Less troublesome way of identifying content-type (#10770)

cl/beacon/beaconhttp/api.go

@@ -97,41 +97,41 @@ func HandleEndpoint[T any](h EndpointHandler[T]) http.HandlerFunc {
 		}
 		// TODO: potentially add a context option to buffer these
 		contentType := r.Header.Get("Accept")
-		contentTypes := strings.Split(contentType, ",")
 
 		// early return for event stream
 		if slices.Contains(w.Header().Values("Content-Type"), "text/event-stream") {
 			return
 		}
 		switch {
-		case slices.Contains(contentTypes, "application/octet-stream"):
+		case contentType == "*/*", contentType == "", strings.Contains(contentType, "text/html"), strings.Contains(contentType, "application/json"):
+			if !isNil(ans) {
+				w.Header().Set("Content-Type", "application/json")
+				err := json.NewEncoder(w).Encode(ans)
+				if err != nil {
+					// this error is fatal, log to console
+					log.Error("beaconapi failed to encode json", "type", reflect.TypeOf(ans), "err", err)
+				}
+			} else {
+				w.WriteHeader(200)
+			}
+		case strings.Contains(contentType, "application/octet-stream"):
 			sszMarshaler, ok := any(ans).(ssz.Marshaler)
 			if !ok {
 				NewEndpointError(http.StatusBadRequest, ErrorSszNotSupported).WriteTo(w)
 				return
 			}
+			w.Header().Set("Content-Type", "application/octet-stream")
 			// TODO: we should probably figure out some way to stream this in the future :)
 			encoded, err := sszMarshaler.EncodeSSZ(nil)
 			if err != nil {
 				WrapEndpointError(err).WriteTo(w)
 				return
 			}
 			w.Write(encoded)
-		case contentType == "*/*", contentType == "", slices.Contains(contentTypes, "text/html"), slices.Contains(contentTypes, "application/json"):
-			if !isNil(ans) {
-				w.Header().Add("content-type", "application/json")
-				err := json.NewEncoder(w).Encode(ans)
-				if err != nil {
-					// this error is fatal, log to console
-					log.Error("beaconapi failed to encode json", "type", reflect.TypeOf(ans), "err", err)
-				}
-			} else {
-				w.WriteHeader(200)
-			}
-		case slices.Contains(contentTypes, "text/event-stream"):
+		case strings.Contains(contentType, "text/event-stream"):
 			return
 		default:
-			http.Error(w, "content type must be application/json, application/octet-stream, or text/event-stream", http.StatusBadRequest)
+			http.Error(w, fmt.Sprintf("content type must include application/json, application/octet-stream, or text/event-stream, got %s", contentType), http.StatusBadRequest)
 		}
 	})
 }