Recommended way to send custom error codes

[mmkal]

We've used throw new TRPCError(...) to send back unauthorized and similar standard type responses, but is there a way to send back arbitrary status codes? Use case - two people try to creating conflicting resources, we want to fail the second one with 409 conflict.

[KATT]

The reason why I currently don't allow custom HTTP codes is that I'm trying to be JSON-RPC compatible in the core as I try it to be independent of the transport layer.

However, I do understand this is might seem a bit too restrictive and I'm open to suggestions on how to make it more flexible.

Here's how the JSON-RPC codes are defined: https://github.com/trpc/trpc/blob/main/packages/server/src/rpc/codes.ts
And here's the HTTP codes for each are mapped: https://github.com/trpc/trpc/blob/main/packages/server/src/http/internals/getHTTPStatusCode.ts

Ideas welcome!

[KATT]

We can also just add your 409 code to the TRPC Error codes, that'd be the quickest fix.

[KATT]

We could also probably add a CUSTOM type which defaults to 500 but overridable by using formatError's httpStatus (which I'm adding in #811)

[KATT]

Even without adding CUSTOM you could throw a specific type of error and use formatError to specify a custom httpStatus after #811

[mmkal]

That last option sounds pretty future proof to me! I'm not familiar with json-rpc but yeah it'd be great to include 409 and 429 (too many requests) as first-class citizens as possible. I haven't poked around in the client much yet but there could be retry logic based on the 4xx response (429 is generally retriable after a delay by well-behaved clients).