cowboy/manual/cowboy_req.md

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, Req}
• action: {Result, Req} | {Result, Value, Req} | {error, atom()}
• modification: Req
• question: boolean()

The only exception is the chunk/2 function which may return ok.

Whenever Req is returned, you must use this returned value and ignore any previous you may have had. This value contains various state informations which are necessary for Cowboy to do some lazy evaluation or cache results where appropriate.

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

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, Req2}

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}], Req2}

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).

cookie(Name, Req) -> cookie(Name, Req, undefined)

cookie(Name, Req, Default) -> {Value, Req2}

Types:

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

Return the value for the given cookie.

Cookie names are case sensitive.

cookies(Req) -> {[{Name, Value}], Req2}

Types:

• Name = binary()
• Value = binary()

Return all cookies.

header(Name, Req) -> header(Name, Req, undefined)

header(Name, Req, Default) -> {Value, Req2}

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, Req2}

Types:

• Headers = cowboy:http_headers()

Return all headers.

host(Req) -> {Host, Req2}

Types:

• Host = binary()

Return the requested host.

host_info(Req) -> {HostInfo, Req2}

Types:

• HostInfo = cowboy_router:tokens() | undefined

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

host_url(Req) -> {HostURL, Req2}

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. This includes the onrequest hook.

meta(Name, Req) -> meta(Name, Req, undefined)

meta(Name, Req, Default) -> {Value, Req2}

Types:

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

Return metadata about the request.

method(Req) -> {Method, Req2}

Types:

• Method = binary()

Return the method.

Methods are case sensitive. Standard methods are always uppercase.

parse_header(Name, Req) ->

parse_header(Name, Req, Default) -> {ok, ParsedValue, Req2}

| {undefined, Value, Req2} | {error, badarg}

Types:

• Name = binary()
• Default = any()
• ParsedValue - see below
• Value = any()

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
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
if-match	`'*'
if-modified-since	calendar:datetime()
if-none-match	`'*'
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. Others will return {error, badarg} if the header value is empty.

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.

path(Req) -> {Path, Req2}

Types:

• Path = binary()

Return the requested path.

path_info(Req) -> {PathInfo, Req2}

Types:

• PathInfo = cowboy_router:tokens() | undefined

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

peer(Req) -> {Peer, Req2}

Types:

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

Return the client's IP address and port number.

port(Req) -> {Port, Req2}

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, Req2}

Types:

• QueryString = binary()

Return the request's query string.

qs_val(Name, Req) -> qs_val(Name, Req, undefined)

qs_val(Name, Req, Default) -> {Value, Req2}

Types:

• Name = binary()
• Default = any()
• Value = binary() | true

Return a value from the request's query string.

The value true will be returned when the name was found in the query string without an associated value.

qs_vals(Req) -> {[{Name, Value}], Req2}

Types:

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

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

The value true will be returned when a name was found in the query string without an associated value.

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, Req2}

Types:

• URL = binary() | undefined

Return the requested URL.

This function will always return undefined until the cowboy_router middleware has been executed. This includes the onrequest hook.

version(Req) -> {Version, Req2}

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} | {error, Reason}

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, Req2}

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} | {error, Reason}

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 | {error, Reason}

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) -> {ok, 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 | {error, Reason}

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) -> {ok, 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 | {error, atom()})

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.

Misc. exports

compact(Req) -> Req2

Remove any non-essential data from the Req object.

Long-lived connections usually only need to manipulate the Req object at initialization. Compacting allows saving up memory by discarding extraneous information.