Java NIO server and Python asyncore client


F

foobarometer

Can someone help answer this?
http://stackoverflow.com/questions/14698020/java-nio-server-and-python-asyncore-client

Blocking python client works, asyncore doesn't work.

Server.java:


import java.net.InetAddress;
import java.net.InetSocketAddress;
import java.nio.channels.SelectionKey;
import java.nio.channels.ServerSocketChannel;
import java.nio.channels.SocketChannel;
import java.nio.channels.SelectableChannel;
import java.nio.channels.Selector;
import java.nio.ByteBuffer;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.Set;

class Server
{
public Selector sel;
public ServerSocketChannel ssc;
public SocketChannel channel;
public static void main(String[] args) throws Exception
{
Server s = new Server();
s.openSocket(12000);
s.run();
}

private void openSocket(int port) throws Exception
{
InetSocketAddress address = new InetSocketAddress("0.0.0.0", port);
ssc = ServerSocketChannel.open();
ssc.configureBlocking(false);
ssc.socket().bind(address);
sel = Selector.open();
ssc.register(sel, SelectionKey.OP_ACCEPT);
}

public void run() throws Exception
{
while (true)
{
sel.select();
Set<SelectionKey> keys = sel.selectedKeys();
Iterator<SelectionKey> i = keys.iterator();
while (i.hasNext())
{
SelectionKey key = (SelectionKey) i.next();
i.remove();
if (!key.isValid())
{
continue;
}
if (key.isAcceptable())
{
channel = ssc.accept();
channel.configureBlocking(false);
System.out.println("Accepted...\n");
channel.register(sel, SelectionKey.OP_READ);
}
if (key.isReadable())
{
if (channel == key.channel())
{
System.out.println("Readable\n");
ByteBuffer buffer = ByteBuffer.wrap(new byte[1024]);
int pos = channel.read(buffer);
buffer.flip();
System.out.println(new String(buffer.array(), 0, pos));
}
}
}
}
}
}

Asyncore Python Code:

import socket
import select
import asyncore

class Connector(asyncore.dispatcher):
def __init__(self, host, port):
asyncore.dispatcher.__init__(self)
self.buffer = "hi"
self.create_socket()
self.connect((host, port))

def handle_connect(self):
print("[]---><---[]") # not called <------------------

def handle_read(self):
pass

def writable(self):
len(self.buffer) > 0

def handle_write(self):
sent = self.send(self.buffer)
print("[]--->" + self.buffer[0:sent])
self.buffer = self.buffer[sent:]

def handle_close(self):
print("[]...x...[]")
self.close()


connector = Connector("localhost", 12000, Handler())
asyncore.loop()

Python Blocking client:
# Echo client program
import socket
import sys

HOST = 'localhost' # The remote host
PORT = 12000 # The same port as used by the server
s = None
for res in socket.getaddrinfo(HOST, PORT, socket.AF_UNSPEC, socket.SOCK_STREAM):
af, socktype, proto, canonname, sa = res
try:
s = socket.socket(af, socktype, proto)
print("socket")
except OSError as msg:
s = None
continue
try:
s.connect(sa)
print("connected")
except OSError as msg:
s.close()
s = None
continue
break
if s is None:
print('could not open socket')
sys.exit(1)
print("Sending")
s.sendall(bytes("Hey server", "UTF-8"))
data = s.recv(1024)
# s.close()
print('Received', repr(data))
 
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D

dieter

Can someone help answer this?
http://stackoverflow.com/questions/14698020/java-nio-server-and-python-asyncore-client

Blocking python client works, asyncore doesn't work.

I fear you must tell us which Python version you are using.
Your call to "dispatcher.create_socket" is incompatible with
the code in Python 2.7 (it lacks parameters "family" and "type").


Otherwise, I could not detect a problem in your code.
I assume that "does not work" does not mean "I get an exception"
but means "I do not get anything".

You might need some debugging to detect the problem.

Check "dispatcher.socket_map" after you have set up your connector.
It should contain your connector object and this should
be both "readable()" and "writable()".

If this is the case, I would debug "asyncore.loop":

"asyncore.dispatcher" treats the socket as "connected"
as soon as it becomes either "readable" or "writable".

Both should happen after "connect" is successful. Thus,
I would look what goes wrong:

* the socket does not become readable/writable

this would proabably mean that the socket never
gets connected, maybe because of bad parameters
to "create_socket".

* the channel is not properly registered

* bad internal state
 
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P

Petri Heinilä

Can someone help answer this?

http://stackoverflow.com/questions/14698020/java-nio-server-and-python-asyncore-client



Blocking python client works, asyncore doesn't work.

There was return missing in writeable().

Modified code::

----
import socket
import select
import asyncore

class Connector(asyncore.dispatcher):
def __init__(self, host, port):
asyncore.dispatcher.__init__(self)
self.debug = True
self.buffer = bytes("hi","ascii")
self.create_socket(socket.AF_INET,socket.SOCK_STREAM)
print("Connector.connect(({},{}))".format(host,port))
self.connect((host, port))

def handle_connect(self):
print("handle_connect()") # not called <------------------

def handle_read(self):
print("handle_read()")
self.recv(4096)
self.close()

def writable(self):
print("writable()")
return len(self.buffer) > 0 # remember RETURN

def handle_write(self):
print("handle_write()")
sent = self.send(self.buffer)
print("send({})".format(self.buffer[0:sent]))
self.buffer = self.buffer[sent:]

def handle_close(self):
print("handle_close()")
self.close()

connector = Connector("localhost", 12000) # Handler()
print("asyncore.loop() enter")
asyncore.loop()
print("asyncore.loop() leave")
----

BSD socket communication framework does not itself support connection indications
on connection-oriented protocols, so asyncore "fakes" the indication by detecting
if socket is writable. As the writable was false => no write event => no connection indication.

asyncore usage and documentation is bad, so when using the module, read the source
code to understand it's usage and functioning, or use other implementation eg.
Tornado.
 

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