Start of something that'll use phantomjs to get performance info about getting a site, and then capture packets in the background.

test.py

import multiprocessing
import pprint
import time
import scapy.all as scapy
import subprocess
import sys
import os
import signal

import psutil


def run_process():
    cmd = "kill -STOP $$; phantomjs confess.js http://jira.youview.co.uk performance"
    cwd = "/Users/ai/Programming/libs/confess"
    proc = subprocess.Popen(cmd,
                            cwd=cwd,
                            shell=True,
                            stdout=subprocess.PIPE,
                            stderr=subprocess.STDOUT)
    return proc


class SniffProcess(multiprocessing.Process):
    def __init__(self, result_queue):
        super(SniffProcess, self).__init__()
        self.result_queue = result_queue

    def run(self):
        a = None
        try:
            a = scapy.sniff(filter="tcp and ( port 80 or port 443 ) or port 53")
        finally:
            print a
            self.result_queue.put(a)


def main():
    proc = run_process()
    wrapped_proc = psutil.Process(proc.pid)

    queue = multiprocessing.Queue()
    sniff_proc = SniffProcess(queue)
    sniff_proc.start()

    proc_to_conn = {}
    is_running = False
    while 1:
        time.sleep(0.01)
        if is_running is False and wrapped_proc.status != psutil.STATUS_RUNNING:
            wrapped_proc.resume()
            is_running = True
        if is_running is True and wrapped_proc.status != psutil.STATUS_RUNNING:
            print proc.communicate()[0]
            os.kill(sniff_proc.pid, signal.SIGINT)
            time.sleep(1)
            sniff_proc.terminate()
            import ipdb; ipdb.set_trace()
            pass

            return 0
        processes = [process for process in wrapped_proc.get_children(recursive=True)]
        for process in processes:
            try:
                connections = [conn for conn in process.get_connections('tcp')]
                if proc_to_conn.get(process, None) != connections:
                    proc_to_conn[process] = connections
                    pprint.pprint([process, connections])
            except psutil.NoSuchProcess:
                del proc_to_conn[process]

if __name__ == "__main__":
    sys.exit(main())