cowboy_req:stream_reply - Send the response headers


stream_reply(Status, Req :: cowboy_req:req())
    -> stream_reply(StatusCode, #{}, Req)

stream_reply(Status, Headers, Req :: cowboy_req:req())
    -> Req

Status  :: cowboy:http_status()
Headers :: cowboy:http_headers()

Send the response headers.

The header names must be given as lowercase binary strings. While header names are case insensitive, Cowboy requires them to be given as lowercase to function properly.

Cowboy does not allow duplicate header names. Headers set by this function may overwrite those set by set_resp_header/3.

Use cowboy_req:set_resp_cookie(3) instead of this function to set cookies.

If a response body was set before calling this function, it will not be sent.

Use cowboy_req:stream_body(3) to stream the response body and optionally cowboy_req:stream_trailers(3) to send response trailer field values.

You may want to set the content-length header when using this function, if it is known in advance. This will allow clients using HTTP/2 and HTTP/1.0 to process the response more efficiently.

The streaming method varies depending on the protocol being used. HTTP/2 will use the usual DATA frames. HTTP/1.1 will use chunked transfer-encoding, if the content-length response header is set the body will be sent without chunked chunked transfer-encoding. HTTP/1.0 will send the body unmodified and close the connection at the end if no content-length was set.

It is not possible to push resources after this function returns. Any attempt will result in an error.



The status code for the response.


The response headers.

Header names must be given as lowercase binary strings.


The Req object.

Return value

A new Req object is returned.

The returned Req object must be used from that point onward in order to be able to stream the response body.


  • 2.0: Only the Req is returned, it is no longer wrapped in a tuple.
  • 2.0: Function introduced. Replaces chunked_reply/1,2.


Initiate the response
Req = cowboy_req:stream_reply(200, Req0).
Stream the response with custom headers
Req = cowboy_req:stream_reply(200, #{
    <<"content-type">> => <<"text/plain">>
}, Req0),
cowboy_req:stream_body(<<"Hello\n">>, nofin, Req),
cowboy_req:stream_body(<<"World!\n">>, fin, Req).

See also

cowboy_req(3), cowboy_req:set_resp_cookie(3), cowboy_req:set_resp_header(3), cowboy_req:set_resp_headers(3), cowboy_req:inform(3), cowboy_req:reply(3), cowboy_req:stream_body(3), cowboy_req:stream_events(3), cowboy_req:stream_trailers(3), cowboy_req:push(3)

Cowboy 2.7 Function Reference


Version select

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