= cowboy_req(3)

== Name

cowboy_req - HTTP request and response

== Description

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:

[options="header"]
|===
| Type         | Name pattern              | Return type
| access       | no verb, parse_*, match_* | `Value`
| question     | has_*                     | `boolean()`
| modification | set_*                     | `Req`
| action       | 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.

== Exports

Raw request:

* link:man:cowboy_req:method(3)[cowboy_req:method(3)] - HTTP method
* link:man:cowboy_req:version(3)[cowboy_req:version(3)] - HTTP version
* link:man:cowboy_req:scheme(3)[cowboy_req:scheme(3)] - URI scheme
* link:man:cowboy_req:host(3)[cowboy_req:host(3)] - URI host name
* link:man:cowboy_req:port(3)[cowboy_req:port(3)] - URI port number
* link:man:cowboy_req:path(3)[cowboy_req:path(3)] - URI path
* link:man:cowboy_req:qs(3)[cowboy_req:qs(3)] - URI query string
* link:man:cowboy_req:uri(3)[cowboy_req:uri(3)] - Reconstructed URI
* link:man:cowboy_req:header(3)[cowboy_req:header(3)] - HTTP header
* link:man:cowboy_req:headers(3)[cowboy_req:headers(3)] - HTTP headers
* link:man:cowboy_req:peer(3)[cowboy_req:peer(3)] - Peer address and port

Processed request:

* link:man:cowboy_req:parse_qs(3)[cowboy_req:parse_qs(3)] - Parse the query string
* link:man:cowboy_req:match_qs(3)[cowboy_req:match_qs(3)] - Match the query string against constraints
* link:man:cowboy_req:parse_header(3)[cowboy_req:parse_header(3)] - Parse the given HTTP header
* link:man:cowboy_req:parse_cookies(3)[cowboy_req:parse_cookies(3)] - Parse cookie headers
* link:man:cowboy_req:match_cookies(3)[cowboy_req:match_cookies(3)] - Match cookies against constraints
* link:man:cowboy_req:binding(3)[cowboy_req:binding(3)] - Access a value bound from the route
* link:man:cowboy_req:bindings(3)[cowboy_req:bindings(3)] - Access all values bound from the route
* link:man:cowboy_req:host_info(3)[cowboy_req:host_info(3)] - Access the route's heading host segments
* link:man:cowboy_req:path_info(3)[cowboy_req:path_info(3)] - Access the route's trailing path segments

Request body:

* link:man:cowboy_req:has_body(3)[cowboy_req:has_body(3)] - Is there a request body?
* link:man:cowboy_req:body_length(3)[cowboy_req:body_length(3)] - Body length
* link:man:cowboy_req:read_body(3)[cowboy_req:read_body(3)] - Read the request body
* link:man:cowboy_req:read_urlencoded_body(3)[cowboy_req:read_urlencoded_body(3)] - Read and parse a urlencoded request body
* link:man:cowboy_req:read_part(3)[cowboy_req:read_part(3)] - Read the next multipart headers
* link:man:cowboy_req:read_part_body(3)[cowboy_req:read_part_body(3)] - Read the current part's body

Response:

* link:man:cowboy_req:set_resp_cookie(3)[cowboy_req:set_resp_cookie(3)] - Set a cookie
* link:man:cowboy_req:set_resp_header(3)[cowboy_req:set_resp_header(3)] - Set a response header
* link:man:cowboy_req:set_resp_headers(3)[cowboy_req:set_resp_headers(3)] - Set several response headers
* link:man:cowboy_req:has_resp_header(3)[cowboy_req:has_resp_header(3)] - Is the given response header set?
* link:man:cowboy_req:resp_header(3)[cowboy_req:resp_header(3)] - Response header
* link:man:cowboy_req:resp_headers(3)[cowboy_req:resp_headers(3)] - Response headers
* link:man:cowboy_req:delete_resp_header(3)[cowboy_req:delete_resp_header(3)] - Delete a response header
* link:man:cowboy_req:set_resp_body(3)[cowboy_req:set_resp_body(3)] - Set the response body
* link:man:cowboy_req:has_resp_body(3)[cowboy_req:has_resp_body(3)] - Is there a response body?
* link:man:cowboy_req:reply(3)[cowboy_req:reply(3)] - Send the response
* link:man:cowboy_req:stream_reply(3)[cowboy_req:stream_reply(3)] - Send the response headers
* link:man:cowboy_req:stream_body(3)[cowboy_req:stream_body(3)] - Stream the response body
* link:man:cowboy_req:push(3)[cowboy_req:push(3)] - Push a resource to the client

== Types

=== push_opts()

[source,erlang]
----
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()

[source,erlang]
----
read_body_opts() :: #{
    length  => non_neg_integer(),
    period  => non_neg_integer(),
    timeout => timeout()
}
----

Body reading options.

The defaults are function-specific.

=== req()

[source,erlang]
----
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
[source,erlang]
----
Req#{_myapp_auth_method => pubkey}.
----

=== resp_body()

[source,erlang]
----
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
[source,erlang]
----
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.

// @todo Make sure we have a test with an empty file...
// @todo cowboy_static should probably NOT return a sendfile tuple if size is 0.

//%% While sendfile allows a Len of 0 that means "everything past Offset",
//%% Cowboy expects the real length as it is used as metadata.
//%% @todo We should probably explicitly reject it.

== See also

link:man:cowboy(7)[cowboy(7)]
