Added/improved charset mapping

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

@@ -1251,28 +1251,27 @@ public class MessageHelper {
 
             try {
                 ContentType ct = new ContentType(part.getContentType());
-                String charset = ct.getParameter("charset");
 
-                // Fix common mistakes
-                if (charset != null) {
+                String charset = ct.getParameter("charset");
+                if (charset == null)
+                    charset = StandardCharsets.ISO_8859_1.name();
+                else {
                     charset = charset.replace("\"", "");
-                    if ("ASCII".equals(charset.toUpperCase()))
-                        charset = "US-ASCII";
-                    else if (charset.toLowerCase().endsWith("8859-16")) // not supported by Android
-                        charset = null; // Use ISO8859-1 instead
-                }
-
-                if (TextUtils.isEmpty(charset) || "US-ASCII".equals(charset.toUpperCase())) {
-                    // The first 127 characters are the same as in US-ASCII
-                    result = new String(result.getBytes(StandardCharsets.ISO_8859_1));
-                } else {
-                    // See UnknownCharsetProvider class
-                    if ("US-ASCII".equals(Charset.forName(charset).name())) {
-                        Log.w("Unsupported encoding charset=" + charset);
+                    charset = MimeUtility.javaCharset(charset);
+
+                    if (!Charset.isSupported(charset)) {
+                        // x-binaryenc
+                        // UseInqueCodePage
+                        // none
+                        // unknown-8bit
+                        // X-UNKNOWN
+                        Log.e("Unsupported encoding charset=" + charset);
                         warnings.add(context.getString(R.string.title_no_charset, charset));
-                        result = new String(result.getBytes(StandardCharsets.ISO_8859_1));
+                        charset = StandardCharsets.ISO_8859_1.name();
                     }
                 }
+
+                result = new String(result.getBytes(Charset.forName(charset)));
             } catch (ParseException ex) {
                 Log.w(ex);
                 warnings.add(Log.formatThrowable(ex, false));

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

@@ -1,48 +0,0 @@
-package eu.faircode.email;
-
-/*
-    This file is part of FairEmail.
-
-    FairEmail is free software: you can redistribute it and/or modify
-    it under the terms of the GNU General Public License as published by
-    the Free Software Foundation, either version 3 of the License, or
-    (at your option) any later version.
-
-    FairEmail is distributed in the hope that it will be useful,
-    but WITHOUT ANY WARRANTY; without even the implied warranty of
-    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
-    GNU General Public License for more details.
-
-    You should have received a copy of the GNU General Public License
-    along with FairEmail.  If not, see <http://www.gnu.org/licenses/>.
-
-    Copyright 2018-2020 by Marcel Bokhorst (M66B)
-*/
-
-import android.text.TextUtils;
-
-import java.nio.charset.Charset;
-import java.nio.charset.StandardCharsets;
-import java.nio.charset.spi.CharsetProvider;
-import java.util.Collections;
-import java.util.Iterator;
-
-public class UnknownCharsetProvider extends CharsetProvider {
-    @Override
-    public Iterator<Charset> charsets() {
-        return Collections.emptyIterator();
-    }
-
-    @Override
-    public Charset charsetForName(String name) {
-        // x-binaryenc
-        // UseInqueCodePage
-        // none
-        // unknown-8bit
-        // X-UNKNOWN
-        // https://javaee.github.io/javamail/FAQ#unsupen
-        if (!TextUtils.isEmpty(name))
-            Log.e("Unknown charset=" + name);
-        return StandardCharsets.US_ASCII;
-    }
-}

app/src/main/resources/META-INF/javamail.charset.map

@@ -1,6 +1,17 @@
 ### JDK-to-MIME charset mapping table ####
 ### This should be the first mapping table ###
 
+### FairEmail
+
+8859_16		ISO-8859-1
+iso8859_16	ISO-8859-1
+ISO8859-16	ISO-8859-1
+
+ascii       ISO-8859-1
+ASCII       ISO-8859-1
+
+### Inherited
+
 8859_1		ISO-8859-1
 iso8859_1	ISO-8859-1
 ISO8859-1	ISO-8859-1

app/src/main/resources/META-INF/services/java.nio.charset.spi.CharsetProvider

@@ -1 +0,0 @@
-eu.faircode.email.UnknownCharsetProvider