cowboy_req:parse_header(3)

Name

cowboy_req:parse_header - Parse the given HTTP header

Description

parse_header(Name, Req)          -> ParsedValue | Default
parse_header(Name, Req, Default) -> ParsedValue | Default

Name        :: binary()
Req         :: cowboy_req:req()
ParsedValue :: any()
Default     :: any()

Parse the given HTTP header.

The header name must be given as a lowercase binary string. While header names are case insensitive, Cowboy requires them to be given as lowercase to function properly.

The type of the parsed value varies depending on the header. Similarly, the default value when calling cowboy_req:parse_header/2 differs depending on the header.

Arguments

Name: Desired HTTP header name as a lowercase binary string.
Req: The Req object.
Default: Default value returned when the header is missing.

Return value

The parsed header value varies depending on the header. When the header is missing, the default argument is returned.

Headers

The following snippets detail the types returned by the different headers. Unless mentioned otherwise, the default value when the header is missing will be undefined:

parse_header(<<"accept">>, Req)
    -> [{{Type, SubType, Params}, Quality, AcceptExt}]

Type      :: binary()               %% case insensitive
SubType   :: binary()               %% case insensitive
Params    :: [{Key, Value}]
Quality   :: 0..1000
AcceptExt :: [Key | {Key, Value}]
Key       :: binary()               %% case insensitive
Value     :: binary()               %% case sensitive

accept-charset, accept-encoding and accept-language

parse_header(Name, Req) -> [{Value, Quality}]

Name    :: <<"accept-charset">>
         | <<"accept-encoding">>
         | <<"accept-language">>
Value   :: binary()                 %% case insensitive
Quality :: 0..1000

access-control-request-headers

parse_header(<<"access-control-request-headers">>, Req)
    -> [Header]

Header :: binary()   %% case insensitive

access-control-request-method

parse_header(<<"access-control-request-method">>)
    -> Method

Method :: binary()   %% case sensitive

authorization and proxy-authorization

parse_header(<<"authorization">>, Req)
    -> {basic, Username :: binary(), Password :: binary()}
     | {bearer, Token :: binary()}
     | {digest, [{Key :: binary(), Value :: binary()}]}

content-encoding and content-language

parse_header(Name, Req) -> [Value]

Name  :: <<"content-encoding">>
       | <<"content-language">>
Value :: binary()                 %% case insensitive

content-length

parse_header(<<"content-length">>, Req) -> non_neg_integer()

When the content-length header is missing, 0 is returned.

content-type

parse_header(<<"content-type">>, Req)
    -> {Type, SubType, Params}

Type      :: binary()               %% case insensitive
SubType   :: binary()               %% case insensitive
Params    :: [{Key, Value}]
Key       :: binary()               %% case insensitive
Value     :: binary()               %% case sensitive;

Note that the value for the charset parameter is case insensitive and returned as a lowercase binary string.

parse_header(<<"cookie">>, Req) -> [{Name, Value}]

Name  :: binary()                   %% case sensitive
Value :: binary()                   %% case sensitive

When the cookie header is missing, [] is returned.

While an empty cookie header is not valid, some clients do send it. Cowboy will in this case also return [].

expect

parse_header(<<"expect">>, Req) -> continue

if-match and if-none-match

parse_header(Name, Req)
    -> '*' | [{weak | strong, OpaqueTag}]

Name      :: <<"if-match">>
           | <<"if-none-match">>
OpaqueTag :: binary()               %% case sensitive

if-modified-since and if-unmodified-since

parse_header(Name, Req) -> calendar:datetime()

max-forwards

parse_header(<<"max-forwards">>, Req) -> non_neg_integer()

origin

parse_header(<<"origin">>, Req)
    -> [{Scheme, Host, Port} | GUID]

Scheme :: <<"http">> | <<"https">>
Host   :: binary()                   %% case insensitive
Port   :: 0..65535
GUID   :: reference()

Cowboy generates a reference in place of a GUID when the URI uses an unsupported uri-scheme or is not an absolute URI.

parse_header(<<"range">>, Req) -> {From, To} | Final

From  :: non_neg_integer()
To    :: non_neg_integer() | infinity
Final :: neg_integer()

sec-websocket-extensions

parse_header(<<"sec-websocket-extensions">>, Req)
    -> [{Extension, Params}]

Extension :: binary()               %% case sensitive
Params    :: [Key | {Key, Value}]
Key       :: binary()               %% case sensitive
Value     :: binary()               %% case sensitive

sec-websocket-protocol and upgrade

parse_header(Name, Req) -> [Token]

Name  :: <<"sec-websocket-protocol">>
       | <<"upgrade">>
Token :: binary()                   %% case insensitive

trailer

parse_header(Name, Req) -> [Header]

Header :: binary()   %% case insensitive

x-forwarded-for

parse_header(<<"x-forwarded-for">>, Req) -> [Token]

Token :: binary()                   %% case sensitive

This function will crash when attempting to parse a header Cowboy does not currently understand.

Changelog

2.8: The function now parses access-control-request-headers, access-control-request-method, content-encoding, content-language, max-forwards, origin, proxy-authorization and trailer.
2.0: Only the parsed header value is returned, it is no longer wrapped in a tuple.
1.0: Function introduced.

Examples

Parse the accept header with a custom default value

%% Accept everything when header is missing.
Accept = cowboy_req:parse_header(<<"accept">>, Req,
    [{{ <<"*">>, <<"*">>, []}, 1000, []}]).

Parse the content-length header

%% Default content-length is 0.
Length = cowboy_req:header(<<"content-length">>, Req).

99s

cowboy_req:parse_header(3)

Name

Description

Arguments

Return value

Headers

Changelog

Examples

See also

Cowboy 2.12 Function Reference

Navigation

Version select

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