Add new configuration directive proxyURL.

The strategy of computing the base URL from the request doesn't
necessarily work if we're behind a reverse proxy.  proxyURL
can be set in cases where our guess is incorrect.

Thanks to Dianne Skoll.

README

@@ -47,15 +47,19 @@ The server may be configured in the JSON file `data/config.json`.  This
 file may look as follows:
 
     {
-        "canonicalHost": "galene.example.org",
         "admin":[{"username":"root","password":"secret"}]
+        "canonicalHost": "galene.example.org",
     }
 
 The fields are as follows:
 
-- `canonicalHost`: the canonical name of the host running the server;
+- `proxyURL`: if running behind a reverse proxy, this specifies the
+  address of the proxy.
 - `admin` defines the users allowed to look at the `/stats.html` file; it
   has the same syntax as user definitions in groups (see below).
+- `canonicalHost`: the canonical name of the host running the server; this
+  will cause clients to be redirected if they use a different hostname to
+  access the server.
 
 
 # Group definitions

group/group.go

@@ -857,6 +857,7 @@ type Configuration struct {
 	fileSize int64     `json:"-"`
 
 	CanonicalHost string          `json:"canonicalHost"`
+	ProxyURL      string          `json:"proxyURL"`
 	Admin         []ClientPattern `json:"admin"`
 }
 

webserver/webserver.go

@@ -332,7 +332,18 @@ func groupHandler(w http.ResponseWriter, r *http.Request) {
 	serveFile(w, r, filepath.Join(StaticRoot, "galene.html"))
 }
 
-func groupBase(r *http.Request) string {
+func groupBase(r *http.Request) (string, error) {
+	conf, err := group.GetConfiguration()
+	if err != nil {
+		return "", nil
+	}
+	if conf.ProxyURL != "" {
+		u, err := url.Parse(conf.ProxyURL)
+		if err != nil {
+			return "", err
+		}
+		return u.JoinPath("/group/").String(), nil
+	}
 	scheme := "https"
 	if r.TLS == nil {
 		scheme = "http"
@@ -342,7 +353,7 @@ func groupBase(r *http.Request) string {
 		Host:   r.Host,
 		Path:   "/group/",
 	}
-	return base.String()
+	return base.String(), nil
 }
 
 func groupStatusHandler(w http.ResponseWriter, r *http.Request) {
@@ -364,7 +375,13 @@ func groupStatusHandler(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	d := g.Status(false, groupBase(r))
+	base, err := groupBase(r)
+	if err != nil {
+		http.Error(w, "Internal server error",
+			http.StatusInternalServerError)
+		return
+	}
+	d := g.Status(false, base)
 	w.Header().Set("content-type", "application/json")
 	w.Header().Set("cache-control", "no-cache")
 
@@ -377,6 +394,13 @@ func groupStatusHandler(w http.ResponseWriter, r *http.Request) {
 }
 
 func publicHandler(w http.ResponseWriter, r *http.Request) {
+	base, err := groupBase(r)
+	if err != nil {
+		log.Println("couldn't determine group base: %v", err)
+		http.Error(w, "Internal server error",
+			http.StatusInternalServerError)
+		return
+	}
 	w.Header().Set("content-type", "application/json")
 	w.Header().Set("cache-control", "no-cache")
 
@@ -384,7 +408,7 @@ func publicHandler(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	g := group.GetPublic(groupBase(r))
+	g := group.GetPublic(base)
 	e := json.NewEncoder(w)
 	e.Encode(g)
 }