rsync - Oct 2011 - handling of final partial block in rsync

Greetings,

I have been using the rsync C source as a guide for porting the rsync 
algorithm to Java. This has been successful, but there is one low level 
detail I am having some issues with.

Assuming the default block size of 700 bytes, when stepping through the 
file and generating checksums for each block it is very likely that 
there will be a partial block at the end of the file. Right now I am 
just generating a checksum for that block and including it in the 
signature. There will end up being a match for this block if the source 
file has the same partial block at the very end of the file, but it 
won't match anywhere else in the file. If I don't generate a checksum 
for the partial block then it will never match even when present at the 
end of the source file, which increases the size of the patch file.

I've read the thesis and the source again, and it looks like rsync is 
generating a signature on the final partial block. Would someone be able 
to confirm this, and is rsync handling this as I describe?

Many thanks in advance,

Peter

On Fri, Oct 21, 2011 at 7:28 PM, Peter A. Friend <pafriend at
octavian.org>wrote:
> I've read the thesis and the source again, and it looks like rsync is
> generating a signature on the final partial block. Would someone be able to
> confirm this, and is rsync handling this as I describe?
>
Search for "remainder" in generator.c and sender.c.  The checksum
summary
mentions the number of checksums to expect, and the remainder length if the
last sum in the sequence is not a full-size block.  The sender makes a note
of each sum's length when it is received using a simple heuristic (if this
is the last sum, the sum's length is the remainder instead of the block
length IIF the remainder is non-zero).  When checksums are compared, a sum
can only match if the sum's length is the same as the block we are trying to
find.

..wayne..
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