overview.edoc

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%% Copyright 2012 Benoît Chesneau
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@copyright 2012 Benoît Chesneau.
@version 0.3
@title hackney - simple HTTP client in Erlang

@doc

# hackney

**hackney** is a simple HTTP client.

Main features:

- no message passing: response is directly streamed to the current
  process and a state is kept in a `#client{}' record.
- binary streams
- SSL support
- Keepalive handling
- basic authentication
- stream the response
- Can send files using the sendfile API
- Chunked encoding support
- Optionnal socket pool
- Used parse transform for shorcut methods calls:
  `hackney:get("https://friendpaste.com")'


    Note: This is a work in progress, see the
[TODO](http://github.com/benoitc/hackney/blob/master/TODO.md) for more
informations on what still need to be done.

## Installation

Download the sources from our [Github
repository](http://github.com/benoitc/hackney)

To buildd the application simply run 'make'. This should build .beam, .app
files and documentation.

To run tests run 'make test'.
To generate doc, run 'make doc'.


Or add it to your rebar config

```
{deps, [
    ....
    {hackney, ".*", {git, "git://github.com/benoitc/hackney.git", {branch, "master"}}}
]}.
'''

## Basic usage

The basic usage of hackney is:

### Start hackney

hackney is an
[OTP](http://www.erlang.org/doc/design_principles/users_guide.html)
application. You have to start it first before using all the functions.
The hackney applications will start for you the default socket pool.

To start in the console run :

```
$ erl -pa ebin
1>> hackney:start().
ok
'''

It will start hackney and all the application it depends:

```
application:start(crypto),
application:start(public_key),
application:start(ssl),
application:start(hackney).
'''

Or add hackney to the applications member of your relase an app


### Simple request without pool

Do a simple a requet that will return a client state:

```
Method = get,
URL = <<"https://friendpaste.com">>,
Headers = [],
Payload = <<>>,
Options = [],
{ok, StatusCode, RespHeaders, Client} = hackney:request(Method, URL,
                                                        Headers, Payload,
                                                        Options).
'''

The request method return the tupple `{ok, StatusCode, Headers, Client}'
or `{error, Reason}'.


If you enable the **parse_transform**, you can also do:

```
hackney:get(URL, Headers, Payload, Options)
'''

To enable parse transform add the following option to the erlang
compiler flags:

```
{parse_transform, hackney_transform}
'''

Alternately, you can add it to the module you wish to compile:

```
-compile([{parse_transform, hackney_transform}]).
'''

### Read the body

```
{ok, Body, Client1} = hackney:body(Client).
'''

`hackney:body/1' fetch the body. To fetch it by chunk you can use the
`hackney:stream/body/1' function:

```
read_body(MaxLength, Client, Acc) when MaxLength > byte_size(Acc) ->
	case stream_body(Client) of
		{ok, Data, Client2} ->
			read_body(MaxLength, Client2, << Acc/binary, Data/binary >>);
		{done, Client2} ->
			{ok, Acc, Client2};
		{error, Reason} ->
			{error, Reason}
	end.
'''

### Reuse the client object

If your connection support the keepalive you can reuse the Client
record using the `hackney:send_request/2' function:

```
ReqBody = << "{
      \"id\": \"some_paste_id\",
      \"rev\": \"some_revision_id\",
      \"changeset\": \"changeset in unidiff format\"
}" >>,
ReqHeaders = [{<<"Content-Type">>, <<"application/json">>}],
NextPath = <<"/">>,
NextMethod = post,
NextReq = {NextMethod, NextPath, ReqHeaders, ReqBody}
{ok, _, _, Client2} = hackney:send_request(Client1, NextReq).
{ok, Body1, Client3} = hackney:body(Client2),
hackney:close(Client3).
'''

Here we are posting a JSON paylod to '/' on the service friendpaste to
create a paste. Then we close the client connection.


### Send a body

hackney helps you send different payload by passing different terms as
the request body:

- `{form, PropList}' : To send a form
- `{multipart, KVs}' : to send you body using the multipart API. KVs can
  be under the form `{file, Name, Content}' or `Value'
- `{file, File}' : To send a file
- Bin: To send a binary or an iolist

> Note: to send a chunked request, just add the `Transfer-Encoding: chunked'
> header to your headers. Binary and Iolist bodies will be then sent using
> the chunked encoding.

#### Send the body by yourself

While the default is to diretcly send the request and fetch the status
and headers if the body is set as the atom `stream` the request and
send_request function will return {ok, Client}. Then you can use the
function `hackney:stream_request_body/2' to stream the request body and
`hackney:start_response/1' to initialize the respone.

The function `hackney:start_response/1' is waiting a Client with
theresponse state equal to the atom `waiting'.

ex:

```
ReqBody = << "{
      \"id\": \"some_paste_id2\",
      \"rev\": \"some_revision_id\",
      \"changeset\": \"changeset in unidiff format\"
}" >>,
ReqHeaders = [{<<"Content-Type">>, <<"application/json">>}],
Path = <<"https://friendpaste.com/">>,
Method = post,
{ok, Client} = hackney:request(Method, Path, ReqHeaders, stream,
                               []),

{ok, Client1} = hackney:stream_request_body(ReqBody, Client),
{ok, _Status, _Headers, Client2} = hackney:start_response(Client1),
{ok, Body, Client3} = hackney:body(Client2),
hackney:close(Client3).
'''

### Use a pool

To reuse a connection globally in your application you can also use a
socket pool. On startup, hackney launch a pool named default. To use it
do the following:

```
Method = get,
URL = <<"https://friendpaste.com">>,
Headers = [],
Payload = <<>>,
Options = [{pool, default}],
{ok, StatusCode, RespHeaders, Client} = hackney:request(Method, URL, Headers,
                                                        Payload, Options).
'''

By adding the tuple `{pool, default}' to the options, hackney will use
the connections stored in that pool.

You can also use different pools in your application which will allows
you to maintain some kind of group of connections.

```
PoolName = mypool,
Options = [{timeout, 150000}, {pool_size, 100}],
{ok, Pid} = hackney:start_pool(PoolName, Options),
'''

`timeout' is the time we keep alive the conneciton in the pool,
`pool_size' is the number of connections maintained in the pool. Each
connection in a pool is monitored and closed connections are removed
automatically.


To close a pool do:

```
hackney:stop_pool(PoolName).
'''

> Note: Sometimes you want to always use the default pool in your app
> without having to set the client option each time. You can now do this
> by setting the hackney application environment key `use_default_pool'
> to true .


### Automatically follow a redirection.

If the option `{follow_redirect, true}' is given to the request, the
client will be abble to automatically follow the redirection and
retrieve the body. The maximum number of connection can be set using the
`{max_redirect, Max}' option. Default is 5.

The client will follow redirection on 301, 302 &amp; 307 if the method is
get or head. If another method is used the tuple
`{ok, maybe_redirect, Status, Headers, Client}' will be returned. It
only follow 303 redirection (see other) if the method is a POST.

Last Location is stored in the client state in the `location' property.

ex:

```
Method = get,
URL = "http://friendpaste.com/",
ReqHeaders = [{<<"accept-encoding">>, <<"identity">>}],
ReqBody = <<>>,
Options = [{follow_redirect, true}, {max_redirect, true}],
{ok, S, H, Client} = hackney:request(Method, URL, ReqHeaders,
                                     ReqBody, Options),
{ok, Body, Client1} = hackney:body(Client).
'''

### Proxy a connection

For now only HTTP tunneling is supported. To use an HTTP tunnel add the
option `{proxy, ProxyUrl}' where `ProxyUrl' can be a simple url or an
`{Host, Port}' tuple. If you need to authetnicate set the option
`{proxy_auth, {User, Password}}'.

## Contribute

For issues, comments or feedback please [create an
issue](http://github.com/benoitc/hackney/issues).



@end