fix: respond with 500 Internal Server Error when an unhandled error has occured and no response has already been sent to the client

Author: Jake Champion

.github/workflows/main.yml

@@ -244,6 +244,7 @@ jobs:
       - e2e-async-select
       - e2e-byte-repeater
       - e2e-edge-dictionary
+      - e2e-error
       - e2e-geoip
       - e2e-hello-world
       - e2e-object-store
@@ -419,6 +420,17 @@ jobs:
       with:
         fixture: 'edge-dictionary'
         fastly-api-token: ${{ secrets.FASTLY_API_TOKEN }}
+  e2e-error:
+    runs-on: ubuntu-latest
+    needs: [build]
+    steps:
+    - uses: actions/checkout@v2
+      with:
+        submodules: false
+    - uses: ./.github/actions/e2e
+      with:
+        fixture: 'error'
+        fastly-api-token: ${{ secrets.FASTLY_API_TOKEN }}
   e2e-geoip:
     runs-on: ubuntu-latest
     needs: [build]

c-dependencies/js-compute-runtime/js-compute-runtime.cpp

@@ -418,10 +418,11 @@ static void dispatch_fetch_event(JSContext *cx, HandleObject event, double *tota
     handler.setObject(*(*FETCH_HANDLERS)[i]);
     if (!JS_CallFunctionValue(cx, GLOBAL, handler, argsv, &rval)) {
       DumpPendingException(cx, "dispatching FetchEvent\n");
-      JS_ClearPendingException(cx);
+      break;
     }
-    if (FetchEvent::state(event) != FetchEvent::State::unhandled)
+    if (FetchEvent::state(event) != FetchEvent::State::unhandled) {
       break;
+    }
   }
 
   FetchEvent::stop_dispatching(event);
@@ -528,8 +529,17 @@ int main(int argc, const char *argv[]) {
 
     // Respond with status `500` if any promise rejections were left unhandled
     // and no response was ever sent.
-    if (!FetchEvent::response_started(fetch_event))
+    if (!FetchEvent::response_started(fetch_event)) {
+      FetchEvent::respondWithError(cx, fetch_event);
+    }
+  }
+
+  // Respond with status `500` if an exception is pending
+  // and no response was ever sent.
+  if (JS_IsExceptionPending(cx)) {
+    if (!FetchEvent::response_started(fetch_event)) {
       FetchEvent::respondWithError(cx, fetch_event);
+    }
   }
 
   auto end = system_clock::now();

integration-tests/js-compute/fixtures/error/bin/index.js

@@ -0,0 +1,38 @@
+/* global fastly */
+
+addEventListener("fetch", ()=>{
+    console.log(1)
+})
+
+addEventListener("fetch", event => {
+    event.respondWith(app(event))
+})
+
+/**
+ * @param {FetchEvent} event
+ * @returns {Response}
+ */
+async function app(event) {
+    try {
+        const path = (new URL(event.request.url)).pathname;
+        console.log(`path: ${path}`)
+        console.log(`FASTLY_SERVICE_VERSION: ${fastly.env.get('FASTLY_SERVICE_VERSION')}`)
+        if (routes.has(path)) {
+            const routeHandler = routes.get(path);
+            return await routeHandler()
+        }
+        return fail(`${path} endpoint does not exist`)
+    } catch (error) {
+        return fail(`The routeHandler threw an error: ${error.message}` + '\n' + error.stack)
+    }
+}
+
+const routes = new Map();
+routes.set('/', () => {
+    routes.delete('/');
+    let test_routes = Array.from(routes.keys())
+    return new Response(JSON.stringify(test_routes), { 'headers': { 'content-type': 'application/json' } });
+});
+routes.set("/error", async () => {
+    throw new Error('uh oh')
+});

integration-tests/js-compute/fixtures/error/fastly.toml.in

@@ -0,0 +1,13 @@
+# This file describes a Fastly Compute@Edge package. To learn more visit:
+# https://developer.fastly.com/reference/fastly-toml/
+
+authors = ["[email protected]"]
+description = ""
+language = "other"
+manifest_version = 2
+name = "empty"
+service_id = ""
+
+[scripts]
+  build = "../../../../target/release/js-compute-runtime"
+

integration-tests/js-compute/fixtures/error/tests.json

@@ -0,0 +1,12 @@
+{
+  "GET /error": {
+    "environments": ["viceroy", "c@e"],
+    "downstream_request": {
+      "method": "GET",
+      "pathname": "/error"
+    },
+    "downstream_response": {
+      "status": 500
+    }
+  }
+}