I'm having trouble using select. I just want a mean to know which clients are still there to receive data. There is my code :
import socket, select
server = socket.socket()
server.bind(('localhost',80))
server.listen(1)
answer = "HTTP/1.1 200 OK\r\n"
answer+= "Content-type: text/plain\r\n"
answer+= "Connection: close\r\n"
body = "test msg"
answer+= "Content-length: %d\r\n\r\n" % len(body)
answer+= body
clients = []
while True:
nextclient,addr = server.accept()
clients.append(nextclient)
clients = select.select([],clients,[],0.0)[1]
for client in clients:
client.send(answer)
The select send me everytime all the sockets opened before, even if the connection was closed on the other end, this results in a Errno1053 : an etablished connection was aborted by the software in your host machine.
I thank you in advance for your help.
Your select never blocks.
A time-out value of zero specifies a poll and never blocks.
Also, your listen method's argument is absolutely extreme.
socket.listen(backlog)
Listen for connections made to the socket. The backlog argument specifies the maximum number of queued connections and should be at
least 0; the maximum value is system-dependent (usually 5)
As far as I can tell, you never close a socket after writing to it and you don't as well remove it from clients.
Besides, you overwrite clients so that your list of clients is lost; some clients will never be processed.
Something like
clients_now = select.select([],clients,[],0.0)[1]
for client in clients_now:
client.send(answer)
client.close()
clients.remove(client)
might help.
BTW, just a small block of 1 or 10 ms will keep your server responsive, but prevents a high CPU load because of idle waiting.
BTW2: Maybe you should include your server socket in the select process as well...
Related
I'm trying to get the machine data from a CNC HAAS controller. It has a built-in software called MDC, which acts as a server. I need to write a client program to send a request to the MDC's IP and port number. when I send a request and receive it seems like the server is sending it one byte at a time and so I could capture only one byte at a time, others are lost. How to get the entire data. I'm using Python's socket module.
I've used a while loop, based on a previous question on Stack Overflow, but it seems like the server is sending the data and closing the connection and by the time my client program loops again, the other data is lost and the connection is closed.
# Import socket module
import socket
# Create a socket object
s = socket.socket(socket.AF_INET,socket.SOCK_STREAM)
# Define the port on which you want to connect
port = 5051
# connect to the server on local computer
s.connect(('192.168.100.3', port))
#sending this message will give me the status of the CNC machine
s.send(("?Q500").encode())
d= (s.recv(1024)).decode()
print(d)
s.close()
The expected output is:
>PROGRAM, MDI, IDLE, PARTS, 380
The output I'm getting is > , which is just the first character (byte) of the actual output.
A bit more code would be helpful but i will try to hlp with what you gave us
you could try this
s.send(("?Q500").encode("utf-8")) # just add an encoding
fullData = ""
while True:
d = (s.recv(1024)).decode("utf-8")
fullData += d
if not d:
print(fullData)
s.close()
break
I'm a beginner in the field of sockets and lately trying ti create a terminal chat app with that.I still have trouble understanding setblocking and select functions
"This is the code i have taken from a website i'm reading from and in the code if there is nothing in data, how does it mean that the socket has been disconnected and please also do explain what affect the setblocking in the server or the client does.I have read somewhere that setblocking allows to move on if the data has been fully not recieved,i'm not quite satisfied with the explaination.Please explain in simple words "
import select
import socket
import sys
import Queue
server = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
server.setblocking(0)
server_address = ('localhost', 10000)
server.bind(server_address)
server.listen(5)
inputs = [ server ]
outputs = [ ]
message_queues = {}
while inputs:
readable, writable, exceptional = select.select(inputs, outputs, inputs)
for s in readable:
if s is server:
connection, client_address = s.accept()
connection.setblocking(0)
inputs.append(connection)
message_queues[connection] = Queue.Queue()
else:
data = s.recv(1024)
if data:
message_queues[s].put(data)
if s not in outputs:
outputs.append(s)
else:
if s in outputs:
outputs.remove(s)
inputs.remove(s)
s.close()
if there is nothing in data, how does it mean that the socket has been disconnected
The POSIX specification of recv() says:
Upon successful completion, recv() shall return the length of the message in bytes. If no messages are available to be
received and the peer has performed an orderly shutdown, recv() shall return 0. …
In the Python interface, return value 0 corresponds to a returned buffer of length 0, i. e. nothing in data.
what affect the setblocking in the server or the client does.
The setblocking(0) sets the socket to non-blocking, i. e. if e. g. the accept() or recv() cannot be completed immediately, the operation fails rather than blocks until complete. In the given code, this can hardly happen, since the operations are not tried before they are possible (due to the use of select()). However, the example is bad in that it includes output in the select() arguments, resulting in a busy loop since output is writable most of the time.
I have a multi-threaded Python 3 application that on thread #1 accepts TCP socket communications. Thread #2 will check all current connections if they have anything to receive, then act accordingly.
So, currently I have a list called all_connections which is a list of accepted socket connection objects.
Using for connection in all_connections: I can loop through all the connection objects. I know I use conn.recv(256) to check if there is anything ready to recive on this socket. Will this block the loop though untill there is something to receive? I have set conn.setblocking(1) beforehand although Im unsure if this is the best way to get around it:
Here is some example code:
Thread 1
self.all_connections = [] # init a list to hold connection objs
while 1:
try:
conn, address = self.socket.accept()
conn.setblocking(1) # non blocking
except Exception as e:
continue
self.all_connections.append(conn) # Save the connection object
Thread 2
while True:
for connection in self.all_connections:
received = connection.recv(256)
return
So, I'm only interested in connections that have actually sent something, as I will be sending them something back most likely.
I know I can use select.select in order to check if there is anything to receive on the socket, but that wouldn't help me reference the specific connection.
Yes, read() will block; this is the default behaviour. Calling socket.setblocking(1) actually enables blocking, which is opposite of what you wanted. setblocking(False) will set non-blocking mode. I/O on non-blocking sockets requires that you use exception handling.
A better way, and you are already headed in the right direction, is to use select(). You do in fact know which socket sent data because select() returns a list of sockets that are available for reading, writing, or that have an error status. You pass to select() a list of the sockets that you are interested in and it returns those that are available for I/O. Here is the function signature:
select(...)
select(rlist, wlist, xlist[, timeout]) -> (rlist, wlist, xlist)
So the code in thread 2 would look something like this:
from select import select
while True:
rlist, wlist, xlist = select(self.all_connections, [], [])
for connection in rlist:
received = connection.recv(256)
The above code only checks for readable sockets in the list of all connections and reads data from those that are ready. The read will not block.
Short description:
Client sends server data via TCP socket. Data varies in length and is strings broken up by the delimiter "~~~*~~~"
For the most part it works fine. For a while. After a few minutes data winds up all over the place. So I start tracking the problem and data is ending up in the wrong place because the full thing has not been passed.
Everything comes into the server script and is parsed by a different delimiter -NewData-* then placed into a Queue. This is the code:
Yes I know the buffer size is huge. No I don't send data that kind of size in one go but I was toying around with it.
class service(SocketServer.BaseRequestHandler):
def handle(self):
data = 'dummy'
#print "Client connected with ", self.client_address
while len(data):
data = self.request.recv(163840000)
#print data
BigSocketParse = []
BigSocketParse = data.split('*-New*Data-*')
print "Putting data in queue"
for eachmatch in BigSocketParse:
#print eachmatch
q.put(str(eachmatch))
#print data
#self.request.send(data)
#print "Client exited"
self.request.close()
class ThreadedTCPServer(SocketServer.ThreadingMixIn, SocketServer.TCPServer):
pass
t = ThreadedTCPServer(('',500), service)
t.serve_forever()
I then have a thread running on while not q.empty(): which parses the data by the other delimiter "~~~*~~~"
So this works for a while. An example of the kind of data I'm sending:
2016-02-23 18:01:24.140000~~~*~~~Snowboarding~~~*~~~Blue Hills~~~*~~~Powder 42
~~~*~~~Board Rental~~~*~~~15.0~~~*~~~1~~~*~~~http://bigshoes.com
~~~*~~~No Wax~~~*~~~50.00~~~*~~~No Ramps~~~*~~~2016-02-23 19:45:00.000000~~~*~~~-15
But things started to break. So I took some control data and sent it in a loop. Would work for a while then results started winding up in the wrong place. And this turned up in my queue:
2016-02-23 18:01:24.140000~~~*~~~Snowboarding~~~*~~~Blue Hills~~~*~~~Powder 42
~~~*~~~Board Rental~~~*~~~15.0~~~*~~~1~~~*~~~http://bigshoes.com
~~~*~~~No Wax~~~*~~~50.00~~~*~~~No Ramps~~~*~~~2016-02-23 19:45:00.000000~~~*~
Cutting out the last "~~-15".
So the exact same data works then later doesn't. That suggests some kind of overflow to me.
The client connects like this:
class Connect(object):
def connect(self):
host = socket.gethostname() # Get local machine name
#host = "127.0.0.1"
port = 500 # Reserve a port for your service.
sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
#print('connecting to host')
sock.connect((host, port))
return sock
def send(self, command):
sock = self.connect()
#recv_data = ""
#data = True
#print('sending: ' + command)
sock.sendall(command)
sock.close()
return
It doesn't wait for a response because I don't want it hanging around waiting for one. But it closes the socket and (as far as I understand) I don't need to flush the socket buffer or anything it should just be clearing itself when the connection closes.
Would really appreciate any help on this one. It's driving me a little spare at this point.
Updates:
I'm running this on both my local machine and a pretty beefy server and I'd be pushed to believe it's a hardware issue. The server/client both run locally and sockets are used as a way for them to communicate so I don't believe latency would be the cause.
I've been reading into the issues with TCP communication. An area where I feel I'll quickly be out of my depth but I'm starting to wonder if it's not an overflow but just some king of congestion.
If sendall on the client does not ensure everything is sent maybe some kind of timer/check on the server side to make sure nothing more is coming.
The basic issue is that your:
data = self.request.recv(163840000)
line is not guaranteed to receive all the data at once (regardless of how big you make the buffer).
In order to function properly, you have to handle the case where you don't get all the data at once (you need to track where you are, and append to it). See the relevant example in the Python docs on using a socket:
Now we come to the major stumbling block of sockets - send and recv operate on the network buffers. They do not necessarily handle all the bytes you hand them (or expect from them), because their major focus is handling the network buffers. In general, they return when the associated network buffers have been filled (send) or emptied (recv). They then tell you how many bytes they handled. It is your responsibility to call them again until your message has been completely dealt with.
As mentioned, you are not receiving the full message even though you have a large buffer size. You need to keep receiving until you get zero bytes. You can write your own generator that takes the request object and yields the parts. The nice side is that you can start processing messages while some are still coming in
def recvblocks(request):
buf = ''
while 1:
newdata = request.recv(10000)
if not newdata:
if buf:
yield buf
return
buf += newdata
parts = buf.split('*-New*Data-*')
buf = parts.pop()
for part in parts:
yield part
But you need a fix on your client also. You need to shutdown the socket before close to really close the TCP connection
sock.sendall(command)
sock.shutdown(request.SHUT_RDWR)
sock.close()
Okay, so in some experimentation with sockets and networking, I've set up a very basic chat client/server that runs on Unix flawlessly. Now I'm hitting some errors in the translation to win32. In preface, I understand that select.select() on Windows won't accept socket objects and have (I think) compensated coherently by not passing it the socket object, but the socket number. However, the script still hangs on the select.select() function and I have no idea why. The script only hangs until the server receives a message, after which it allows the client to send messages, however the client can't receive messages from the server, no matter what. I'm trying to troubleshoot these two bugs as best as I can, but my research has turned up dry. Here's the problem code, thanks in advance.
while True:
socket_list.append(s)
read_sockets, write_sockets, error_sockets = select.select(socket_list, [], [], 20)
if not (read_sockets or write_sockets or error_sockets):
if afk == False:
s.send('[Status]: '+str(_user)+' has gone afk.\n')
sys.stdout.write('\n[+]: You have gone afk.\n')
afk = True
prompt()
for sock in read_sockets:
print ('Starting for sock in read_sockets') #DEBUG#
if sock == s:
print ('Getting here.') #DEBUG#
data = sock.recv(4096)
if not data:
sys.stdout.write('[!]: Disconnected from chat server by server.\n'+W)
choice = raw_input('[*]: Press Enter to continue.')
_logic()
else:
sys.stdout.write(data)
else:
# Rest of the Program (Runs correctly) #
It sounds like you forgot to set the sockets non-blocking. Like pretty much all status reporting functions, select does not make future guarantees. You also need to handle the case where read returns a "would block" indication. You can't rely on select to predict the results of future read operations.