func()

in sandbox.go [95:167]
61 lines of code
17 McCabe index (conditional complexity)

func (s *server) commandHandler(cachePrefix string, cmdFunc func(context.Context, *request) (*response, error)) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		cachePrefix := cachePrefix // so we can modify it below
		w.Header().Set("Access-Control-Allow-Origin", "*")
		if r.Method == "OPTIONS" {
			// This is likely a pre-flight CORS request.
			return
		}

		var req request
		// Until programs that depend on golang.org/x/tools/godoc/static/playground.js
		// are updated to always send JSON, this check is in place.
		if b := r.FormValue("body"); b != "" {
			req.Body = b
			req.WithVet, _ = strconv.ParseBool(r.FormValue("withVet"))
		} else if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
			s.log.Errorf("error decoding request: %v", err)
			http.Error(w, http.StatusText(http.StatusBadRequest), http.StatusBadRequest)
			return
		}

		if req.WithVet {
			cachePrefix += "_vet" // "prog" -> "prog_vet"
		}

		resp := &response{}
		key := cacheKey(cachePrefix, req.Body)
		if err := s.cache.Get(key, resp); err != nil {
			if !errors.Is(err, memcache.ErrCacheMiss) {
				s.log.Errorf("s.cache.Get(%q, &response): %v", key, err)
			}
			resp, err = cmdFunc(r.Context(), &req)
			if err != nil {
				s.log.Errorf("cmdFunc error: %v", err)
				http.Error(w, http.StatusText(http.StatusInternalServerError), http.StatusInternalServerError)
				return
			}
			if strings.Contains(resp.Errors, goBuildTimeoutError) || strings.Contains(resp.Errors, runTimeoutError) {
				// TODO(golang.org/issue/38576) - This should be a http.StatusBadRequest,
				// but the UI requires a 200 to parse the response. It's difficult to know
				// if we've timed out because of an error in the code snippet, or instability
				// on the playground itself. Either way, we should try to show the user the
				// partial output of their program.
				s.writeJSONResponse(w, resp, http.StatusOK)
				return
			}
			for _, e := range internalErrors {
				if strings.Contains(resp.Errors, e) {
					s.log.Errorf("cmdFunc compilation error: %q", resp.Errors)
					http.Error(w, http.StatusText(http.StatusInternalServerError), http.StatusInternalServerError)
					return
				}
			}
			for _, el := range resp.Events {
				if el.Kind != "stderr" {
					continue
				}
				for _, e := range internalErrors {
					if strings.Contains(el.Message, e) {
						s.log.Errorf("cmdFunc runtime error: %q", el.Message)
						http.Error(w, http.StatusText(http.StatusInternalServerError), http.StatusInternalServerError)
						return
					}
				}
			}
			if err := s.cache.Set(key, resp); err != nil {
				s.log.Errorf("cache.Set(%q, resp): %v", key, err)
			}
		}

		s.writeJSONResponse(w, resp, http.StatusOK)
	}
}