hackney - HTTP client library in Erlang
Copyright © 2012-2023 Benoît Chesneau.
Version: 1.20.1
hackney
hackney is an HTTP client library for Erlang.
Useful modules are:
hackney
: main module. It contains all HTTP client functions.hackney_http
: HTTP parser in pure Erlang. This parser is able to parse HTTP responses and requests in a streaming fashion. If not set it will be autodetected if it’s a request or a response that’s needed.hackney_headers
Module to manipulate HTTP headers.hackney_cookie
: Module to manipulate cookies.hackney_multipart
: Module to encode/decode multipart.hackney_url
: Module to parse and create URIs.hackney_date
: Module to parse HTTP dates.
Read the NEWS file to get the last changelog.
Start hackney
hackney is an OTP application. You have to start it first before using any of the functions. The hackney application will start the default socket pool for you.
To start in the console run:
$ ./rebar3 shell
It is suggested that you install rebar3 user-wide as described here. This fixes zsh (and maybe other shells) escript-related bugs. Also this should speed things up.
> application:ensure_all_started(hackney).
ok
It will start hackney and all of the application it depends on:
application:start(crypto),
application:start(public_key),
application:start(ssl),
application:start(hackney).
Or add hackney to the applications property of your .app in a release
Simple request
Do a simple request that will return a client state:
Method = get,
URL = <<"https://friendpaste.com">>,
Headers = [],
Payload = <<>>,
Options = [],
{ok, StatusCode, RespHeaders, ClientRef} = hackney:request(Method, URL,
Headers, Payload,
Options).
The request method returns the tuple {ok, StatusCode, Headers, ClientRef}
or {error, Reason}
. A ClientRef
is simply a reference to the current
request that you can reuse.
If you prefer the REST syntax, you can also do:
hackney:Method(URL, Headers, Payload, Options)
where Method
, can be any HTTP method in lowercase.
Read the body
{ok, Body} = hackney:body(ClientRef).
hackney:body/1
fetch the body. To fetch it by chunk you can use the
hackney:stream_body/1
function:
read_body(MaxLength, Ref, Acc) when MaxLength > byte_size(Acc) ->
case hackney:stream_body(Ref) of
{ok, Data} ->
read_body(MaxLength, Ref, << Acc/binary, Data/binary >>);
done ->
{ok, Acc};
{error, Reason} ->
{error, Reason}
end.
Note: you can also fetch a multipart response using the functions
hackney:stream_multipart/1
andhackney:skip_multipart/1
.Note 2: using the
with_body
option will return the body directly instead of a reference.
Reuse a connection
By default all connections are created and closed dynamically by hackney but sometimes you may want to reuse the same reference for your connections. It’s especially useful if you just want to handle serially a couple of requests.
A closed connection will automatically be reconnected.
To create a connection:
Transport = hackney_ssl,
Host = << "friendpaste.com" >>,
Port = 443,
Options = [],
{ok, ConnRef} = hackney:connect(Transport, Host, Port, Options).
To create a connection that will use an HTTP proxy use
hackney_http_proxy:connect_proxy/5
instead.
To get local and remote ip and port information of a connection:
> hackney:peername(ConnRef).
> hackney:sockname(ConnRef).
Send a body
hackney helps you send different payloads by passing different terms as the request body:
{form, PropList}
: To send a form{multipart, Parts}
: to send your body using the multipart API. Parts follow this format:eof
: end the multipart request{file, Path}
: to stream a file{file, Path, ExtraHeaders}
: to stream a file{file, Path, Name, ExtraHeaders}
: to send a file with DOM element name and extra headers{Name, Content}
: to send a full part{Name, Content, ExtraHeaders}
: to send a full part{mp_mixed, Name, MixedBoundary}
: To notify we start a part with a a mixed multipart content{mp_mixed_eof, MixedBoundary}
: To notify we end a part with a a mixed multipart content
{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 directly 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:send_body/2
to stream the request body and
hackney:start_response/1
to initialize the response.
Note: The function
hackney:start_response/1
will only accept a Client that is waiting for a response (with a response state equal to the atomwaiting
).
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, ClientRef} = hackney:request(Method, Path, ReqHeaders, stream, []),
ok = hackney:send_body(ClientRef, ReqBody),
{ok, _Status, _Headers, ClientRef} = hackney:start_response(ClientRef),
{ok, Body} = hackney:body(ClientRef),
Note: to send a multipart body in a streaming fashion use the
hackney:send_multipart_body/2
function.
Use the default pool
Hackney uses socket pools to reuse connections globally. By default,
hackney uses a pool named default
. You may want to use different
pools in your application which allows you to maintain a group of
connections. To use a different pool, do the following:
Method = get,
URL = <<"https://friendpaste.com">>,
Headers = [],
Payload = <<>>,
Options = [{pool, mypool}],
{ok, StatusCode, RespHeaders, ClientRef} = hackney:request(Method, URL, Headers,
Payload, Options).
By adding the tuple {pool, mypool}
to the options, hackney will use
the connections stored in that pool. The pool gets started automatically
the first time it is used. You can also explicitly configure and start
the pool like this:
PoolName = mypool,
Options = [{timeout, 150000}, {max_connections, 100}],
ok = hackney_pool:start_pool(PoolName, Options),
timeout
is the time we keep the connection alive in the pool,
max_connections
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_pool:stop_pool(PoolName).
Note: Sometimes you want to disable 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 false. This means that hackney will not use socket pools unless specifically requested using thepool
option as described above.To disable socket pools for a single request, specify the option
{pool, false}
.
Use a custom pool handler.
Since the version 0.8 it is now possible to use your own Pool to maintain the connections in hackney.
A pool handler is a module that handles the hackney_pool_handler
behaviour.
See for example the hackney_disp a load-balanced Pool dispatcher based on dispcount].
Note: for now you can`t force the pool handler / client.
Automatically follow a redirection
If the option {follow_redirect, true}
is given to the request, the
client will be able to automatically follow the redirection and
retrieve the body. The maximum number of connections can be set using the
{max_redirect, Max}
option. Default is 5.
The client will follow redirects 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 will
only follow 303 redirects (see other) if the method is a POST.
Last Location is stored in the location
property of the client state.
ex:
Method = get,
URL = "http://friendpaste.com/",
ReqHeaders = [{<<"accept-encoding">>, <<"identity">>}],
ReqBody = <<>>,
Options = [{follow_redirect, true}, {max_redirect, 5}],
{ok, S, H, Ref} = hackney:request(Method, URL, ReqHeaders,
ReqBody, Options),
{ok, Body1} = hackney:body(Ref).
Use SSL/TLS with self signed certificates
Hackney uses CA bundles adapted from Mozilla by
certifi.
Recognising an organisation specific (self signed) certificates is possible
by providing the necessary ssl_options
. Note that ssl_options
overrides all
options passed to the ssl module.
ex (>= Erlang 21):
CACertFile = <path_to_self_signed_ca_bundle>,
CrlCheckTimeout = 5000,
SSLOptions = [
{verify, verify_peer},
{versions, ['tlsv1.2']},
{cacertfile, CACertFile},
{crl_check, peer},
{crl_cache, {ssl_crl_cache, {internal, [{http, CrlCheckTimeout}]}}},
{customize_hostname_check,
[{match_fun, public_key:pkix_verify_hostname_match_fun(https)}]}],
Method = get,
URL = "http://my-organisation/",
ReqHeaders = [],
ReqBody = <<>>,
Options = [{ssl_options, SSLoptions}],
{ok, S, H, Ref} = hackney:request(Method, URL, ReqHeaders,
ReqBody, Options),
%% To provide client certificate:
CertFile = <path_to_client_certificate>,
KeyFile = <path_to_client_private_key>,
SSLOptions1 = SSLoptions ++ [
{certfile, CertFile},
{keyfile, KeyFile}
],
Options1 = [{ssl_options, SSLoptions1}],
{ok, S1, H1, Ref1} = hackney:request(Method, URL, ReqHeaders,
ReqBody, Options1).
Proxy a connection
HTTP Proxy
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 authenticate set the option {proxy_auth, {User, Password}}
.
Metrics
Hackney offers the following metrics
You can enable metrics collection by adding a mod_metrics
entry to hackney’s
app config. Metrics are disabled by default. The module specified must have an
API matching that of the hackney metrics module.
To use folsom, specify {mod_metrics,
folsom}
, or if you want to use
exometer, specify{mod_metrics,
exometer}
and ensure that folsom or exometer is in your code path and has
been started.
Generic Hackney metrics
Name | Type | Description |
---|---|---|
hackney.nb_requests | counter | Number of running requests |
hackney.total_requests | counter | Total number of requests |
hackney.finished_requests | counter | Total number of requests finished |
Metrics per Hosts
Name | Type | Description |
---|---|---|
hackney.HOST.nb_requests | counter | Number of running requests |
hackney.HOST.request_time | histogram | Request time |
hackney.HOST.connect_time | histogram | Connect time |
hackney.HOST.response_time | histogram | Response time |
hackney.HOST.connect_timeout | counter | Number of connect timeout |
hackney.HOST.connect_error | counter | Number of timeout errors |
hackney_pool.HOST.new_connection | counter | Number of new pool connections per host |
hackney_pool.HOST.reuse_connection | counter | Number of reused pool connections per host |
Metrics per Pool
Name | Type | Description |
---|---|---|
hackney_pool.POOLNAME.take_rate | meter | meter recording rate at which a connection is retrieved from the pool |
hackney_pool.POOLNAME.no_socket | counter | Count of new connections |
hackney_pool.POOLNAME.in_use_count | histogram | How many connections from the pool are used |
hackney_pool.POOLNAME.free_count | histogram | Number of free sockets in the pool |
hackney_pool.POOLNAME.queue_count | histogram | queued clients |
Contribute
For issues, comments or feedback please create an issue.