Reference Manual

Version 6.4

Table of Contents




Module Summary

An HTTP/1.1 client


This module provides the API to an HTTP/1.1 compatible client according to RFC 2616. Caching is not supported.


When starting the Inets application, a manager process for the default profile is started. The functions in this API that do not explicitly use a profile accesses the default profile. A profile keeps track of proxy options, cookies, and other options that can be applied to more than one request.

If the scheme https is used, the SSL application must be started. When https links need to go through a proxy, the CONNECT method extension to HTTP-1.1 is used to establish a tunnel and then the connection is upgraded to TLS. However, "TLS upgrade" according to RFC 2817is not supported.

Pipelining is only used if the pipeline time-out is set, otherwise persistent connections without pipelining are used. That is, the client always waits for the previous response before sending the next request.

Some examples are provided in the Inets User's Guide.


Type definitions that are used more than once in this module:

boolean() = true | false

string() = list of ASCII characters

request_id() = reference()

profile() = atom()

path() = string() representing a file path or directory path

ip_address() = See the inet(3) manual page in Kernel.

socket_opt() = See the options used by gen_tcp(3) gen_tcp(3) and ssl(3) connect(s)


Type definitions related to HTTP:

method() = head | get | put | post | trace | options | delete | patch


= {url(), headers()}

| {url(), headers(), content_type(), body()}

url() = string() syntax according to the URI definition in RFC 2396, for example ""

status_line() = {http_version(), status_code(), reason_phrase()}

http_version() = string(), for example, "HTTP/1.1"

status_code() = integer()

reason_phrase() = string()

content_type() = string()

headers() = [header()]

header() = {field(), value()}

field() = string()

value() = string()


= string() | binary()

| {fun(accumulator())

-> body_processing_result(), accumulator()}

| {chunkify, fun(accumulator())

-> body_processing_result(), accumulator()}

body_processing_result() = eof | {ok, iolist(), accumulator()}

accumulator() = term()

filename() = string()

For more information about HTTP, see RFC 2616.


See ssl(3) for information about SSL options (ssloptions()).


An HTTP client can be configured to start when starting the Inets application or started dynamically in runtime by calling the Inets application API inets:start(httpc, ServiceConfig) or inets:start(httpc, ServiceConfig, How), see inets(3). The configuration options are as follows:

{profile, profile()}

Name of the profile, see DATA TYPES. This option is mandatory.

{data_dir, path()}

Directory where the profile can save persistent data. If omitted, all cookies are treated as session cookies.

The client can be stopped using inets:stop(httpc, Pid) or inets:stop(httpc, Profile).


cancel_request(RequestId) ->
cancel_request(RequestId, Profile) -> ok


RequestId = request_id() - A unique identifier as returned by request/4
Profile = profile() | pid()
When started stand_alone only the pid can be used.

Cancels an asynchronous HTTP request. Notice that this does not guarantee that the request response is not delivered. Because it is asynchronous, the request can already have been completed when the cancellation arrives.

cookie_header(Url) ->
cookie_header(Url, Profile | Opts) -> header() | {error, Reason}
cookie_header(Url, Opts, Profile) -> header() | {error, Reason}


Url = url()
Opts = [cookie_header_opt()]
Profile = profile() | pid()
When started stand_alone.
cookie_header_opt() = {ipv6_host_with_brackets, boolean()}

Returns the cookie header that would have been sent when making a request to Url using profile Profile. If no profile is specified, the default profile is used.

Option ipv6_host_with_bracket deals with how to parse IPv6 addresses. For details, see argument Options of request/[4,5].

get_options(OptionItems) -> {ok, Values} | {error, Reason}
get_options(OptionItems, Profile) -> {ok, Values} | {error, Reason}


OptionItems = all | [option_item()]
option_item() = proxy | https_proxy | max_sessions | keep_alive_timeout | max_keep_alive_length | pipeline_timeout | max_pipeline_length | cookies | ipfamily | ip | port | socket_opts | verbose
Profile = profile() | pid()
When started stand_alone only the pid can used.
Values = [{option_item(), term()}]
Reason = term()

Retrieves the options currently used by the client.

info() -> list()
info(Profile) -> list()


Profile = profile() | pid()
When started stand_alone only the pid can be used.

Produces a list of miscellaneous information. Intended for debugging. If no profile is specified, the default profile is used.

reset_cookies() -> void()
reset_cookies(Profile) -> void()


Profile = profile() | pid()
When started stand_alone only the pid can be used.

Resets (clears) the cookie database for the specified Profile. If no profile is specified the default profile is used.

request(Url) ->
request(Url, Profile) -> {ok, Result} | {error, Reason}


Url = url()
Result = {status_line(), headers(), Body} | {status_code(), Body} | request_id()
Body = string() | binary()
Profile = profile() | pid()
When started stand_alone only the pid can be used.
Reason = term()

Equivalent to httpc:request(get, {Url, []}, [], []).

request(Method, Request, HTTPOptions, Options) ->
request(Method, Request, HTTPOptions, Options, Profile) -> {ok, Result} | {ok, saved_to_file} | {error, Reason}


Method = method()
Request = request()
HTTPOptions = http_options()
http_options() = [http_option()]
http_option() = {timeout, timeout()} | {connect_timeout, timeout()} | {ssl, ssloptions()} | {essl, ssloptions()} | {autoredirect, boolean()} | {proxy_auth, {userstring(), passwordstring()}} | {version, http_version()} | {relaxed, boolean()} | {url_encode, boolean()}
timeout() = integer() >= 0 | infinity
Options = options()
options() = [option()]
option() = {sync, boolean()} | {stream, stream_to()} | {body_format, body_format()} | {full_result, boolean()} | {headers_as_is, boolean() | {socket_opts, socket_opts()} | {receiver, receiver()}, {ipv6_host_with_brackets, boolean()}}
stream_to() = none | self | {self, once} | filename()
socket_opts() = [socket_opt()]
receiver() = pid() | function()/1 | {Module, Function, Args}
Module = atom()
Function = atom()
Args = list()
body_format() = string | binary
Result = {status_line(), headers(), Body} | {status_code(), Body} | request_id()
Body = string() | binary()
Profile = profile() | pid()
When started stand_alone only the pid can be used.
Reason = {connect_failed, term()} | {send_failed, term()} | term()

Sends an HTTP request. The function can be both synchronous and asynchronous. In the latter case, the function returns {ok, RequestId} and then the information is delivered to the receiver depending on that value.

HTTP option (http_option()) details:


Time-out time for the request.

The clock starts ticking when the request is sent.

Time is in milliseconds.

Default is infinity.


Connection time-out time, used during the initial request, when the client is connecting to the server.

Time is in milliseconds.

Default is the value of option timeout.


This is the SSL/TLS connectin configuration option.

Defaults to []. See ssl:connect/[2,3,4] for available options.


The client automatically retrieves the information from the new URI and returns that as the result, instead of a 30X-result code.

For some 30X-result codes, automatic redirect is not allowed. In these cases the 30X-result is always returned.

Default is true.


A proxy-authorization header using the provided username and password is added to the request.


Can be used to make the client act as an HTTP/1.0 or HTTP/0.9 client. By default this is an HTTP/1.1 client. When using HTTP/1.0 persistent connections are not used.

Default is the string "HTTP/1.1".


If set to true, workarounds for known server deviations from the HTTP-standard are enabled.

Default is false.


Applies Percent-encoding, also known as URL encoding on the URL.

Default is false.

Option (option()) details:


Option for the request to be synchronous or asynchronous.

Default is true.


Streams the body of a 200 or 206 response to the calling process or to a file. When streaming to the calling process using option self, the following stream messages are sent to that process: {http, {RequestId, stream_start, Headers}}, {http, {RequestId, stream, BinBodyPart}}, and {http, {RequestId, stream_end, Headers}}.

When streaming to the calling processes using option {self, once}, the first message has an extra element, that is, {http, {RequestId, stream_start, Headers, Pid}}. This is the process id to be used as an argument to http:stream_next/1 to trigger the next message to be sent to the calling process.

Notice that chunked encoding can add headers so that there are more headers in the stream_end message than in stream_start. When streaming to a file and the request is asynchronous, the message {http, {RequestId, saved_to_file}} is sent.

Default is none.


Defines if the body is to be delivered as a string or binary. This option is only valid for the synchronous request.

Default is string.


Defines if a "full result" is to be returned to the caller (that is, the body, the headers, and the entire status line) or not (the body and the status code).

Default is true.


Defines if the headers provided by the user are to be made lower case or to be regarded as case sensitive.

The HTTP standard requires them to be case insensitive. Use this feature only if there is no other way to communicate with the server or for testing purpose. When this option is used, no headers are automatically added. All necessary headers must be provided by the user.

Default is false.


Socket options to be used for this and subsequent requests.

Overrides any value set by function set_options.

The validity of the options is not checked by the HTTP client they are assumed to be correct and passed on to ssl application and inet driver, which may reject them if they are not correct. Note that the current implementation assumes the requests to the same host, port combination will use the same socket options.

By default the socket options set by function set_options/[1,2] are used when establishing a connection.


Defines how the client delivers the result of an asynchronous request (sync has the value false).


Messages are sent to this process in the format {http, ReplyInfo}.


Information is delivered to the receiver through calls to the provided fun Receiver(ReplyInfo).

{Module, Function, Args}

Information is delivered to the receiver through calls to the callback function apply(Module, Function, [ReplyInfo | Args]).

In all of these cases, ReplyInfo has the following structure:

{RequestId, saved_to_file}
{RequestId, {error, Reason}}
{RequestId, Result}
{RequestId, stream_start, Headers}
{RequestId, stream_start, Headers, HandlerPid}
{RequestId, stream, BinBodyPart}
{RequestId, stream_end, Headers}

Default is the pid of the process calling the request function (self()).


Defines when parsing the Host-Port part of an URI with an IPv6 address with brackets, if those brackets are to be retained (true) or stripped (false).

Default is false.

set_options(Options) ->
set_options(Options, Profile) -> ok | {error, Reason}


Options = [Option]
Option = {proxy, {Proxy, NoProxy}}
| {https_proxy, {Proxy, NoProxy}}
| {max_sessions, MaxSessions}
| {max_keep_alive_length, MaxKeepAlive}
| {keep_alive_timeout, KeepAliveTimeout}
| {max_pipeline_length, MaxPipeline}
| {pipeline_timeout, PipelineTimeout}
| {cookies, CookieMode}
| {ipfamily, IpFamily}
| {ip, IpAddress}
| {port, Port}
| {socket_opts, socket_opts()}
| {verbose, VerboseMode}
Proxy = {Hostname, Port}
Hostname = string()
Example: "localhost" or ""
Port = integer()
Example: 8080
NoProxy = [NoProxyDesc]
NoProxyDesc = DomainDesc | HostName | IPDesc
DomainDesc = "*.Domain"
Example: "*"
IpDesc = string()
Example: "134.138" or "[FEDC:BA98" (all IP addresses starting with 134.138 or FEDC:BA98), "" or "[2010:836B:4179::836B:4179]" (a complete IP address). proxy defaults to {undefined, []}, that is, no proxy is configured and https_proxy defaults to the value of proxy.
MaxSessions = integer()
Maximum number of persistent connections to a host. Default is 2.
MaxKeepAlive = integer()
Maximum number of outstanding requests on the same connection to a host. Default is 5.
KeepAliveTimeout = integer()
If a persistent connection is idle longer than the keep_alive_timeout in milliseconds, the client closes the connection. The server can also have such a time-out but do not take that for granted. Default is 120000 (= 2 min).
MaxPipeline = integer()
Maximum number of outstanding requests on a pipelined connection to a host. Default is 2.
PipelineTimeout = integer()
If a persistent connection is idle longer than the pipeline_timeout in milliseconds, the client closes the connection. Default is 0, which results in pipelining not being used.
CookieMode = enabled | disabled | verify
If cookies are enabled, all valid cookies are automatically saved in the cookie database of the client manager. If option verify is used, function store_cookies/2 has to be called for the cookies to be saved. Default is disabled.
IpFamily = inet | inet6
Default is inet.
IpAddress = ip_address()
If the host has several network interfaces, this option specifies which one to use. See gen_tcp:connect/3,4 for details.
Port = integer()
Local port number to use. See gen_tcp:connect/3,4 for details.
socket_opts() = [socket_opt()]
The options are appended to the socket options used by the client. These are the default values when a new request handler is started (for the initial connect). They are passed directly to the underlying transport (gen_tcp or SSL) without verification.
VerboseMode = false | verbose | debug | trace
Default is false. This option is used to switch on (or off) different levels of Erlang trace on the client. It is a debug feature.
Profile = profile() | pid()
When started stand_alone only the pid can be used.

Sets options to be used for subsequent requests.


If possible, the client keeps its connections alive and uses persistent connections with or without pipeline depending on configuration and current circumstances. The HTTP/1.1 specification does not provide a guideline for how many requests that are ideal to be sent on a persistent connection. This depends much on the application.

A long queue of requests can cause a user-perceived delay, as earlier requests can take a long time to complete. The HTTP/1.1 specification suggests a limit of two persistent connections per server, which is the default value of option max_sessions.

store_cookies(SetCookieHeaders, Url) ->
store_cookies(SetCookieHeaders, Url, Profile) -> ok | {error, Reason}


SetCookieHeaders = headers() - where field = "set-cookie"
Url = url()
Profile = profile() | pid()
When started stand_alone only the pid can be used.

Saves the cookies defined in SetCookieHeaders in the client profile cookie database. Call this function if option cookies is set to verify. If no profile is specified, the default profile is used.

stream_next(Pid) -> ok


Pid = pid()
As received in the stream_start message

Triggers the next message to be streamed, that is, the same behavior as active ones for sockets.

which_cookies() -> cookies()
which_cookies(Profile) -> cookies()


Profile = profile() | pid()
When started stand_alone only the pid can be used.
cookies() = [cookie_stores()]
cookie_stores() = {cookies, cookies()} | {session_cookies, cookies()}
cookies() = [cookie()]
cookie() = term()

Produces a list of the entire cookie database. Intended for debugging/testing purposes. If no profile is specified, the default profile is used.

which_sessions() -> session_info()
which_sessions(Profile) -> session_info()


Profile = profile() | pid()
When started stand_alone only the pid can be used.
session_info() = {GoodSessions, BadSessions, NonSessions}
GoodSessions = session()
BadSessions = tuple()
NonSessions = term()

Produces a slightly processed dump of the session database. It is intended for debugging. If no profile is specified, the default profile is used.