--- a/viewer.py	Sun Sep 27 22:35:27 2015 +0800
+++ b/viewer.py	Mon Sep 28 00:03:36 2015 +0800
@@ -2,6 +2,7 @@
 import colorsys
 import json
 import logging
+import os
 import re
 import sqlite3
 import subprocess
@@ -50,6 +51,11 @@
 
 class ResultsHandler(BaseHandler):
     def get(self, ext):
+        self.set_etag_header()
+        if self.check_etag_header():
+            self.set_status(304)
+            return
+
         if ext == 'tsv':
             self.results_tsv()
         elif ext == 'asc':
@@ -57,6 +63,12 @@
         elif ext == 'html':
             self.results_html()
 
+    def compute_etag(self):
+        dbmt = os.stat(DBPATH).st_mtime
+        changelog = os.path.join(TESTHGREPO, '.hg', 'store', '00changelog.i')
+        repomt = os.stat(changelog).st_mtime
+        return 'W/"{},{}"'.format(dbmt, repomt)
+
     def getchangesets(self):
         rev = self.get_argument('rev', 'tip')
         revcount = 120