cowboy_req:read_body - Read the request body


read_body(Req :: cowboy_req:req())
    -> read_body(Req, #{})

read_body(Req :: cowboy_req:req(), Opts)
    -> {ok,   Data :: binary(), Req}
     | {more, Data :: binary(), Req}

Opts :: cowboy_req:read_body_opts()

Read the request body.

This function reads a chunk of the request body. A more tuple is returned when more data remains to be read. Call the function repeatedly until an ok tuple is returned to read the entire body.

An ok tuple with empty data is returned when the request has no body, or when calling this function again after the body has already been read. It is therefore safe to call this function directly. Note that the body can only be read once.

This function reads the request body from the connection process. The connection process is responsible for reading from the socket. The exact behavior varies depending on the protocol.

The options therefore are only related to the communication between the request process and the connection process.

Cowboy will automatically handle protocol details including the expect header, chunked transfer-encoding and others.

Once the body has been read fully, Cowboy sets the content-length header if it was not previously provided.



The Req object.


A map of body reading options.

The length option can be used to request smaller or bigger chunks of data to be sent. It is a best effort approach, Cowboy may send more data than configured on occasions. It defaults to 8MB.

The period indicates how long the connection process will wait before it provides us with the data it received. It defaults to 15 seconds.

The connection process sends data to the request process when either the length of data or the period of time is reached.

The timeout option is a safeguard in case the connection process becomes unresponsive. The function will crash if no message was received in that interval. The timeout should be larger than the period. It defaults to the period + 1 second.

Return value

A more tuple is returned when there are more data to be read.

An ok tuple is returned when there are no more data to be read, either because this is the last chunk of data, the body has already been read, or there was no body to begin with.

The data is always returned as a binary.

The Req object returned in the tuple must be used from that point onward. It contains a more up to date representation of the request. For example it may have an added content-length header once the body has been read.


  • 2.0: Function introduced. Replaces body/1,2.


Read the entire body
read_body(Req0, Acc) ->
    case cowboy_req:read_body(Req0) of
        {ok, Data, Req} -> {ok, << Acc/binary, Data/binary >>, Req};
        {more, Data, Req} -> read_body(Req, << Acc/binary, Data/binary >>)
Read the body in small chunks
cowboy_req:read_body(Req, #{length => 64000}).

See also

cowboy_req(3), cowboy_req:has_body(3), cowboy_req:body_length(3), cowboy_req:read_urlencoded_body(3), cowboy_req:read_and_match_urlencoded_body(3), cowboy_req:read_part(3), cowboy_req:read_part_body(3)

Cowboy 2.7 Function Reference


Version select

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