[module] print better errors when module loading fails

CHANGELOG.md

@@ -14,6 +14,10 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 
 - Experimental caching proxy to the http client [PR #357](https://github.com/3scale/apicast/pull/357)
 
+### Changed
+
+- Print better errors when module loading fails [PR #360](https://github.com/3scale/apicast/pull/360)
+
 ## [3.0.0-rc1] - 2017-04-04
 
 ### Added

apicast/src/module.lua

@@ -1,23 +1,26 @@
-local pcall = pcall
+local xpcall = xpcall
 local require = require
 local dofile = dofile
 local type = type
 
 local env = require 'resty.env'
 
+local function error_message(error)
+  ngx.log(ngx.WARN, error)
+  return error
+end
+
 local prequire = function(file)
-  local ok, ret = pcall(require, file)
+  local ok, ret = xpcall(require, error_message, file)
 
   if not ok and ret then
     -- dofile can load absolute paths, require can't
-    ok, ret = pcall(dofile, file)
+    ok, ret = xpcall(dofile, error_message, file)
   end
 
   if not ok and ret then
     if type(ret) == 'userdata' then
       ngx.log(ngx.WARN, 'cyclic require detected: ', debug.traceback())
-    elseif type(ret) == 'string' then
-      ngx.log(ngx.WARN, ret, ', ', debug.traceback())
     end
     return false, ret
   end
@@ -30,10 +33,15 @@ local name = env.get('APICAST_MODULE') or 'apicast'
 local ok, mod = prequire(name)
 
 if ok and mod then
-  if mod.new then
-    return mod.new()
+  if type(mod) == 'table' then
+    if mod.new then
+      return mod.new()
+    else
+      return mod
+    end
   else
-    return mod
+    ngx.log(ngx.ERR, 'module ', name, ' did not return a table but: ', type(mod))
+    return false
   end
 else
   return ok, mod

t/018-module-loading.t

@@ -0,0 +1,63 @@
+use Test::Nginx::Socket 'no_plan';
+use Cwd qw(cwd);
+
+my $pwd = cwd();
+my $apicast = $ENV{TEST_NGINX_APICAST_PATH} || "$pwd/apicast";
+
+$ENV{TEST_NGINX_LUA_PATH} = "$pwd/t/servroot/html/?.lua;$apicast/src/?.lua;;";
+$ENV{TEST_NGINX_HTTP_CONFIG} = "$apicast/http.d/init.conf";
+$ENV{TEST_NGINX_APICAST_PATH} = $apicast;
+$ENV{APICAST_MODULE} = 'custom';
+
+env_to_nginx(
+    'APICAST_MODULE'
+);
+
+log_level('warn');
+repeat_each(2);
+no_root_location();
+run_tests();
+
+__DATA__
+
+=== TEST 1: print error when file is missing
+
+--- http_config
+  include $TEST_NGINX_HTTP_CONFIG;
+  lua_package_path "$TEST_NGINX_LUA_PATH";
+--- config
+--- must_die
+--- request
+GET
+--- error_log
+module 'custom' not found
+
+
+=== TEST 2: print error on syntax error
+
+--- http_config
+  include $TEST_NGINX_HTTP_CONFIG;
+  lua_package_path "$TEST_NGINX_LUA_PATH";
+--- config
+--- must_die
+--- request
+GET
+--- error_log
+custom.lua:1: unexpected symbol near 'not'
+--- user_files
+>>> custom.lua
+not valid lua
+
+=== TEST 3: print error on empty file
+
+--- http_config
+  include $TEST_NGINX_HTTP_CONFIG;
+  lua_package_path "$TEST_NGINX_LUA_PATH";
+--- config
+--- request
+GET
+--- error_log
+module custom did not return a table but: boolean
+--- must_die
+--- user_files
+>>> custom.lua