Proxy is working in a simple mode now

mtglib/internal/relay/relay.go

@@ -0,0 +1,100 @@
+package relay
+
+import (
+	"context"
+	"io"
+	"sync"
+	"time"
+)
+
+type Relay struct {
+	ctx          context.Context
+	ctxCancel    context.CancelFunc
+	logger       Logger
+	eastBuffer   []byte
+	westBuffer   []byte
+	tickChannel  chan struct{}
+	errorChannel chan error
+	tickTimeout  time.Duration
+}
+
+func (r *Relay) Process(eastConn, westConn io.ReadWriteCloser) error {
+	eastConn = conn{
+		ReadWriteCloser: eastConn,
+		relay:           r,
+	}
+	westConn = conn{
+		ReadWriteCloser: westConn,
+		relay:           r,
+	}
+
+	defer func() {
+		r.ctxCancel()
+		eastConn.Close()
+		westConn.Close()
+	}()
+
+	go r.runObserver()
+
+	wg := &sync.WaitGroup{}
+	wg.Add(2) // nolint: gomnd
+
+	go r.transmit(eastConn, westConn, r.westBuffer, "west", wg)
+
+	r.transmit(westConn, eastConn, r.eastBuffer, "east", wg)
+
+	wg.Wait()
+
+	return <-r.errorChannel
+}
+
+func (r *Relay) transmit(src io.ReadCloser, dst io.WriteCloser,
+	buffer []byte, direction string, wg *sync.WaitGroup) {
+	defer func() {
+		wg.Done()
+		src.Close()
+		dst.Close()
+	}()
+
+	if _, err := io.CopyBuffer(dst, src, buffer); err != nil {
+		r.logger.Printf("error '%v' happened on direction %s", err, direction)
+
+		select {
+		case <-r.ctx.Done():
+		case r.errorChannel <- err:
+		default:
+		}
+	}
+}
+
+func (r *Relay) runObserver() {
+	ticker := time.NewTicker(time.Second)
+
+	defer func() {
+		ticker.Stop()
+
+		select {
+		case <-ticker.C:
+		default:
+		}
+	}()
+
+	lastTickAt := time.Now()
+	ctx := r.ctx
+
+	for {
+		select {
+		case <-ctx.Done():
+			return
+		case <-r.tickChannel:
+			lastTickAt = time.Now()
+		case <-ticker.C:
+			if time.Since(lastTickAt) > r.tickTimeout {
+				r.logger.Printf("exit due to a timeout")
+				r.ctxCancel()
+
+				return
+			}
+		}
+	}
+}