YAWs embedded with appmod not working for me - erlang

Question

Alright, what am I doing wrong here. I'm trying the simple example of embedded YAWs from http://yaws.hyber.org/embed.yaws but with an appmod. I've added the my_app.erl file and compiled it. It works if not in embedded YAWs so I think it is specific to embedded.
-module(ybed).
-compile(export_all).
start() ->
{ok, spawn(?MODULE, run, [])}.
run() ->
Id = "embedded",
GconfList = [{ebin_dir, ["/Users/someuser/yawsembedded/ebin"]}],
Docroot = "/Users/someuser/yawstest",
SconfList = [{port, 8888},
{listen, {0,0,0,0}},
{docroot, Docroot},
{appmods, [{"/", my_app}]}
],
{ok, SCList, GC, ChildSpecs} =
yaws_api:embedded_start_conf(Docroot, SconfList, GconfList),
[supervisor:start_child(ybed_sup, Ch) || Ch <- ChildSpecs],
yaws_api:setconf(GC, SCList),
{ok, self()}.
Getting this Error:
ERROR erlang code threw an uncaught exception:
File: appmod:0
Class: error
Exception: undef
Req: {http_request,'GET',{abs_path,"/demo"},{1,1}}
Stack: [{my_app,out,
[{arg,#Port<0.2721>,
{{127,0,0,1},63720},
{headers,"keep-alive",
"text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8",
"0.0.0.0:8888",undefined,undefined,undefined,undefined,
undefined,undefined,undefined,
"Mozilla/5.0 (Macintosh; Intel Mac OS X 10.10; rv:40.0) Gecko/20100101 Firefox/40.0",
undefined,[],undefined,undefined,undefined,undefined,
undefined,undefined,undefined,undefined,
[{http_header,0,"Dnt",undefined,"1"},
{http_header,10,'Accept-Encoding',undefined,
"gzip, deflate"},
{http_header,11,'Accept-Language',undefined,"null"}]},
{http_request,'GET',{abs_path,"/demo"},{1,1}},
{http_request,'GET',{abs_path,"/demo"},{1,1}},
undefined,"/demo",undefined,undefined,
"/Users/someuser/yawstest","/",
"/Users/someuser/yawstest/demo",undefined,undefined,
<0.63.0>,[],"/","/",undefined}],
[]},
{yaws_server,deliver_dyn_part,8,
[{file,"yaws_server.erl"},{line,2818}]},
{yaws_server,aloop,4,[{file,"yaws_server.erl"},{line,1232}]},
{yaws_server,acceptor0,2,[{file,"yaws_server.erl"},{line,1068}]},
{proc_lib,init_p_do_apply,3,[{file,"proc_lib.erl"},{line,239}]}]

Answer 1

The stack trace shows that your my_app:out/1 function is getting called, but you're getting an undef exception. This is occurring because the runtime can't find the my_app:out/1 function, which means either it can't find the module or the module exists but does not export an out/1 function. For example, I was able to duplicate the error using the example code by not providing a my_app module.
First, make sure your my_app.erl file exports an out/1 function. Here's a trivial one that just returns a 405 error for all requests:
-module(my_app).
-export([out/1]).
out(_Arg) ->
{status, 405}.
Compile your my_app.erl file and put the compiled my_app.beam file either in a load path already known to the Erlang runtime, or in a directory you add to the load path. In your code it appears you're trying the latter approach, since you're specifically adding an ebin_dir with this Yaws global configuration directive:
GconfList = [{ebin_dir, ["/Users/someuser/yawsembedded/ebin"]}],
You need to verify that the /Users/someuser/yawsembedded/ebin directory exists, and that the compiled my_app.beam file is located there.