treat mailto: URI parameters case-insensitive

Although RFC defines such parameters case-sensitive, some applications
still use capitalized versions like "Subject" and "Body". Since the Java
Uri parser is case-sensitive, this patch replaces all URI parameter
names with a lower-case version, and since all parameter name requests
are also done in lower-case, this effectively makes the mailto: handler
logic case-insensitive.

src/com/fsck/k9/activity/MessageCompose.java

@@ -3257,7 +3257,7 @@ private void initializeFromMailto(Uri mailtoUri) {
          * creating a new hierarchical dummy Uri object with the query
          * parameters of the original URI.
          */
-        Uri uri = Uri.parse("foo://bar?" + mailtoUri.getEncodedQuery());
+        Uri uri = Uri.parse("foo://bar?" + lowerCaseHfNames(mailtoUri.getEncodedQuery()));
 
         // Read additional recipients from the "to" parameter.
         List<String> to = uri.getQueryParameters("to");
@@ -3291,6 +3291,25 @@ private void initializeFromMailto(Uri mailtoUri) {
         }
     }
 
+    // Regex for URI parameter names
+    private static final Pattern QUERY_HFNAME = Pattern.compile("(?:^|&)([a-zA-Z]+)=");
+
+    /**
+     * Convert URI parameter names to lower case
+     * "foo=BaR&amp;Qux=BAZ&amp;ALLCAPS=lowcase" becomes "foo=BaR&amp;qux=BAZ&amp;allcaps=lowcase"
+     *
+     * @param encodedQuery
+     *         URI-encoded parameter list string
+     */
+    private String lowerCaseHfNames(String encodedQuery) {
+        final StringBuilder sb = new StringBuilder(encodedQuery);
+        final Matcher m = QUERY_HFNAME.matcher(sb);
+        while (m.find()) {
+            sb.replace(m.start(1), m.end(1), m.group(1).toLowerCase());
+        }
+        return sb.toString();
+    }
+
     private class SendMessageTask extends AsyncTask<Void, Void, Void> {
         @Override
         protected Void doInBackground(Void... params) {