Use Bad Request for invalid inputs in /chares

[cowbon]

Use HTTP 400 Bad Request when the subattester fail to parse the input JSON tsructure, or the expcted length of the nonce doesn't match.

[thomas-fossati]

Is this always supposed to carry an HTTP status code?
If so, I suggest we make it self-evident in the name.

[cowbon]

Should we call it httpStatusCode? I believe the usage is mainly to tell what type of HTTP error is encountered by the leaf attesters, though this patch sets the statusCode to be 200 when the API call is successful.

[thomas-fossati]

Coupling the REST API with the backend protocol may or may not be a good idea 😄

This kind of coupling can be problematic if we want to reuse the backend protocol with another API (e.g., CoAP), for example.

A better, albeit clunkier, approach would be to define the backend protocol and its own codes, and have a mapping function defined by each frontend protocol (HTTP, CoAP, other).

[cowbon]

I looked over RFC 7252 and it seems CoAP also uses 400 for Bad Requests, 500 for internal server errors. Now, all errors reported by the leaf attesters are treated as 500 Internal Server Error even the error is caused by the client (e.g. invalid nonce), and we want to categorize the errors returned by the leaf attesters. To make the naming of statusCode more self-evident, we could call it subattesterResponseCode, or just respondCode.
Given ratsd core is still HTTP-based, i.e. writing to the httpResponseWriter, should we adopt 400 Bad Request, 500 Internal Server error from HTTP/CoAP as the statusCode between the lead attester and the leafs, and defer the decoupling until we refactor the ratsd core to support other protocols using the same backend?

[thomas-fossati]

I believe that the two categories you have highlighted are good:

• caller input errors (that map to HTTP 4xx and CoAP 4.xx)
• business logic error (that map to HTTP 5xx, CoAP 5.xx)

If we also add a "frontend protocol” error mapper, e.g.:

func responseCodeToHTTP(uint32 responseCode) (code int) {
    // switch ...
}

we are good to go.

[cowbon]

Added the mapper in the server code.