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MacBinary.md

File metadata and controls

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MacBinary format

MacBinary is a file format that combines the two forks of a classic Mac OS file into a single file, along with HFS's extended metadata. It was used to share Mac OS files over FTP, Web or e-mail because it could be stored on computers that run operating systems with no HFS support, such as Unix or Windows.

This file describes a summary of MacBinnary I, II and III.
All integers are big-endians.

Data are arranged as follows:

data = <header 128B> + <data fork> + <padding 1> + <res fork> + <padding 2>

Header – <header 128B>

Offset Length Contents 
000 Byte Always zero
001 Byte Length of filename (in the range 1-31)
002 63 Bytes Filename (remaning bytes are zero)
065 Word File type (4 characters)
069 Word File creator (4 characters)
073 Byte Finder flags: Bit 7 - isAlias. Bit 6 - isInvisible. Bit 5 - hasBundle. Bit 4 - nameLocked. Bit 3 - isStationery. Bit 2 - hasCustomIcon. Bit 1 - reserved. Bit 0 - hasBeenInited.
074 Byte Always zero
075 Half File's vertical position within its window
077 Half File's horizontal position within its window
079 Half File's window or folder ID.
081 Byte "Protected" flag (in low order bit)
082 Byte Always zero
083 Word Data Fork length in B (zero if no Data Fork)
087 Word Resource Fork length in B (zero if no R.F.)
091 Word File's creation date
095 Word File's "last modified" date
099 Half Length of Get Info comment to be sent after the resource fork (if implemented, see below).
101 ² Byte Finder Flags, bits 0-7. (Bits 8-15 are already in byte 73) Bit 7 - hasNoInits Bit 6 - isShared Bit 5 - requiresSwitchLaunch Bit 4 - ColorReserved Bits 1-3 - color Bit 0 - isOnDesk
102 ³ Word Signature for indentification purposes (always mBIN)
106 ³ Byte Script of file name (from the fdScript field of an fxInfo record)
107 ³ Byte Extended Finder flags (from the fdXFlags field of an fxInfo record)
108 8 Bytes Unused (must be zeroed by creators, must be ignored by readers)
116 ² Word Length of total files when packed files are unpacked. As of the writing of this document, this field has never been used.
120 ² Half Length of a secondary header. If this is non-zero, skip this many bytes (rounded up to the next multiple of 128). This is for future expansion only, when sending files with MacBinary, this word should be zero.
122 ² Byte Version number of MacBinary (129 for MacBinary II, 130 for MacBinary III)
123 ² Byte Minimum MacBinary version needed to read this file (set this value at 129 for backwards compatibility with MacBinary II)
124 ² Half CRC-16 of previous 124 bytes
126 Half Padding (always zero)

² These fields have been added in MacBinary II.
³ These fields have been added in MacBinary III.

Cyclic redundancy check (CRC) used in header is CRC-16-CCITT, i.e. uses polynomial number 0x1021 and starts with 0.

Data and ressource forks

Data fork directly follows the header (at byte 128). The length of these data (which can be zero) must correspond with the length given in the header (at byte 83).

Data are completed with some padding bytes (usually 0x00 but some implementations use 0x7F) until the total length of file is a multiple of 128. If the total length is already a multiple of 128 after adding the data fork, no padding is added.

The ressource fork follows the same rules (i.e. padding bytes are added after the fork to keep the total length a multiple of 128).


Sources

https://en.wikipedia.org/wiki/MacBinary https://github.com/mietek/theunarchiver/wiki/MacBinarySpecs https://files.stairways.com/other/macbinaryii-standard-info.txt