A Sendmail replacement in Python

I know I blog about odd things, but it's just that those odd things happen to me! The problem we have now is the following: we need to have a sendmail-like command that will send email through an external SMTP server. Why? Well its a long story that can be resumed to the fact that I just don't want to install Sendmail into my VoIP server ;).

So instead of doing what everyone would do (apt-get install sendmail) I wrote a simple script in Python that works somewhat like Sendmail does, with the exception that it just forwards everything to another server. I *could* make it work without an external server, but that would require to resolve the DNS of the destination server and to find the MX registers... and I'm lazy. Plus that would require an external Python Module to do the DNS resolution, and I wanted my script to be pure-Python with no dependencies other than the Python library. Anyway if anyone, ever, needs a script to do the DNS thing, ask and I'll do it *sigh*.

So here comes the script. The script accepts the sendmail -t parameter so the "To" header from the Email is used to specify the recipients, otherwise recipients should be specified by command line.

#!/usr/bin/python

import email
import smtplib
import sys

SMTP_SERVER="YourMailServer.com"
SMTP_USER="YourUser"
SMTP_PASS="Ssh-Sekrat!"

def sendmail(from_addr, to_addrs, msg):
    smtp = smtplib.SMTP(SMTP_SERVER)
    smtp.login(SMTP_USER, SMTP_PASS)
    smtp.sendmail(from_addr, to_addrs, msg)
    smtp.quit()

def main():
    msgstr = sys.stdin.read()

    msg = email.message_from_string(msgstr)
    if sys.argv[1] == "-t":
        to_addrs = msg["To"]
    else:
        to_addrs = sys.argv[1:]
    sendmail(msg["From"], to_addrs, msgstr)

main()


Thats it! To test it:

./sendmail.py someone@somewhere.com
From: your@friend.com
Subject: Hello!

Hello! Hows life?
<CTRL+D>

I hope you liked it, happy hacking!

The Holy Grail of Binary Data in PostgreSQL and Python

I'm not sure if you've ever had this problem.  I've had it a lot of times and I suppose I'm not alone. The thing is the following, say you want to store binary data in PostgreSQL. For those who use MySQL, I've heard it's a very simple task, however I don't care since I never use MySQL :). On the other hand, doing this from Python to a PostgreSQL database, can be quite tricky. What I used to do is to Base64 encode everything and store it on the database, that worked but it was slow and bloated. There's another way, the "bytea" data type. The problem with bytea is that PostgreSQL wants things escaped and it is quite unclear how to do it. However, today I found it out and I was so happy I decided to blog it! It is actually simple once you know the trick. First you have to create a table with a bytea field (where you store your bytes), for example:

CREATE TABLE IMAGES (ID SERIAL, NAME VARCHAR, DATA BYTEA);

This is the easy part and I think we all have gotten this far. Now the thing is in the Python side. The secret is to escape things properly. To insert binary data to a PostgreSQL database you need to follow this scheme: E' + data in octal + '::bytea For example:

INSERT INTO IMAGES VALUES(default, 'PARIS.JPG', E'\\001\\002\\003\\031\\313'::bytea);

Notice the double "\" since the bar is un-escaped by the database. Easy? Yeah! But hard to find out. Now it's just writing a simple Python function to do the escaping:

def octize(data):
    out = "E'"
    for char in data:
        octdata = oct(ord(char))[1:].zfill(3)
        out += "\\\\" + octdata
     return out + "'::bytea" 

And now we could do something like:

conn = psycopg.connect()
cur = conn.cursor()
cur.insert("INSERT INTO IMAGES VALUES(default, 'PARIS.JPG', %s)"  
           % octize(image_data))
cur.close()
conn.commit()
Hope you liked it! Happy hacking!