Add close_boundary option to write closing boundary on multipart writ…

…er (#3106)

CHANGES/3104.feature

@@ -0,0 +1 @@
+Add `close_boundary` option in `MultipartWriter.write` method. Support streaming

CONTRIBUTORS.txt

@@ -188,6 +188,7 @@ Thanos Lefteris
 Thijs Vermeir
 Thomas Grainger
 Tolga Tezel
+Trinh Hoang Nhu
 Vadim Suharnikov
 Vaibhav Sagar
 Vamsi Krishna Avula

aiohttp/multipart.py

@@ -796,7 +796,7 @@ def size(self):
         total += 2 + len(self._boundary) + 4  # b'--'+self._boundary+b'--\r\n'
         return total
 
-    async def write(self, writer):
+    async def write(self, writer, close_boundary=True):
         """Write body."""
         if not self._parts:
             return
@@ -818,7 +818,8 @@ async def write(self, writer):
 
             await writer.write(b'\r\n')
 
-        await writer.write(b'--' + self._boundary + b'--\r\n')
+        if close_boundary:
+            await writer.write(b'--' + self._boundary + b'--\r\n')
 
 
 class MultipartPayloadWriter:

docs/multipart.rst

@@ -187,6 +187,27 @@ Please note, that on :meth:`MultipartWriter.write` all the file objects
 will be read until the end and there is no way to repeat a request without
 rewinding their pointers to the start.
 
+Example MJPEG Streaming ``multipart/x-mixed-replace``. By default
+:meth:`MultipartWriter.write` appends closing ``--boundary--`` and breaks your
+content. Providing `close_boundary = False` prevents this.::
+
+    my_boundary = 'some-boundary'
+    response = web.StreamResponse(
+        status=200,
+        reason='OK',
+        headers={
+            'Content-Type': 'multipart/x-mixed-replace;boundary=--%s' % my_boundary
+        }
+    )
+    while True:
+        frame = get_jpeg_frame()
+        with MultipartWriter('image/jpeg', boundary=my_boundary) as mpwriter:
+            mpwriter.append(frame, {
+                'Content-Type': 'image/jpeg'
+            })
+            await mpwriter.write(response, close_boundary=False)
+        await response.drain()
+
 Hacking Multipart
 -----------------
 

docs/multipart_reference.rst

@@ -157,7 +157,7 @@ Multipart reference
       Returns the next body part reader.
 
 
-.. class:: MultipartWriter(subtype='mixed', boundary=None)
+.. class:: MultipartWriter(subtype='mixed', boundary=None, close_boundary=True)
 
    Multipart body writer.
 
@@ -191,6 +191,14 @@ Multipart reference
 
       Size of the payload.
 
-   .. comethod:: write(writer)
+   .. comethod:: write(writer, close_boundary=True)
 
       Write body.
+
+      :param bool close_boundary: The (:class:`bool`) that will emit
+                                  boundary closing. You may want to disable
+                                  when streaming (``multipart/x-mixed-replace``)
+
+      .. versionadded:: 3.4
+
+         Support ``close_boundary`` argument.

tests/test_multipart.py

@@ -806,6 +806,40 @@ async def test_writer_write(buf, stream, writer):
          b'--:--\r\n') == bytes(buf))
 
 
+async def test_writer_write_no_close_boundary(buf, stream):
+    writer = aiohttp.MultipartWriter(boundary=':')
+    writer.append('foo-bar-baz')
+    writer.append_json({'test': 'passed'})
+    writer.append_form({'test': 'passed'})
+    writer.append_form([('one', 1), ('two', 2)])
+    await writer.write(stream, close_boundary=False)
+
+    assert (
+        (b'--:\r\n'
+         b'Content-Type: text/plain; charset=utf-8\r\n'
+         b'Content-Length: 11\r\n\r\n'
+         b'foo-bar-baz'
+         b'\r\n'
+
+         b'--:\r\n'
+         b'Content-Type: application/json\r\n'
+         b'Content-Length: 18\r\n\r\n'
+         b'{"test": "passed"}'
+         b'\r\n'
+
+         b'--:\r\n'
+         b'Content-Type: application/x-www-form-urlencoded\r\n'
+         b'Content-Length: 11\r\n\r\n'
+         b'test=passed'
+         b'\r\n'
+
+         b'--:\r\n'
+         b'Content-Type: application/x-www-form-urlencoded\r\n'
+         b'Content-Length: 11\r\n\r\n'
+         b'one=1&two=2'
+         b'\r\n') == bytes(buf))
+
+
 async def test_writer_serialize_with_content_encoding_gzip(buf, stream,
                                                            writer):
     writer.append('Time to Relax!', {CONTENT_ENCODING: 'gzip'})