Articles

Fixes in Firebird 2.5 regarding connection string charset

Author: Adriano dos Santos Fernandes <[email protected]>

Date: 2008-12-15


Before FB 2.5, filenames used in the connection string are always passed from the client to the

server without any conversion. On the server, those filenames are used with OS API functions without

any conversion, too. This creates the situation where filenames using non-ASCII characters do not

interoperate well when the client and the server are different OS or even same OS using different

codepages.


The problem is addressed in FB 2.5 in the following way:


The filename is considered, by default, to be on the OS codepage.


A new DPB is introduced, named isc_dpb_utf8_filename. Its meaning is to change the rule above, so FB

should consider the passed filename as being in UTF-8.


If a v2.5 (or newer) client is communicating with a remote server older than v2.5, and

isc_dpb_utf8_filename was used, the client converts the filename from UTF-8 to the client

codepage and passes that filename to the server. The client removes isc_dpb_utf8_filename DPB.

This guarantees backward compatibility when people are using the same codepage on the client and

server OS.


If a v2.5 (or newer) client is communicating with a v2.5 (or newer) server, and

isc_dpb_utf8_filename was not used, the client converts the filename from the OS codepage to

UTF-8 and inserts the isc_dpb_utf8_filename DPB. If isc_dpb_utf8_filename was used, the client just

passes the original filename withing the DPB to the server. So the client always passes to the server

an UTF-8 filename and the isc_dpb_utf8_filename DPB.


The filename received on the server is subject to the same rules above. But note that v2.5 client

may automatically convert the filename and insert the DPB. Clients older than v2.5 do not,

so the received filenames are going to be considered as on the server codepage. We again guarantee

backward compatibility when client and server codepage are the same.


The OS codepage and UTF-8 may not be the better choice for filenames. For example, if you had a

ISQL (or some other tool) script and that script uses another connection charset. You could not

correctly edit a script (or any file) using multiple character sets (codepages). So you may now

encode any Unicode character as ASCII characters on the connection string filename. That's

accomplished using the symbol #. It is a prefix for an Unicode code point number (in hexadecimal

format, like U+XXXX notation). You should write it in this way: #XXXX with X being 0-9, a-f, A-F.

If you want to use the literal #, you could use ## or #0023 (the code point number for it).

That character is interpreted with this new semantics at the server even if the client is older

than v2.5.


The OS codepage used for conversions is:

- Windows: The Windows ANSI code page

- Others: UTF-8



Updated for 2.5 Beta 2: 2008-07-11


These rules are now valid for string DPB items too.