Nine Nines: cowboy

cowboy_req(3)

Name

cowboy_req - HTTP request and response

Description

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() = [Option]

Option = {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() = [Option]

Option = {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 some of them return a new object labelled Req2 in the function descriptions below.

Request related exports

binding(Name, Req) → binding(Name, Req, undefined)

Alias of cowboy_req:binding/3.

binding(Name, Req, Default) → Value

Name = atom(): Binding name.
Default = any(): Default value.
Value = any() | Default: Binding value.

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}]

Name = atom(): Binding name.
Value = any(): Binding value.

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)

Alias of cowboy_req:header/3.

header(Name, Req, Default) → Value

Name = binary(): Request header name.
Default = any(): Default value.
Value = binary() | Default: Request header value.

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

Headers = cowboy:http_headers(): Request headers.

Return all headers.

host(Req) → Host

Host = binary(): Requested host.

Return the requested host.

host_info(Req) → HostInfo

HostInfo = cowboy_router:tokens() | undefined: Extra tokens for the host.

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

host_url(Req) → HostURL

HostURL = binary() | undefined: Requested URL, without the path component.

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

Fields = cowboy:fields(): Cookie fields match rules.
Map = map(): Cookie fields matched.

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

Fields = cowboy:fields(): Query string fields match rules.
Map = map(): Query string fields matched.

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)

Alias for cowboy_req:meta/3.

meta(Name, Req, Default) → Value

Name = atom(): Metadata name.
Default = any(): Default value.
Value = any(): Metadata value.

Return metadata about the request.

method(Req) → Method

Method = binary(): Request method.

Return the method.

Methods are case sensitive. Standard methods are always uppercase.

parse_cookies(Req) → [{Name, Value}]

Name = binary(): Cookie name.
Value = binary(): Cookie value.

Parse and return all cookies.

Cookie names are case sensitive.

parse_header(Name, Req) → see below

Alias of cowboy_req:parse_header/3.

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

parse_header(Name, Req, Default) → ParsedValue | Default

Name = binary(): Request header name.
Default = any(): Default value.
ParsedValue - see below: Parsed request header value.

Parse the given header.

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

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

Header name	Type of parsed header value
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}]

Name = binary(): Query string field name.
Value = binary() | true: Query string field value.

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

Path = binary(): Requested path.

Return the requested path.

path_info(Req) → PathInfo

PathInfo = cowboy_router:tokens() | undefined: Extra tokens for the path.

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

peer(Req) → Peer

Peer = {inet:ip_address(), inet:port_number()}: Peer IP address and port number.

Return the client’s IP address and port number.

port(Req) → Port

Port = inet:port_number(): Requested 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

QueryString = binary(): Unprocessed query string.

Return the request’s query string.

set_meta(Name, Value, Req) → Req2

Name = atom(): Metadata name.
Value = any(): Metadata value.

Set metadata about the request.

An existing value will be overwritten.

url(Req) → URL

URL = binary() | undefined: Requested URL.

Return the requested URL.

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

version(Req) → Version

Version = cowboy:http_version(): Client’s advertised HTTP version.

Return the HTTP version used for this request.

Request body related exports

body(Req) → body(Req, [])

Alias of cowboy_req:body/2.

body(Req, Opts) → {ok, Data, Req2} | {more, Data, Req2}

Opts = [body_opt()]: Request body reading options.
Data = binary(): Data read from the body.

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

Length = non_neg_integer() | undefined: Length of the request body.

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}])

Alias of cowboy_req:body_qs/2.

body_qs(Req, Opts) → {ok, [{Name, Value}], Req2} | {badlength, Req2}

Opts = [body_opt()]: Request body reading options.
Name = binary(): Field name.
Value = binary() | true: Field value.

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}])

Alias of cowboy_req:part/2.

part(Req, Opts) → {ok, Headers, Req2} | {done, Req2}

Opts = [body_opt()]: Request body reading options.
Headers = cow_multipart:headers(): Part’s 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, [])

Alias of cowboy_req:part_body/2.

part_body(Req, Opts) → {ok, Data, Req2} | {more, Data, Req2}

Opts = [body_opt()]: Request body reading options.
Data = binary(): Part’s body.

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

Data = iodata(): Chunk data to be sent.

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)

Alias of cowboy_req:chunked_reply/3.

chunked_reply(StatusCode, Headers, Req) → Req2

StatusCode = cowboy:http_status(): Response status code.
Headers = cowboy:http_headers(): Response 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

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

Name = binary(): Response header name.

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()

Name = binary(): Response header name.

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)

Alias of cowboy_req:reply/3.

reply(StatusCode, Headers, Req) - see below

Alias of cowboy_req:reply/4, with caveats.

reply(StatusCode, Headers, Body, Req) → Req2

StatusCode = cowboy:http_status(): Response status code.
Headers = cowboy:http_headers(): Response headers.
Body = iodata(): Response body.

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

Body = iodata(): Response body.

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

Alias of cowboy_req:set_resp_body_fun/3.

set_resp_body_fun(Length, Fun, Req) → Req2

Fun = fun((Socket, Transport) → ok): Fun that will send the response body.
Socket = inet:socket(): Socket for this connection.
Transport = module(): Transport module for this socket.
Length = non_neg_integer(): Length of the response body.

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

Fun = fun((ChunkFun) → ok): Fun that will send the response body.
ChunkFun = funiodata( → ok): Fun to call for every chunk to be sent.

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

Name = iodata(): Cookie name.
Value = iodata(): Cookie value.
Opts = cookie_opts(): Cookie options.

Set a cookie in the response.

Cookie names are case sensitive.

set_resp_header(Name, Value, Req) → Req2

Name = binary(): Response header name.
Value = iodata(): Response header value.

Set a response header.

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

cowboy_req(3)

Name

Description

Types

body_opts() = [Option]

cookie_opts() = [Option]

req() - opaque to the user

Request related exports

binding(Name, Req) → binding(Name, Req, undefined)

binding(Name, Req, Default) → Value

bindings(Req) → [{Name, Value}]

header(Name, Req) → header(Name, Req, undefined)

header(Name, Req, Default) → Value

headers(Req) → Headers

host(Req) → Host

host_info(Req) → HostInfo

host_url(Req) → HostURL

match_cookies(Fields, Req) → Map

match_qs(Fields, Req) → Map

meta(Name, Req) → meta(Name, Req, undefined)

meta(Name, Req, Default) → Value

method(Req) → Method

parse_cookies(Req) → [{Name, Value}]

parse_header(Name, Req) → see below

parse_header(Name, Req, Default) → ParsedValue | Default

parse_qs(Req) → [{Name, Value}]

path(Req) → Path

path_info(Req) → PathInfo

peer(Req) → Peer

port(Req) → Port

qs(Req) → QueryString

set_meta(Name, Value, Req) → Req2

url(Req) → URL

version(Req) → Version

Request body related exports

body(Req) → body(Req, [])

body(Req, Opts) → {ok, Data, Req2} | {more, Data, Req2}

body_length(Req) → Length

body_qs(Req) → body_qs(Req, [{length, 64000}, {read_length, 64000}, {read_timeout, 5000}])

body_qs(Req, Opts) → {ok, [{Name, Value}], Req2} | {badlength, Req2}

has_body(Req) → boolean()

part(Req) → part(Req, [{length, 64000}, {read_length, 64000}, {read_timeout, 5000}])

part(Req, Opts) → {ok, Headers, Req2} | {done, Req2}

part_body(Req) → part_body(Req, [])

part_body(Req, Opts) → {ok, Data, Req2} | {more, Data, Req2}

Response related exports

chunk(Data, Req) → ok

chunked_reply(StatusCode, Req) → chunked_reply(StatusCode, [], Req)

chunked_reply(StatusCode, Headers, Req) → Req2

continue(Req) → ok

delete_resp_header(Name, Req) → Req2

has_resp_body(Req) → boolean()

has_resp_header(Name, Req) → boolean()

reply(StatusCode, Req) → reply(StatusCode, [], Req)

reply(StatusCode, Headers, Req) - see below

reply(StatusCode, Headers, Body, Req) → Req2

set_resp_body(Body, Req) → Req2

set_resp_body_fun(Fun, Req) → Req2

set_resp_body_fun(Length, Fun, Req) → Req2

set_resp_body_fun(chunked, Fun, Req) → Req2

set_resp_cookie(Name, Value, Opts, Req) → Req2

set_resp_header(Name, Value, Req) → Req2

Cowboy 2.0 Function Reference

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