Fix unhandled rejection when S3 route used without the optional SDK

response.getLink() invokes s3-service.getSignedUrl in callback style and ignores
its returned promise, relying on the callback always firing. The lazy-import
refactor could reject getSignedUrl (SDK missing) before the callback ran, turning
the ignored promise into an unhandled rejection (which crashes the process under
Node's default) instead of the graceful 500 main produced.

Wrap getSignedUrl in try/catch so it always resolves via the callback and never
rejects — restoring the original contract. Add an e2e guard (s3-no-sdk fixture):
an S3 route without @aws-sdk must return a handled 5xx and not crash. Layer 1
now 17/17.

Author: naorpeled

e2e/fixtures/s3-no-sdk/handler.js

@@ -0,0 +1,18 @@
+'use strict';
+// An S3 route in a project WITHOUT the optional @aws-sdk installed must fail GRACEFULLY
+// (handled 5xx), never crash the process with an unhandled rejection. Node's default
+// (unhandled rejections terminate the process) means a leak here exits non-zero -> the
+// runner sees a non-zero status and fails. The 50ms settle lets any stray rejection surface.
+const createAPI = require('lambda-api');
+const { readFileSync } = require('fs');
+const api = createAPI({ version: 'v1' });
+api.get('/ok', (req, res) => res.json({ ok: true }));
+api.get('/link', async (req, res) => {
+  const url = await res.getLink('s3://bucket/key.txt');
+  return { url };
+});
+const event = JSON.parse(readFileSync(process.argv[2], 'utf8'));
+api
+  .run(event, {})
+  .then((r) => setTimeout(() => process.stdout.write(JSON.stringify(r)), 50))
+  .catch((e) => { process.stderr.write(String(e.stack || e)); process.exit(1); });

e2e/fixtures/s3-no-sdk/package.json

@@ -0,0 +1 @@
+{ "name": "fixture-s3-no-sdk", "private": true }

e2e/run-layer1.mjs

@@ -70,6 +70,23 @@ section('esm-import (no optional @aws-sdk installed)');
   });
 }
 
+// 2b. An S3 route WITHOUT the optional SDK must fail gracefully (handled 5xx), never crash
+//     the process with an unhandled rejection (regression guard: getSignedUrl must not reject).
+section('s3 route without @aws-sdk -> graceful 5xx (no unhandled rejection)');
+{
+  const dir = stageFixture(base, 's3-no-sdk');
+  check('non-S3 route still 200', () => {
+    const r = parseResponse(runNode(dir, 'handler.js', writeEvent(dir, 'ok.json', apiGatewayV1('/ok'))), 's3-no-sdk /ok');
+    assert(r.statusCode === 200, `status ${r.statusCode}`);
+  });
+  check('S3 route -> handled 5xx, process did not crash', () => {
+    const res = runNode(dir, 'handler.js', writeEvent(dir, 'link.json', apiGatewayV1('/link')));
+    assert(res.status === 0, `process crashed (unhandled rejection?) status=${res.status}\n${res.stderr || ''}`);
+    const r = JSON.parse(res.stdout);
+    assert(r.statusCode >= 500 && r.statusCode < 600, `expected 5xx, got ${r.statusCode}`);
+  });
+}
+
 // 3. deep imports via the exports `./lib/*` map
 section('deep-import lambda-api/lib/utils (cjs + esm)');
 {

src/lib/s3-service.js

@@ -49,27 +49,28 @@ export const getSignedUrl = async (
   { Expires, ...params },
   callback = () => {}
 ) => {
-  const { GetObjectCommand } = await import('@aws-sdk/client-s3');
-  const { getSignedUrl: awsGetSignedUrl } = await import(
-    '@aws-sdk/s3-request-presigner'
-  );
-  let command;
-  switch (type) {
-    case 'getObject':
-      command = new GetObjectCommand(params);
-      break;
-    default:
-      throw new Error('Invalid command type');
+  // Callers (response.getLink) use the callback and ignore the returned promise, so this must
+  // ALWAYS resolve via the callback and never reject — including when the lazy SDK import fails.
+  try {
+    const { GetObjectCommand } = await import('@aws-sdk/client-s3');
+    const { getSignedUrl: awsGetSignedUrl } = await import(
+      '@aws-sdk/s3-request-presigner'
+    );
+    let command;
+    switch (type) {
+      case 'getObject':
+        command = new GetObjectCommand(params);
+        break;
+      default:
+        throw new Error('Invalid command type');
+    }
+    const client = await getClient();
+    const url = await awsGetSignedUrl(client, command, { expiresIn: Expires });
+    callback(null, url);
+    return url;
+  } catch (err) {
+    callback(err);
   }
-  const client = await getClient();
-  return awsGetSignedUrl(client, command, { expiresIn: Expires })
-    .then((url) => {
-      callback(null, url);
-      return url;
-    })
-    .catch((err) => {
-      callback(err);
-    });
 };
 
 const service = {