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authorRoberto Tyley <roberto.tyley@guardian.co.uk>2011-08-07 19:46:13 +0100
committerJunio C Hamano <gitster@pobox.com>2011-08-11 13:02:47 -0700
commit7f684a2aff636f44a5063c05cf84c0db0460ae1a (patch)
tree3d7b763261b6aeb1e01cbb2b4a8bdc144c9f029a
parente9e0643fe64b613b6596b79b59df8ff10746f1a1 (diff)
downloadgit-7f684a2aff636f44a5063c05cf84c0db0460ae1a.tar.gz
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>
-rw-r--r--sha1_file.c32
-rwxr-xr-xt/t1013-loose-object-format.sh68
-rw-r--r--t/t1013/objects/14/9cedb5c46929d18e0f118e9fa31927487af3b6bin0 -> 117 bytes
-rw-r--r--t/t1013/objects/16/56f9233d999f61ef23ef390b9c71d75399f435bin0 -> 17 bytes
-rw-r--r--t/t1013/objects/1e/72a6b2c4a577ab0338860fa9fe87f761fc9bbdbin0 -> 18 bytes
-rw-r--r--t/t1013/objects/25/7cc5642cb1a054f08cc83f2d943e56fd3ebe99bin0 -> 19 bytes
-rw-r--r--t/t1013/objects/2e/65efe2a145dda7ee51d1741299f848e5bf752ebin0 -> 10 bytes
-rw-r--r--t/t1013/objects/6b/aee0540ea990d9761a3eb9ab183003a71c3696bin0 -> 181 bytes
-rw-r--r--t/t1013/objects/70/e6a83d8dcb26fc8bc0cf702e2ddeb6adca18fdbin0 -> 26 bytes
-rw-r--r--t/t1013/objects/76/e7fa9941f4d5f97f64fea65a2cba436bc79cbb2
-rw-r--r--t/t1013/objects/78/75c6237d3fcdd0ac2f0decc7d3fa6a50b66c09bin0 -> 139 bytes
-rw-r--r--t/t1013/objects/7a/37b887a73791d12d26c0d3e39568a8fb0fa6e8bin0 -> 54 bytes
-rw-r--r--t/t1013/objects/85/df50785d62d3b05ab03d9cbf7e4a0b49449730bin0 -> 13 bytes
-rw-r--r--t/t1013/objects/8d/4e360d6c70fbd72411991c02a09c442cf7a9fabin0 -> 156 bytes
-rw-r--r--t/t1013/objects/95/b1625de3ba8b2214d1e0d0591138aea733f64fbin0 -> 252 bytes
-rw-r--r--t/t1013/objects/9a/e9e86b7bd6cb1472d9373702d8249973da0832bin0 -> 11 bytes
-rw-r--r--t/t1013/objects/bd/15045f6ce8ff75747562173640456a394412c8bin0 -> 34 bytes
-rw-r--r--t/t1013/objects/e6/9de29bb2d1d6434b8b29ae775ad8c2e48c5391bin0 -> 9 bytes
-rw-r--r--t/t1013/objects/f8/16d5255855ac160652ee5253b06cd8ee14165a1
19 files changed, 97 insertions, 6 deletions
diff --git a/sha1_file.c b/sha1_file.c
index 697f4a43c5..475d215c14 100644
--- a/sha1_file.c
+++ b/sha1_file.c
@@ -1217,14 +1217,34 @@ static int experimental_loose_object(unsigned char *map)
unsigned int word;
/*
- * Is it a zlib-compressed buffer? If so, the first byte
- * must be 0x78 (15-bit window size, deflated), and the
- * first 16-bit word is evenly divisible by 31. If so,
- * we are looking at the official format, not the experimental
- * one.
+ * We must determine if the buffer contains the standard
+ * zlib-deflated stream or the experimental format based
+ * on the in-pack object format. Compare the header byte
+ * for each format:
+ *
+ * RFC1950 zlib w/ deflate : 0www1000 : 0 <= www <= 7
+ * Experimental pack-based : Stttssss : ttt = 1,2,3,4
+ *
+ * If bit 7 is clear and bits 0-3 equal 8, the buffer MUST be
+ * in standard loose-object format, UNLESS it is a Git-pack
+ * format object *exactly* 8 bytes in size when inflated.
+ *
+ * However, RFC1950 also specifies that the 1st 16-bit word
+ * must be divisible by 31 - this checksum tells us our buffer
+ * is in the standard format, giving a false positive only if
+ * the 1st word of the Git-pack format object happens to be
+ * divisible by 31, ie:
+ * ((byte0 * 256) + byte1) % 31 = 0
+ * => 0ttt10000www1000 % 31 = 0
+ *
+ * As it happens, this case can only arise for www=3 & ttt=1
+ * - ie, a Commit object, which would have to be 8 bytes in
+ * size. As no Commit can be that small, we find that the
+ * combination of these two criteria (bitmask & checksum)
+ * can always correctly determine the buffer format.
*/
word = (map[0] << 8) + map[1];
- if (map[0] == 0x78 && !(word % 31))
+ if ((map[0] & 0x8F) == 0x08 && !(word % 31))
return 0;
else
return 1;
diff --git a/t/t1013-loose-object-format.sh b/t/t1013-loose-object-format.sh
new file mode 100755
index 0000000000..f45702c45c
--- /dev/null
+++ b/t/t1013-loose-object-format.sh
@@ -0,0 +1,68 @@
+#!/bin/sh
+#
+# Copyright (c) 2011 Roberto Tyley
+#
+
+test_description='Correctly identify and parse loose object headers
+
+There are two file formats for loose objects - the original standard
+format, and the experimental format introduced with Git v1.4.3, later
+deprecated with v1.5.3. Although Git no longer writes the
+experimental format, objects in both formats must be read, with the
+format for a given file being determined by the header.
+
+Detecting file format based on header is not entirely trivial, not
+least because the first byte of a zlib-deflated stream will vary
+depending on how much memory was allocated for the deflation window
+buffer when the object was written out (for example 4KB on Android,
+rather that 32KB on a normal PC).
+
+The loose objects used as test vectors have been generated with the
+following Git versions:
+
+standard format: Git v1.7.4.1
+experimental format: Git v1.4.3 (legacyheaders=false)
+standard format, deflated with 4KB window size: Agit/JGit on Android
+'
+
+. ./test-lib.sh
+LF='
+'
+
+assert_blob_equals() {
+ printf "%s" "$2" >expected &&
+ git cat-file -p "$1" >actual &&
+ test_cmp expected actual
+}
+
+test_expect_success setup '
+ cp -R "$TEST_DIRECTORY/t1013/objects" .git/
+ git --version
+'
+
+test_expect_success 'read standard-format loose objects' '
+ git cat-file tag 8d4e360d6c70fbd72411991c02a09c442cf7a9fa &&
+ git cat-file commit 6baee0540ea990d9761a3eb9ab183003a71c3696 &&
+ git ls-tree 7a37b887a73791d12d26c0d3e39568a8fb0fa6e8 &&
+ assert_blob_equals "257cc5642cb1a054f08cc83f2d943e56fd3ebe99" "foo$LF"
+'
+
+test_expect_success 'read experimental-format loose objects' '
+ git cat-file tag 76e7fa9941f4d5f97f64fea65a2cba436bc79cbb &&
+ git cat-file commit 7875c6237d3fcdd0ac2f0decc7d3fa6a50b66c09 &&
+ git ls-tree 95b1625de3ba8b2214d1e0d0591138aea733f64f &&
+ assert_blob_equals "2e65efe2a145dda7ee51d1741299f848e5bf752e" "a" &&
+ assert_blob_equals "9ae9e86b7bd6cb1472d9373702d8249973da0832" "ab" &&
+ assert_blob_equals "85df50785d62d3b05ab03d9cbf7e4a0b49449730" "abcd" &&
+ assert_blob_equals "1656f9233d999f61ef23ef390b9c71d75399f435" "abcdefgh" &&
+ assert_blob_equals "1e72a6b2c4a577ab0338860fa9fe87f761fc9bbd" "abcdefghi" &&
+ assert_blob_equals "70e6a83d8dcb26fc8bc0cf702e2ddeb6adca18fd" "abcdefghijklmnop" &&
+ assert_blob_equals "bd15045f6ce8ff75747562173640456a394412c8" "abcdefghijklmnopqrstuvwx"
+'
+
+test_expect_success 'read standard-format objects deflated with smaller window buffer' '
+ git cat-file tag f816d5255855ac160652ee5253b06cd8ee14165a &&
+ git cat-file tag 149cedb5c46929d18e0f118e9fa31927487af3b6
+'
+
+test_done
diff --git a/t/t1013/objects/14/9cedb5c46929d18e0f118e9fa31927487af3b6 b/t/t1013/objects/14/9cedb5c46929d18e0f118e9fa31927487af3b6
new file mode 100644
index 0000000000..472fd1458e
--- /dev/null
+++ b/t/t1013/objects/14/9cedb5c46929d18e0f118e9fa31927487af3b6
Binary files differ
diff --git a/t/t1013/objects/16/56f9233d999f61ef23ef390b9c71d75399f435 b/t/t1013/objects/16/56f9233d999f61ef23ef390b9c71d75399f435
new file mode 100644
index 0000000000..c379d74ae2
--- /dev/null
+++ b/t/t1013/objects/16/56f9233d999f61ef23ef390b9c71d75399f435
Binary files differ
diff --git a/t/t1013/objects/1e/72a6b2c4a577ab0338860fa9fe87f761fc9bbd b/t/t1013/objects/1e/72a6b2c4a577ab0338860fa9fe87f761fc9bbd
new file mode 100644
index 0000000000..93706305bc
--- /dev/null
+++ b/t/t1013/objects/1e/72a6b2c4a577ab0338860fa9fe87f761fc9bbd
Binary files differ
diff --git a/t/t1013/objects/25/7cc5642cb1a054f08cc83f2d943e56fd3ebe99 b/t/t1013/objects/25/7cc5642cb1a054f08cc83f2d943e56fd3ebe99
new file mode 100644
index 0000000000..bdcf704c9e
--- /dev/null
+++ b/t/t1013/objects/25/7cc5642cb1a054f08cc83f2d943e56fd3ebe99
Binary files differ
diff --git a/t/t1013/objects/2e/65efe2a145dda7ee51d1741299f848e5bf752e b/t/t1013/objects/2e/65efe2a145dda7ee51d1741299f848e5bf752e
new file mode 100644
index 0000000000..ad62c43e41
--- /dev/null
+++ b/t/t1013/objects/2e/65efe2a145dda7ee51d1741299f848e5bf752e
Binary files differ
diff --git a/t/t1013/objects/6b/aee0540ea990d9761a3eb9ab183003a71c3696 b/t/t1013/objects/6b/aee0540ea990d9761a3eb9ab183003a71c3696
new file mode 100644
index 0000000000..3d2f0337db
--- /dev/null
+++ b/t/t1013/objects/6b/aee0540ea990d9761a3eb9ab183003a71c3696
Binary files differ
diff --git a/t/t1013/objects/70/e6a83d8dcb26fc8bc0cf702e2ddeb6adca18fd b/t/t1013/objects/70/e6a83d8dcb26fc8bc0cf702e2ddeb6adca18fd
new file mode 100644
index 0000000000..b3f71a6ee5
--- /dev/null
+++ b/t/t1013/objects/70/e6a83d8dcb26fc8bc0cf702e2ddeb6adca18fd
Binary files differ
diff --git a/t/t1013/objects/76/e7fa9941f4d5f97f64fea65a2cba436bc79cbb b/t/t1013/objects/76/e7fa9941f4d5f97f64fea65a2cba436bc79cbb
new file mode 100644
index 0000000000..af4e9a7b0c
--- /dev/null
+++ b/t/t1013/objects/76/e7fa9941f4d5f97f64fea65a2cba436bc79cbb
@@ -0,0 +1,2 @@
+ x%A0@}O1{cSZ(νthZޠ? m6di9GhبZR'QRpqL9=gsIoopeϫ_1$*SiNwpPRB
+[(d-L9 \ No newline at end of file
diff --git a/t/t1013/objects/78/75c6237d3fcdd0ac2f0decc7d3fa6a50b66c09 b/t/t1013/objects/78/75c6237d3fcdd0ac2f0decc7d3fa6a50b66c09
new file mode 100644
index 0000000000..3dd28be5c6
--- /dev/null
+++ b/t/t1013/objects/78/75c6237d3fcdd0ac2f0decc7d3fa6a50b66c09
Binary files differ
diff --git a/t/t1013/objects/7a/37b887a73791d12d26c0d3e39568a8fb0fa6e8 b/t/t1013/objects/7a/37b887a73791d12d26c0d3e39568a8fb0fa6e8
new file mode 100644
index 0000000000..2b97b264c3
--- /dev/null
+++ b/t/t1013/objects/7a/37b887a73791d12d26c0d3e39568a8fb0fa6e8
Binary files differ
diff --git a/t/t1013/objects/85/df50785d62d3b05ab03d9cbf7e4a0b49449730 b/t/t1013/objects/85/df50785d62d3b05ab03d9cbf7e4a0b49449730
new file mode 100644
index 0000000000..6dff746876
--- /dev/null
+++ b/t/t1013/objects/85/df50785d62d3b05ab03d9cbf7e4a0b49449730
Binary files differ
diff --git a/t/t1013/objects/8d/4e360d6c70fbd72411991c02a09c442cf7a9fa b/t/t1013/objects/8d/4e360d6c70fbd72411991c02a09c442cf7a9fa
new file mode 100644
index 0000000000..cb41e92d07
--- /dev/null
+++ b/t/t1013/objects/8d/4e360d6c70fbd72411991c02a09c442cf7a9fa
Binary files differ
diff --git a/t/t1013/objects/95/b1625de3ba8b2214d1e0d0591138aea733f64f b/t/t1013/objects/95/b1625de3ba8b2214d1e0d0591138aea733f64f
new file mode 100644
index 0000000000..7ac46b4f70
--- /dev/null
+++ b/t/t1013/objects/95/b1625de3ba8b2214d1e0d0591138aea733f64f
Binary files differ
diff --git a/t/t1013/objects/9a/e9e86b7bd6cb1472d9373702d8249973da0832 b/t/t1013/objects/9a/e9e86b7bd6cb1472d9373702d8249973da0832
new file mode 100644
index 0000000000..9d8316d4e5
--- /dev/null
+++ b/t/t1013/objects/9a/e9e86b7bd6cb1472d9373702d8249973da0832
Binary files differ
diff --git a/t/t1013/objects/bd/15045f6ce8ff75747562173640456a394412c8 b/t/t1013/objects/bd/15045f6ce8ff75747562173640456a394412c8
new file mode 100644
index 0000000000..eebf23956e
--- /dev/null
+++ b/t/t1013/objects/bd/15045f6ce8ff75747562173640456a394412c8
Binary files differ
diff --git a/t/t1013/objects/e6/9de29bb2d1d6434b8b29ae775ad8c2e48c5391 b/t/t1013/objects/e6/9de29bb2d1d6434b8b29ae775ad8c2e48c5391
new file mode 100644
index 0000000000..134cf19379
--- /dev/null
+++ b/t/t1013/objects/e6/9de29bb2d1d6434b8b29ae775ad8c2e48c5391
Binary files differ
diff --git a/t/t1013/objects/f8/16d5255855ac160652ee5253b06cd8ee14165a b/t/t1013/objects/f8/16d5255855ac160652ee5253b06cd8ee14165a
new file mode 100644
index 0000000000..26b75aec56
--- /dev/null
+++ b/t/t1013/objects/f8/16d5255855ac160652ee5253b06cd8ee14165a
@@ -0,0 +1 @@
+H0 a{ Ie&*G^D҆wUҗS4 ,f[VAۺx6[wtGLu?@"g{+by%M \ No newline at end of file