Parse X-Forwarded-For header if provided

Parse the X-Forwarded-For header if it exists in the connection.  This
will allow bans to work if the server is sitting behind an Nginx
reverse proxy (that has been configured to add the header).

Also added a safe-guard to disallow bans for localhost so you cannot
accidentally ban everybody from connecting if the server is behind a
reverse proxy.

This should resolve #49

chatclient.go

@@ -3,7 +3,6 @@ package main
 import (
 	"fmt"
 	"html"
-	"net"
 	"strings"
 	"unicode"
 
@@ -150,11 +149,7 @@ func (cl *Client) Unmod() {
 }
 
 func (cl *Client) Host() string {
-	host, _, err := net.SplitHostPort(cl.conn.RemoteAddr().String())
-	if err != nil {
-		host = "err"
-	}
-	return host
+	return cl.conn.Host()
 }
 
 var dumbSpaces = []string{

connection.go

@@ -1,6 +1,7 @@
 package main
 
 import (
+	"net"
 	"sync"
 
 	"github.com/gorilla/websocket"
@@ -8,7 +9,8 @@ import (
 
 type chatConnection struct {
 	*websocket.Conn
-	mutex sync.Mutex
+	mutex        sync.Mutex
+	forwardedFor string
 }
 
 func (cc *chatConnection) ReadData(data interface{}) error {
@@ -24,3 +26,15 @@ func (cc *chatConnection) WriteData(data interface{}) error {
 
 	return cc.WriteJSON(data)
 }
+
+func (cc *chatConnection) Host() string {
+	if len(cc.forwardedFor) > 0 {
+		return cc.forwardedFor
+	}
+
+	host, _, err := net.SplitHostPort(cc.RemoteAddr().String())
+	if err != nil {
+		return cc.RemoteAddr().String()
+	}
+	return host
+}

handlers.go

@@ -96,7 +96,10 @@ func wsHandler(w http.ResponseWriter, r *http.Request) {
 	}
 
 	chatConn := &chatConnection{
-		Conn: conn,
+		Conn:         conn,
+		// If the server is behind a reverse proxy (eg, Nginx), look
+		// for this header to get the real IP address of the client.
+		forwardedFor: r.Header.Get("X-Forwarded-For"),
 	}
 
 	go func() {

settings.go

@@ -107,6 +107,10 @@ func (s *Settings) Save() error {
 }
 
 func (s *Settings) AddBan(host string, names []string) error {
+	if host == "127.0.0.1" {
+		return fmt.Errorf("Cannot add a ban for localhost.")
+	}
+
 	b := BanInfo{
 		Names: names,
 		IP:    host,