Is it possible to merge multiple patches?

[Gabriel Menegatti]

Hello all,

I created this issue below on Github, but I'm also replicating the question here:

https://github.com/librsync/librsync/issues/148

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Considering that I generate a diff/patch for a specific file every time that it is modified and that I store all these diffs/patches individually and sequentially, would it be possible to merge all patches into a single (final) patch that covers all the changes on the file and only apply this final patch?

Is it possible to do that using librsync? If not, is there any conceptual limitation/challenge that would make it impossible to implement it?

If my interpretation is not wrong, the Xdelta lib has support for what I'm asking above. Just to make it clear, the intention here is not to compare the two, but just to clarify what I'm trying to achieve with librsync.

"The new merge command allows you to combine a sequence of deltas, to produce a single output that represents the net effect of the sequence. The command is reasonably efficient because it computes the result directly, without constructing any intermediate copies (and without access to the first-of-chain source).

Source: https://github.com/jmacd/xdelta/issues/36

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Thanks in advance.

Regards,
Gabriel

[Martin Pool]

It's not implemented today (afaik) but it could be done

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[Gabriel Menegatti]

Hi Martin,

Thanks for your reply.

Unfortunately, we don't think that our team would have the necessary competence to implement it correctly. We wouldn't know where to start.

Recently our team did find a memory leak on librsync and made a PR [1], but we don't think we are prepared for a big contribution like that.

That being said, please, is there anyone that could be interest in implementing this feature on librsync, having our company as the financial sponsor?

We would be happy to sponsor this development, that would also be public available to anyone to use, obviously.

[1] - https://github.com/librsync/librsync/pull/147

Thanks in advance.

Regards,

Gabriel.

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[Martin Pool]

I'm not able to take that on at the moment but it would be great if someone else can.

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[Gabriel Menegatti]

Hello Martin and others,

Apparently no one is interested in adding this feature/capability to librsync or available to implement it. :-(

Is any librsync experienced developer at least available/interested to give some broad overview/guidance on how this could be implemented? Maybe with some guidance my team would be able to try to implement it.

Thanks in advance.

Regards,

Gabriel.

[Martin Pool]

If you read the description of the Delta format I think you'll find it pretty straightforward. You just need to read through them in parallel and keep track of an offset to the positions originally used.