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shotgun

For the times you need more than just a gun.

Rationale

After using the gun library on a project where we needed to consume Server-sent Events (SSE) we found that it provided great flexibility, at the cost of having to handle each raw message and data, including the construction of the response body data. Although this is great for a lot of scenarios, it can get cumbersome and repetitive after implementing it a couple of times. This is why we ended up creating shotgun, an HTTP client that uses gun behind the curtains but provides a simple API that has out-of-the-box support for SSE.

Usage

shotgun uses maps and hence requires Erlang 17 to compile and run.

shotgun is an OTP application, so before being able to use it, it has to be started. Either add it as one of the applications in your .app file or run the following code:

application:ensure_all_started(shotgun).

Regular Requests

Once the application is started a connection needs to be created in order to start making requests:

{ok, Conn} = shotgun:open("google.com", 80),
{ok, Response} = shotgun:get(Conn, "/"),
io:format("~p~n", [Response]),
shotgun:close(Conn).

Which results in:

#{body => <<"<HTML><HEAD>"...>>,
  headers => [
     {<<"location">>,<<"http://www.google.com/adfs">>},
     {<<"content-type">>,<<"text/html; charset=UTF-8">>},
     {<<"x-content-type-options">>,<<"nosniff">>},
     {<<"date">>,<<"Fri, 17 Oct 2014 17:18:32 GMT">>},
     {<<"expires">>,<<"Sun, 16 Nov 2014 17:18:32 GMT">>},
     {<<"cache-control">>,<<"public, max-age=2592000">>},
     {<<"server">>,<<"sffe">>},
     {<<"content-length">>,<<"223">>},
     {<<"x-xss-protection">>,<<"1; mode=block">>},
     {<<"alternate-protocol">>,<<"80:quic,p=0.01">>}
   ],
   status_code => 302}
}

%= ok

Immediately after opening a connection we did a GET request, where we didn't specify any headers or options. Every HTTP method has its own shotgun function that takes a connection, a uri (which needs to include the slash), a headers map or a proplist containing the headers, and an options map. Some of the functions (post/5, put/5 and patch/5) also take a body argument.

Alternatively there's a generic request/6 function in which the user can specify the HTTP method as an argument in the form of an atom: get, head, options, delete, post, put or patch.

IMPORTANT: When you are done using the shotgun connection remember to close it with shotgun:close/1.

HTTP Secure Requests

It is possible to tell shotgun to use SSL by providing the atom https as the third argument when creating a connection with to the open function. Just like when performing HTTP requests it is also necessary to specify a port. HTTPS servers typically listen for connections on port 443 and this will be the most likely value you'll need to use.

Basic Authentication

If you need to provide basic authentication credentials in your requests, it is as easy as specifying a basic_auth entry in the headers map:

{ok, Conn} = shotgun:open("site.com", 80),
{ok, Response} = shotgun:get(Conn, "/user", #{basic_auth => {"user", "password"}}),
, or
{ok, Response} = shotgun:get(Conn, "/user", [{basic_auth, {"user", "password"}}]),
shotgun:close(Conn).

Specifying a Timeout

The timeout option can be used to specify a value for all types of requests:

{ok, Conn} = shotgun:open("google.com", 80).
{error, Error} = shotgun:get(Conn, "/", #{}, #{timeout => 10}).
io:format("~p~n", [Error]).
%%= {timeout,{gen_fsm,sync_send_event,[<0.368.0>,{get,{"/",[],[]}},10]}}
shotgun:close(Conn).

The default timeout value is 5000 if none is specified.

Consuming Server-sent Events

To use shotgun with endpoints that generate SSE the request must be configured using some values in the options map, which supports the following entries:

  • async ::boolean(): specifies if the request performed will return a chunked response. It currently only works for GET requests.. Default value is false.

  • async_mode :: binary | sse: when async is true the mode specifies how the data received will be processed. binary mode treats each chunk received as raw binary. sse mode buffers each chunk, splitting the data received into SSE. Default value is binary.

  • handle_event :: fun((fin | nofin, reference(), binary()) -> any()): this function will be called each time either a chunk is received (async_mode = binary) or an event is parsed (async_mode = sse). If no handle_event function is provided the data received is added to a queue, whose values can be obtained calling the shotgun:events/1. Default value is undefined.

The following is an example of the usage of shotgun when consuming SSE.

{ok, Conn} = shotgun:open("localhost", 8080).
%= {ok,<0.6003.0>}

Options = #{async => true, async_mode => sse},
{ok, Ref} = shotgun:get(Conn, "/events", #{}, Options).
%= {ok,#Ref<0.0.1.186238>}

% Some event are generated on the server...
Events = shotgun:events(Conn).
%= [{nofin, #Ref<0.0.1.186238>, <<"data: pong">>}, {nofin, #Ref<0.0.1.186238>, <<"data: pong">>}]

shotgun:events(Conn).
%= []

Notice how the second call to shotgun:events/1 returns an empty list. This is because events are stored in a queue and each call to events returns all events queued so far and then removes these from the queue. So it's important to understand that shotgun:events/1 is a function with side-effects when using it.

Additionally shotgun provides a parse_event/1 helper function that turns a server-sent event binary into a map:

shotgun:parse_event(<<"data: pong\ndata: ping\nid: 1\nevent: pinging">>).
%= #{data => [<<"pong">>,<<"ping">>],event => <<"pinging">>,id => <<"1">>}

Building & Test-Driving

To build shotgun just run the following on your command shell:

rebar3 compile

To start up a shell where you can try things out run the following (after building the project as described above):

rebar3 shell

Contact Us

If you find any bugs or have a problem while using this library, please open an issue in this repo (or a pull request :)).

And you can check all of our open-source projects at inaka.github.io