[PATCH v2 3/7] t1051: introduce a smudge filter test for extremely large files

From: Matt Cooper <vtbassmatt@gmail.com>

The filter system allows for alterations to file contents when they're added to the database or workdir. ("Smudge" when moving to the workdir; "clean" when moving to the database.) This is used natively to handle CRLF to LF conversions. It's also employed by Git-LFS to replace large files from the workdir with small tracking files in the repo and vice versa.

Git pulls the entire smudged file into memory. While this is inefficient, there's a more insidious problem on some platforms due to inconsistency between using unsigned long and size_t for the same type of data (size of a file in bytes). On most 64-bit platforms, unsigned long is 64 bits, and size_t is typedef'd to unsigned long. On Windows, however, unsigned long is only 32 bits (and therefore on 64-bit Windows, size_t is typedef'd to unsigned long long in order to be 64 bits).

Practically speaking, this means 64-bit Windows users of Git-LFS can't handle files larger than 2^32 bytes. Other 64-bit platforms don't suffer this limitation.

This commit introduces a test exposing the issue; future commits make it pass. The test simulates the way Git-LFS works by having a tiny file checked into the repository and expanding it to a huge file on checkout.

Helped-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Matt Cooper <vtbassmatt@gmail.com>
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
---
 t/t1051-large-conversion.sh | 13 +++++++++++++
 1 file changed, 13 insertions(+)