diff options
| -rw-r--r-- | org.eclipse.jgit/src/org/eclipse/jgit/storage/file/UnpackedObject.java | 35 |
1 files changed, 28 insertions, 7 deletions
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/storage/file/UnpackedObject.java b/org.eclipse.jgit/src/org/eclipse/jgit/storage/file/UnpackedObject.java index b04a294b63..de38caa231 100644 --- a/org.eclipse.jgit/src/org/eclipse/jgit/storage/file/UnpackedObject.java +++ b/org.eclipse.jgit/src/org/eclipse/jgit/storage/file/UnpackedObject.java @@ -270,14 +270,35 @@ public class UnpackedObject { } private static boolean isStandardFormat(final byte[] hdr) { - // Try to determine if this is a standard format loose object or - // a pack style loose object. The standard format is completely - // compressed with zlib so the first byte must be 0x78 (15-bit - // window size, deflated) and the first 16 bit word must be - // evenly divisible by 31. Otherwise its a pack style object. - // + /* + * 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. + */ final int fb = hdr[0] & 0xff; - return fb == 0x78 && (((fb << 8) | hdr[1] & 0xff) % 31) == 0; + return (fb & 0x8f) == 0x08 && (((fb << 8) | hdr[1] & 0xff) % 31) == 0; } private static InputStream inflate(final InputStream in, final long size, |