allow redirect to webDefaultFile on bad http request

scripts/distro-files/config-full.toml

@@ -6,6 +6,7 @@ host = "mygreatserver.test.com"  # Lets you specify a user-friendly alias for he
 httpAddress = "localhost:8000"
 rpcAddress = "localhost:8001"
 webClient = "/path/to/webclient"
+webDefaultFile = "index.html" # path to optional default file within webClient directory to return.
 
 note = """
 You can put anything you want in here and have it available via /api/server/note.

server/server.go

@@ -48,6 +48,9 @@ type Config interface {
 	// Path to web client files
 	WebClient() string
 
+	// Path to default file within WebClient() path to return if HTTP request doesn't exist
+	WebDefaultFile() string
+
 	// Set timing in HTTP header
 	AllowTiming() bool
 

server/server_local.go

@@ -208,6 +208,10 @@ func (c *tomlConfig) WebClient() string {
 	return c.Server.WebClient
 }
 
+func (c *tomlConfig) WebDefaultFile() string {
+	return c.Server.WebDefaultFile
+}
+
 func (c *tomlConfig) AllowTiming() bool {
 	return c.Server.AllowTiming
 }
@@ -258,11 +262,12 @@ func WebServer() string {
 
 // ServerConfig holds ports, host name, and other properties of this dvid server.
 type ServerConfig struct {
-	Host        string
-	HTTPAddress string
-	RPCAddress  string
-	WebClient   string
-	Note        string
+	Host           string
+	HTTPAddress    string
+	RPCAddress     string
+	WebClient      string
+	WebDefaultFile string
+	Note           string
 
 	AllowTiming        bool   // If true, returns * for Timing-Allow-Origin in response headers.
 	StartWebhook       string // http address that should be called when server is started up.

server/web.go

@@ -1109,6 +1109,17 @@ func mainHandler(w http.ResponseWriter, r *http.Request) {
 		dvid.SendHTTP(w, r, path, data)
 	} else {
 		filename := filepath.Join(config.WebClient(), path)
+		redirectURL := config.WebDefaultFile()
+		if len(redirectURL) > 0 {
+			_, err := os.Stat(filename)
+			if os.IsNotExist(err) {
+				if redirectURL[0] != '/' {
+					redirectURL = "/" + redirectURL
+				}
+				http.Redirect(w, r, redirectURL, http.StatusPermanentRedirect)
+				return
+			}
+		}
 		dvid.Debugf("[%s] Serving from webclient directory: %s\n", r.Method, filename)
 		http.ServeFile(w, r, filename)
 	}