v5 beta: non-proxy API Gateway REST (v1) resources strip entire path via event.resource, causing 404s

[john-gay]

Bug Description

In v5, getDefaultStripBasePath was introduced in src/event-sources/utils.js:

function getDefaultStripBasePath(event) {
  const basePathMatched = event?.requestContext?.customDomain?.basePathMatched || '';
  const resource = event?.pathParameters?.proxy ? '' : event.resource;
  return basePathMatched ? `/${basePathMatched}${resource}` : resource;
}

For non-proxy resources (no {proxy+} parameter), event.resource is the full path template defined in API Gateway — e.g. /service/endpoint. When there is no custom domain, stripBasePath is set to /service/endpoint, which is then used as a regex to strip the entire path, leaving an empty string that gets normalised to /.

The path Express receives is / instead of /service/endpoint, causing a 404.

v4 Behaviour

In v4, stripBasePath always defaulted to '', so event.path was passed through untouched:

stripBasePath = '',

Reproduction

API Gateway REST API (v1) with any static (non-proxy) resource, e.g.:

GET /service/endpoint  →  static resource (no {proxy+})

Lambda receives:

{
  "resource": "/service/endpoint",
  "path": "/service/endpoint",
  "pathParameters": null,
  ...
}

v5 computes stripBasePath = '/service/endpoint', strips the full path → Express sees GET / → 404.

Meanwhile, a proxy resource on the same service works fine because pathParameters.proxy is set, which causes resource to be set to '' and the strip is a no-op.

This means in a typical setup where a {proxy+} resource handles most routes alongside a small number of static resources (e.g. a health check), the proxy routes work but the static ones all 404.

Expected Behaviour

Same as v4 — event.resource should not be used as a base path to strip unless a custom domain basePathMatched is explicitly set. The event.resource field reflects the API Gateway resource template, not a mount prefix.

Workaround

For now, downgrading to v4.17.1 restores the previous behaviour.

Environment

• @codegenie/serverless-express: 5.0.0-beta.1
• API Gateway: REST API (v1)
• Resource type: static (non-proxy), no custom domain