[MERGE] Give nicer errors for some write operations on read-only transports.

[Robert Collins]

On Mon, 2007-09-03 at 22:39 +0100, James Westby wrote:
> On (03/09/07 17:24), Robert Collins wrote:
> > This is the wrong approach to the problem. On local disk we will encounter 
> > read only problems from time to time. LBYL should be avoided, instead 
> > handle the problem when you fail to write more accurately.
> 
> The problem I have with this is that the message that I was displaying
> was trying to hint to people that if they were on http then they could
> use sftp or similar to approach the problem.
> 
> If you then involve lack of write permission on local transport then
> changing transport probably wont help.
> 
> This means that there may need to be a different approach, as you need
> to differentiate write problems because the transport is unsuitable, and
> to problems for other reasons.
> 
> As I understand it your aversion to "look before you leap" was for
> performance issues, but I don't think that would make a big enough
> impact here to rule out a change that will hopefully help confused new
> users find out what they need to do to solve their problem.

If you consider webdav where 'is_readonly' requires a round trip to
establish writability, you're adding (for me) 300ms to write operations
that succeed - which is the common case.

> I will look in to catching and throwing exceptions, but I don't want to
> get to a situation where we attempt to suggest users consider the
> transport they are using when they try and push to a read-only
> directory. This will depend on the exceptions that are currently thrown,
> and it is not very consistent currently.

This paragraph suggests a route to fix the problem :)

Rob
-- 
GPG key available at: <http://www.robertcollins.net/keys.txt>.
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