HTTP Streaming

By default, mitmproxy will read the entire request/response, perform any indicated manipulations on it and then send the (possibly modified) message to the other party. In some cases this is undesirable and you may wish to “stream” the request/response. When streaming is enabled, the request/response is not buffered on the proxy but directly sent to the server/client instead. HTTP headers are still fully buffered before being sent.

Request Streaming

Request streaming can be used to incrementally stream a request body to the server before it has been fully received by the proxy. This is useful for large file uploads.

Response Streaming

By using mitmproxy’s streaming feature, response contents can be passed to the client incrementally before they have been fully received by the proxy. This is especially useful for large binary files such as videos, where buffering the whole file slows down the client’s browser.

On the command-line

Streaming can be enabled on the command line for all request and response bodies exceeding a certain size. The SIZE argument understands k/m/g suffixes, e.g. 3m for 3 megabytes.

command-line --set stream_large_bodies=SIZE

Warning

When streaming is enabled, streamed request/response contents will not be recorded or preserved in any way.

Note

When streaming is enabled, the request/response body cannot be modified by the usual means.

Customizing Streaming

You can also use a script to customize exactly which requests or responses are streamed.

Requests/Responses that should be tagged for streaming by setting their .stream attribute to True:

examples/complex/stream.py
def responseheaders(flow):
    """
    Enables streaming for all responses.
    This is equivalent to passing `--set stream_large_bodies=1` to mitmproxy.
    """
    flow.response.stream = True

Implementation Details

When response streaming is enabled, portions of the code which would have otherwise performed changes on the request/response body will see an empty body. Any modifications will be ignored.

Streamed bodies are usually sent in chunks of 4096 bytes. If the response is sent with a Transfer-Encoding: chunked header, the response will be streamed one chunk at a time.

Modifying streamed data

If the .stream attribute is callable, .stream will wrap the generator that yields all chunks.

examples/complex/stream_modify.py
"""
This inline script modifies a streamed response.
If you do not need streaming, see the modify_response_body example.
Be aware that content replacement isn't trivial:
    - If the transfer encoding isn't chunked, you cannot simply change the content length.
    - If you want to replace all occurences of "foobar", make sure to catch the cases
      where one chunk ends with [...]foo" and the next starts with "bar[...].
"""


def modify(chunks):
    """
    chunks is a generator that can be used to iterate over all chunks.
    """
    for chunk in chunks:
        yield chunk.replace("foo", "bar")


def responseheaders(flow):
    flow.response.stream = modify

WebSocket Streaming

The WebSocket streaming feature can be used to send the frames as soon as they arrive. This can be useful for large binary file transfers.

On the command-line

Streaming can be enabled on the command line for all WebSocket frames

command-line --set stream_websockets=true

Note

When Web Socket streaming is enabled, the message payload cannot be modified.

Implementation Details

When WebSocket streaming is enabled, portions of the code which may perform changes to the WebSocket message payloads will not have any effect on the actual payload sent to the server as the frames are immediately forwarded to the server. In contrast to HTTP streaming, where the body is not stored, the message payload will still be stored in the WebSocket Flow.

See also