Patching Files

For updating files WoW uses bsdiff. Have a look at "http://www.daemonology.net/bsdiff/" or "http://www.pokorra.de/coding/bsdiff.html"

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I had try bsdiff, but it doesn't work.

 1. extract achievement.dbc from enUS\DBFilesClient in Patches\WoW-3.1.3-to-3.2.0-enUS-Win-patch\wow-partial-1.MPQ
 2. rename it to achievement.dbc.patch (45K)
 3. extract achievement.dbc from DBFilesClient in Data\enUS\patch-enUS-2.MPQ
 4. rename it to achievement.dbc.old
 5. bsdiff
   usage: bspatch.exe oldfile newfile patchfile
 6. bsdiff chievement.dbc.old achievement.dbc achievement.dbc.patch
   Corrupt patch
 7. extract achievement.dbc from DBFilesClient in PTR:Data\enUS\patch-enUS-2.MPQ
 8. rename it to achievement.dbc.ptr
 9. bsdiff achievement.dbc.old achievement.dbc.ptr achievement.dbc.patch-ptr (20K)

althought it shows "BSDIFF40" in it's header, but it is not a bsdiff?

-- chuanhsing

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I got some information about files in pre-download mpq. All files inside it are "patch" files.

Followings are for binary/new patch header:

 0x0000 2 bytes: Size of the patch header (I've only seen 0x18)
 0x0002 2 bytes: signature,
          * 0x0104 means binary patch
 0x0004 8 bytes: unknown, always 8 bytes 0x00
 0x000C 4 bytes: file size n
 0x0010 8 bytes: timestamp
 ---- body ----
 0x0018 n bytes: the real thing

Followings are for plain text patch header:

 0x0000 2 bytes: Size of the patch header (I've only seen 0x18)
 0x0002 2 bytes: signature,
          * 0x0404 means plain text patch
 0x0004 8 bytes: maybe timestamp
 0x000C 4 bytes: file size
 0x0010 8 bytes: timestamp
 ---- body ----
 0x0018 4 bytes: file size
 0x001C 1 byte: unknown
 0x001D 8 bytes: signature, "BSDIFF40"
 0x0025 n bytes: unknown

For the new files, I can skip heading 24 bytes and get the real thing! But I still can't understand the things after BSDIFF40.

-- chuanhsing

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As about patch files in MPQs, I found this structure so far:

 0x0000 (2 bytes) Size of the patch header (I've only seen 0x18)
 0x0002 (2 bytes) Flags.
 - 0x0004 - Seems to be always set
 - 0x0100 - Unknown
 - 0x0400 - The patch file is made by bin patch generator)
 0x0004 (4 bytes) Looks like CRC
 0x0008 (4 bytes) Unknown
 (looks like size of something when 0x0100 flag set)
 0x000C (4 bytes) File size (only if Flags = 0x0104)
 0x0010 (8 bytes) Time stamp as FILETIME
 ---- body ----

-- chuanhsing