Comment 1 for bug 202243

HI !
For what it's worth, Specto actually already uses this, I *think*. In the 0.2.2 series, if you look at the code in watch_web_static.py, you can see in lines 109-121:

        if (self.cached == 1) or (os.path.exists(self.cacheFullPath_)):
            self.cached = 1
            f = file(self.cacheFullPath_, "r")# Load up the cached version
            self.infoB_ = HTTPMessage(f)
            if self.infoB_.has_key('last-modified'):
                request.add_header("If-Modified-Since", self.infoB_['last-modified'])
            if self.infoB_.has_key('ETag'):
                request.add_header("If-None-Match", self.infoB_['ETag'])
        try:
            response = urllib2.urlopen(request)
        except (urllib2.URLError, BadStatusLine), e:
            self.error = True
            self.specto.logger.log(_("Watch: \"%s\" has error: ") % self.name + str(e), "error", self.__class__)

However,
- the code might not be elegant
- the code/logic might be wrong (after all, I took a long time doing it and I'm not sure I did it properly)

I don't know if that is conforming to your suggestions, or if you meant that
- some piece is missing?
- something is not working properly?

Also, I think the etag headers may not work properly with websites that use advertising/dynamic content, so, if I remember correctly my own code, the "error margin" (difference percentage based on file sizes) would override it.