FBExport file format

FBExport
Tool for exporting and importing data with Firebird and InterBase databases

FBExport file format

In case anyone wants to know, or (s)he needs to read/write fbx file from other programs.
I did my best to show this correctly. If you don't get something to match the real file, take a look at the code, or e-mail me.

Structure of the file:

Byte	Length	Value	Explained
0	1	0	Always zero
1	1	125	FBExport file version, currently: 125
2	1	FC	Field count (number of columns)
3	FC	TYPE	Column types
The following part repeats (except for BLOBs which don't have it at all)
FC + 4	1	length	Length of the next data in bytes (read below)
FC + 5	length	data	Data itself
End of file

Column types:

Type code	IBPP Name	SQL Name
0	Array	Array
1	Blob	Blob
2	Date	Date
3	Time	Time
4	Timestamp	Timestamp (date in Dialect 1)
5	String	Char, Varchar
6	Smallint	Short
7	Integer	Int
8	LargeInt	Decimal(18, 0) only in Dialect 3
9	Float	Float
10	Double	Double precision and Decimal/Numeric with scale

BLOBs are special case, they are written like this:

Byte	Length	Value	Explained
0	1	0 or 1	0 when column is NULL, 1 when it is not NULL. (hex values 0x00 and 0x01)
The following bytes repeat until the end of BLOB data
1	4	xxxx	size of next segment (0-8192) converted to string Example: length of 1280 is written as 0x31 0x32 0x38 0x30
xxxx + 5	xxxx	DATA	Blob data (one segment)

Length:

Possible values range from 0 to 255. Value of 255 marks the NULL value. To keep the file small, I only use 1 byte for length since it is quite enough for most values. But sometimes, there are char columns larger than 254 bytes, so more than one byte is needed to represent the length. In such cases two additional bytes are used. Here's the final explanation:

Length byte value	Meaning
0-253	Single byte length, just read it.
254	Special mark, the following two bytes represent the real length of data (byte1 * 256 + byte2)
255	NULL value

Example: Timestamp 21. July 1997 07:30:00 is stored in file as string 19970721073000. Length of that string is 14 bytes, so value 14 (hex: 0e) is written for the length.

Data:

All data is written as readable ASCII characters, except char/varchar which are written as they are (if they contain any non-ASCII character, those will be used). All numers are converted to strings. I know it is not optimal, but it is human readable and compresses very good.

IBPP Type	Written as
Array	- not yet supported by FBExport -
Blob	special case
Date	string representation of number of days since 1.1.1900
Time	string representation of number of seconds since midnight
Timestamp	YYYYMMDDhhmmss
String	as is
Smallint	as string
Integer
LargeInt
Float	as string, dot (.) is used as decimal separator
Double	as string, dot (.) is used as decimal separator

If you have any suggestions or remarks, please contact me.