haiku/docs/develop/kits/app/bmessage.txt

Message header:
Data		Bytes	Meaning
FOB1		4		version
			4		checksum
			4		flattened size
			4		'what'
			1		flags

Data field:
Data		Bytes	Meaning
			1		flags
			4		type
	// Mini data (all data less than 256 bytes total)
			1		item count (*if* there is more than one)
			1		data length
	// Maxi data (all data more than 255 bytes total)
			4		item count (*if* there is more than one)
			4		data length
			1		name length
			X		name
	// Single item
			4		item size (*if* this is a variable sized item)
			Y		item data - NULL padded to 8-byte boundary
	// Multiple items
			4		item size (*if* this is a variable sized item)
			Y		item data - NULL padded to 8-byte boundary

//------------------------------------------------------------------------------
// An example
//------------------------------------------------------------------------------
// PrintToStream()
Data		Bytes	Meaning

//BMessage: what =  (0x0, or 0)
FOB1		4		version
0x90010001	4		checksum
0x00000192	4		flattened size (402 bytes)
0x0			4		'what' (none specified)
0x01		1		flags

//    entry ATTRIBUTE_MENU, type='LONG', c=5, size= 4,
0x07		1		flags
LONG		4		type
0x05		1		item count
0x14		1		data length
0x0e		1		name length
ATTRIBUTE_	14		name (ATTRIBUTE_MENU)
//			data[0]: 0x8 (8, '')
0x8			4		data[0]
//          data[1]: 0x8 (8, '')
0x8			4		data[1]
//          data[2]: 0x6 (6, '')
0x6			4		data[2]
//          data[3]: 0x8 (8, '')
0x8			4		data[3]
//          data[4]: 0x6 (6, '')
0x6			4		data[4]

//    entry  CRITERIA_MENU, type='LONG', c=5, size= 4,
0x07		1		flags
LONG		4		type
0x05		1		item count
0x14		1		data length
0x0d		1		name length
CRITERIA_	13		name (CRITERIA_MENU)
//			data[0]: 0x0 (0, '')
0x0			4		data[0]
//          data[1]: 0x0 (0, '')
0x0			4		data[1]
//          data[2]: 0x0 (0, '')
0x0			4		data[2]
//          data[3]: 0x0 (0, '')
0x0			4		data[3]
//          data[4]: 0x0 (0, '')
0x0			4		data[4]

//    entry          VALUE, type='CSTR', c=5,
0x03		1		flags
CSTR		4		type
0x5			1		item count
0x90		1		data length
0x5			1		name length
VALUE		5		name (VALUE)
//			size=18, data[0]: "listar@freelists."
0x12		4		item size
listar@fre	18		data[0]
			2		padding to 8-byte boundary
//          size=27, data[1]: "freelists-users@freelists."
0x1b		4		item size
freelists@	27		data[1]
			1		padding to 8-byte boundary
//          size=27, data[2]: "freelists-users@freelists."
0x1b		4		item size
freelists@	27		data[2]
			1		padding to 8-byte boundary
//          size=19, data[3]: "ecartis@freelists."
0x13		4		item size
ecartis@fr	19		data[3]
			1		padding to 8-byte boundary
//          size=26, data[4]: "freelists-news@freelists."
0x1a		4		item size
freelists@	26		data[4]
			2		padding to 8-byte boundary

//    entry    AND_OR_MENU, type='LONG', c=5, size= 4,
0x07		1		flags
LONG		4		type
0x5			1		item count
0x14		1		data length
0x0b		1		name length
AND_OR_MEN	11		name (AND_OR_MENU)
//			data[0]: 0x1 (1, '')
0x1			4		data[0]
//          data[1]: 0x1 (1, '')
0x1			4		data[1]
//          data[2]: 0x1 (1, '')
0x1			4		data[2]
//          data[3]: 0x1 (1, '')
0x1			4		data[3]
//          data[4]: 0x0 (0, '')
0x0			4		data[4]

//    entry          COUNT, type='LONG', c=1, size= 4, data[0]: 0x5 (5, '')
0x0f		1		flags
LONG		4		type
0x4			1		data length
0x5			1		name length
COUNT		5		name (COUNT)
0x5			4		data

//    entry    ACTION_MENU, type='LONG', c=1, size= 4, data[0]: 0x2 (2, '')
0x0f		1		flags
LONG		4		type
0x4			1		data length
0x0b		1		name length
ACTION_MEN	11		name (ACTION_MENU)
0x2			4		data

//    entry   ACTION_VALUE, type='CSTR', c=1, size=42, data[0]: "/boot/home/mail/Erik's Mail/freelists.org"
0x0b		1		flags
CSTR		4		type
0x30		1		data length
0x0c		1		name length
ACTION_VAL	12		name (ACTION_VALUE)
0x2a		4		item size
/boot/home	42		data
			2		padding to 8-byte boundary

//------------------------------------------------------------------------------
// An old example
Data		Bytes	Meaning

1BOF(ascii)	4		version					
??			4		??
0x76		4		flattened size
DPUQ		4		what(B_QUERY_UPDATE)
??			1		??

0F			1		flags (including fixed chunk size)
GNOL		4		type
04			1		chunk size
06			1		name length
opcode		6		name
1			4		data(B_ENTRY_CREATED)

0F			1		flags (including fixed chunk size)
GNOL		4		type
04			1		chunk size
06			1		name length
device		6		name
4			4		data

0F			1		flags (including fixed chunk size)
GNLL		4		type
08			1		chunk size
09			1		name length
directory	9		name
524992		8		data

0F			1		flags (including fixed chunk size)
GNLL		4		type
08			1		chunk size
04			1		name length
node		4		name
524295		8		data

0B			1		flags (including variable chunk size)
RTSC		4		type
08			1		chunk size
04			1		name length
name		4		name
08			1		chunk size?
			8		padded string?