gossh-python 0.9

GoSSH Python

gossh-python

The purpose of this module is to provide a Python interface to the Golang ssh module.

It was made very easy with the help of the Golang gopy module.

It has come about because I found Paramiko to be a bit unwieldy and have some odd behaviours under certain conditions (we connect to a lot of wireless devices that often have very poor connectivity); I've also done some testing with SSH2-Python but I think it's a bit too young ( good performance when it worked, but odd behaviour that I couldn't explain from time-to-time, especially when comparing Python vs PyPy).

Versions

This version (0.2.4) is the last version to support Python 2; all versions after this have been subject to a refactor and support Python 3 only.

Limitations

• Python command needs to be prefixed with GODEBUG=cgocheck=0 (or have that in the environment)
• It's implemented in a very basic non-blocking approach (calls to .Read(size) will always finish instantly)
• Seems to have some odd memory problems with PyPy (via CFFI); lots of locks and stuff to try and alleviate that

How do I make use of this?

Right now I'm still working on how to put it all together as a Python module, so here are the raw steps.

Prerequisites

• Go 1.13
• Python 2.7+
• pip
• virtualenvwrapper
• pkgconfig/pkg-config

Setup (for dev)

• mkvirtualenvwrapper -p (/path/to/pypy) gossh-python
• pip install -r requirements.txt
• ./build.sh
• GODEBUG=cgocheck=0 py.test -v

What's worth knowing if I want to further the development?

• gopy doesn't like Go interfaces; so make sure you don't have any public (exported) interfaces
  • this includes a struct with a public property that may eventually lead to an interface

Example Go RPCSession usage (simple session ID, calls return strings)

There's no real reason why you'd want to do this (just use x/crypto/ssh on it's own)- it's more for reference:

package main

import (
	"gossh_python"
	"fmt"
    "time"
)

func main() {

	sessionID := gossh_python.NewRPCSession(
		"1.2.3.4",
		"some_username",
        "some_password",
        22,
		5,
	)

	err := gossh_python.RPCConnect(sessionID)
	if err != nil {
		panic(err)
	}

	err := gossh_python.RPCGethell(sessionID) // this starts a goroutine to read from session's STDOUT
	if err != nil {
		panic(err)
	}

	err := gossh_python.RPCWrite(sessionID, "uname -a\n")
	if err != nil {
		panic(err)
	}

    time.Sleep(time.Second * 5) // because .Read(size) is non-blocking, give the buffer some time to fill up

	data, err := gossh_python.RPCRead(sessionID, 1024)
    if err != nil {
        panic(err)
    }

    fmt.Println(data)

	err = gossh_python.RPCClose(sessionID) // stops the goroutine
	if err != nil {
		panic(err)
	}

}

Example Python usage (uses RPCSession underneath because of memory leaks between Go and Python with structs)

To create an SSH session in Python do the following:

import time

from gossh_python import create_session

session = create_session(
    hostname='1.2.3.4',
    username='some_username',
    password='some_password',
)

session.connect()

session.get_shell()

session.write('uname -a\n')

time.sleep(5)

print(session.read())

session.close()

To test the build in a docker container

./test.sh