Add stub/wrapper for reuseport.Listen on Windows platforms (#638)

* Create Windows stub for reuseport.Listen

reuseport/reuseport.go

@@ -1,4 +1,4 @@
-// +build linux darwin dragonfly freebsd netbsd openbsd rumprun
+// +build !windows
 
 // Package reuseport provides TCP net.Listener with SO_REUSEPORT support.
 //
@@ -9,23 +9,12 @@
 package reuseport
 
 import (
-	"fmt"
 	"net"
 	"strings"
 
 	"github.com/valyala/tcplisten"
 )
 
-// ErrNoReusePort is returned if the OS doesn't support SO_REUSEPORT.
-type ErrNoReusePort struct {
-	err error
-}
-
-// Error implements error interface.
-func (e *ErrNoReusePort) Error() string {
-	return fmt.Sprintf("The OS doesn't support SO_REUSEPORT: %s", e.err)
-}
-
 // Listen returns TCP listener with SO_REUSEPORT option set.
 //
 // The returned listener tries enabling the following TCP options, which usually

reuseport/reuseport_error.go

@@ -0,0 +1,15 @@
+package reuseport
+
+import (
+	"fmt"
+)
+
+// ErrNoReusePort is returned if the OS doesn't support SO_REUSEPORT.
+type ErrNoReusePort struct {
+	err error
+}
+
+// Error implements error interface.
+func (e *ErrNoReusePort) Error() string {
+	return fmt.Sprintf("The OS doesn't support SO_REUSEPORT: %s", e.err)
+}

reuseport/reuseport_test.go

@@ -1,3 +1,5 @@
+// +build !windows
+
 package reuseport
 
 import (

reuseport/reuseport_windows.go

@@ -0,0 +1,11 @@
+package reuseport
+
+import (
+	"fmt"
+	"net"
+)
+
+// Listen always returns ErrNoReusePort on Windows
+func Listen(network, addr string) (net.Listener, error) {
+	return nil, &ErrNoReusePort{fmt.Errorf("Not supported on Windows")}
+}

reuseport/reuseport_windows_test.go

@@ -0,0 +1,18 @@
+// +build windows
+
+package reuseport
+
+import (
+	"testing"
+)
+
+func TestListen(t *testing.T) {
+  _, err := Listen("tcp6", "[::1]:10082")
+  if err == nil {
+    t.Fatalf("unexpected non-error creating listener")
+  }
+
+  if _, errnoreuseport := err.(*ErrNoReusePort); !errnoreuseport {
+    t.Fatalf("unexpected error creating listener: %s", err)
+  }
+}