumed, is_reliable,
+                EncodingName(encoding_hint), ref, LanguageCode(language_hint), lang);
 
     // https://developer.android.com/training/articles/perf-jni#primitive-arrays
     env->ReleaseByteArrayElements(_octets, octets, JNI_ABORT);
+    env->ReleaseStringUTFChars(_ref, ref);
+    env->ReleaseStringUTFChars(_lang, lang);
 
     jclass cls = env->FindClass("eu/faircode/email/CharsetHelper$DetectResult");
     jmethodID ctor = env->GetMethodID(cls, "<init>", "(Ljava/lang/String;IIZ)V");