path: root/doc/src/manual/gun.asciidoc

= gun(3)

== Name

gun - asynchronous HTTP client

== Description

The `gun` module provides an asynchronous interface for
connecting and communicating with Web servers over HTTP,
HTTP/2 or Websocket.

== Types

=== opts() = map()

Configuration for the connection.

The following keys are defined:

connect_timeout => timeout()::
	Connection timeout. Defaults to `infinity`.
http_opts => http_opts()::
	Options specific to the HTTP protocol. See below.
http2_opts => http2_opts()::
	Options specific to the HTTP/2 protocol. See below.
protocols => [http | http2]::
	Ordered list of preferred protocols. When the transport is tcp,
	this list must contain exactly one protocol. When the transport
	is ssl, this list must contain at least one protocol and will be
	used using the ALPN protocol negotiation method. When the server
	does not support ALPN then http will always be used. Defaults to
	[http] when the transport is tcp, and [http2, http] when the
	transport is ssl.
retry => non_neg_integer()::
	Number of times Gun will try to reconnect on failure before giving up.
	Defaults to 5.
retry_timeout => pos_integer()::
	Time between retries in milliseconds. Defaults to 5000.
trace => boolean()::
	Whether to enable `dbg` tracing of the connection process. Should
	only be used during debugging. Defaults to false.
transport => tcp | ssl::
	Whether to use SSL or plain TCP. The default varies depending on the
	port used. Port 443 defaults to ssl. All other ports default to tcp.
transport_opts => proplists:proplist()::
	Transport options. They are TCP options or SSL options depending on
	the selected transport.
ws_opts => ws_opts()::
	Options specific to the Websocket protocol. See below.

// @todo better spec for transport_opts

=== http_opts() = map()

Configuration for the HTTP protocol.

The following keys are defined:

keepalive => timeout()::
	Time between pings in milliseconds. Since the HTTP protocol has
	no standardized way to ping the server, Gun will simply send an
	empty line when the connection is idle. Gun only makes a best
	effort here as servers usually have configurable limits to drop
	idle connections. Use `infinity` to disable. Defaults to 5000.
transform_header_name => fun((LowercaseName :: binary()) -> TransformedName :: binary()) | undefined::
	A function that will be applied to all header names before they
	are sent to the server. Gun assumes that all header names are in
	lower case. This function is useful if you, for example, need to
	re-case header names in the event that the server incorrectly
	considers header name case to be significant.
version => 'HTTP/1.1' | 'HTTP/1.0'::
	HTTP version to use. Defaults to 'HTTP/1.1'.

=== http2_opts() = map()

Configuration for the HTTP/2 protocol.

The following keys are defined:

keepalive => pos_integer()::
	Time between pings in milliseconds. Defaults to 5000.

=== req_opts() = map()

Configuration for a particular request.

The following keys are defined:

reply_to => pid()::
	The pid of a process that is responsible for the response handling.

=== ws_opts() = map()

Configuration for the Websocket protocol.

The following keys are defined:

compress => boolean()::
	Whether to enable permessage-deflate compression. This does
	not guarantee that compression will be used as it is the
	server that ultimately decides. Defaults to false.

== Messages

Calling functions from this module may result in the following
messages being sent.

=== {gun_up, ConnPid, Protocol}

ConnPid = pid():: The pid of the Gun connection process.
Protocol = http | http2:: The protocol selected for this connection.

The connection is up.

This message informs the owner process that the connection or
reconnection completed.

The protocol selected during the connection is sent in this
message. It can be used to determine the capabilities of the
server.

Gun will now start processing the messages it received while
waiting for the connection to be up. If this is a reconnection,
then this may not be desirable for all requests. Those requests
should be cancelled when the connection goes down, and any
subsequent messages ignored.

=== {gun_down, ConnPid, Protocol, Reason, KilledStreams, UnprocessedStreams}

ConnPid = pid():: The pid of the Gun connection process.
Protocol = http | http2 | ws:: The protocol in use when the connection was lost.
Reason = normal | closed | {error, atom()}:: The reason for the loss of the connection.
KilledStreams = [reference()]:: List of streams that have been brutally terminated.
UnprocessedStreams = [reference()]:: List of streams that have not been processed by the server.

The connection is down.

This message informs the owner process that the connection is
currently down. Gun will automatically attempt to reconnect
depending on the `retry` and `retry_timeout` options.

The reason of the termination is there for debugging purposes
only. You should not rely on this value to know what streams
were processed or completed.

The _killed streams_ are the active streams that did not complete
before the closing of the connection. Whether they can be retried
safely depends on the protocol used and the idempotence property
of the requests.

The _unprocessed streams_ are streams that the server did not
start processing yet. They may be retried safely depending on
what streams were killed before.

When the connection goes back up, Gun will not attempt to retry
requests. It will also not upgrade to Websocket automatically
if that was the protocol in use when the connection was lost.

=== {gun_push, ConnPid, StreamRef, NewStreamRef, URI, Headers}

ConnPid = pid():: The pid of the Gun connection process.
StreamRef = reference():: Identifier of the stream initiated by the owner process.
NewStreamRef = reference():: Identifier of the stream being pushed.
URI = binary():: URI of the resource.
Headers = [{binary(), binary()}]:: Headers @todo

A resource pushed alongside an HTTP response.

This message can only be sent when the protocol is HTTP/2.

@todo I fear we also need the scheme; resource is identified by URI
@todo Perhaps we really should send the URI entirely, because cache
@todo relies on URI to work and this feature is for caching...
@todo Not sure why Method is there, spec says it is only for GET

=== {gun_response, ConnPid, StreamRef, IsFin, Status, Headers}

ConnPid = pid():: The pid of the Gun connection process.
StreamRef = reference():: Identifier of the stream initiated by the owner process.
IsFin = fin | nofin:: Whether this message terminates the response.
Status = binary():: Status line for the response.
Headers = [{binary(), binary()}]:: Headers sent with the response.

A response to an HTTP request.

=== {gun_data, ConnPid, StreamRef, IsFin, Data}

ConnPid = pid():: The pid of the Gun connection process.
StreamRef = reference():: Identifier of the stream this data belongs to.
IsFin = fin | nofin:: Whether this message terminates the response.
Data = binary():: Data from the stream.

Data associated with a stream.

The stream in question can be either one initiated by the owner
process or a stream initiated by the server through the push
mechanism. In any case a `gun_response` or a `gun_push` message
will be sent before any `gun_data` message.

=== {gun_error, ConnPid, StreamRef, Reason}

ConnPid = pid():: The pid of the Gun connection process.
StreamRef = reference():: Identifier of the stream this error relates to.
Reason = any():: Error reason.

Stream-specific error.

=== {gun_error, ConnPid, Reason}

ConnPid = pid():: The pid of the Gun connection process.
Reason = any():: Error reason.

General error.

=== {gun_ws_upgrade, ConnPid, ok, Headers}

ConnPid = pid():: The pid of the Gun connection process.
Headers = [{binary(), binary()}]:: Headers sent with the response.

Successful upgrade to the Websocket protocol.

=== {gun_ws, ConnPid, Frame}

ConnPid = pid():: The pid of the Gun connection process.
Frame = @todo:: Frame.

Websocket frame.

== Exports

=== open(Host, Port) -> open(Host, Port, [])

Alias of `gun:open/3`.

=== open(Host, Port, Opts) -> {ok, ConnPid} | {error, Reason}

Host = inet:hostname():: Host to connect to.
Port = inet:port_number():: Port to connect to.
Opts = opts():: Options for this connection.
ConnPid = pid():: The pid of the Gun connection process.
Reason = any():: Error reason. @todo really any?

Open a connection to the given host and port.

=== close(ConnPid) -> ok

ConnPid = pid():: The pid of the Gun connection process.

Brutally close the connection.

=== shutdown(ConnPid) -> ok

ConnPid = pid():: The pid of the Gun connection process.

Gracefully close the connection.

A monitor can be used to be notified when the connection is
effectively closed.

=== delete(ConnPid, Path) -> delete(ConnPid, Path, [], #{})

Alias of `gun:delete/4`.

=== delete(ConnPid, Path, Headers) -> delete(ConnPid, Path, Headers, #{})

Alias of `gun:delete/4`.

=== delete(ConnPid, Path, Headers, ReqOpts) -> StreamRef

ConnPid = pid():: The pid of the Gun connection process.
Path = iodata():: Path to the resource.
Headers = [{binary(), iodata()}]:: Additional request headers.
ReqOpts = req_opts():: Request options.
StreamRef = reference():: Identifier of the stream for this request.

Delete a resource.

=== get(ConnPid, Path) -> get(ConnPid, Path, [], #{})

Alias of `gun:get/4`.

=== get(ConnPid, Path, Headers) -> get(ConnPid, Path, Headers, #{})

Alias of `gun:get/4`.

=== get(ConnPid, Path, Headers, ReqOpts) -> StreamRef

ConnPid = pid():: The pid of the Gun connection process.
Path = iodata():: Path to the resource.
Headers = [{binary(), iodata()}]:: Additional request headers.
ReqOpts = req_opts():: Request options.
StreamRef = reference():: Identifier of the stream for this request.

Get a resource.

=== head(ConnPid, Path) -> head(ConnPid, Path, [], #{})

Alias of `gun:head/4`.

=== head(ConnPid, Path, Headers) -> head(ConnPid, Path, Headers, #{})

Alias of `gun:head/4`.

=== head(ConnPid, Path, Headers, ReqOpts) -> StreamRef

ConnPid = pid():: The pid of the Gun connection process.
Path = iodata():: Path to the resource.
Headers = [{binary(), iodata()}]:: Additional request headers.
ReqOpts = req_opts():: Request options.
StreamRef = reference():: Identifier of the stream for this request.

Get headers of a resource.

This function performs the same operation as `get/{2,3}` except
the server will not send the resource representation, only the
response's status line and headers.

While servers should send the same headers they would if the
request was a GET, like `content-length`, it is not always
the case and differences may exist.

=== options(ConnPid, Path) -> options(ConnPid, Path, [], #{})

Alias of `gun:options/4`.

=== options(ConnPid, Path, Headers) -> options(ConnPid, Path, Headers, #{})

Alias of `gun:options/4`.

=== options(ConnPid, Path, Headers, ReqOpts) -> StreamRef

ConnPid = pid():: The pid of the Gun connection process.
Path = iodata():: Path to the resource.
Headers = [{binary(), iodata()}]:: Additional request headers.
ReqOpts = req_opts():: Request options.
StreamRef = reference():: Identifier of the stream for this request.

Obtain information about the capabilities of the server or of a resource.

The special path `"*"` can be used to obtain information about
the server as a whole. Any other path will return information
about the resource only.

=== patch(ConnPid, Path, Headers) -> StreamRef

ConnPid = pid():: The pid of the Gun connection process.
Path = iodata():: Path to the resource.
Headers = [{binary(), iodata()}]:: Additional request headers.
StreamRef = reference():: Identifier of the stream for this request.

Request that a set of changes be applied to the resource.

This function expects either `content-length` or `content-type`
to be set to know a body is going to be sent afterwards.
Gun will assume the request has no body otherwise. It is
highly recommended to set both when possible.

The body sent in this request should be a patch document
with instructions on how to update the resource.

You can use the `gun:data/4` function to send the body, if any.

=== patch(ConnPid, Path, Headers, Body) -> patch(ConnPid, Path, Headers, Body, #{})

Alias of `gun:patch/5`.

=== patch(ConnPid, Path, Headers, Body, ReqOpts) -> StreamRef

ConnPid = pid():: The pid of the Gun connection process.
Path = iodata():: Path to the resource.
Headers = [{binary(), iodata()}]:: Additional request headers.
Body = iodata():: Body of the request.
ReqOpts = req_opts():: Request options.
StreamRef = reference():: Identifier of the stream for this request.

Request that a set of changes be applied to the resource.

It is highly recommended to set the `content-type` header
to inform the server what media type the body contains.
Gun will automatically set the `content-length` header.

The body sent in this request should be a patch document
with instructions on how to update the resource.

The complete request is sent when calling this function.
It is not possible to stream more of the body after
calling it.

=== post(ConnPid, Path, Headers) -> StreamRef

ConnPid = pid():: The pid of the Gun connection process.
Path = iodata():: Path to the resource.
Headers = [{binary(), iodata()}]:: Additional request headers.
StreamRef = reference():: Identifier of the stream for this request.

Process the enclosed representation according to the resource's own semantics.

This function expects either `content-length` or `content-type`
to be set to know a body is going to be sent afterwards.
Gun will assume the request has no body otherwise. It is
highly recommended to set both when possible.

The body sent in this request will be processed
according to the resource's own semantics. A new
resource may be created as a result, and may be
located at a different URI.

You can use the `gun:data/4` function to send the body, if any.

=== post(ConnPid, Path, Headers, Body) -> post(ConnPid, Path, Headers, Body, #{})

Alias of `gun:post/5`.

=== post(ConnPid, Path, Headers, Body, ReqOpts) -> StreamRef

ConnPid = pid():: The pid of the Gun connection process.
Path = iodata():: Path to the resource.
Headers = [{binary(), iodata()}]:: Additional request headers.
Body = iodata():: Body of the request.
ReqOpts = req_opts():: Request options.
StreamRef = reference():: Identifier of the stream for this request.

Process the enclosed representation according to the resource's own semantics.

It is highly recommended to set the `content-type` header
to inform the server what media type the body contains.
Gun will automatically set the `content-length` header.

The body sent in this request will be processed
according to the resource's own semantics. A new
resource may be created as a result, and may be
located at a different URI.

The complete request is sent when calling this function.
It is not possible to stream more of the body after
calling it.

=== put(ConnPid, Path, Headers) -> StreamRef

ConnPid = pid():: The pid of the Gun connection process.
Path = iodata():: Path to the resource.
Headers = [{binary(), iodata()}]:: Additional request headers.
StreamRef = reference():: Identifier of the stream for this request.

Create or replace a resource.

The body of the request is the entire representation of the resource.

This function expects either `content-length` or `content-type`
to be set to know a body is going to be sent afterwards.
Gun will assume the request has no body otherwise. It is
highly recommended to set both when possible.

You can use the `gun:data/4` function to send the body, if any.

=== put(ConnPid, Path, Headers, Body) -> put(ConnPid, Path, Headers, Body, #{})

Alias of `gun:put/5`.

=== put(ConnPid, Path, Headers, Body, ReqOpts) -> StreamRef

ConnPid = pid():: The pid of the Gun connection process.
Path = iodata():: Path to the resource.
Headers = [{binary(), iodata()}]:: Additional request headers.
Body = iodata():: Body of the request.
ReqOpts = req_opts():: Request options.
StreamRef = reference():: Identifier of the stream for this request.

Create or replace a resource.

The body of the request is the entire representation of the resource.

It is highly recommended to set the `content-type` header
to inform the server what media type the body contains.
Gun will automatically set the `content-length` header.

The complete request is sent when calling this function.
It is not possible to stream more of the body after
calling it.

=== request(ConnPid, Method, Path, Headers) -> StreamRef

ConnPid = pid():: The pid of the Gun connection process.
Method = iodata():: Request method.
Path = iodata():: Path of the resource.
Headers = [{binary(), iodata()}]:: Additional request headers.
StreamRef = reference():: Identifier of the stream for this request.

Perform the given request.

This is a general purpose function that should only be used
when existing method-specific functions don't apply.

This function expects either `content-length` or `content-type`
to be set to know a body is going to be sent afterwards.
Gun will assume the request has no body otherwise. It is
highly recommended to set both when possible.

You can use the `gun:data/4` function to send the body, if any.

=== request(ConnPid, Method, Path, Headers, Body) -> request(ConnPid, Method, Path, Headers, Body, #{})

Alias of `gun:request/6`.

=== request(ConnPid, Method, Path, Headers, Body, ReqOpts) -> StreamRef

ConnPid = pid():: The pid of the Gun connection process.
Method = iodata():: Request method.
Path = iodata():: Path of the resource.
Headers = [{binary(), iodata()}]:: Additional request headers.
Body = iodata():: Body of the request.
ReqOpts = req_opts():: Request options.
StreamRef = reference():: Identifier of the stream for this request.

Perform the given request.

This is a general purpose function that should only be used
when existing method-specific functions don't apply.

It is highly recommended to set the `content-type` header
to inform the server what media type the body contains.
Gun will automatically set the `content-length` header.

The complete request is sent when calling this function.
It is not possible to stream more of the body after
calling it.

=== data(ConnPid, StreamRef, IsFin, Data) -> ok

ConnPid = pid():: The pid of the Gun connection process.
StreamRef = reference():: Identifier of the stream this data belongs to.
IsFin = fin | nofin:: Whether this message terminates the request.
Data = iodata():: Data to be sent with the request.

Stream the body of a request.

@todo empty chunks

This function can only be used if the request identified by
`StreamRef` came with headers indicating the presence of a
body and that body not being given when creating the request.

All calls to this function must use `nofin` except for the
last which must use `fin` to indicate the end of the request
body.

Empty data is allowed regardless of the value of `IsFin`.
Gun will not send empty data chunks unless required to
indicate the request body is finished, however.

=== await(ConnPid, StreamRef) -> await(ConnPid, StreamRef, 5000, MonitorRef)

Alias of `gun:await/4`.

A monitor `MonitorRef` is automatically created for the duration of
this call and an error will be returned if the Gun connection process
terminates.

=== await(ConnPid, StreamRef, MonitorRef) -> await(ConnPid, StreamRef, 5000, MonitorRef)

Alias of `gun:await/4`.

=== await(ConnPid, StreamRef, Timeout) -> await(ConnPid, StreamRef, Timeout, MonitorRef)

Alias of `gun:await/4`.

A monitor `MonitorRef` is automatically created for the duration of
this call and an error will be returned if the Gun connection process
terminates.

=== await(ConnPid, StreamRef, Timeout, MonitorRef) -> tuple() -- see below

ConnPid = pid():: The pid of the Gun connection process.
StreamRef = reference():: Identifier of the stream to await messages from.
Timeout = timeout():: How long this function will wait for messages.
MonitorRef = reference():: Monitor reference for the Gun connection process.

Wait for a response message.

This function can be used when a synchronous handling of
responses is desired. It will only return when a message
for the given stream is received, on error or on timeout.

The return values are described in the next few subsections.

==== {response, IsFin, Status, Headers}

IsFin = fin | nofin:: Whether this message terminates the response.
Status = binary():: Status line for the response.
Headers = [{binary(), binary()}]:: Headers sent with the response.

Equivalent of a `gun_response` message.

==== {data, IsFin, Data}

IsFin = fin | nofin:: Whether this message terminates the response.
Data = binary():: Data from the stream.

Equivalent of a `gun_data` message.

==== {push, NewStreamRef, URI, Headers}

NewStreamRef = reference():: Identifier of the stream being pushed.
URI = binary():: URI of the resource.
Headers = [{binary(), binary()}]:: Headers @todo

Equivalent of a `gun_push` message.

@todo Same changes as gun_push

==== {error, Reason}

Reason = any():: Error reason. @todo any?

Equivalent of a `gun_error` message.

@todo I think we want to distinguish a stream error, a general error,
@todo a DOWN and a timeout error

=== await_body(ConnPid, StreamRef) -> await_body(ConnPid, StreamRef, 5000, MonitorRef)

Alias of `gun:await_body/4`.

A monitor `MonitorRef` is automatically created for the duration of
this call and an error will be returned if the Gun connection process
terminates.

=== await_body(ConnPid, StreamRef, MonitorRef) -> await_body(ConnPid, StreamRef, 5000, MonitorRef)

Alias of `gun:await_body/4`.

=== await_body(ConnPid, StreamRef, Timeout) -> await_body(ConnPid, StreamRef, Timeout, MonitorRef)

Alias of `gun:await_body/4`.

A monitor `MonitorRef` is automatically created for the duration of
this call and an error will be returned if the Gun connection process
terminates.

=== await_body(ConnPid, StreamRef, Timeout, MonitorRef) -> {ok, Body} | {error, Reason}

ConnPid = pid():: The pid of the Gun connection process.
StreamRef = reference():: Identifier of the stream to await messages from.
Timeout = timeout():: How long this function will wait for each message.
MonitorRef = reference():: Monitor reference for the Gun connection process.
Body = binary():: Body for the given stream.
Reason = any():: Error reason. @todo any?

Wait for a response body.

This function can be used when a synchronous handling of
responses is desired. It will only return when it has
finished fetching the entire response body.

The timeout value is *per message*. The actual function call
can last much longer for large bodies.

@todo I think we want to distinguish a stream error, a general error,
@todo a DOWN and a timeout error

@todo guide might be a little incorrect about await/await_body

=== flush(ConnPid) -> ok

ConnPid = pid():: The pid of the Gun connection process.

Flush all messages from the Gun connection process from the mailbox.

=== flush(StreamRef) -> ok

StreamRef = reference():: Stream identifier.

Flush all messages related to the given stream.

=== cancel(ConnPid, StreamRef) -> ok

ConnPid = pid():: The pid of the Gun connection process.
StreamRef = reference():: Identifier of the stream to cancel.

Cancel the given stream.

HTTP/1.1 streams can't be cancelled. Gun will simply silence
the stream and stop relaying messages.

@todo Depending on the length
@todo of a response Gun may also attempt to reconnect rather than
@todo receive the entire response body.

HTTP/2 streams can however be cancelled at any time.

=== ws_upgrade(ConnPid, Path) -> ws_upgrade(ConnPid, Path, [], #{})

Alias of `gun:ws_upgrade/3`.

=== ws_upgrade(ConnPid, Path, Headers) -> ok

Similar to `gun:ws_upgrade/4`, except `WsOpts` is taken from
the options given in the `gun:open/{2,3}` call when opening
the connection.

=== ws_upgrade(ConnPid, Path, Headers, WsOpts) -> ok

ConnPid = pid():: The pid of the Gun connection process.
Path = iodata():: Path to the resource.
Headers = [{binary(), iodata()}]:: Additional request headers.
WsOpts = map():: Options for the Websocket connection.

Request the connection to be upgraded to the Websocket protocol.

This function can only be used when the current protocol is `http`.

=== ws_send(ConnPid, Frames) -> ok

ConnPid = pid():: The pid of the Gun connection process.
Frames = @todo:: @todo

Send one or more Websocket frames.

This function can only be used following a successful `ws_upgrade` call.