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Re: Change #6: Move textdeltas to the "other side" of the editor.

From: Greg Stein <gstein_at_lyra.org>
Date: 2001-01-20 10:27:10 CET

On Fri, Jan 19, 2001 at 08:38:19PM -0600, Ben Collins-Sussman wrote:
> Specifically:
> - remove the editor's apply_txdelta() routine
> - create two new routines:
> apply_delta (filebaton, [src_stream], target_stream)
> set_file_contents (filebaton, [src_stream], delta,
> enum delta_type)


                 set_file_contents (filebaton, [src_stream], target_stream)
                 apply_delta (filebaton, [src_stream], delta,
                                    enum delta_type)

                 apply_delta() sends svndiff deltas.

Actually, it sends a delta in the format described by DELTA_TYPE. At the
moment, that can only be SVNDIFF. In the future, we might have UNIDIFF,
GNUDIFF, or whatever.

> set_file_contents() can send plain text or other
> types.

Nope. set_file_contents() *only* passes "plain text". (actually, it might
not be "text" ... could be a binary)

> It becomes the obligation of the editor implementation to
> implement at least one of these two routines; if one
> routine is NULL, the driver must use the other.

The editor should implement at least one, preferably both. The driver will
choose its "preferred" form; if the editor doesn't implement it, then the
driver (hopefully) will defer to the other. This is a simple negotiation
between the driver/editor on what can be used, and which is preferred.

> Rationale:
> It's too restrictive to force every editor implementation to accept
> and deal with small svndiff windows. For example: Greg Stein wants
> to send plain text while debugging his commit-editor and network
> layer. It's best to allow the RA layer to make it's own choice
> about how to break up the two streams most efficiently.

We also have the situation of ra_xml: the output form is defined by command
line switches. The interpretation of those switches is performed by ra_xml.
The new form allows ra_xml to output SVNDIFF or plain text or whatever it
likes. In the old scheme, the WC would only pass deltas -- the RA layer had
no choice for what it would spit out, and in which form.

> The reason [src_stream] is optional is that it may be NULL; this
> presumably means that the editor already has access to the src
> stream.

This means the driver doesn't have it. Hopefully, the editor *does*. If you
call apply_delta() with a NULL source and the editor doesn't have it, then
you're going to get an error.


Greg Stein, http://www.lyra.org/
Received on Sat Oct 21 14:36:19 2006

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