Support 7bit, 8bit, binary transfer-encodings (#61)

Check for transparent encodings and ignore them.

Author: thosakwe

CHANGELOG.md

@@ -1,5 +1,8 @@
 # 0.9.8+4-dev
 
+* Allow multipart form data with specified encodings that don't require
+  decoding.
+
 # 0.9.8+3
 
 * Prepare for `HttpClientResponse` SDK change (implements `Stream<Uint8List>`

lib/src/http_multipart_form_data_impl.dart

@@ -25,14 +25,21 @@ class HttpMultipartFormDataImpl extends Stream
 
   Stream _stream;
 
+  /// The values which indicate that no incoding was performed.
+  ///
+  /// https://www.w3.org/Protocols/rfc1341/5_Content-Transfer-Encoding.html
+  static const _transparentEncodings = ['7bit', '8bit', 'binary'];
+
   HttpMultipartFormDataImpl(
       this.contentType,
       this.contentDisposition,
       this.contentTransferEncoding,
       this._mimeMultipart,
       Encoding defaultEncoding) {
     _stream = _mimeMultipart;
-    if (contentTransferEncoding != null) {
+    if (contentTransferEncoding != null &&
+        !_transparentEncodings
+            .contains(contentTransferEncoding.value.toLowerCase())) {
       // TODO(ajohnsen): Support BASE64, etc.
       throw HttpException('Unsupported contentTransferEncoding: '
           '${contentTransferEncoding.value}');

test/http_multipart_test.dart

@@ -133,6 +133,19 @@ Content of file\r
     ]);
   });
 
+  test('With content transfer encoding', () async {
+    var message = '''
+\r\n--AaB03x\r
+Content-Disposition: form-data; name="submit-name"\r
+Content-Transfer-Encoding: 8bit\r
+\r
+Larry\r
+--AaB03x--\r\n''';
+
+    await _postDataTest(message.codeUnits, 'multipart/form-data', 'AaB03x',
+        [FormField('submit-name', 'Larry')]);
+  });
+
   test('Windows/IE style file upload', () async {
     var message = '''
 \r\n--AaB03x\r