Handling Errors

Proposal on how to fix issues like https://github.com/cloudflare/kv-asset-handler/issues/44

Custom Error class

I suggest we create a custom error class that looks something like

export class KVError extends Error {
  constructor(message?: string, code: number = 500) {
    super(message)
    Object.setPrototypeOf(this, new.target.prototype) // restore prototype chain
    this.name = KVError.name // stack traces display correctly now
    this.code = code
  }
  code: number // Appropriate HTTP status code
}

getAssetFromKV throws custom error

getAssetFromKV will now throw custom errors that we can identify as KVError.

Example inside getAssetFromKV

    throw new KVError(`${request.method} is not a valid request method`, 405)
    throw new KVError(`there is no ${ASSET_NAMESPACE} namespace bound to the script`, 500)

Workers sites template

now instead of having crazy try/catch blocks and assuming a 404 error in the sites template, we’d have workers-site-template look like:

try {
  let resp = await getAssetFromKV()
  return new Response(resp.message, { status: resp.code })
} catch (e) {
  if (resp instanceof KVError) {
    switch (e.code) {
      case 404:
        return notFoundResponse
        break
      case 401:
        return methodNotAllowedResponse
        break
      default:
        return new Response(resp.message, { status: resp.code })
    }
  }
}

Alternative option: getAssetFromKV returns a custom error

getAssetFromKV will now not throw generated errors, but instead optionally return KVError.

const getAssetFromKV: (event..) => Promise<KVError | Response>

Examples of returning these errors instead of throwing them:

    return new KVError(`${request.method} is not a valid request method`, 405)
    return new KVError(`there is no ${ASSET_NAMESPACE} namespace bound to the script`, 500)

[EverlastingBugstopper]

i think we should throw the errors rather than returning it so that it is

1. not a breaking change
2. you can use a switch statement in the catch block on errors, or it can continue to function like it currently does

[EverlastingBugstopper]

the question i’ve always had is whether the kv-asset-handler should automatically include the asset found at 404.html (if any) when it throws the NotFound error. developers can use it or not, but that would prevent another round of “was it found?”

I kinda like that - but we should allow the path to be configurable in case people want it to be called something else like notfound.html