Add darwin support

Updates golang/go#27613
Updates tailscale/tailscale#1347
Updates tailscale/tailscale#1348

go.mod

@@ -2,4 +2,4 @@ module inet.af/peercred
 
 go 1.14
 
-require golang.org/x/sys v0.0.0-20210216163648-f7da38b97c65
+require golang.org/x/sys v0.0.0-20210216224549-f992740a1bac

go.sum

@@ -1,2 +1,4 @@
 golang.org/x/sys v0.0.0-20210216163648-f7da38b97c65 h1:pTMjDVnP5eVRRlWO76rEWJ8JoC6Lf1CmyjPZXRiy2Sw=
 golang.org/x/sys v0.0.0-20210216163648-f7da38b97c65/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
+golang.org/x/sys v0.0.0-20210216224549-f992740a1bac h1:9glrpwtNjBYgRpb67AZJKHfzj1stG/8BL5H7In2oTC4=
+golang.org/x/sys v0.0.0-20210216224549-f992740a1bac/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=

peercred_darwin.go

@@ -0,0 +1,62 @@
+// Copyright (c) 2021 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 peercred
+
+import (
+	"fmt"
+	"net"
+	"strconv"
+
+	"golang.org/x/sys/unix"
+)
+
+func init() {
+	osGet = getLinux
+}
+
+func getLinux(c net.Conn) (*Creds, error) {
+	switch c := c.(type) {
+	case *net.UnixConn:
+		return getUnix(c)
+	case *net.TCPConn:
+		// TODO: use /proc tcp info for localhost connections like Windows?
+	}
+	return nil, ErrUnsupportedConnType
+}
+
+func getUnix(c *net.UnixConn) (*Creds, error) {
+	raw, err := c.SyscallConn()
+	if err != nil {
+		return nil, fmt.Errorf("SyscallConn: %w", err)
+	}
+
+	var cred *unix.Xucred
+	var pid int
+	cerr := raw.Control(func(fd uintptr) {
+		cred, err = unix.GetsockoptXucred(int(fd),
+			unix.SOL_LOCAL,
+			unix.LOCAL_PEERCRED)
+		if err != nil {
+			err = fmt.Errorf("unix.GetsockoptXucred: %w", err)
+			return
+		}
+		pid, err = unix.GetsockoptInt(int(fd),
+			unix.SOL_LOCAL,
+			unix.LOCAL_PEERPID)
+		if err != nil {
+			err = fmt.Errorf("unix.GetsockoptInt: %w", err)
+		}
+	})
+	if cerr != nil {
+		return nil, fmt.Errorf("raw.Control: %w", err)
+	}
+	if err != nil {
+		return nil, err
+	}
+	return &Creds{
+		pid: pid,
+		uid: strconv.FormatUint(uint64(cred.Uid), 10),
+	}, nil
+}

peercred_unix_test.go

@@ -3,7 +3,7 @@
 // license that can be found in the LICENSE file.
 
 // +build go1.15
-// +build linux
+// +build linux darwin
 
 package peercred // import "inet.af/peercred"
 
@@ -15,7 +15,7 @@ import (
 	"testing"
 )
 
-func TestUnix(t *testing.T) {
+func TestUnixSock(t *testing.T) {
 	d := t.TempDir()
 	path := filepath.Join(d, "foo.sock")
 	sock, err := net.Listen("unix", path)
@@ -24,14 +24,21 @@ func TestUnix(t *testing.T) {
 	}
 	defer sock.Close()
 
+	clientConnCh := make(chan net.Conn, 1)
 	go func() {
+		defer close(clientConnCh)
 		c, err := net.Dial("unix", path)
 		if err != nil {
 			t.Error(err)
 			return
 		}
-		c.Close()
+		clientConnCh <- c
 	}()
+	clientConn, ok := <-clientConnCh
+	if !ok {
+		return
+	}
+	defer clientConn.Close()
 
 	c, err := sock.Accept()
 	if err != nil {