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The options were added to allow developers to fix timeout issues when reading large bodies. It is also a cleaner and easier to extend interface. This commit deprecates the functions init_stream, stream_body and skip_body which are no longer needed. They will be removed in 1.0. The body function can now take an additional argument that is a list of options. The body_qs, part and part_body functions can too and simply pass this argument down to the body call. There are options for disabling the automatic continue reply, setting a maximum length to be returned (soft limit), setting the read length and read timeout, and setting the transfer and content decode functions. The return value of the body and body_qs have changed slightly. The body function now works similarly to the part_body function, in that it returns either an ok or a more tuple depending on whether there is additional data to be read. The body_qs function can return a badlength tuple if the body is too big. The default size has been increased from 16KB to 64KB. The default read length and timeout have been tweaked and vary depending on the function called. The body function will now adequately process chunked bodies, which means that the body_qs function will too. But this means that the behavior has changed slightly and your code should be tested properly when updating your code. The body and body_qs still accept a length as first argument for compatibility purpose with older code. Note that this form is deprecated and will be removed in 1.0. The part and part_body function, being new and never having been in a release yet, have this form completely removed in this commit. Again, while most code should work as-is, you should make sure that it actually does before pushing this to production.
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Reading the request body
The Req object also allows you to read the request body.
Because the request body can be of any size, all body reading operations will only work once, as Cowboy will not cache the result of these operations.
Cowboy will not attempt to read the body until you do. If handler execution ends without reading it, Cowboy will simply skip it.
Cowboy provides different ways to read the request body. You can read it directly, stream it, but also read and parse in a single call for form urlencoded formats or multipart. All of these except multipart are covered in this chapter. Multipart is covered later on in the guide.
Check for request body
You can check whether a body was sent with the request.
cowboy_req:has_body(Req).
It will return true if there is a request body, and
false otherwise.
Note that it is generally safe to assume that a body is
sent for POST, PUT and PATCH requests, without
having to explicitly check for it.
Request body length
You can obtain the body length if it was sent with the request.
{Length, Req2} = cowboy_req:body_length(Req).
The value returned will be undefined if the length
couldn't be figured out from the request headers. If
there's a body but no length is given, this means that
the chunked transfer-encoding was used. You can read
chunked bodies by using the stream functions.
Reading the body
You can read the whole body directly in one call.
{ok, Body, Req2} = cowboy_req:body(Req).
By default, Cowboy will attempt to read up to a size of 8MB. You can override this limit as needed.
{ok, Body, Req2} = cowboy_req:body(Req, [{length, 100000000}]).
You can also disable it.
{ok, Body, Req2} = cowboy_req:body(Req, [{length, infinity}]).
It is recommended that you do not disable it for public facing websites.
If the body is larger than the limit, then Cowboy will return
a more tuple instead, allowing you to stream it if you
would like to.
Streaming the body
You can stream the request body by chunks.
Cowboy returns a more tuple when there is more body to
be read, and an ok tuple for the last chunk. This allows
you to loop over all chunks.
body_to_console(Req) ->
case cowboy_req:body(Req) of
{ok, Data, Req2} ->
io:format("~s", [Data]),
Req2;
{more, Data, Req2} ->
io:format("~s", [Data]),
body_to_console(Req2)
end.
You can of course set the length option to configure the
size of chunks.
Rate of data transmission
You can control the rate of data transmission by setting options when calling body functions. This applies not only to the functions described in this chapter, but also to the multipart functions.
The read_length option defines the maximum amount of data
to be received from the socket at once, in bytes.
The read_timeout option defines the time Cowboy waits
before that amount is received, in milliseconds.
Transfer and content decoding
Cowboy will by default decode the chunked transfer-encoding if any. It will not decode any content-encoding by default.
The first time you call a body function you can set the
transfer_decode and content_decode options. If the body
was already started being read these options are simply
ignored.
The following example shows how to set both options.
{ok, Req2} = cowboy_req:body(Req, [
{transfer_decode, fun transfer_decode/2, TransferState},
{content_decode, fun content_decode/1}
]).
Reading a form urlencoded body
You can directly obtain a list of key/value pairs if the body was sent using the application/x-www-form-urlencoded content-type.
{ok, KeyValues, Req2} = cowboy_req:body_qs(Req).
You can then retrieve an individual value from that list.
{_, Lang} = lists:keyfind(lang, 1, KeyValues).
You should not attempt to match on the list as the order of the values is undefined.
By default Cowboy will reject bodies with a size above
64KB when using this function. You can override this limit
by setting the length option.
{ok, KeyValues, Req2} = cowboy_req:body_qs(Req,
[{length, 2000000}]).