Handle exception during runtime

Previously, exceptions raised during the policy processing phase were ignored
unless the on_failed policy was added to the chain.

This PR terminates the request and prints the stacktrace by default when an
exception is thrown.

Author: tkan145

gateway/src/apicast/policy/on_failed/on_failed.lua

@@ -1,3 +1,5 @@
+local get_phase = ngx.get_phase
+
 local _M  = require('apicast.policy').new('On failed', 'builtin')
 local new = _M.new
 
@@ -11,6 +13,12 @@ end
 function _M:export()
   return {
     policy_error_callback = function(policy_name, error_message)
+      local phase = get_phase()
+      -- skip calling plugins on body_filter/log phase as ngx.exit does not
+      -- exist in these phases
+      if phase == "body_filter" or phase == "log" then
+        return
+      end
       ngx.log(ngx.DEBUG, "Stop request because policy: '", policy_name, "' failed, error='", error_message, "'")
       ngx.exit(self.error_status_code)
     end

gateway/src/apicast/policy_chain.lua

@@ -216,6 +216,8 @@ local function call_chain(phase_name)
             if not status then
               if context.policy_error_callback then
                   context.policy_error_callback(self[i]._NAME, return_val)
+              else
+                error(return_val)
               end
               -- This is important because Openresty just died on error on init
               -- phase, and we should keep in this way.

t/apicast-policy-chains-crash.t

@@ -32,3 +32,34 @@ GET /test HTTP/1.1
 --- error_code: 200
 --- error_log
 Policy error_policy crashed in .new()
+
+
+
+=== TEST 2: policy chain with a policy that crashes on rewrite/access()
+Policies that crash during request phase should ternimate the request
+--- configuration
+{
+    "services": [
+      {
+        "id": 42,
+        "proxy": {
+            "policy_chain" : [
+              { "name" : "error_policy", "version" : "2.0.0" },
+              { "name" : "apicast.policy.echo" }
+            ]
+        }
+      }
+    ]
+}
+--- request
+GET /test
+--- ignore_response
+--- error_code: 500
+--- error_log eval
+[
+'lua entry thread aborted: runtime error:',
+'terminated in rewrite phase',
+'stack traceback:',
+" in function 'error'",
+": in function 'rewrite'",
+]