I want to use flask, flask-socketio to implement an application which accept "command string" (like: ping 8.8.8.8) at the browser, then the server execute it and return the command's output to browser in real time.
My implementation is as below.
The client side emits 'exec_event' event to the server, the server runs the command and continually emit 'exec_response' event to client when new output is generated by the command.
The client can also send 'ctrlc_event' to server if it want to terminate the command.
Problem I got is:
The server can't handle the 'ctrlc_event' when it's handling the previous 'exec_event'. If I directly killed the long-running command like 'ping 8.8.8.8' on the server, then the server begin to handle 'ctrlc_event'.
Can anyone point me out the reason or give me some direction?
Server side code
from gevent import monkey
monkey.patch_all()
from flask import Flask, render_template, session, Response
from flask.ext.wtf import Form
from wtforms import StringField, SubmitField
from wtforms.validators import DataRequired
from flask.ext.socketio import SocketIO, emit
import os
import time
from subprocess import Popen, PIPE
class ExecForm(Form):
command = StringField('Command: ', validators=[DataRequired()])
submit = SubmitField('Execute')
class CtrlCForm(Form):
submit = SubmitField('Ctrl C')
app = Flask(__name__)
app.debug = True
app.config['SECRET_KEY'] = 'hard-to-guess'
socketio = SocketIO(app)
@app.route('/')
def index():
exec_form = ExecForm()
ctrlc_form = CtrlCForm()
return render_template('index.html',
exec_form=exec_form,
ctrlc_form=ctrlc_form)
@socketio.on('exec_event', namespace='/test')
def execute(message):
command = message['data']
process = Popen(command, shell=True, stdout=PIPE, stderr=PIPE,
close_fds=True, preexec_fn=os.setsid)
session['pid'] = process.pid
for out in iter(process.stdout.readline, ''):
out = '<pre>' + out + '</pre>'
emit('exec_response', {'data': out})
time.sleep(0.001)
out = "Command finished." + '<br /><br />'
emit('exec_terminate', {'data': out})
@socketio.on('ctrlc_event', namespace='/test')
def ctrlc(message):
print("Received ctrlc")
# do something to kill the process
# finally emit an event.
out = "Process killed." + '<br /><br/>'
emit('ctrlc_response', {'data': out})
if __name__ == '__main__':
socketio.run(app, host='0.0.0.0', port=8080)
Client code is
<html>
<head>
<title>Example</title>
<script type="text/javascript" src='//code.jquery.com/jquery-1.11.0.min.js'></script>
<script type="text/javascript" src="//cdnjs.cloudflare.com/ajax/libs/socket.io/0.9.16/socket.io.min.js"></script>
<script type="text/javascript">
$(document).ready(function(){
var socket = io.connect('http://' + document.domain + ':' + location.port + '/test');
$('#exec_form').submit(function(event) {
socket.emit('exec_event', {data: $('#exec_input').val()});
return false;
});
$('#ctrlc_form').submit(function(event) {
socket.emit('ctrlc_event', {data: 'nothing'});
return false;
});
socket.on('exec_response', function(msg) {
$('#result').append(msg.data);
});
socket.on('exec_terminate', function(msg) {
$('#result').append(msg.data);
});
socket.on('ctrlc_response', function(msg) {
$('#result').append(msg.data);
});
});
</script>
<style>
.result {
overflow-y: scroll;
width: 100%;
height: 400px;
border: 4px solid red;
}
.result pre {
margin: 2px;
}
</style>
</head>
<body>
<h3>Flask Example</h3>
<form id="exec_form" method='POST' action='#' target='result'>
{{ exec_form.command.label }}
{{ exec_form.command(id="exec_input", placeholder="command", size=100) }}
{{ exec_form.submit(id="exec_btn") }}
</form>
<form id="ctrlc_form" method='POST' action='#' target='result'>
{{ ctrlc_form.submit(id="ctrlc_btn") }}
</form>
<div id="result" class="result"></div>
</body>
</html>
The problem is caused by the way the
gevent-socketioserver is structured. When the server receives an event from a client (let's say yourexec_event), it dispatches the event by calling the appropriate handler. That thread will then run the event handler, and only once the handler returns it will go back to check for new client originated events.The solution is to send the
ctrlc_eventon a different communication channel, not the same that you use forexec_event. For example, open two connections on different namespaces, then each connection will get its own server thread.