More on using FreeTDS on a server (was Re: [freetds] Serverdumpscore...)

ZIGLIO, Frediano, VF-IT Frediano.Ziglio at vodafone.com
Fri Apr 23 07:12:13 EDT 2004


> 
> "James K. Lowden" <jklowden at schemamania.org> wrote on 
> Thursday, Apr 22, 2004:
> > On Tue, 20 Apr 2004, Steve Kirkendall 
> <skirkendall at dsl-only.net> wrote:
> > > There's no way for high-level functions to know what type 
> of packet is
> > >   received, because the tds_read_packet() function 
> discards that byte.
> > >   I added an in_flag field to the TDSSOCKET structure, 
> > 
> > Perhaps "in_flag" would be better named "token" or "packet_type"?
> 
> I chose the name "in_flag" because TDSSOCKET already contains a field
> named "out_flag" which seems to control the packet type for 
> any outgoing
> packets.  There are a lot of "in_XXX" and "out_XXX" field names, so I
> was trying to continue that symmetry.
> 
> But now I wonder if it really matters.  The received packet type seems
> to be superfluous.  I originally wanted to know the packet 
> type partly so
> my server could automatically distinguish between TDS7.0 and 
> TDS4.2/5.0
> logins (in 0x10 and 0x02 packets, respectively), and partly 
> so it could
> treat the entire content of a 0x01 query packet as the text 
> of a query,
> while still allowing RPC calls in 0x04 packets.
> 
> But Mike C. points out that 7.0 uses a prelogin packet, so my server
> should be able to detect the login type that way.
> 

I don't understand why you want to use mssql2k syntax... if the reason
is to use default ms sql odbc drivers (or ADODB or other proprietary
libraries) I discourage you. The reason is that you MUST implement:
- advanced types (unicode, guid, variant)
- system tables (syscomments and others)
- prepared statement (server side)
- some internal store procedure (sp_prepare, sp_tables, sp_typeinfo...)
...
Version 4.2 is easier to implement (no prepared, no guid, variant, fewer
procedure).

> I thought the entire content of a 0x01 packet was a query because the
> tsql program seems to send them that way.  The 
> tds_get_query() function
> expects a 6-byte header at the start of each query, so it doesn't work
> correctly with tsql.  But it looks like the tds_get_query() 
> function is
> right, and tsql is wrong.  Maybe.  I'm not 100% confident of 
> that; I'll
> look into it tomorrow.
> 

I don't think tsql is wrong... Language query are just the payload
(without packet header) content, packet type 1.

> If both of those things are right (prelogin to detect 7.0 logins, and
> token header for queries) then the server doesn't need to know the
> received packet type anymore than the client does.  My "in_flag"
> modification wouldn't be necessary.
> 

prelogin detect 8.0 login, not 7.0. 7.0 are detected with tds 7 type
login.

freddy77



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