Unexpected errors on empty HTTP request bodies

[torkelrogstad]

When doing a HTTP request without a body I end up with this response:

{"code":"invalid_argument","message":"unmarshal into *emptypb.Empty: proto: syntax error (line 1:1): unexpected token "}   

This is fixed by adding an empty body {} to my HTTP request, so it's not a major issue. However, I'd expect empty bodies to result in the empty value for my requests. Is that a strange expectation?

Basically, I want this to happen on the server side before my request handler is invoked, in Go-pseudo:

if r.ContentLength == 0 {
  r.Body = bytes.NewBuffer("{}")
}

// rest of the Connect magic

[joshcarp]

I think that it's semantically correct to say that an empty string is not valid json: "" should always show as invalid with content-type: application/json.
Adding on {} to the body would also be adding json encoding specific logic to connect, which wouldn't be desired.

[torkelrogstad]

In that case I think the error message should be improved. It took me quite a bit of head-scratching to understand what this meant. Something along the lines of "cannot unmarshal MESSAGE_TYPE: empty request body", for example?

[akshayjshah]

Improving the error message is definitely doable!

I'm particularly reluctant to implicitly treat "" and "{}" identically because it diverges from protojson, and is likely to introduce incompatibilities with other gRPC implementations. (This is a pretty soft objection, but I'd rather be conservative.)

[mattrobenolt]

imo this is pretty easy to solve in your own tiny bit of middleware. I agree, it's technically invalid and incorrect. If someone using connect-go wants to deviate, they have the tools to do so.

Something like:

func EnsureBody(next http.Handler) http.Handler {
    return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
        if r.Method == "POST" && r.ContentLength == 0 && r.Headers.Get("Content-Type") == "application/json" {
            r.Body = bytes.NewBuffer("{}")
            r.ContentLength = 2
        }
        next.ServeHTTP(w, r)
    })
}

var mux http.Handler = http.NewServeMux()
mux = EnsureBody(mux)

something like that, entirely untested, etc, but this is simple enough to implement your logic for your use case.