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Re: svn commit: r1803140 - in /subversion/trunk/subversion: include/svn_delta.h libsvn_delta/svndiff.c tests/libsvn_delta/random-test.c

From: Evgeny Kotkov <evgeny.kotkov_at_visualsvn.com>
Date: Thu, 27 Jul 2017 18:50:08 +0300

Daniel Shahaf <d.s_at_daniel.shahaf.name> writes:

>> +static svn_error_t *
>> +svndiff_stream_write_fn(void *baton, const char *data, apr_size_t *len)
>> +{
>> + svndiff_stream_baton_t *b = baton;
>> +
>> + svn_stringbuf_appendbytes(b->window_buffer, data, *len);
>> +
>> + return SVN_NO_ERROR;
>> +}
>
> Isn't this using O(filesize in bytes) memory? File content streams are
> supposed to be O(1) memory.

[...]

>> +/** Return a readable generic stream which will produce svndiff-encoded
>> + * text delta from the delta stream @a txstream. @a svndiff_version and
>> + * @a compression_level are same as in svn_txdelta_to_svndiff3().
>> + *
>
> Why is a write handler implemented, when the docstring doesn't promise
> the returned stream would be writable?

Thanks for the review.

Could it be that you misinterpreted how the svn_txdelta_to_svndiff_stream()
function works?

Its implementation creates two streams, the writable push_stream, and the
readable pull_stream. The writable stream is used to accumulate svndiff-
encoded data in the shared buffer. The readable stream is returned to the
caller, and reads it data from the same shared buffer. The internal buffer
doesn't grow beyond the (header size + max window size in svndiff format),
which is O(1).

As a side note, this function _could be_ implemented with just a single
readable stream with an internal buffer that would be manually emitting
the header, encoding delta windows and copying them to buffer supplied by
the caller. However, I don't see why we'd want to have such implementation
in favor of the existing one, at this time.

Regards,
Evgeny Kotkov
Received on 2017-07-27 17:50:33 CEST

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