1 files changed, 93 insertions, 0 deletions
diff --git a/listener.go b/listener.go
new file mode 100644
index 0000000..6b0442d
--- /dev/null
+++ b/listener.go
@@ -0,0 +1,93 @@
+// Copyright 2017 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package tcpproxy
+
+import (
+	"io"
+	"net"
+	"sync"
+)
+
+// TargetListener implements both net.Listener and Target.
+// Matched Targets become accepted connections.
+type TargetListener struct {
+	Address string // Address is the string reported by TargetListener.Addr().String().
+
+	mu       sync.Mutex
+	cond     *sync.Cond
+	closed   bool
+	nextConn net.Conn
+}
+
+var (
+	_ net.Listener = (*TargetListener)(nil)
+	_ Target       = (*TargetListener)(nil)
+)
+
+func (tl *TargetListener) lock() {
+	tl.mu.Lock()
+	if tl.cond == nil {
+		tl.cond = sync.NewCond(&tl.mu)
+	}
+}
+
+type tcpAddr string
+
+func (a tcpAddr) Network() string { return "tcp" }
+func (a tcpAddr) String() string  { return string(a) }
+
+func (tl *TargetListener) Addr() net.Addr { return tcpAddr(tl.Address) }
+
+func (tl *TargetListener) Close() error {
+	tl.lock()
+	if tl.closed {
+		tl.mu.Unlock()
+		return nil
+	}
+	tl.closed = true
+	tl.mu.Unlock()
+	tl.cond.Broadcast()
+	return nil
+}
+
+// HandleConn implements the Target interface. It blocks until tl is
+// closed or another goroutine has called Accept and received c.
+func (tl *TargetListener) HandleConn(c net.Conn) {
+	tl.lock()
+	defer tl.mu.Unlock()
+	for tl.nextConn != nil && !tl.closed {
+		tl.cond.Wait()
+	}
+	if tl.closed {
+		c.Close()
+		return
+	}
+	tl.nextConn = c
+	tl.cond.Broadcast() // Signal might be sufficient; verify.
+	for tl.nextConn == c && !tl.closed {
+		tl.cond.Wait()
+	}
+	if tl.closed {
+		c.Close()
+		return
+	}
+}
+
+func (tl *TargetListener) Accept() (net.Conn, error) {
+	tl.lock()
+	for tl.nextConn == nil && !tl.closed {
+		tl.cond.Wait()
+	}
+	if tl.closed {
+		tl.mu.Unlock()
+		return nil, io.EOF
+	}
+	c := tl.nextConn
+	tl.nextConn = nil
+	tl.mu.Unlock()
+	tl.cond.Broadcast() // Signal might be sufficient; verify.
+
+	return c, nil
+}