func runHandler()

in sandbox/sandbox.go [524:635]
102 lines of code
16 McCabe index (conditional complexity)

func runHandler(w http.ResponseWriter, r *http.Request) {
	t0 := time.Now()
	tlast := t0
	var logmu sync.Mutex
	logf := func(format string, args ...interface{}) {
		if !*dev {
			return
		}
		logmu.Lock()
		defer logmu.Unlock()
		t := time.Now()
		d := t.Sub(tlast)
		d0 := t.Sub(t0)
		tlast = t
		log.Print(fmt.Sprintf("+%10v +%10v ", d0, d) + fmt.Sprintf(format, args...))
	}
	logf("/run")

	if r.Method != "POST" {
		http.Error(w, "expected a POST", http.StatusBadRequest)
		return
	}

	// Bound the number of requests being processed at once.
	// (Before we slurp the binary into memory)
	select {
	case runSem <- struct{}{}:
	case <-r.Context().Done():
		return
	}
	defer func() { <-runSem }()

	bin, err := ioutil.ReadAll(http.MaxBytesReader(w, r.Body, maxBinarySize))
	if err != nil {
		log.Printf("failed to read request body: %v", err)
		http.Error(w, err.Error(), http.StatusInternalServerError)
		return
	}
	logf("read %d bytes", len(bin))

	c, err := getContainer(r.Context())
	if err != nil {
		if cerr := r.Context().Err(); cerr != nil {
			log.Printf("getContainer, client side cancellation: %v", cerr)
			return
		}
		http.Error(w, "failed to get container", http.StatusInternalServerError)
		log.Printf("failed to get container: %v", err)
		return
	}
	logf("got container %s", c.name)

	ctx, cancel := context.WithTimeout(context.Background(), runTimeout)
	closed := make(chan struct{})
	defer func() {
		logf("leaving handler; about to close container")
		cancel()
		<-closed
	}()
	go func() {
		<-ctx.Done()
		if ctx.Err() == context.DeadlineExceeded {
			logf("timeout")
		}
		c.Close()
		close(closed)
	}()
	var meta processMeta
	meta.Args = r.Header["X-Argument"]
	metaJSON, _ := json.Marshal(&meta)
	metaJSON = append(metaJSON, '\n')
	if _, err := c.stdin.Write(metaJSON); err != nil {
		log.Printf("failed to write meta to child: %v", err)
		http.Error(w, "unknown error during docker run", http.StatusInternalServerError)
		return
	}
	if _, err := c.stdin.Write(bin); err != nil {
		log.Printf("failed to write binary to child: %v", err)
		http.Error(w, "unknown error during docker run", http.StatusInternalServerError)
		return
	}
	c.stdin.Close()
	logf("wrote+closed")
	err = c.Wait()
	select {
	case <-ctx.Done():
		// Timed out or canceled before or exactly as Wait returned.
		// Either way, treat it as a timeout.
		sendError(w, "timeout running program")
		return
	default:
		logf("finished running; about to close container")
		cancel()
	}
	res := &sandboxtypes.Response{}
	if err != nil {
		if c.stderr.n < 0 || c.stdout.n < 0 {
			// Do not send truncated output, just send the error.
			sendError(w, errTooMuchOutput.Error())
			return
		}
		var ee *exec.ExitError
		if !errors.As(err, &ee) {
			http.Error(w, "unknown error during docker run", http.StatusInternalServerError)
			return
		}
		res.ExitCode = ee.ExitCode()
	}
	res.Stdout = c.stdout.dst.Bytes()
	res.Stderr = cleanStderr(c.stderr.dst.Bytes())
	sendResponse(w, res)
}