Re: [PATCH 2/5] http: use `size_t` for byte position in fwrite_sha1_file

[Junio C Hamano <gitster@pobox.com>]

Simon Richter <Simon.Richter@hogyros.de> writes:

>> I agree that changing the type of posn from int to size_t is the
>> right move.
>
> It is a position in a file that is being read as binary data[1], so 
> off_t would be the best choice I think.

Interesting.

The function writes out eltsize * nmemb bytes (both of type
size_t), which means the product could theoretically exceed the
range of size_t.  However, posn is used in xwrite() to offset
into a contiguous in-core buffer starting at ptr:

        ssize_t retval = xwrite(freq->localfile,
                                (char *) ptr + posn,
                                size - posn);

Because we are indexing into an allocated in-core region, any
valid offset must fit within size_t.  If posn were to exceed
the bounds of size_t, the pointer arithmetic ptr + posn would
already be invalid.  As posn only runs up to the allocation
size of the region, it indeed should be measured in size_t, no?