Skip to content

Instantly share code, notes, and snippets.

What would you like to do?



cowboy_req - HTTP request and response


The module cowboy_req provides functions to access, manipulate and respond to requests.

There are four types of functions in this module. They can be differentiated by their name and their return type:

Type Name pattern Return type


no verb, parse_*, match_*









any other verb

ok | {Result, Value, Req}

Any Req returned must be used in place of the one passed as argument. Functions that perform an action in particular write state in the Req object to make sure you are using the function correctly. For example, it’s only possible to send one response, and to read the body once.


Raw request:

  • cowboy_req:method(3) - HTTP method

  • cowboy_req:version(3) - HTTP version

  • cowboy_req:scheme(3) - URI scheme

  • cowboy_req:host(3) - URI host name

  • cowboy_req:port(3) - URI port number

  • cowboy_req:path(3) - URI path

  • cowboy_req:qs(3) - URI query string

  • cowboy_req:uri(3) - Reconstructed URI

  • cowboy_req:header(3) - Raw HTTP header value

  • cowboy_req:headers(3) - Raw HTTP headers

  • cowboy_req:peer(3) - Peer address and port

Processed request:

  • cowboy_req:parse_qs(3) - Parse the query string

  • cowboy_req:match_qs(3) - Match the query string against constraints

  • cowboy_req:parse_header(3) - Parse the given HTTP header

  • cowboy_req:parse_cookies(3) - Parse cookie headers

  • cowboy_req:match_cookies(3) - Match cookies against constraints

  • cowboy_req:binding(3) - Access a value bound from the route

  • cowboy_req:bindings(3) - Access all values bound from the route

  • cowboy_req:host_info(3) - Access the route’s heading host segments

  • cowboy_req:path_info(3) - Access the route’s trailing path segments

Request body:

  • cowboy_req:has_body(3) - Is there a request body?

  • cowboy_req:body_length(3) - Body length

  • cowboy_req:read_body(3) - Read the request body

  • cowboy_req:read_urlencoded_body(3) - Read and parse a urlencoded request body

  • cowboy_req:read_part(3) - Read the next part of a multipart body

  • cowboy_req:read_part_body(3) - Read the current part’s body in a multipart body


  • cowboy_req:set_resp_cookie(3) - Set a cookie

  • cowboy_req:set_resp_header(3) - Set a response header

  • cowboy_req:has_resp_header(3) - Is the given response header set?

  • cowboy_req:delete_resp_header(3) - Delete a response header

  • cowboy_req:set_resp_body(3) - Set the response body

  • cowboy_req:has_resp_body(3) - Is there a response body?

  • cowboy_req:reply(3) - Send the response

  • cowboy_req:stream_reply(3) - Send the response and stream its body

  • cowboy_req:stream_body(3) - Send a chunk of the response body

  • cowboy_req:push(3) - Push a resource to the client



push_opts() :: #{
    method => binary(),            %% case sensitive
    scheme => binary(),            %% lowercase; case insensitive
    host   => binary(),            %% lowercase; case insensitive
    port   => inet:port_number(),
    qs     => binary()             %% case sensitive

Push options.

By default, Cowboy will use the GET method, an empty query string, and take the scheme, host and port directly from the current request’s URI.


read_body_opts() :: #{
    length  => non_neg_integer(),
    period  => non_neg_integer(),
    timeout => timeout()

Body reading options.

The defaults are function-specific.


req() :: #{
    method  := binary(),               %% case sensitive
    version := cowboy:http_version() | atom(),
    scheme  := binary(),               %% lowercase; case insensitive
    host    := binary(),               %% lowercase; case insensitive
    port    := inet:port_number(),
    path    := binary(),               %% case sensitive
    qs      := binary(),               %% case sensitive
    headers := cowboy:http_headers(),
    peer    := {inet:ip_address(), inet:port_number()}

The Req object.

Contains information about the request and response. While some fields are publicly documented, others aren’t and shouldn’t be used.

You may add custom fields if required. Make sure to namespace them by prepending an underscore and the name of your application:

Setting a custom field
Req#{_myapp_auth_method => pubkey}.


resp_body() :: iodata()
    | {sendfile, Offset, Length, Filename}

Offset   :: non_neg_integer()
Length   :: pos_integer()
Filename :: file:name_all()

Response body.

It can take two forms: the actual data to be sent or a tuple indicating which file to send.

When sending data directly, the type is either a binary or an iolist. Iolists are an efficient way to build output. Instead of concatenating strings or binaries, you can simply build a list containing the fragments you want to send in the order they should be sent:

Example iolists usage
1> RespBody = ["Hello ", [<<"world">>, $!]].
["Hello ",[<<"world">>,33]]
2> io:format("~s~n", [RespBody]).
Hello world!

When using the sendfile tuple, the Length value is mandatory and must be higher than 0. It is sent with the response in the content-length header.

See also




cowboy_req:method - HTTP method


method(Req :: cowboy_req:req()) -> Method :: binary()

Return the request’s HTTP method.

The method can also be obtained using pattern matching:

#{method := Method} = Req.



The Req object.

Return value

The request’s HTTP method is returned as a binary string. While methods are case sensitive, standard methods are always uppercase.


  • 2.0: Only the method is returned, it is no longer wrapped in a tuple.

  • 1.0: Function introduced.


Ensure the request’s method is GET
<<"GET">> = cowboy_req:method(Req).
Allow methods from list
init(Req, State) ->
    case lists:member(cowboy_req:method(Req), [<<"GET">>, <<"POST">>]) of
        true -> handle(Req, State);
        false -> method_not_allowed(Req, State)

See also


Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment
You can’t perform that action at this time.