proxy: add exposePort and unexposePort stubs

This patch removes `proxyForever` and adds `sendError` and `sendOK` for
signalling to the parent process. The main function now sequences these
functions and calls stub functions `exposePort` and `unexposePort` which
will be hooked up in a later patch.

Signed-off-by: David Scott <dave.scott@docker.com>

alpine/packages/proxy/main.go

@@ -2,6 +2,7 @@ package main
 
 import (
 	"log"
+	"net"
 	"os"
 	"pkg/proxy"
 )
@@ -9,10 +10,27 @@ import (
 func main() {
 	host, container := parseHostContainerAddrs()
 
-	err := proxyForever(proxy.NewProxy(host, container))
-
+	err := exposePort(host)
 	if err != nil {
-		os.Exit(0)
+		sendError(err)
 	}
-	os.Exit(1)
+	p, err := proxy.NewProxy(host, container)
+	if err != nil {
+		unexposePort(host)
+		sendError(err)
+	}
+	go handleStopSignals(p)
+	sendOK()
+	p.Run()
+	unexposePort(host)
+	os.Exit(0)
+}
+
+func exposePort(host net.Addr) error {
+	log.Printf("exposePort %#v\n", host)
+	return nil
+}
+
+func unexposePort(host net.Addr) {
+	log.Printf("unexposePort %#v\n", host)
 }

alpine/packages/proxy/proxy.go

@@ -12,22 +12,20 @@ import (
 	"pkg/proxy"
 )
 
-// proxyForever signals the parent success/failure and runs the proxy forever
-func proxyForever(p proxy.Proxy, err error) error {
+// sendError signals the error to the parent and quits the process.
+func sendError(err error) {
 	f := os.NewFile(3, "signal-parent")
 
-	if err != nil {
-		fmt.Fprintf(f, "1\n%s", err)
-		f.Close()
-		return err
-	}
-	go handleStopSignals(p)
+	fmt.Fprintf(f, "1\n%s", err)
+	f.Close()
+	os.Exit(1)
+}
+
+// sendOK signals the parent that the forward is running.
+func sendOK() {
+	f := os.NewFile(3, "signal-parent")
 	fmt.Fprint(f, "0\n")
 	f.Close()
-
-	// Run will block until the proxy stops
-	p.Run()
-	return nil
 }
 
 // From docker/libnetwork/portmapper/proxy.go: