[clug] browser connection question

David Deaves David.Deaves at dd.id.au
Mon Aug 17 06:04:04 UTC 2015

> On 17/08/15 10:49, David Deaves wrote:
> >
> >> First, I apologise for interrupting the less technical discussions going on...
> >>
> >> I start firefox and have nothing open. I am observing the activity on my privoxy log.
> >>
> >> I connect to DuckDuckGo and see that connection in the log.
> >> Without any query I close the window, then even clear cookies and the cache.
> >>
> >> About 3 minutes later I see a connection
> >> 	"CONNECT duckduckgo.com:443 HTTP/1.1" 200 257620
> >> The log shows activity without delay and the messages are timestamped anyway.
> >>
> >> What is causing this? I expected the closed tab to be done with this site.
> >
> > Your browser is being helpful.  Setting up a SSL connection is costly, and
> > HTTP/1.1 allows multiple requests over one connection.  So when you first
> > connected to duckduckgo it opened the SSL connection, but rather than close it
> > immediately only to have to open it again later, it keeps it open for future
> > use.  After a period of no use it prunes the no longer required connection.
> > The same is true of regular TCP connections, they are not as costly as SSL,
> > but caching connections is still of value.
> I understand caching, but do not see why a new connection is required when dropping
> the idle connection - after all the connection is cached and alive already.

There is no specific mapping of page displays to conections.  One requirement 
of re-using a connection is that any replies include a 'content-length:' field 
in the header.  If a requested item does not have a predictable length (for 
what ever reason) the then end of the response has to be indicated by the connection 
close.  Remember that the log entry happens a connection close, not when it is 
started.  Your log lines would also normally include a duration (in seconds) 
often the 2nd field, directly after the timestamp.  Subtract that from the 
timestamp and I expect you will find the connection was actually opened during 
the initial page display.

Dave !

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