From 17148b7d2981d98309f7346435f5d3e77c586ab4 Mon Sep 17 00:00:00 2001
From: Grégoire Duchêne <gduchene@awhk.org>
Date: Sun, 5 Jun 2022 23:52:55 +0100
Subject: Add ListenPipe

Also, PipeListener.Close now returns syscall.EINVAL if the PipeListener
was closed already. This imitates the behavior of net.UnixListener.
---
 net.go      | 32 +++++++++++++-------------------
 net_test.go | 12 +++++++++---
 2 files changed, 22 insertions(+), 22 deletions(-)

diff --git a/net.go b/net.go
index b1331e9..bf2081b 100644
--- a/net.go
+++ b/net.go
@@ -4,7 +4,7 @@ import (
 	"context"
 	"net"
 	"strings"
-	"sync"
+	"sync/atomic"
 	"syscall"
 )
 
@@ -24,21 +24,20 @@ func Listen(addr string) (net.Listener, error) {
 // PipeListener is a net.Listener that works over a pipe. It provides
 // dialer functions that can be used in an HTTP client or gRPC options.
 //
-// Its zero value is safe to use. PipeListener must not be copied after
-// its first use.
+// PipeListener must not be copied after its first use.
 type PipeListener struct {
-	conns chan net.Conn
-	done  chan struct{}
-
-	closeOnce sync.Once
-	initOnce  sync.Once
+	closed int32
+	conns  chan net.Conn
+	done   chan struct{}
 }
 
 var _ net.Listener = &PipeListener{}
 
-func (p *PipeListener) Accept() (net.Conn, error) {
-	p.initOnce.Do(p.init)
+func ListenPipe() *PipeListener {
+	return &PipeListener{conns: make(chan net.Conn), done: make(chan struct{})}
+}
 
+func (p *PipeListener) Accept() (net.Conn, error) {
 	select {
 	case conn := <-p.conns:
 		return conn, nil
@@ -50,8 +49,10 @@ func (p *PipeListener) Accept() (net.Conn, error) {
 func (p *PipeListener) Addr() net.Addr { return pipeListenerAddr{} }
 
 func (p *PipeListener) Close() error {
-	p.initOnce.Do(p.init)
-	p.closeOnce.Do(func() { close(p.done) })
+	if !atomic.CompareAndSwapInt32(&p.closed, 0, 1) {
+		return syscall.EINVAL
+	}
+	close(p.done)
 	return nil
 }
 
@@ -60,8 +61,6 @@ func (p *PipeListener) Dial(_, _ string) (net.Conn, error) {
 }
 
 func (p *PipeListener) DialContext(ctx context.Context, _, _ string) (net.Conn, error) {
-	p.initOnce.Do(p.init)
-
 	s, c := net.Pipe()
 	select {
 	case p.conns <- s:
@@ -77,11 +76,6 @@ func (p *PipeListener) DialContextGRPC(ctx context.Context, _ string) (net.Conn,
 	return p.DialContext(ctx, "", "")
 }
 
-func (p *PipeListener) init() {
-	p.conns = make(chan net.Conn)
-	p.done = make(chan struct{})
-}
-
 type pipeListenerAddr struct{}
 
 func (pipeListenerAddr) Network() string { return "pipe" }
diff --git a/net_test.go b/net_test.go
index 505579e..3c01a15 100644
--- a/net_test.go
+++ b/net_test.go
@@ -12,7 +12,7 @@ func TestPipeListener(s *testing.T) {
 	t := core.T{T: s}
 
 	t.Run("Success", func(t *core.T) {
-		p := &core.PipeListener{}
+		p := core.ListenPipe()
 
 		t.Go(func() {
 			conn, err := p.Accept()
@@ -26,7 +26,7 @@ func TestPipeListener(s *testing.T) {
 	})
 
 	t.Run("WhenClosed", func(t *core.T) {
-		p := &core.PipeListener{}
+		p := core.ListenPipe()
 		p.Close()
 
 		conn, err := p.Accept()
@@ -38,8 +38,14 @@ func TestPipeListener(s *testing.T) {
 		t.AssertEqual(nil, conn)
 	})
 
+	t.Run("WhenClosedTwice", func(t *core.T) {
+		p := core.ListenPipe()
+		t.AssertEqual(nil, p.Close())
+		t.AssertEqual(syscall.EINVAL, p.Close())
+	})
+
 	t.Run("WhenContextCanceled", func(t *core.T) {
-		p := &core.PipeListener{}
+		p := core.ListenPipe()
 
 		ctx, cancel := context.WithCancel(context.Background())
 		cancel()
-- 
cgit v1.2.3-70-g09d2