Yaws “process died” when yaws_api specific code is used

Question

I have a small yaws appmod test:

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

http(parse_query,Arg) ->
    yaws_api:parse_query(Arg);

out(Arg) -> 
    {html, [http(parse_query,Arg)]}.

When the yaws_api:parse_query function is ran I get the following ERROR REPORT from the yaws interactive mode:

Yaws process died: {function_clause,
                   [{yaws_server,binary_size,
                        [0,{"i",undefined}],
                        [{file,"yaws_server.erl"},{line,3015}]},
                    {yaws_server,binary_size,2,
                        [{file,"yaws_server.erl"},{line,3018}]},
                    {yaws_server,binary_size,2,
                        [{file,"yaws_server.erl"},{line,3018}]},
                    {yaws_server,deflate_accumulated,4,
                        [{file,"yaws_server.erl"},{line,3712}]},
                    {yaws_server,deliver_accumulated,4,
                        [{file,"yaws_server.erl"},{line,3666}]},
                    {yaws_server,finish_up_dyn_file,2,
                        [{file,"yaws_server.erl"},{line,2745}]},
                    {yaws_server,aloop,4,
                        [{file,"yaws_server.erl"},{line,1175}]},
                    {yaws_server,acceptor0,2,
                        [{file,"yaws_server.erl"},{line,1016}]}]}

The appmod is setup in config with:

<server localhost>
    port = 8080
    listen = 127.0.0.1
    #docroot = /usr/share/yaws
    docroot = /usr/lib/yaws/www
    appmods = </,webservice>
    # dir_listings = true
</server>

Answer 1

Though you don't show it, it looks like the URL you're trying to access has a query string with at least one variable named i, something like this:

http://example.com/foo?i=10

For that URL, yaws_api:parse_query/1 will return [{"i","10"}], which you're then trying to return to Yaws as HTML using the {html, iolist()} construct. Unfortunately, [{"i","10"}] is not an iolist, string, or binary, so Yaws fails.

You can fix this by converting [{"i","10"}] to a string using the yaws_api:f/2 call, like this:

out(Arg) ->
    {html, yaws_api:f("~p", [http(parse_query,Arg)])}.

or using the standard io_lib:format/2 call:

out(Arg) ->
    {html, io_lib:format("~p", [http(parse_query,Arg)])}.

The yaws_api:f/2 function is just a wrapper around io_lib:format/2.