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simple HTTP client in Erlang
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hackney - simple HTTP client in Erlang

Copyright (c) 2012 Benoît Chesneau.

Version: 0.2


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("")

Note: This is a work in progress, see the TODO for more informations on what still need to be done.


Download the sources from our Github repository

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://", {branch, "master"}}}

Basic usage

The basic usage of hackney is:

Start hackney

hackney is an OTP 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().

It will start hackney and all the application it depends:


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 = <<"">>,
Headers = [],
Payload = <<>>,
Options = [],
{ok, StatusCode, RespHeaders, Client} = hackney:request(Method, URL,
                                                        Headers, Payload,

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}

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),

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
  • {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.


ReqBody = << "{
      \"id\": \"some_paste_id2\",
      \"rev\": \"some_revision_id\",
      \"changeset\": \"changeset in unidiff format\"
}" >>,
ReqHeaders = [{<<"Content-Type">>, <<"application/json">>}],
Path = <<"">>,
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 = <<"">>,
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:


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 & 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.


Method = get,
URL = "",
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).


For issues, comments or feedback please [create an issue!] [1][1]: "hackney issues"


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