portmapper: don't compile linux-only code on Windows

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

libnetwork/portmapper/proxy_linux.go

@@ -1,12 +1,18 @@
 package portmapper
 
 import (
+	"fmt"
+	"io/ioutil"
 	"net"
+	"os"
 	"os/exec"
 	"strconv"
 	"syscall"
+	"time"
 )
 
+var userlandProxyCommandName = "docker-proxy"
+
 func newProxyCommand(proto string, hostIP net.IP, hostPort int, containerIP net.IP, containerPort int, proxyPath string) (userlandProxy, error) {
 	path := proxyPath
 	if proxyPath == "" {
@@ -36,3 +42,57 @@ func newProxyCommand(proto string, hostIP net.IP, hostPort int, containerIP net.
 		},
 	}, nil
 }
+
+// proxyCommand wraps an exec.Cmd to run the userland TCP and UDP
+// proxies as separate processes.
+type proxyCommand struct {
+	cmd *exec.Cmd
+}
+
+func (p *proxyCommand) Start() error {
+	r, w, err := os.Pipe()
+	if err != nil {
+		return fmt.Errorf("proxy unable to open os.Pipe %s", err)
+	}
+	defer r.Close()
+	p.cmd.ExtraFiles = []*os.File{w}
+	if err := p.cmd.Start(); err != nil {
+		return err
+	}
+	w.Close()
+
+	errchan := make(chan error, 1)
+	go func() {
+		buf := make([]byte, 2)
+		r.Read(buf)
+
+		if string(buf) != "0\n" {
+			errStr, err := ioutil.ReadAll(r)
+			if err != nil {
+				errchan <- fmt.Errorf("Error reading exit status from userland proxy: %v", err)
+				return
+			}
+
+			errchan <- fmt.Errorf("Error starting userland proxy: %s", errStr)
+			return
+		}
+		errchan <- nil
+	}()
+
+	select {
+	case err := <-errchan:
+		return err
+	case <-time.After(16 * time.Second):
+		return fmt.Errorf("Timed out proxy starting the userland proxy")
+	}
+}
+
+func (p *proxyCommand) Stop() error {
+	if p.cmd.Process != nil {
+		if err := p.cmd.Process.Signal(os.Interrupt); err != nil {
+			return err
+		}
+		return p.cmd.Wait()
+	}
+	return nil
+}