fix(aws-lambda): destroy the body when response stream setup throws

packages/aws-lambda/src/response.test.ts

@@ -274,6 +274,37 @@ describe('sendStandardResponse', () => {
     await sendPromise
   })
 
+  it.each([
+    ['`from` throws', () => {
+      fromSpy.mockImplementationOnce(() => {
+        throw new Error('Cannot set content-type, too late.')
+      })
+    }],
+    ['the first write throws', (responseStream: HttpResponseStream) => {
+      responseStream.write = () => {
+        throw new Error('write failed')
+      }
+    }],
+    ['the `awslambda` global is missing', () => {
+      vi.unstubAllGlobals()
+    }],
+  ])('rejects, destroys the response stream and the body when %s', async (_, setup) => {
+    const responseStream = createResponseStream()
+    setup(responseStream)
+
+    const error = await sendStandardResponse(responseStream, {
+      status: 200,
+      headers: {},
+      body: new Blob(['foo']),
+    }).catch(error => error)
+
+    expect(error).toBeInstanceOf(Error)
+    expect(responseStream.errored).toBe(error)
+
+    const [resBody] = toNodeHttpBodySpy.mock.results[0]!.value
+    expect((resBody as any).destroyed).toBe(true)
+  })
+
   describe('response stream closed before sending', () => {
     it('resolves and destroys the body', async () => {
       const responseStream = createResponseStream()

packages/aws-lambda/src/response.ts

@@ -41,41 +41,50 @@ export async function sendStandardResponse(
       return
     }
 
-    const [headers, setCookies] = toLambdaHeaders(resHeaders)
+    responseStream.once('error', reject)
+    responseStream.once('close', resolve)
 
-    // arms the metadata prelude (status, headers, cookies) and
-    // returns the stream the body should be written to
-    const res = awslambda.HttpResponseStream.from(responseStream, {
-      statusCode: standardResponse.status,
-      headers,
-      cookies: setCookies,
-    })
+    try {
+      const [headers, setCookies] = toLambdaHeaders(resHeaders)
 
-    res.once('error', reject)
-    res.once('close', resolve)
+      // arms the metadata prelude (status, headers, cookies) and
+      // returns the stream the body should be written to
+      const res = awslambda.HttpResponseStream.from(responseStream, {
+        statusCode: standardResponse.status,
+        headers,
+        cookies: setCookies,
+      })
 
-    // The runtime only sends the armed prelude ahead of the first `write` call:
-    // `end(chunk)` bypasses it and an empty body never writes, so trigger it now
-    res.write('')
+      // The runtime only sends the armed prelude ahead of the first `write` call:
+      // `end(chunk)` bypasses it and an empty body never writes, so trigger it now
+      res.write('')
 
-    if (resBody === undefined) {
-      // NOTE: Lambda functions don't allow passing undefined to `res.end`
-      res.end()
-    }
-    else if (typeof resBody === 'string') {
-      res.end(resBody)
-    }
-    else {
-      res.once('close', () => {
-        if (!resBody.closed) {
-          resBody.destroy(getNodeResponseError(res) ?? undefined)
-        }
-      })
+      if (resBody === undefined) {
+        // NOTE: Lambda functions don't allow passing undefined to `res.end`
+        res.end()
+      }
+      else if (typeof resBody === 'string') {
+        res.end(resBody)
+      }
+      else {
+        res.once('close', () => {
+          if (!resBody.closed) {
+            resBody.destroy(getNodeResponseError(res) ?? undefined)
+          }
+        })
+
+        resBody.once('error', error => res.destroy(error))
 
-      // WARNING: errors that occur here are silently ignored and not reported to the Promise
-      resBody.once('error', error => res.destroy(error))
+        resBody.pipe(res)
+      }
+    }
+    catch (error) {
+      destroyNodeHttpBody(resBody, error, reject)
 
-      resBody.pipe(res)
+      // Destroy instead of leaving the response half-open:
+      // the metadata prelude may be partially applied
+      responseStream.destroy(error as any)
+      reject(error)
     }
   })
 }