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GOpher MAchine ("goma") is a toolkit for serving resources over The Internet Gopher Protocol. Its design is influenced by Webmachine, in that applications provide resource modules, the functions of which are called in order to navigate the decisions of a flowchart.

A simple resource

This is your basic Hello World resource:

-module(goma_hw).

-compile([export_all]).

init(Args) ->
    {ok, Args}.

resource_exists(_Selector, Context) ->
    {true, Context}.

produce_content(Selector, Context) ->
    Content = io_lib:format("Hello ~s World!",
                            [Selector#goma_selector.raw]),
    {{text, Content}, Context}.

The wiki has more information about what the parameters and expected outputs of these functions. A more interesting resource is found in goma_fs_resource.erl.

Dispatching

Goma chooses the module to handle a selector by splitting the selector on / characters, and then comparing the pieces to a dispatch table. The dispatch table is a list of 3-tuples of the form:

{SelectorMatch, ModuleName, InitArg}

The first element, SelectorMatch is a list of strings and atoms. Each string must match its corresponding selector piece exactly. Each atom is "bound" to its corresponding selector piece, and a list of those bindings is passed to the module's functions. The atom '*' is special: it must come last, and it matches the rest of the selector.

As an example, the SelectorMatch

["foo", bar, '*']

Would match the selector

foo/bar/baz/quux

And create bindings of

[{bar, <<"bar">>}, {'*', <<"baz/quux">>}]

Startup

To startup goma with your dispatch table, use goma:child_spec/1 to create a supervisor child specification, and add that child to your app's supervisor. For example:

-module(myapp_sup).

%% ...other supervisor functions...

init([]) ->
    Name = myapp_goma,
    IP = {127,0,0,1},
    Port = 7070,
    Dispatch = {['*'], goma_hw, []},
    GomaSupSpec = goma:child_spec(Name, IP, Port, Dispatch),
    {ok, {{one_for_one,5,10}, [GomaSupSpec]}}.