Patch landed in Firebird 2.5.x and is now possible to use API to do remote backups/restores

Here is the Firebird bug fixed : #CORE-2666
Today you can use the API remotely to create a serverside backup. You can use GBAK to create a remote backup (e.g. via Internet). And Today you can use API to create remote backup, i.e. create a backup serverside and flush it to the client.

Here is the documentation from the doc/README.services_extension

4) Services API extension – running gbak at server side with .fbk at the client.
(Alex Peshkov, 2011-2012)

This way of doing backups is specially efficient when one needs to perform
backup/restore operation for database, located on ther server accessed using
internet, due to serious performance increase.

The simplest way to use this feature is fbsvcmgr. To backup database run
approximately the following:
fbsvcmgr remotehost:service_mgr -user sysdba -password XXX \
action_backup -dbname some.fdb -bkp_file stdout >some.fbk

and to restore it:
fbsvcmgr remotehost:service_mgr -user sysdba -password XXX \
action_restore -dbname some.fdb -bkp_file stdin <some.fbk

Please notice – you can't use "verbose" switch when performing backup because
data channel from server to client is used to deliver blocks of fbk files. You
will get appropriate error message if you try to do it. When restoring database
verbose mode may be used without limitations.

If you want to perform backup/restore from your own program, you should use
services API for it. Backup is very simple – just pass "stdout" as backup file
name to server and use isc_info_svc_to_eof in isc_service_query() call. Data,
returned by repeating calls to isc_service_query() (certainly with
isc_info_svc_to_eof tag) is a stream, representing image of backup file. Restore
is a bit more tricky. Client sends new spb parameter isc_info_svc_stdin to server
in isc_service_query(). If service needs some data in stdin, it returns
isc_info_svc_stdin in query results, followed by 4-bytes value – number of bytes
server is ready to accept from client. (0 value means no more data is needed right
now.) The main trick is that client should NOT send more data than requested by
server – this causes an error "Size of data is more than requested". The data is
sent in next isc_service_query() call in the send_items block, using
isc_info_svc_line tag in tradition form: isc_info_svc_line, 2 bytes length, data.
When server needs next portion, it once more returns non-zero isc_info_svc_stdin
value from isc_service_query().

A sample of how services API should be used for remote backup and restore can be
found in source code of fbsvcmgr.

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