admin: Fix redirections when using baseurl

admin/main.go

@@ -19,18 +19,40 @@ import (
 var PKIDir string
 var StaticDir string
 
+type ResponseWriterPrefix struct {
+	real http.ResponseWriter
+	prefix string
+}
+
+func (r ResponseWriterPrefix) Header() http.Header {
+	return r.real.Header()
+}
+
+func (r ResponseWriterPrefix) WriteHeader(s int) {
+	if v, exists := r.real.Header()["Location"]; exists {
+		r.real.Header().Set("Location", r.prefix + v[0])
+	}
+	r.real.WriteHeader(s)
+}
+
+func (r ResponseWriterPrefix) Write(z []byte) (int, error) {
+	return r.real.Write(z)
+}
+
 func StripPrefix(prefix string, h http.Handler) http.Handler {
 	if prefix == "" {
 		return h
 	}
 	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
-		if p := strings.TrimPrefix(r.URL.Path, prefix); len(p) < len(r.URL.Path) {
+		if prefix != "/" && r.URL.Path == "/" {
+			http.Redirect(w, r, prefix + "/", http.StatusFound)
+		} else if p := strings.TrimPrefix(r.URL.Path, prefix); len(p) < len(r.URL.Path) {
 			r2 := new(http.Request)
 			*r2 = *r
 			r2.URL = new(url.URL)
 			*r2.URL = *r.URL
 			r2.URL.Path = p
-			h.ServeHTTP(w, r2)
+			h.ServeHTTP(ResponseWriterPrefix{w, prefix}, r2)
 		} else {
 			h.ServeHTTP(w, r)
 		}