[client] Add port forwarding to ssh proxy (#5031)

* Implement port forwarding for the ssh proxy

* Allow user switching for port forwarding

client/ssh/common.go

@@ -193,3 +193,64 @@ func buildAddressList(hostname string, remote net.Addr) []string {
 	}
 	return addresses
 }
+
+// BidirectionalCopy copies data bidirectionally between two io.ReadWriter connections.
+// It waits for both directions to complete before returning.
+// The caller is responsible for closing the connections.
+func BidirectionalCopy(logger *log.Entry, rw1, rw2 io.ReadWriter) {
+	done := make(chan struct{}, 2)
+
+	go func() {
+		if _, err := io.Copy(rw2, rw1); err != nil && !isExpectedCopyError(err) {
+			logger.Debugf("copy error (1->2): %v", err)
+		}
+		done <- struct{}{}
+	}()
+
+	go func() {
+		if _, err := io.Copy(rw1, rw2); err != nil && !isExpectedCopyError(err) {
+			logger.Debugf("copy error (2->1): %v", err)
+		}
+		done <- struct{}{}
+	}()
+
+	<-done
+	<-done
+}
+
+func isExpectedCopyError(err error) bool {
+	return errors.Is(err, io.EOF) || errors.Is(err, context.Canceled)
+}
+
+// BidirectionalCopyWithContext copies data bidirectionally between two io.ReadWriteCloser connections.
+// It waits for both directions to complete or for context cancellation before returning.
+// Both connections are closed when the function returns.
+func BidirectionalCopyWithContext(logger *log.Entry, ctx context.Context, conn1, conn2 io.ReadWriteCloser) {
+	done := make(chan struct{}, 2)
+
+	go func() {
+		if _, err := io.Copy(conn2, conn1); err != nil && !isExpectedCopyError(err) {
+			logger.Debugf("copy error (1->2): %v", err)
+		}
+		done <- struct{}{}
+	}()
+
+	go func() {
+		if _, err := io.Copy(conn1, conn2); err != nil && !isExpectedCopyError(err) {
+			logger.Debugf("copy error (2->1): %v", err)
+		}
+		done <- struct{}{}
+	}()
+
+	select {
+	case <-ctx.Done():
+	case <-done:
+		select {
+		case <-ctx.Done():
+		case <-done:
+		}
+	}
+
+	_ = conn1.Close()
+	_ = conn2.Close()
+}