Streaming response not appearing in chunks

[Harry Julian]

Is there an existing issue for this?

• I have searched the existing issues

Describe the bug

I'm using an older version of Sanic 20.3.0 as I'm working on an old project. I'm trying to stream a chunked response back to the client, which is currently just curl.

Even though I'm streaming the response back using the StreamingHttpResponse.stream() method, the response doesn't appear in chunks in curl - it all appears simultaneously. I'm wondering how I'd get the streamed response to appear properly chunked when interacting with an external client.

Code snippet

from sanic import Blueprint, response

# Response called as so

blueprint = Blueprint(obj, filename)

async def streaming_func(response):
      # chunks data, writes it to response
      for chunk in chunks:
            await response.write(json.dumps(chunk), "\n")

@blueprint.route("/webhook_stream", methods=["POST"])
def func(...):
      # logic
      return response.stream(
      streaming_func(*args, **kwargs),
      headers = {"Transfer-Encoding": "chunked"},
      content_type="text/event-stream",
)

Expected Behavior

I expected to see the individual chunks of the request being sent back to the client one by one -- instead they all appear simultaneously.

How do you run Sanic?

As a script (app.run or Sanic.serve)

Operating System

Linux

Sanic Version

20.3.0

Additional context

Had to omit project specific logic as it's a commercial project.

[Adam Hopkins]

In order to not buffer with curl you need to us -N flag.

[Harry Julian]

@ahopkins I am using the -N flag. Same behaviour calling it with requests.

import requests

with requests.post("http://localhost:5008/myroute", json = {"data": 1}, stream = True) as resp:
    for line in resp.iter_lines():
        if line:
            print(line)

[L. Kärkkäinen]

FWIW, you might find the new style streaming API easier https://sanic.dev/en/guide/advanced/streaming.html#response-streaming

If you think there is a bug, can you provide a runnable test case? The code snippet you gave apparently writes all chunks at the same time, so they would appear at the same time too (even if they were encoded as separate HTTP chunks).

Note that in server-sent events the messages are separated by an empty line, not by HTTP chunked encoding.

[Adam Hopkins]

It is v20.3, which is unsupported. But from my memory, there was no known streaming issues back then.