Обсуждение: connecting to server process via sockets

For fun and learning, I would like to connect to the Postgresql backend
and issue queries using sockets.  I'm using Python's socket module.  I'm
new to socket programming, but I'm experienced with Python and
Postgresql.  I've been using the JDBC driver and the online
documentation as a guide, but I'm afraid my ignorance has led me to
failure thus far.

This is what I think I understand.

1.  Send the startup message as such.
    a.  length of message.
    b.  protocol major (3)
    c.  protocol minor (0) (don't know what this is).
    d.  message
    e.  send 0 (Don't know why?)

O.K.  Here I show my ignorance.

#!/usr/bin/python

import socket

# Connection string
cnstring = 'user=randall, database=dws, client_encoding=UNICODE,
DateStyle=ISO'  # This just wrapped in my email.
msg_len = str(len(cnstring))
protocol_major = '3'
protocol_minor = '0'

pgsocket = socket.socket()
pgsocket.connect(('localhost', 5432))
pgsocket.send(msg_len)
pgsocket.send(protocol_major)
pgsocket.send(protocol_minor)
pgsocket.send(cnstring)
pgsocket.send('0')
pgsocket.close()


When I run this, this is what shows up in the logs.

2005-05-16 10:11:34 [2638] LOG:  connection received: host=127.0.0.1
port=42607
2005-05-16 10:11:34 [2638] LOG:  invalid length of startup packet

Please do not recommend that I use an existing API.  I'm doing this for
fun and maybe to come up with a simple pure python database driver.

Randall

On May 16, 2005, at 11:14 AM, Randall Smith wrote:

> When I run this, this is what shows up in the logs.
>
> 2005-05-16 10:11:34 [2638] LOG:  connection received: host=127.0.0.1
> port=42607
> 2005-05-16 10:11:34 [2638] LOG:  invalid length of startup packet


We just had a thread about this on the Novice (!) list. It should
answer your question about what the startup packet needs to look like.

http://archives.postgresql.org/pgsql-novice/2005-05/msg00130.php


John DeSoi, Ph.D.
http://pgedit.com/
Power Tools for PostgreSQL

Randall Smith <randall@tnr.cc> writes:

> For fun and learning, I would like to connect to the Postgresql
> backend and issue queries using sockets.  I'm using Python's socket
> module.  I'm new to socket programming, but I'm experienced with
> Python and Postgresql.  I've been using the JDBC driver and the online
> documentation as a guide, but I'm afraid my ignorance has led me to
> failure thus far.

[...]

No direct help, but a couple of suggestions:

1) Take a look at pg-dot-lisp, which does the same thing you are
   trying to do, but in Lisp.  You might find it more readable than
   the JDBC driver.  I am not sure which protocol versions it
   supports, though.  It's at:

      http://www.chez.com/emarsden/downloads/

2) Write a simple libpq app (or use one of the existing Python
   interfaces linked against libpq) and watch the session with
   Etherial or tcpdump.  That'll show you the differences between your
   failing app and a working connection...

-Doug

Randall Smith wrote:
>
> For fun and learning, I would like to connect to the Postgresql backend
> and issue queries using sockets.  I'm using Python's socket module.  I'm
> new to socket programming, but I'm experienced with Python and
> Postgresql.

Look in the postgres docs for the section on frontend/backend protocol.
The handshaking and format of the bytes that go across the socket
are explained in that doc. section.

You also might want to look at:

    http://ca.geocities.com/zazu@rogers.com/pgsqueak/

where there are links to a class diagram and state diagram
of an implementation done in Squeak Smalltalk. I don't know
Python, but IMHO the basic design should be transferable.

Note that frontend/backend protocol version 2 is implemented
in that code, and the current docs will reflect version 3
(so you'd have to look at the older docs to match up the code).

Hope that helps.
--yanni