Compiling and running Yaws appmods

Question

Appmods are a way to let the application programmer take control over the URL path. They are implemented as Erlang modules. For example myappmod.erl

-module(myappmod).
-include("../../yaws_api.hrl").
-compile(export_all).

out(Arg) ->
    Method = (Arg#arg.req)#http_request.method,
    handle(Method, Arg).

handle(Method,Arg) ->
    %%  Do something 
    ok.

How should I carry out the compiling to make this appmod easily manageable?

In which directory of the yaws directory tree should I save the myappmod.erl and where does the myappmod.beam go after compiling?

How do generate the URL path to refer to this appmod?

All the help is welcomed!

Answer 1

Compiling your appmod is a matter of calling the erlc compiler. You then install the resulting beam file into a load directory known to Yaws, which are specified in the yaws.conf file using the ebin_dir directive:

ebin_dir = /path/to/some/ebin
ebin_dir = /path/to/another/ebin

You can specify your own paths here. Multiple ebin_dir settings are cumulative — all such paths are added to the Yaws load path.

For actively developing your appmod, with automatic reloading of your changes, you can use something like the sync project.

The URL for your appmod is also specified in yaws.conf, in a server block, using the appmods directive. You can find examples in the Yaws documentation. For example, if you want your appmod to control the whole URL space for a server, you specify / as its URL path:

<server foo>
    port = 8001
    listen = 0.0.0.0
    docroot = /filesystem/path/to/www
    appmods = </, myappmod>
</server>

Note also the optional exclude_paths directive you can specify in an appmods setting, typically used for excluding paths storing statically loaded resources. For example, the following setting means that myappmod handles the entire URL space / except for any URL path starting with /icons:

appmods = </, myappmod exclude_paths icons>