traceapp: take a base URL parameter in New

traceapp/app.go

@@ -17,6 +17,7 @@ import (
 	"encoding/base64"
 	"encoding/json"
 	"errors"
+	"fmt"
 	htmpl "html/template"
 	"io/ioutil"
 	"log"
@@ -45,17 +46,35 @@ type App struct {
 	tmplLock sync.Mutex
 	tmpls    map[string]*htmpl.Template
 
-	Log *log.Logger
+	Log     *log.Logger
+	baseURL *url.URL
 }
 
 // New creates a new application handler. If r is nil, a new router is
 // created.
-func New(r *Router) *App {
+//
+// The given base URL is the absolute base URL under which traceapp is being
+// served, e.g., "https://appdash.mysite.com" or "https://mysite.com/appdash".
+// The base URL must contain a scheme and host, or else an error will be
+// returned.
+func New(r *Router, base *url.URL) (*App, error) {
 	if r == nil {
 		r = NewRouter(nil)
 	}
 
-	app := &App{Router: r, Log: log.New(os.Stderr, "appdash: ", log.LstdFlags)}
+	// Validate the base URL and use the root path if none was specified.
+	if base.Scheme == "" || base.Host == "" {
+		return nil, fmt.Errorf("appdash: base URL must contain both scheme and port, found %q", base.String())
+	}
+	if base.Path == "" {
+		base.Path = "/"
+	}
+
+	app := &App{
+		Router:  r,
+		Log:     log.New(os.Stderr, "appdash: ", log.LstdFlags),
+		baseURL: base,
+	}
 
 	r.r.Get(RootRoute).Handler(handlerFunc(app.serveRoot))
 	r.r.Get(TraceRoute).Handler(handlerFunc(app.serveTrace))
@@ -71,7 +90,7 @@ func New(r *Router) *App {
 	// Static file serving.
 	r.r.Get(StaticRoute).Handler(http.StripPrefix("/static/", http.FileServer(static.Data)))
 
-	return app
+	return app, nil
 }
 
 // ServeHTTP implements http.Handler.

traceapp/tmpl.go

@@ -61,14 +61,10 @@ func (a *App) renderTemplate(w http.ResponseWriter, r *http.Request, name string
 
 	if data != nil {
 		// Set TemplateCommon values.
-		baseURL, err := a.URLTo(RootRoute)
-		if err != nil {
-			return err
-		}
 		reflect.ValueOf(data).Elem().FieldByName("TemplateCommon").Set(reflect.ValueOf(TemplateCommon{
 			CurrentRoute: mux.CurrentRoute(r).GetName(),
 			CurrentURI:   r.URL,
-			BaseURL:      baseURL,
+			BaseURL:      a.baseURL,
 		}))
 	}