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| author | Roberto Tyley <roberto.tyley@guardian.co.uk> | 2011-08-07 19:46:13 +0100 |
|---|---|---|
| committer | Junio C Hamano <gitster@pobox.com> | 2011-08-11 13:02:47 -0700 |
| commit | 7f684a2aff636f44a5063c05cf84c0db0460ae1a (patch) | |
| tree | 3d7b763261b6aeb1e01cbb2b4a8bdc144c9f029a /t/t1013 | |
| parent | e9e0643fe64b613b6596b79b59df8ff10746f1a1 (diff) | |
| download | git-7f684a2aff636f44a5063c05cf84c0db0460ae1a.tar.gz git-7f684a2aff636f44a5063c05cf84c0db0460ae1a.tar.xz | |
Tolerate zlib deflation with window size < 32Kb
Git currently reports loose objects as 'corrupt' if they've been
deflated using a window size less than 32Kb, because the
experimental_loose_object() function doesn't recognise the header
byte as a zlib header. This patch makes the function tolerant of
all valid window sizes (15-bit to 8-bit) - but doesn't sacrifice
it's accuracy in distingushing the standard loose-object format
from the experimental (now abandoned) format.
On memory constrained systems zlib may use a much smaller window
size - working on Agit, I found that Android uses a 4KB window;
giving a header byte of 0x48, not 0x78. Consequently all loose
objects generated appear 'corrupt', which is why Agit is a read-only
Git client at this time - I don't want my client to generate Git
repos that other clients treat as broken :(
This patch makes Git tolerant of different deflate settings - it
might appear that it changes experimental_loose_object() to the point
where it could incorrectly identify the experimental format as the
standard one, but the two criteria (bitmask & checksum) can only
give a false result for an experimental object where both of the
following are true:
1) object size is exactly 8 bytes when uncompressed (bitmask)
2) [single-byte in-pack git type&size header] * 256
+ [1st byte of the following zlib header] % 31 = 0 (checksum)
As it happens, for all possible combinations of valid object type
(1-4) and window bits (0-7), the only time when the checksum will be
divisible by 31 is for 0x1838 - ie object type *1*, a Commit - which,
due the fields all Commit objects must contain, could never be as
small as 8 bytes in size.
Given this, the combination of the two criteria (bitmask & checksum)
always correctly determines the buffer format, and is more tolerant
than the previous version.
The alternative to this patch is simply removing support for the
experimental format, which I am also totally cool with.
References:
Android uses a 4KB window for deflation:
http://android.git.kernel.org/?p=platform/libcore.git;a=blob;f=luni/src/main/native/java_util_zip_Deflater.cpp;h=c0b2feff196e63a7b85d97cf9ae5bb2583409c28;hb=refs/heads/gingerbread#l53
Code snippet searching for false positives with the zlib checksum:
https://gist.github.com/1118177
Signed-off-by: Roberto Tyley <roberto.tyley@guardian.co.uk>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Diffstat (limited to 't/t1013')
17 files changed, 3 insertions, 0 deletions
diff --git a/t/t1013/objects/14/9cedb5c46929d18e0f118e9fa31927487af3b6 b/t/t1013/objects/14/9cedb5c46929d18e0f118e9fa31927487af3b6 Binary files differnew file mode 100644 index 000000000..472fd1458 --- /dev/null +++ b/t/t1013/objects/14/9cedb5c46929d18e0f118e9fa31927487af3b6 diff --git a/t/t1013/objects/16/56f9233d999f61ef23ef390b9c71d75399f435 b/t/t1013/objects/16/56f9233d999f61ef23ef390b9c71d75399f435 Binary files differnew file mode 100644 index 000000000..c379d74ae --- /dev/null +++ b/t/t1013/objects/16/56f9233d999f61ef23ef390b9c71d75399f435 diff --git a/t/t1013/objects/1e/72a6b2c4a577ab0338860fa9fe87f761fc9bbd b/t/t1013/objects/1e/72a6b2c4a577ab0338860fa9fe87f761fc9bbd Binary files differnew file mode 100644 index 000000000..93706305b --- /dev/null +++ b/t/t1013/objects/1e/72a6b2c4a577ab0338860fa9fe87f761fc9bbd diff --git a/t/t1013/objects/25/7cc5642cb1a054f08cc83f2d943e56fd3ebe99 b/t/t1013/objects/25/7cc5642cb1a054f08cc83f2d943e56fd3ebe99 Binary files differnew file mode 100644 index 000000000..bdcf704c9 --- /dev/null +++ b/t/t1013/objects/25/7cc5642cb1a054f08cc83f2d943e56fd3ebe99 diff --git a/t/t1013/objects/2e/65efe2a145dda7ee51d1741299f848e5bf752e b/t/t1013/objects/2e/65efe2a145dda7ee51d1741299f848e5bf752e Binary files differnew file mode 100644 index 000000000..ad62c43e4 --- /dev/null +++ b/t/t1013/objects/2e/65efe2a145dda7ee51d1741299f848e5bf752e diff --git a/t/t1013/objects/6b/aee0540ea990d9761a3eb9ab183003a71c3696 b/t/t1013/objects/6b/aee0540ea990d9761a3eb9ab183003a71c3696 Binary files differnew file mode 100644 index 000000000..3d2f0337d --- /dev/null +++ b/t/t1013/objects/6b/aee0540ea990d9761a3eb9ab183003a71c3696 diff --git a/t/t1013/objects/70/e6a83d8dcb26fc8bc0cf702e2ddeb6adca18fd b/t/t1013/objects/70/e6a83d8dcb26fc8bc0cf702e2ddeb6adca18fd Binary files differnew file mode 100644 index 000000000..b3f71a6ee --- /dev/null +++ b/t/t1013/objects/70/e6a83d8dcb26fc8bc0cf702e2ddeb6adca18fd diff --git a/t/t1013/objects/76/e7fa9941f4d5f97f64fea65a2cba436bc79cbb b/t/t1013/objects/76/e7fa9941f4d5f97f64fea65a2cba436bc79cbb new file mode 100644 index 000000000..af4e9a7b0 --- /dev/null +++ b/t/t1013/objects/76/e7fa9941f4d5f97f64fea65a2cba436bc79cbb @@ -0,0 +1,2 @@ + x%A0@}O1{cSZ(νthZޠ?
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