net: prevent spurious TCP connection setup notification on darwin

On the latest darwin kernels, kevent in runtime-integrated network
poller sometimes reports SYN-SENT state sockets as ESTABLISHED ones,
though it's still unclear what's the root cause.

This change prevents such spurious notifications by additional connect
system calls.

Fixes #14548.

Change-Id: Ie29788e38ca735ca77259befeba3229d6a30ac52
Reviewed-on: https://go-review.googlesource.com/20468
Run-TryBot: Mikio Hara <mikioh.mikioh@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/net/error_unix_test.go

@@ -6,7 +6,10 @@
 
 package net
 
-import "syscall"
+import (
+	"os"
+	"syscall"
+)
 
 var (
 	errTimedout       = syscall.ETIMEDOUT
@@ -19,3 +22,13 @@ func isPlatformError(err error) bool {
 	_, ok := err.(syscall.Errno)
 	return ok
 }
+
+func samePlatformError(err, want error) bool {
+	if op, ok := err.(*OpError); ok {
+		err = op.Err
+	}
+	if sys, ok := err.(*os.SyscallError); ok {
+		err = sys.Err
+	}
+	return err == want
+}

src/net/fd_unix.go

@@ -139,7 +139,16 @@ func (fd *netFD) connect(la, ra syscall.Sockaddr, deadline time.Time, cancel <-c
 		switch err := syscall.Errno(nerr); err {
 		case syscall.EINPROGRESS, syscall.EALREADY, syscall.EINTR:
 		case syscall.Errno(0), syscall.EISCONN:
-			return nil
+			if runtime.GOOS != "darwin" {
+				return nil
+			}
+			// See golang.org/issue/14548.
+			// On Darwin, multiple connect system calls on
+			// a non-blocking socket never harm SO_ERROR.
+			switch err := connectFunc(fd.sysfd, ra); err {
+			case nil, syscall.EISCONN:
+				return nil
+			}
 		default:
 			return os.NewSyscallError("getsockopt", err)
 		}

src/net/tcpsock_unix_test.go

@@ -0,0 +1,79 @@
+// Copyright 2016 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.
+
+// +build darwin
+
+package net
+
+import (
+	"runtime"
+	"sync"
+	"syscall"
+	"testing"
+	"time"
+)
+
+// See golang.org/issue/14548.
+func TestTCPSupriousConnSetupCompletion(t *testing.T) {
+	if testing.Short() {
+		t.Skip("skipping in short mode")
+	}
+
+	ln, err := newLocalListener("tcp")
+	if err != nil {
+		t.Fatal(err)
+	}
+	var wg sync.WaitGroup
+	wg.Add(1)
+	go func(ln Listener) {
+		defer wg.Done()
+		for {
+			c, err := ln.Accept()
+			if err != nil {
+				return
+			}
+			wg.Add(1)
+			go func(c Conn) {
+				var b [1]byte
+				c.Read(b[:])
+				c.Close()
+				wg.Done()
+			}(c)
+		}
+	}(ln)
+
+	attempts := int(1e4) // larger is better
+	wg.Add(attempts)
+	throttle := make(chan struct{}, runtime.GOMAXPROCS(-1)*2)
+	for i := 0; i < attempts; i++ {
+		throttle <- struct{}{}
+		go func(i int) {
+			defer func() {
+				<-throttle
+				wg.Done()
+			}()
+			d := Dialer{Timeout: 50 * time.Millisecond}
+			c, err := d.Dial(ln.Addr().Network(), ln.Addr().String())
+			if err != nil {
+				if perr := parseDialError(err); perr != nil {
+					t.Errorf("#%d: %v", i, err)
+				}
+				return
+			}
+			var b [1]byte
+			if _, err := c.Write(b[:]); err != nil {
+				if perr := parseWriteError(err); perr != nil {
+					t.Errorf("#%d: %v", i, err)
+				}
+				if samePlatformError(err, syscall.ENOTCONN) {
+					t.Errorf("#%d: %v", i, err)
+				}
+			}
+			c.Close()
+		}(i)
+	}
+
+	ln.Close()
+	wg.Wait()
+}