Generated client cannot handle http2 GOAWAY

[duckbrain]

Using the generated goa client, I've been getting this error somewhat regularly while under load.

http2: Transport: cannot retry err [http2: Transport received Server's graceful shutdown GOAWAY] after Request.Body was written; define Request.GetBody to avoid this error

In http.NewRequestFromContext, there's special logic to assign GetBody when the passed in body is a *bytes.Buffer. This avoids that issue. Goa passes nil and later assigns a request body via goa.design/goa/v3/http.RequestEncoder, which does not assign GetBody. It should be updated to return an Encoder that assigns r.GetBody.

[duckbrain]

I think something like this would do it, but need to do some testing.

// RequestEncoder returns a HTTP request encoder.
// The encoder uses package encoding/json.
func RequestEncoder(r *http.Request) Encoder {
	const k = "Content-Type"
	if h := r.Header.Get(k); h == "" {
		r.Header.Set(k, "application/json")
	}
	enc := new(jsonEncoder)
	r.Body = enc
	r.GetBody = enc.GetBody
	return enc
}

type jsonEncoder struct {
	b []byte
	bytes.Reader
}

func (je *jsonEncoder) Close() (err error) { return nil }

func (je *jsonEncoder) Encode(v any) error {
	b, err := json.Marshal(v)
	if err != nil {
		return err
	}
	je.b = b
	je.Reader = *bytes.NewReader(b)
	return nil
}

func (je *jsonEncoder) GetBody() (io.ReadCloser, error) {
	return io.NopCloser(bytes.NewReader(je.b)), nil
}

The jsonEncoder implements Encoder and io.ReadCloser, but until Encode is called, it's empty. After that, calls to GetBody will return new readers with the last encoded value.

[raphael]

That makes sense! Couldn't the fix simply be:

// RequestEncoder returns a HTTP request encoder.
// The encoder uses package encoding/json.
func RequestEncoder(r *http.Request) Encoder {
        if h := r.Header.Get(k); h == "" {
                r.Header.Set(k, "application/json")
        }
-       var buf bytes.Buffer
-       r.Body = io.NopCloser(&buf)
-       return json.NewEncoder(&buf)
+       buf := &bytes.Buffer{}
+       r.Body = io.NopCloser(buf)
+       r.GetBody = func() (io.ReadCloser, error) {
+               return io.NopCloser(bytes.NewReader(buf.Bytes())), nil
+       }
+       return json.NewEncoder(buf)
}