Transport connection caches must go.

[Martin Pool]

On 30/05/2006, at 8:22 AM, Robert Collins wrote:

> This is a promising approach. To sum up, we have the following
> constraints:
>  * Connections to multiple resources on different urls should only
> initiate new connections, prompt for auth etc, if actually required -
> i.e.  if they are not on the same host.
>  * Two common operations that may lead us to connect to the same host
> twice with no a-priori knowledge we are doing so are 'bzr branch A B',
> and 'bzr checkout A B'. In the code for these operations we are  
> opening
> a new bzrdir at a URL and there is currently no way to provide the
> transport in use by the bzrdir for A, to the call to open B, *as a
> possible transport to clone/chdir from*.
> requirements
>  * We do not want a global cache: separate code paths, i.e. different
> connections initiated by a webserver should not interact with each
> other. (In this example, the credentials for the transport would be
> coming from the end user, so having two requests share a transport  
> would
> be a security hole). Tests also have had nasty interactions with  
> cached
> transports.
>  * We want something that is easy to use.
>
> So heres a concrete proposal:
>
> We add to the transport api a new clone_url() method. This is called
> clone_url because like clone() it makes a new transport, but unlike
> clone it requires a url, not a relative reference. We could name it
> chdir or something, but we should rename clone at that point too.  
> (Also,
> clone() is well known in some object patterns as giving a new instance
> of the same type, so clone is IMO still appropriate). This new method
> will raise an error like 'RequiresNewTransport' when the url its being
> asked to clone to is one it cannot reach by any pattern of clone()
> calls.
>
> We add to get_transport a keyword parameter 'reuse_connections' which
> will accept an iterable that yields transports. These connections will
> have clone_url() called on them preferentially. The first to return a
> Transport will short circuit the whole call. We probably need to be
> careful to ensure that local transports dont inappropriately accept
> things - probably having LocalTransport raise RequiresNewTransport
> unconditionally is the right thing to do.
>
> Now, to reuse a connection in our examples above, its just:
> b_bzrdir =
> bzrlib.bzrdir.BzrDir.open_containing_with_transport(get_transport 
> (b_url,
> reuse_connections=[a_bzrdir.root_transport]))
>
>
> Thoughts ?

I like it.

-- 
Martin