stillhq.com : Mikal, a geek from Canberra living in Silicon Valley (no blather posts)

Executing a command with paramiko

Wed, 03 Sep 2008 15:11:00 GMT

I wanted to provide a simple example of how to execute a command with paramiko as well. This is quite similar to the scp example, but is nicer than executing a command in a shell because there isn't any requirement to do parsing to determine when the command has finished executing.

#!/usr/bin/python

# A simple command example for Paramiko.
# Args:
#   1: hostname
#   2: username
#   3: command to run

import getpass
import os
import paramiko
import socket
import sys

# Socket connection to remote host
sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
sock.connect((sys.argv[1], 22))

# Build a SSH transport
t = paramiko.Transport(sock)
t.start_client()
t.auth_password(sys.argv[2], getpass.getpass('Password: '))

# Start a cmd channel
cmd_channel = t.open_session()
cmd_channel.exec_command(sys.argv[3])

data = cmd_channel.recv(1024)
while data:
  sys.stdout.write(data)
  data = cmd_channel.recv(1024)

# Cleanup
cmd_channel.close()
t.close()
sock.close()

Tags for this post: python() paramiko()

Comment

Implementing SCP with paramiko

Wed, 03 Sep 2008 13:28:00 GMT

Regular readers will note that I've been interested in how scp works and paramiko for the last couple of days. There are previous examples of how to do scp with paramiko out there, but the code isn't all on one page, you have to read through the mail thread and work it out from there. I figured I might save someone some time (possibly me!) and note a complete example of scp with paramiko...

#!/usr/bin/python

# A simple scp example for Paramiko.
# Args:
#   1: hostname
#   2: username
#   3: local filename
#   4: remote filename

import getpass
import os
import paramiko
import socket
import sys

# Socket connection to remote host
sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
sock.connect((sys.argv[1], 22))

# Build a SSH transport
t = paramiko.Transport(sock)
t.start_client()
t.auth_password(sys.argv[2], getpass.getpass('Password: '))

# Start a scp channel
scp_channel = t.open_session()
          
f = file(sys.argv[3], 'rb')
scp_channel.exec_command('scp -v -t %s\n'
                         % '/'.join(sys.argv[4].split('/')[:-1]))
scp_channel.send('C%s %d %s\n'
                 %(oct(os.stat(sys.argv[3]).st_mode)[-4:],
                   os.stat(sys.argv[3])[6],
                   sys.argv[4].split('/')[-1]))
scp_channel.sendall(f.read())

# Cleanup
f.close()
scp_channel.close()
t.close()
sock.close()

Tags for this post: python() paramiko()

Comment

SSL, X509, ASN.1 and certificate validity dates

Tue, 05 Aug 2008 15:53:00 GMT

I was curious about how SSL certificates store validity information (for example when a certificate expires), so I ended up reading the X509 specification (excitingly called "Internet X.509 Public Key Infrastructure Certificate and CRL Profile"), as well as the ASN.1 information for UTCTimes. This is all new to me, but I am sure lots of other people understand this.

In the end it wasn't too hard, and now I have hacked support for displaying certificate validity into Python's TLSlite. The point of this post is mainly so I can find that documentation again if I need it, although I'll put the TLSlite patch online as soon as I have had a chance to test it a little better.

Tags for this post: python() tlslite()

Comment

Dealing with remote HTTP servers with buggy chunking implementations

Thu, 10 Jul 2008 22:27:00 GMT

HTTP 1.1 implements chunking as a way of servers telling clients how much content is left for a given request, which enables you to send more than one piece of content in a given HTTP connection. Unfortunately for me, the site I was trying to access has a buggy chunking implementation, and that causes the somewhat fragile python urllib2 code to throw an exception:

Traceback (most recent call last):
  File "./mythingie.py", line 55, in ?
    xml = remote.readlines()
  File "/usr/lib/python2.4/socket.py", line 382, in readlines
    line = self.readline()
  File "/usr/lib/python2.4/socket.py", line 332, in readline
    data = self._sock.recv(self._rbufsize)
  File "/usr/lib/python2.4/httplib.py", line 460, in read
    return self._read_chunked(amt)
  File "/usr/lib/python2.4/httplib.py", line 499, in _read_chunked
    chunk_left = int(line, 16)
ValueError: invalid literal for int():

I muttered about this earlier today, including finding the bug tracking the problem in pythonistan. However, finding the will not fix bug wasn't satisfying enough...

It turns out you can just have urllib2 lie to the server about what HTTP version it talks, and therefore turn off chunking. Here's my sample code for how to do that:

import httplib
import urllib2

class HTTP10Connection(httplib.HTTPConnection):
  """HTTP10Connection -- a HTTP connection which is forced to ask for HTTP
     1.0
  """

  _http_vsn_str = 'HTTP/1.0'


class HTTP10Handler(urllib2.HTTPHandler):
  """HTTP10Handler -- don't use HTTP 1.1"""

  def http_open(self, req):
    return self.do_open(HTTP10Connection, req)

// ...

  request = urllib2.Request(feed)
  request.add_header('User-Agent', 'mythingie')
  opener = urllib2.build_opener(HTTP10Handler())
  
  remote = opener.open(request)
  content = remote.readlines()
  remote.close()

I hereby declare myself Michael Still, bringer of the gross python hacks.

Tags for this post: python()

Comment

Universal Feedparser and XML namespaces

Wed, 09 Jul 2008 05:22:00 GMT

I've always found python's Universal Feedparser to be a bit hard to work with when using feeds with XML namespaces. Specifically, if you don't care about the stuff in the namespaces then you're fine, but if you want that data it gets a lot harder.

In the past I've had to do some gross hacks. For example this gem is from the MythNetTV code:

  # Modify the XML to work around namespace handling bugs in FeedParser
  lines = []
  re_mediacontent = re.compile('(.*)<media:content([^>]*)/ *>(.*)')

  for line in xmllines:
    m = re_mediacontent.match(line)
    count = 1
    while m:
      line = '%s<media:wannabe%d>%s</media:wannabe%d>%s' %(m.group(1), count,
                                                         m.group(2),
                                                         count, m.group(3))
      m = re_mediacontent.match(line)
      count = count + 1

    lines.append(line)

  # Parse the modified XML
  xml = ''.join(lines)
  parser = feedparser.parse(xml)

Which is horrible, but works. This time around the problem is that I am having trouble getting to the gr:annotation tags in my Google reader shared items feed. How annoying.

In the case of the Google reader feed, the problem seems to be that the annotation is presented like this:

<gr:annotation><content type="html">Awesome. Canberra has needed
something better than buses between the towncenters for a while, and light rail 
seems like a great way to do it. I much prefer trains to buses, and catch a 
light rail service to work every day when I am in Mountain View.
</content><author gr:user-id="09387883873401903052" 
gr:profile-id="114835605728492647856"><name>mikal</name>
</author></gr:annotation>

Feedparser can only handle simple elements (not elements that contain other elements). Therefore, this gross hack is required to get this to parse correctly:

  simplify_re = re.compile('(.*)<gr:annotation>'
                           '<content type="html">(.*)</content>'
                           '<author .*><name>.*</name></author>'
                           '</gr:annotation>(.*)')

  new_lines = []
  for line in lines:
    m = simplify_re.match(line)
    if m:
      new_lines.append('%s<gr:annotation>%s</gr:annotation>%s'
                       %(m.group(1), m.group(2), m.group(3)))
    else:
      new_lines.append(line)

  d = feedparser.parse(''.join(new_lines))

Gross, and fragile, but working. This is cool, because it now means that I can apply more logic in the shared links that end up in my blather feed. I'm thinking of something along the lines of only shared links with an annotation will end up in that feed, and the blather entry will include the annotation. Or something like that.

Tags for this post: python() feedparser()

Comment

Domain name lookup helper for python?

Tue, 01 May 2007 21:00:00 GMT

Hi. I have a list of the domain portion of URLs which looks a bit like this:

Whois lookup for fycnds.digitalpoimt.com
Whois lookup for wvgpzdea.digitalpoimt.com
Whois lookup for zhnsht.digitalpoimt.com
Whois lookup for frigo25.php5.cz
Whois lookup for handrovina.php5.cz
Whois lookup for blabota.php5.cz
Whois lookup for pctuzing.php5.cz
Whois lookup for viagraviagra.php5.cz
Whois lookup for poiu.php5.cz
Whois lookup for flasa.php5.cz
Whois lookup for yoy4.digitalpoimt.com
Whois lookup for hskly.digitalpoimt.com
Whois lookup for 2i0wjwbc.digitalpoimt.com
Whois lookup for harnhjc.digitalpoimt.com
Whois lookup for gqru.digitalpoimt.com

I need some code which determines which portion of these hostnames is a whois-able domain name. My problem is this doesn't seem all that simple to do -- some countries have a second layer of TLDs, and some do not.

Does anyone know of a python library, or failing that simple algorithm, which will do this for me?

(For those left wondering, I am trying to do some analysis of the spam I get on this blog, and for that I want to know if the whois information for a domain that left a suspect comment indicates anything suspicious.)

Tags for this post: python()

Comment

Dear lazy web: writing to the win32 event log in Python

Thu, 14 Dec 2006 23:01:00 GMT

Dear Lazy Web,

I have a need to be able to write to the MS Windows event log in Python. I must admit I don't know a lot about Python on Windows. Does anyone have a good short sample they would like to share?

Hugs and kisses,
Mikal

Tags for this post: python()

Comment

Twisted conch

Mon, 08 May 2006 09:55:00 GMT

It seems to me that every time I go to write some networking code in Python, the twisted guys have got there before me. Today's adventures are involving twisted conch, which seems very cool. The documentation is a bit patchy though.

Tags for this post: python() twisted()

Comment

Twisted Python and Jabber SSL

Tue, 18 Apr 2006 22:07:00 GMT

Ok, so I thought it would be cool to be able to send Google Talk messages to my MythTV box. Can't be too hard to write a twisted python jabber client can it? Well, after an hour of surfing, I give up. I have the simple jabber client example, but it totally doesn't work with the Google servers, I suspect because it doesn't do SSL. I can see one of the twisted.words maintainers filing bugs against the xish stuff too, which I suspect means it's going to be a while.

A little bit disappointing me thinks.

Tags for this post: python() twisted()

Comment

Python DNS modules

Fri, 30 Dec 2005 17:07:00 GMT

My first python script involves doing some DNS lookups (for TXT records if that matters), and I am currently working through using the pydns module for this. Is this really the best DNS module to use for python though? For a start, it was last released in May 2002, and the documentation is somewhat sparse...

Tags for this post: python()

Comment

Example 2.1 from Dive Into Python

Mon, 28 Nov 2005 11:16:00 GMT

I've just started working through Dive Into Python, so I don't really have an opinion of the book yet. I did notice that Example 2.1 produces different output on my machine than from the example...

The example says I should get:

server=mpilgrim;uid=sa;database=master;pwd=secret

I get:

pwd=secret;database=master;uid=sa;server=mpilgrim

It's interesting that this is exactly the reverse of what the book says I should get. I have no idea why, as I can't read Python yet, but there you go.

Tags for this post: python() diveintopython()

Comment

Learning Python

Wed, 23 Nov 2005 14:37:00 GMT

Due to a personality crisis I've now decided it's the time in my life to learn Python. So, does anyone have good pointers to tutorials and so forth?

Tags for this post: python()

Comment