Add reverse proxy endpoint.

It works by using the Host of the request. When it receives something in
the form of: `<node>.<session>.play-with-docker.com` it does a reverse
proxy http request to `node`, validating that the `node` actually belongs
to the `session`.
If the node has a prefix `ip` and continues with a valid IP address
where the dots where replaces by underscores (like `ip10_0_0_1`) then it
will remove the `ip` prefix and and replace the underscores by dots, and
assume it is an ip address.

api.go

@@ -59,6 +59,9 @@ func main() {
 
 	r.Handle("/sessions/{sessionId}/ws/", server)
 
+	// Reverse proxy
+	r.Host(`{node}.{session}.play-with-docker.com`).Handler(handlers.NewMultipleHostReverseProxy())
+
 	n := negroni.Classic()
 	n.UseHandler(r)
 

handlers/reverseproxy.go

@@ -0,0 +1,37 @@
+package handlers
+
+import (
+	"net"
+	"net/http"
+	"net/http/httputil"
+	"strings"
+
+	"github.com/gorilla/mux"
+)
+
+func NewMultipleHostReverseProxy() *httputil.ReverseProxy {
+	director := func(req *http.Request) {
+		v := mux.Vars(req)
+		node := v["node"]
+		if strings.HasPrefix(node, "ip") {
+			// Node is actually an ip, need to convert underscores by dots.
+			ip := strings.Replace(strings.TrimPrefix(node, "ip"), "_", ".", -1)
+
+			if net.ParseIP(ip) == nil {
+				// Not a valid IP, so treat this is a hostname.
+			} else {
+				node = ip
+			}
+		}
+
+		// Validate that the node actually exists in the network
+		// TODO:
+
+		// Only proxy http for now
+		req.URL.Scheme = "http"
+
+		req.URL.Host = node
+	}
+
+	return &httputil.ReverseProxy{Director: director}
+}

services/docker.go

@@ -52,6 +52,17 @@ func CreateNetwork(name string) error {
 
 	return nil
 }
+func ConnectNetwork(containerId, networkId string) error {
+	err := c.NetworkConnect(context.Background(), networkId, containerId, &network.EndpointSettings{})
+
+	if err != nil {
+		log.Printf("Connection container to network err [%s]\n", err)
+
+		return err
+	}
+
+	return nil
+}
 
 func DeleteNetwork(id string) error {
 	err := c.NetworkRemove(context.Background(), id)

services/session.go

@@ -109,6 +109,12 @@ func NewSession() (*Session, error) {
 		return nil, err
 	}
 
+	// Connect PWD daemon to the new network
+	if err := ConnectNetwork("pwd", s.Id); err != nil {
+		log.Println("ERROR NETWORKING")
+		return nil, err
+	}
+
 	// We store sessions as soon as we create one so we don't delete new sessions on an api restart
 	if err := saveSessionsToDisk(); err != nil {
 		return nil, err