Multipart stream docs

components/multipart-stream-builder.rst

@@ -0,0 +1,63 @@
+Multipart Stream Builder
+========================
+
+A multipart stream is a special kind of stream that is used to transfer files over HTTP. There is currently no PSR-7 support for multipart streams as they are considered to be normal streams with a special content. A multipart stream HTTP request may look like this:
+
+.. code-block:: none
+
+    POST / HTTP/1.1
+    Host: example.com
+    Content-Type: multipart/form-data; boundary=578de3b0e3c46
+
+    --578de3b0e3c46
+    Content-Disposition: form-data; name="foo"
+    Content-Length: 15
+
+    A normal stream
+    --578de3b0e3c46
+    Content-Disposition: form-data; name="bar"; filename="bar.png"
+    Content-Length: 71
+    Content-Type: image/png
+
+    ?PNG
+    
+    ???
+    IHDR??? ??? ?????? ???? IDATx
c???51?)?:??????IEND?B`?
+    --578de3b0e3c46
+    Content-Type: text/plain
+    Content-Disposition: form-data; name="baz"
+    Content-Length: 6
+
+    string
+    --578de3b0e3c46--
+
+
+In the request above you see a set of HTTP headers and a body with two streams. The body starts and ends with a "boundary" and it is also this boundary that separates the streams. That boundary also needs to be specified in the ``Content-Type`` header.
+
+Building a multipart stream
+```````````````````````````
+
+To build a multipart stream you may use the ``MultipartStreamBuilder``. It is not coupled to any stream implementation so it needs a ``StreamFactory`` to create the streams.
+
+.. code-block:: php
+
+    $streamFactory = StreamFactoryDiscovery::find();
+    $builder = new MultipartStreamBuilder($streamFactory);
+    $builder
+      ->addResource('foo', $stream)
+      ->addResource('bar', fopen($filePath, 'r'), ['filename' => 'bar.png'])
+      ->addResource('baz', 'string', ['headers' => ['Content-Type' => 'text/plain']]);
+
+    $multipartStream = $builder->build();
+    $boundary = $builder->getBoundary();
+
+    $request = MessageFactoryDiscovery::find()->createRequest(
+      'POST',
+      'http://example.com',
+      ['Content-Type' => 'multipart/form-data; boundary='.$boundary],
+      $multipartStream
+    );
+
+    $response = HttpClientDiscovery::find()->sendRequest($request);
+
+The second parameter of ``MultipartStreamBuilder::addResource()`` is the content of the stream. The supported input is the same as ``StreamFactory::createStream()``.

index.rst

@@ -83,6 +83,7 @@ for discussion around a future HTTP client PSR.
    components/adapter-integration-tests
    components/promise
    discovery
+   components/multipart-stream-builder
 
 .. toctree::
    :hidden:

spelling_word_list.txt

@@ -15,6 +15,7 @@ namespace
 plugin
 plugins
 matchers
+multipart
 param
 params
 Puli