Issue #433: Ensure proxy.noroutestatus has three digits

go1.10 requires that http.WriteHeader() is called with
a valid status code.

Fixes #433

config/load.go

@@ -120,7 +120,7 @@ func load(cmdline, environ, envprefix []string, props *properties.Properties) (c
 	f.IntVar(&cfg.Proxy.MaxConn, "proxy.maxconn", defaultConfig.Proxy.MaxConn, "maximum number of cached connections")
 	f.StringVar(&cfg.Proxy.Strategy, "proxy.strategy", defaultConfig.Proxy.Strategy, "load balancing strategy")
 	f.StringVar(&cfg.Proxy.Matcher, "proxy.matcher", defaultConfig.Proxy.Matcher, "path matching algorithm")
-	f.IntVar(&cfg.Proxy.NoRouteStatus, "proxy.noroutestatus", defaultConfig.Proxy.NoRouteStatus, "status code for invalid route")
+	f.IntVar(&cfg.Proxy.NoRouteStatus, "proxy.noroutestatus", defaultConfig.Proxy.NoRouteStatus, "status code for invalid route. Must be three digits")
 	f.DurationVar(&cfg.Proxy.ShutdownWait, "proxy.shutdownwait", defaultConfig.Proxy.ShutdownWait, "time for graceful shutdown")
 	f.DurationVar(&cfg.Proxy.DialTimeout, "proxy.dialtimeout", defaultConfig.Proxy.DialTimeout, "connection timeout for backend connections")
 	f.DurationVar(&cfg.Proxy.ResponseHeaderTimeout, "proxy.responseheadertimeout", defaultConfig.Proxy.ResponseHeaderTimeout, "response header timeout")
@@ -252,6 +252,11 @@ func load(cmdline, environ, envprefix []string, props *properties.Properties) (c
 		return nil, fmt.Errorf("invalid ui.access: %s", cfg.UI.Access)
 	}
 
+	// go1.10 will not accept a non-three digit status code
+	if cfg.Proxy.NoRouteStatus < 100 || cfg.Proxy.NoRouteStatus > 999 {
+		return nil, fmt.Errorf("proxy.noroutestatus must be between 100 and 999")
+	}
+
 	// handle deprecations
 	deprecate := func(name, msg string) {
 		if f.IsSet(name) {

config/load_test.go

@@ -917,6 +917,18 @@ func TestLoad(t *testing.T) {
 			cfg:  func(cfg *Config) *Config { return nil },
 			err:  errors.New("cert source requires proto 'https' or 'tcp'"),
 		},
+		{
+			desc: "-proxy.noroutestatus too small",
+			args: []string{"-proxy.noroutestatus", "10"},
+			cfg:  func(cfg *Config) *Config { return nil },
+			err:  errors.New("proxy.noroutestatus must be between 100 and 999"),
+		},
+		{
+			desc: "-proxy.noroutestatus too big",
+			args: []string{"-proxy.noroutestatus", "1000"},
+			cfg:  func(cfg *Config) *Config { return nil },
+			err:  errors.New("proxy.noroutestatus must be between 100 and 999"),
+		},
 		{
 			args: []string{"-cfg"},
 			cfg:  func(cfg *Config) *Config { return nil },

proxy/http_proxy.go

@@ -72,7 +72,11 @@ func (p *HTTPProxy) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 
 	t := p.Lookup(r)
 	if t == nil {
-		w.WriteHeader(p.Config.NoRouteStatus)
+		status := p.Config.NoRouteStatus
+		if status < 100 || status > 999 {
+			status = http.StatusNotFound
+		}
+		w.WriteHeader(status)
 		html := noroute.GetHTML()
 		if html != "" {
 			io.WriteString(w, html)