If you do a lot of web programming, it's most likely that you will come across this task: to get some information from a website that runs an XML-RPC service. Before we go into the depth of an XML-RPC service, let's launch an XML-RPC server and talk to it first.
In this recipe, we will use the Python Supervisor program that is widely used to launch and manage a bunch of executable programs. Supervisor can be run as a background daemon and can monitor child processes and restart if they die suddenly. We can install Supervisor by simply running the following command:
$pip install supervisor
We need to create a configuration file for Supervisor. A sample configuration is given in this recipe. In this example, we define the Unix HTTP server socket and a few other parameters. Note the rpcinterface:supervisor section where rpcinterface_factory is defined to communicate with clients.
Using Supervisor, we configure a simple server program in the program:8_2_multithreaded_multicall_xmlrpc_server.py section by specifying the command and some other parameters.
Listing 8.1a gives the code for a minimal Supervisor configuration, as shown:
[unix_http_server] file=/tmp/supervisor.sock ; (the path to the socket file) chmod=0700 ; socket file mode (default 0700) [supervisord] logfile=/tmp/supervisord.log loglevel=info pidfile=/tmp/supervisord.pid nodaemon=true [rpcinterface:supervisor] supervisor.rpcinterface_factory = supervisor.rpcinterface:make_main_rpcinterface [program:8_2_multithreaded_multicall_xmlrpc_server.py] command=python 8_2_multithreaded_multicall_xmlrpc_server.py ; the program (relative uses PATH, can take args) process_name=%(program_name)s ; process_name expr (default %(program_name)s)
If you create the preceding Supervisor configuration file in your favorite editor, you can run Supervisor by simply calling it.
Now, we can code an XML-RPC client that can act as a Supervisor proxy and give us the information about the running processes.
Listing 8.1b gives the code for querying a local XML-RPC server, as shown:
#!/usr/bin/env python
# Python Network Programming Cookbook -- Chapter – 8
# This program is optimized for Python 2.7.
# It may run on any other version with/without modifications.
import supervisor.xmlrpc
import xmlrpclib
def query_supervisr(sock):
transport = supervisor.xmlrpc.SupervisorTransport(None, None,
'unix://%s' %sock)
proxy = xmlrpclib.ServerProxy('http://127.0.0.1',
transport=transport)
print "Getting info about all running processes via Supervisord..."
print proxy.supervisor.getAllProcessInfo()
if __name__ == '__main__':
query_supervisr(sock='/tmp/supervisor.sock')If you run the Supervisor daemon, it will show the output similar to the following:
chapter8$ supervisord 2013-09-27 16:40:56,861 INFO RPC interface 'supervisor' initialized 2013-09-27 16:40:56,861 CRIT Server 'unix_http_server' running without any HTTP authentication checking 2013-09-27 16:40:56,861 INFO supervisord started with pid 27436 2013-09-27 16:40:57,864 INFO spawned: '8_2_multithreaded_multicall_xmlrpc_server.py' with pid 27439 2013-09-27 16:40:58,940 INFO success: 8_2_multithreaded_multicall_xmlrpc_server.py entered RUNNING state, process has stayed up for > than 1 seconds (startsecs)
Note that our child process, 8_2_multithreaded_multicall_xmlrpc_server.py, has been launched.
Now, if you run the client code, it will query the XML-RPC server interface of Supervisor and list the running processes, as shown:
$ python 8_1_query_xmlrpc_server.py Getting info about all running processes via Supervisord... [{'now': 1380296807, 'group': '8_2_multithreaded_multicall_xmlrpc_server.py', 'description': 'pid 27439, uptime 0:05:50', 'pid': 27439, 'stderr_logfile': '/tmp/8_2_multithreaded_multicall_xmlrpc_server.py-stderr--- supervisor-i_VmKz.log', 'stop': 0, 'statename': 'RUNNING', 'start': 1380296457, 'state': 20, 'stdout_logfile': '/tmp/8_2_multithreaded_multicall_xmlrpc_server.py-stdout--- supervisor-eMuJqk.log', 'logfile': '/tmp/8_2_multithreaded_multicall_xmlrpc_server.py-stdout--- supervisor-eMuJqk.log', 'exitstatus': 0, 'spawnerr': '', 'name': '8_2_multithreaded_multicall_xmlrpc_server.py'}]
This recipe relies on running the Supervisor daemon (configured with rpcinterface) in the background. Supervisor launches another XML-RPC server, as follows: 8_2_multithreaded_multicall_xmlrpc_server.py.
The client code has a query_supervisr()method, which takes an argument for the Supervisor socket. In this method, an instance of SupervisorTransport is created with the Unix socket path. Then, an XML-RPC server proxy is created by instantiating the ServerProxy() class of xmlrpclib by passing the server address and previously created transport.
The XML-RPC server proxy then calls the Supervisor's getAllProcessInfo() method, which prints the process information of the child process. This process includes pid, statename, description, and so on.