Assume ISO-8859-1 if text/plain without charset

ICU4J is too large

README.md

@@ -137,7 +137,7 @@ FairEmail uses:
 * [JavaMail](https://projects.eclipse.org/projects/ee4j.javamail). Copyright (c) 1997-2018 Oracle® and/or its affiliates. All rights reserved. [GPLv2+CE license](https://javaee.github.io/javamail/JavaMail-License).
 * [jsoup](https://jsoup.org/). Copyright © 2009 - 2017 Jonathan Hedley. [MIT license](https://jsoup.org/license).
 * ~~[JCharset](http://www.freeutils.net/source/jcharset/). Copyright © 2005-2015 Amichai Rothman. [GNU General Public License](http://www.freeutils.net/source/jcharset/#license)~~
-* [ICU4J](http://site.icu-project.org). Copyright © 1991-2019 Unicode, Inc. All rights reserved. [UNICODE, INC. LICENSE AGREEMENT](http://www.unicode.org/copyright.html#License)
+* ~~[ICU4J](http://site.icu-project.org). Copyright © 1991-2019 Unicode, Inc. All rights reserved. [UNICODE, INC. LICENSE AGREEMENT](http://www.unicode.org/copyright.html#License)~~
 * [Android Support Library](https://developer.android.com/tools/support-library/). Copyright (C) 2011 The Android Open Source Project. [Apache license](https://android.googlesource.com/platform/frameworks/support/+/master/LICENSE.txt).
 * [Android Architecture Components](https://developer.android.com/topic/libraries/architecture/). Copyright 2018 The Android Open Source Project, Inc. [Apache license](https://github.com/googlesamples/android-architecture-components/blob/master/LICENSE).
 * [colorpicker](https://android.googlesource.com/platform/frameworks/opt/colorpicker). Copyright (C) 2013 The Android Open Source Project. [Apache license](https://android.googlesource.com/platform/frameworks/opt/colorpicker/+/master/src/com/android/colorpicker/ColorPickerDialog.java).

app/build.gradle

@@ -162,7 +162,7 @@ dependencies {
     //implementation "net.freeutils:jcharset:$jcharset_version"
 
     // https://mvnrepository.com/artifact/com.ibm.icu/icu4j
-    implementation "com.ibm.icu:icu4j:$icu4j_version"
+    //implementation "com.ibm.icu:icu4j:$icu4j_version"
 
     // http://www.xbill.org/dnsjava/
     implementation "dnsjava:dnsjava:$dnsjava_version"

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

@@ -23,9 +23,6 @@ import android.content.Context;
 import android.text.TextUtils;
 import android.webkit.MimeTypeMap;
 
-import com.ibm.icu.text.CharsetDetector;
-import com.ibm.icu.text.CharsetMatch;
-
 import org.jsoup.Jsoup;
 import org.jsoup.nodes.Element;
 
@@ -568,16 +565,15 @@ public class MessageHelper {
             ContentType ct = new ContentType(part.getContentType());
             String charset = ct.getParameter("charset");
             if (TextUtils.isEmpty(charset)) {
-                try {
-                    CharsetDetector detector = new CharsetDetector();
-                    String defset = (part.isMimeType("text/plain") ? "US-ASCII" : "ISO-8859-1");
-                    detector.setText(result.getBytes(defset));
-                    CharsetMatch match = detector.detect();
-                    result = new String(result.getBytes(match.getName()));
-                    warnings.add(context.getString(R.string.title_guessed_charset, match.getName()));
-                } catch (UnsupportedEncodingException ex) {
-                    warnings.add(Helper.formatThrowable(ex));
-                }
+                if (BuildConfig.DEBUG)
+                    warnings.add(context.getString(R.string.title_no_charset, ct.toString()));
+                if (part.isMimeType("text/plain"))
+                    try {
+                        // The first 127 characters are the same as in US-ASCII
+                        result = new String(result.getBytes("ISO-8859-1"));
+                    } catch (UnsupportedEncodingException ex) {
+                        warnings.add(Helper.formatThrowable(ex));
+                    }
             } else {
                 if ("US-ASCII".equals(Charset.forName(charset).name()) &&
                         !"US-ASCII".equals(charset.toUpperCase()))

app/src/main/res/values/strings.xml

@@ -457,7 +457,6 @@
     <string name="title_no_adobe">Adobe Acrobat reader cannot open safely shared files, see the FAQ for more information</string>
     <string name="title_no_body">No message text found</string>
     <string name="title_no_charset">Unsupported encoding: %1$s</string>
-    <string name="title_guessed_charset">Guessed encoding: %1$s</string>
 
     <string name="title_try">Try FairEmail, an open source, privacy friendly email app for Android</string>