::: cowboy_req

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

The functions in this module follow patterns for their return types,
based on the kind of function.

* access: `Value`
* action: `ok | {Result, Req} | {Result, Value, Req}`
* modification: `Req`
* question: `boolean()`

Whenever `Req` is returned, you must use this returned value and
ignore any previous you may have had. This value contains various
values which are necessary for Cowboy to keep track of the request
and response states.

All functions which perform an action should only be called once.
This includes reading the request body or replying. Cowboy will
throw an error on the second call when it detects suspicious behavior.

It is highly discouraged to pass the Req object to another process.
Doing so and calling `cowboy_req` functions from it leads to
undefined behavior.

:: Types

: body_opts() = [{continue, boolean()}
	| {length, non_neg_integer()}
	| {read_length, non_neg_integer()}
	| {read_timeout, timeout()}
	| {transfer_decode, transfer_decode_fun(), any()}
	| {content_decode, content_decode_fun()}]

Request body reading options.

: cookie_opts() = [{max_age, non_neg_integer()}
	| {domain, binary()} | {path, binary()}
	| {secure, boolean()} | {http_only, boolean()}]

Cookie options.

: req() - opaque to the user

The Req object.

All functions in this module receive a `Req` as argument,
and most of them return a new object labelled `Req2` in
the function descriptions below.

:: Request related exports

: binding(Name, Req) -> binding(Name, Req, undefined)
: binding(Name, Req, Default) -> Value

Types:

* Name = atom()
* Default = any()
* Value = any() | Default

Return the value for the given binding.

By default the value is a binary, however constraints may change
the type of this value (for example automatically converting
numbers to integer).

: bindings(Req) -> [{Name, Value}]

Types:

* Name = atom()
* Value = any()

Return all bindings.

By default the value is a binary, however constraints may change
the type of this value (for example automatically converting
numbers to integer).

: header(Name, Req) -> header(Name, Req, undefined)
: header(Name, Req, Default) -> Value

Types:

* Name = binary()
* Default = any()
* Value = binary() | Default

Return the value for the given header.

While header names are case insensitive, this function expects
the name to be a lowercase binary.

: headers(Req) -> Headers

Types:

* Headers = cowboy:http_headers()

Return all headers.

: host(Req) -> Host

Types:

* Host = binary()

Return the requested host.

: host_info(Req) -> HostInfo

Types:

* HostInfo = cowboy_router:tokens() | undefined

Return the extra tokens from matching against `...` during routing.

: host_url(Req) -> HostURL

Types:

* HostURL = binary() | undefined

Return the requested URL excluding the path component.

This function will always return `undefined` until the
`cowboy_router` middleware has been executed.

: match_cookies(Fields, Req) -> Map

Types:

* Fields = cowboy:fields()
* Map = map()

Match cookies against the given fields.

Cowboy will only return the cookie values specified in the
fields list, and ignore all others. Fields can be either
the name of the cookie requested; the name along with a
list of constraints; or the name, a list of constraints
and a default value in case the cookie is missing.

This function will crash if the cookie is missing and no
default value is provided. This function will also crash
if a constraint fails.

The name of the cookie must be provided as an atom. The
key of the returned map will be that atom. The value may
be converted through the use of constraints, making this
function able to extract, validate and convert values all
in one step.

: match_qs(Fields, Req) -> Map

Types:

* Fields = cowboy:fields()
* Map = map()

Match the query string against the given fields.

Cowboy will only return the query string values specified
in the fields list, and ignore all others. Fields can be
either the key requested; the key along with a list of
constraints; or the key, a list of constraints and a
default value in case the key is missing.

This function will crash if the key is missing and no
default value is provided. This function will also crash
if a constraint fails.

The key must be provided as an atom. The key of the
returned map will be that atom. The value may be converted
through the use of constraints, making this function able
to extract, validate and convert values all in one step.

: meta(Name, Req) -> meta(Name, Req, undefined)
: meta(Name, Req, Default) -> Value

Types:

* Name = atom()
* Default = any()
* Value = any()

Return metadata about the request.

: method(Req) -> Method

Types:

* Method = binary()

Return the method.

Methods are case sensitive. Standard methods are always uppercase.

: parse_cookies(Req) -> [{Name, Value}]

Types:

* Name = binary()
* Value = binary()

Parse and return all cookies.

Cookie names are case sensitive.

: parse_header(Name, Req) -> see below
: parse_header(Name, Req, Default) -> ParsedValue | Default

Types:

* Name = binary()
* Default = any()
* ParsedValue - see below

Parse the given header.

While header names are case insensitive, this function expects
the name to be a lowercase binary.

The `parse_header/2` function will call `parser_header/3` with a
different default value depending on the header being parsed. The
following table summarizes the default values used.

||	Header name			Default value
|
|	content-length		`0`
|	cookie				`[]`
|	transfer-encoding	`[<<"identity">>]`
|	Any other header	`undefined`

The parsed value differs depending on the header being parsed. The
following table summarizes the different types returned.

||	Header name				Type
|
|	accept					`[{{Type, SubType, Params}, Quality, AcceptExt}]`
|	accept-charset			`[{Charset, Quality}]`
|	accept-encoding			`[{Encoding, Quality}]`
|	accept-language			`[{LanguageTag, Quality}]`
|	authorization			`{AuthType, Credentials}`
|	content-length			`non_neg_integer()`
|	content-type			`{Type, SubType, ContentTypeParams}`
|	cookie					`[{binary(), binary()}]`
|	expect					`[Expect | {Expect, ExpectValue, Params}]`
|	if-match				`'*' | [{weak | strong, OpaqueTag}]`
|	if-modified-since		`calendar:datetime()`
|	if-none-match			`'*' | [{weak | strong, OpaqueTag}]`
|	if-unmodified-since		`calendar:datetime()`
|	range					`{Unit, [Range]}`
|	sec-websocket-protocol	`[binary()]`
|	transfer-encoding		`[binary()]`
|	upgrade					`[binary()]`
|	x-forwarded-for			`[binary()]`

Types for the above table:

* Type = SubType = Charset = Encoding = LanguageTag = binary()
* AuthType = Expect = OpaqueTag = Unit = binary()
* Params = ContentTypeParams = [{binary(), binary()}]
* Quality = 0..1000
* AcceptExt = [{binary(), binary()} | binary()]
* Credentials - see below
* Range = {non_neg_integer(), non_neg_integer() | infinity} | neg_integer()

The cookie names and values, the values of the sec-websocket-protocol
and x-forwarded-for headers, the values in `AcceptExt` and `Params`,
the authorization `Credentials`, the `ExpectValue` and `OpaqueTag`
are case sensitive. All values in `ContentTypeParams` are case sensitive
except the value of the charset parameter, which is case insensitive.
All other values are case insensitive and will be returned as lowercase.

The headers accept, accept-encoding and cookie headers can return
an empty list. Some other headers are expected to have a value if provided
and may crash if the value is missing.

The authorization header parsing code currently only supports basic
HTTP authentication. The `Credentials` type is thus `{Username, Password}`
with `Username` and `Password` being `binary()`.

The range header value `Range` can take three forms:

* `{From, To}`: from `From` to `To` units
* `{From, infinity}`: everything after `From` units
* `-Final`: the final `Final` units

An `undefined` tuple will be returned if Cowboy doesn't know how
to parse the requested header.

: parse_qs(Req) -> [{Name, Value}]

Types:

* Name = binary()
* Value = binary() | true

Return the request's query string as a list of tuples.

The atom `true` is returned for keys which have no value.
Keys with no value are different from keys with an empty
value in that they do not have a `=` indicating the presence
of a value.

: path(Req) -> Path

Types:

* Path = binary()

Return the requested path.

: path_info(Req) -> PathInfo

Types:

* PathInfo = cowboy_router:tokens() | undefined

Return the extra tokens from matching against `...` during routing.

: peer(Req) -> Peer

Types:

* Peer = {inet:ip_address(), inet:port_number()}

Return the client's IP address and port number.

: port(Req) -> Port

Types:

* Port = inet:port_number()

Return the request's port.

The port returned by this function is obtained by parsing
the host header. It may be different than the actual port
the client used to connect to the Cowboy server.

: qs(Req) -> QueryString

Types:

* QueryString = binary()

Return the request's query string.

: set_meta(Name, Value, Req) -> Req2

Types:

* Name = atom()
* Value = any()

Set metadata about the request.

An existing value will be overwritten.

: url(Req) -> URL

Types:

* URL = binary() | undefined

Return the requested URL.

This function will always return `undefined` until the
`cowboy_router` middleware has been executed.

: version(Req) -> Version

Types:

* Version = cowboy:http_version()

Return the HTTP version used for this request.

:: Request body related exports

: body(Req) -> body(Req, [])
: body(Req, Opts) -> {ok, Data, Req2} | {more, Data, Req2}

Types:

* Opts = [body_opt()]
* Data = binary()
* Reason = atom()

Read the request body.

This function will read a chunk of the request body. If there is
more data to be read after this function call, then a `more` tuple
is returned. Otherwise an `ok` tuple is returned.

Cowboy will automatically send a `100 Continue` reply if
required. If this behavior is not desirable, it can be disabled
by setting the `continue` option to `false`.

Cowboy will by default attempt to read up to 8MB of the body,
but in chunks of 1MB. It will use a timeout of 15s per chunk.
All these values can be changed using the `length`, `read_length`
and `read_timeout` options respectively. Note that the size
of the data may not be the same as requested as the decoding
functions may grow or shrink it, and Cowboy makes not attempt
at returning an exact amount.

Cowboy will properly handle chunked transfer-encoding by
default. If any other transfer-encoding or content-encoding
has been used for the request, custom decoding functions
can be used. The `content_decode` and `transfer_decode`
options allow setting the decode functions manually.

After the body has been streamed fully, Cowboy will remove
the transfer-encoding header from the Req object, and add
the content-length header if it wasn't already there.

This function can only be called once. Cowboy will not cache
the result of this call.

: body_length(Req) -> Length

Types:

* Length = non_neg_integer() | undefined

Return the length of the request body.

The length will only be returned if the request does not
use any transfer-encoding and if the content-length header
is present.

: body_qs(Req) -> body_qs(Req,
	[{length, 64000}, {read_length, 64000}, {read_timeout, 5000}])
: body_qs(Req, Opts) -> {ok, [{Name, Value}], Req2} | {badlength, Req2}

Types:

* Opts = [body_opt()]
* Name = binary()
* Value = binary() | true
* Reason = chunked | badlength | atom()

Return the request body as a list of tuples.

This function will parse the body assuming the content-type
application/x-www-form-urlencoded, commonly used for the
query string.

This function calls `body/2` for reading the body, with the
same options it received. By default it will attempt to read
a body of 64KB in one chunk, with a timeout of 5s. If the
body is larger then a `badlength` tuple is returned.

This function can only be called once. Cowboy will not cache
the result of this call.

: has_body(Req) -> boolean()

Return whether the request has a body.

: part(Req) -> part(Req,
	[{length, 64000}, {read_length, 64000}, {read_timeout, 5000}])
: part(Req, Opts) -> {ok, Headers, Req2} | {done, Req2}

Types:

* Opts = [body_opt()]
* Headers = cow_multipart:headers()

Read the headers for the next part of the multipart message.

Cowboy will skip any data remaining until the beginning of
the next part. This includes the preamble to the multipart
message but also the body of a previous part if it hasn't
been read. Both are skipped automatically when calling this
function.

The headers returned are MIME headers, NOT HTTP headers.
They can be parsed using the functions from the `cow_multipart`
module. In addition, the `cow_multipart:form_data/1` function
can be used to quickly figure out `multipart/form-data` messages.
It takes the list of headers and returns whether this part is
a simple form field or a file being uploaded.

Note that once a part has been read, or skipped, it cannot
be read again.

This function calls `body/2` for reading the body, with the
same options it received. By default it will only read chunks
of 64KB with a timeout of 5s. This is tailored for reading
part headers, not for skipping the previous part's body.
You might want to consider skipping large parts manually.

: part_body(Req) -> part_body(Req, [])
: part_body(Req, Opts) -> {ok, Data, Req2} | {more, Data, Req2}

Types:

* Opts = [body_opt()]
* Data = binary()

Read the body of the current part of the multipart message.

This function calls `body/2` for reading the body, with the
same options it received. It uses the same defaults.

If there are more data to be read from the socket for this
part, the function will return what it could read inside a
`more` tuple. Otherwise, it will return an `ok` tuple.

Calling this function again after receiving a `more` tuple
will return another chunk of body. The last chunk will be
returned inside an `ok` tuple.

Note that once the body has been read, fully or partially,
it cannot be read again.

:: Response related exports

: chunk(Data, Req) -> ok

Types:

* Data = iodata()
* Reason = atom()

Send a chunk of data.

This function should be called as many times as needed
to send data chunks after calling `chunked_reply/{2,3}`.

When the method is HEAD, no data will actually be sent.

If the request uses HTTP/1.0, the data is sent directly
without wrapping it in an HTTP/1.1 chunk, providing
compatibility with older clients.

: chunked_reply(StatusCode, Req) -> chunked_reply(StatusCode, [], Req)
: chunked_reply(StatusCode, Headers, Req) -> Req2

Types:

* StatusCode = cowboy:http_status()
* Headers = cowboy:http_headers()

Send a response using chunked transfer-encoding.

This function effectively sends the response status line
and headers to the client.

This function will not send any body set previously. After
this call the handler must use the `chunk/2` function
repeatedly to send the body in as many chunks as needed.

If the request uses HTTP/1.0, the data is sent directly
without wrapping it in an HTTP/1.1 chunk, providing
compatibility with older clients.

This function can only be called once, with the exception
of overriding the response in the `onresponse` hook.

: continue(Req) -> ok

Types:

* Reason = atom()

Send a 100 Continue intermediate reply.

This reply is required before the client starts sending the
body when the request contains the `expect` header with the
`100-continue` value.

Cowboy will send this automatically when required. However
you may want to do it manually by disabling this behavior
with the `continue` body option and then calling this
function.

: delete_resp_header(Name, Req) -> Req2

Types:

* Name = binary()

Delete the given response header.

While header names are case insensitive, this function expects
the name to be a lowercase binary.

: has_resp_body(Req) -> boolean()

Return whether a response body has been set.

This function will return false if a response body has
been set with a length of 0.

: has_resp_header(Name, Req) -> boolean()

Types:

* Name = binary()

Return whether the given response header has been set.

While header names are case insensitive, this function expects
the name to be a lowercase binary.

: reply(StatusCode, Req) -> reply(StatusCode, [], Req)
: reply(StatusCode, Headers, Req) - see below
: reply(StatusCode, Headers, Body, Req) -> Req2

Types:

* StatusCode = cowboy:http_status()
* Headers = cowboy:http_headers()
* Body = iodata()

Send a response.

This function effectively sends the response status line,
headers and body to the client, in a single send function
call.

The `reply/2` and `reply/3` functions will send the body
set previously, if any. The `reply/4` function overrides
any body set previously and sends `Body` instead.

If a body function was set, and `reply/2` or `reply/3` was
used, it will be called before returning.

No more data can be sent to the client after this function
returns.

This function can only be called once, with the exception
of overriding the response in the `onresponse` hook.

: set_resp_body(Body, Req) -> Req2

Types:

* Body = iodata()

Set a response body.

This body will not be sent if `chunked_reply/{2,3}` or
`reply/4` is used, as they override it.

: set_resp_body_fun(Fun, Req) -> Req2
: set_resp_body_fun(Length, Fun, Req) -> Req2

Types:

* Fun = fun((Socket, Transport) -> ok)
* Socket = inet:socket()
* Transport = module()
* Length = non_neg_integer()

Set a fun for sending the response body.

If a `Length` is provided, it will be sent in the
content-length header in the response. It is recommended
to set the length if it can be known in advance. Otherwise,
the transfer-encoding header will be set to identity.

This function will only be called if the response is sent
using the `reply/2` or `reply/3` function.

The fun will receive the Ranch `Socket` and `Transport` as
arguments. Only send and sendfile operations are supported.

: set_resp_body_fun(chunked, Fun, Req) -> Req2

Types:

* Fun = fun((ChunkFun) -> ok)
* ChunkFun = fun((iodata()) -> ok)

Set a fun for sending the response body using chunked transfer-encoding.

This function will only be called if the response is sent
using the `reply/2` or `reply/3` function.

The fun will receive another fun as argument. This fun is to
be used to send chunks in a similar way to the `chunk/2` function,
except the fun only takes one argument, the data to be sent in
the chunk.

: set_resp_cookie(Name, Value, Opts, Req) -> Req2

Types:

* Name = iodata()
* Value = iodata()
* Opts = cookie_opts()

Set a cookie in the response.

Cookie names are case sensitive.

: set_resp_header(Name, Value, Req) -> Req2

Types:

* Name = binary()
* Value = iodata()

Set a response header.

You should use `set_resp_cookie/4` instead of this function
to set cookies.
