From d281fb00e3388321557efcf5167babec09bf3203 Mon Sep 17 00:00:00 2001
From: Christian Schwarz <me@cschwarz.com>
Date: Sun, 30 Dec 2018 20:22:54 +0100
Subject: [PATCH] socketpair: directly export *net.UnixConn (and add test for
 that behavior)

---
 util/socketpair/socketpair.go      | 28 +++++++++-------------------
 util/socketpair/socketpair_test.go | 18 ++++++++++++++++++
 2 files changed, 27 insertions(+), 19 deletions(-)
 create mode 100644 util/socketpair/socketpair_test.go

diff --git a/util/socketpair/socketpair.go b/util/socketpair/socketpair.go
index 615c8f2..c1da9e3 100644
--- a/util/socketpair/socketpair.go
+++ b/util/socketpair/socketpair.go
@@ -1,42 +1,32 @@
 package socketpair
 
 import (
-	"golang.org/x/sys/unix"
 	"net"
 	"os"
+
+	"golang.org/x/sys/unix"
 )
-type fileConn struct {
-	net.Conn // net.FileConn
-	f *os.File
-}
 
-func (c fileConn) Close() error {
-	if err := c.Conn.Close(); err != nil {
-		return err
-	}
-	if err := c.f.Close(); err != nil {
-		return err
-	}
-	return nil
-}
-
-func SocketPair() (a, b net.Conn, err error) {
+func SocketPair() (a, b *net.UnixConn, err error) {
 	// don't use net.Pipe, as it doesn't implement things like lingering, which our code relies on
 	sockpair, err := unix.Socketpair(unix.AF_UNIX, unix.SOCK_STREAM, 0)
 	if err != nil {
 		return nil, nil, err
 	}
-	toConn := func(fd int) (net.Conn, error) {
+	toConn := func(fd int) (*net.UnixConn, error) {
 		f := os.NewFile(uintptr(fd), "fileconn")
 		if f == nil {
 			panic(fd)
 		}
 		c, err := net.FileConn(f)
+		f.Close() // net.FileConn uses dup under the hood
 		if err != nil {
-			f.Close()
 			return nil, err
 		}
-		return fileConn{Conn: c, f: f}, nil
+		// strictly, the following type assertion is an implementation detail
+		// however, will be caught by test TestSocketPairWorks
+		fileConnIsUnixConn := c.(*net.UnixConn)
+		return fileConnIsUnixConn, nil
 	}
 	if a, err = toConn(sockpair[0]); err != nil { // shadowing
 		return nil, nil, err
diff --git a/util/socketpair/socketpair_test.go b/util/socketpair/socketpair_test.go
new file mode 100644
index 0000000..95cbdc5
--- /dev/null
+++ b/util/socketpair/socketpair_test.go
@@ -0,0 +1,18 @@
+package socketpair
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+// This is test is mostly to verify that the assumption about
+// net.FileConn returning *net.UnixConn for AF_UNIX FDs works.
+func TestSocketPairWorks(t *testing.T) {
+	assert.NotPanics(t, func() {
+		a, b, err := SocketPair()
+		assert.NoError(t, err)
+		a.Close()
+		b.Close()
+	})
+}