I'm trying to write a simple socket-based client in Python that will connect to a telnet server. I can test the server by telnetting to its port (5007), and entering text. It responds with a NAK (error) or an AK (success), sometimes accompanied by other text. Seems very simple.
I wrote a client to connect and communicate with the server, but it hangs on the first attempt to read the response. The connection is successful. Queries like getsockname and getpeername are successful. The send command returns a value that equals the number of characters I'm sending, so it seems to be sending correctly. But in the end, it always hangs when I try to read the response.
I've tried using both file-based objects like readline and write (via socket.makefile), as well as using send and recv. With the file object I tried making it with "rw" and reading and writing via that object, and later tried one object for "r" and another for "w" to separate them. None of these worked.
I used a packet sniffer to watch what's going on. I'm not versed in all that I'm seeing, but during a telnet session I can see my typed text and the server's text coming back. During my Python socket connection, I can see my text going to the server, but packets back don't seem to have any text in them.
Any ideas on what I'm doing wrong, or any strategies to try?
Here's the code I'm using (in this case, it's with send and recv):
#!/usr/bin/python
host = "localhost"
port = 5007
msg = "HELLO EMC 1 1"
msg2 = "HELLO"
import socket
import sys
try:
skt = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
except socket.error, e:
print("Error creating socket: %s" % e)
sys.exit(1)
try:
skt.connect((host,port))
except socket.gaierror, e:
print("Address-related error connecting to server: %s" % e)
sys.exit(1)
except socket.error, e:
print("Error connecting to socket: %s" % e)
sys.exit(1)
try:
print(skt.send(msg))
print("SEND: %s" % msg)
except socket.error, e:
print("Error sending data: %s" % e)
sys.exit(1)
while 1:
try:
buf = skt.recv(1024)
print("RECV: %s" % buf)
except socket.error, e:
print("Error receiving data: %s" % e)
sys.exit(1)
if not len(buf):
break
sys.stdout.write(buf)
Oh, in case it's useful, here's an example telnet session done manually:
ubuntu:~/mac/python$ telnet localhost 5007
Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]'.
HELLO EMC 1 1
HELLO ACK EMCNETSVR 1.1
The first 'HELLO' line is what I typed, the second one is the response.
You probably need to terminate your msg with some kind of "line-ending characters" -- perhaps \r\n, perhaps just one of the two. When you're in telnet, didn't you terminate your typed text by hitting a Return or Enter key? In the Python code, you're not doing the equivalent of that.
You need to flush the socket right after the send, to force the TCP stack to actually send the data. Otherwise it will wait for more data to send, in order to fill a packet effectively. While you are waiting for a response from the server nothing has actually been sent yet.
Related
I am trying to create HL7 listener in python. I am able to receive the messages through socket , but not able to send valid acknowledgement
ack=u"\x0b MSH|^~\\&|HL7Listener|HL7Listener|SOMEAPP|SOMEAPP|20198151353||ACK^A08||T|2.3\x1c\x0d MSA|AA|153681279959711 \x1c\x0d"
ack = "MSH|^~\&|HL7Listener|HL7Listener|SOMEAPP|SOMEAPP|20198151353||ACK^A08||T|2.3 \r MSA|AA|678888295637322 \r"
ack= bytes(ack,'utf-8')
Python code :
def listner_hl7():
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
try:
s.bind((socket.gethostname(), 4444))
except Exception as e:
print(str(e))
s.listen(5)
while True:
clientSocket, addr = s.accept()
message = clientSocket.recv(2048)
id = (str(message.splitlines()[0]).split('|')[9])
print('received {} bytes from {}'.format(
len(message), addr))
print('sending acknowledgement: ')
ack = b"\x0b MSH|^~\\&|HL7Listener|HL7Listener|SOMEAPP|SOMEAPP|20198151353||ACK^A08||T|2.3\x1c\x0d MSA|AA|" + bytes(
id, 'utf-8') + b" \x1c\x0d"
clientSocket.send(ack)
I think your complete acknowledge is not being sent. You are using clientSocket.send(ack).
Use clientSocket.sendall(ack) instead.
Please refer to this answer from #kwarunek for more details.
socket.send is a low-level method and basically just the C/syscall method send(3) / send(2). It can send less bytes than you requested, but returns the number of bytes sent.
socket.sendall is a high-level Python-only method that sends the entire buffer you pass or throws an exception. It does that by calling socket.send until everything has been sent or an error occurs.
If you're using TCP with blocking sockets and don't want to be bothered by internals (this is the case for most simple network applications), use sendall.
try adding enter in front of MSA|AA in the \n syntax I think it works
Im having trouble getting my very basic and simple TCP Server to properly work with http requests. This is what I have so far
from socket import *
import sys
serverSocket = socket(AF_INET, SOCK_STREAM)
serverSocket.bind(('', 4567))
serverSocket.listen(1)
while True:
print('Ready to serve...')
connectionSocket, addr = serverSocket.accept()
print("connected from: ", addr)
try:
message = connectionSocket.recv(1024)
filename = message.split()[1]
f = open(filename[1:])
outputdata = f.read()
connectionSocket.send("HTTP/1.1 200 OK\r\n")
for i in range(0, len(outputdata)):
connectionSocket.send(outputdata[i].encode())
connectionSocket.send("\r\n".encode())
connectionSocket.close()
except IOError:
connectionSocket.send("file not found")
serverSocket.close()
sys.exit()
The error comes from the open statement. I dont fully understand how this line of code's return value is organized.
message = connectionSocket.recv(1024)
I know that the return value is in bytes but when I try to use a fuction to turn it into a string like decode() i get errors as well
I have the .py file and the html file sitting in the same directory on my local machine and the way I test this is I just run this and open up a browser and type in
http://127.0.0.1:4567/helloworld.html
My code then promptly crashes after receiving the HTTP request.
Any and all help will be greatly appreciated!
There are numerous problems with your code and since you don't state what specific issues you are concerned about, here is what I see:
connectionSocket.send(outputdata[i].encode())
connectionSocket.send("\r\n".encode())
That appears to send a newline after every character you send back to the client.
Also, it doesn't deal with the client disconnecting because you're sending back invalid data.
Even if what you were trying to do didn't have these errors in it, you don't appear to be attempting to send back a valid http response.
https://www.w3.org/Protocols/rfc2616/rfc2616-sec6.html
I am working on socket programming in python. Using ESP python i have created a socket to server and sending a request (in API packet format, according to server code it will respond). In receiving socket, i need to check the data(if data is received, it need continue to next operation. If not, i need to send request once again).
sending is okay. In receiving socket, if it is not receiving data, it is not going to next instruction.. please help me out.
code:
try:
s = socket(AF_INET, SOCK_DGRAM)
print "socket created"
except socket.error:
print "failed to create socket"
sys.exit()
sending data:
s.sendto("packet of data", 0, (HOST,PORT))
In receiving:
recvpack, payload=s.recvfrom(1024)
if not recvpack:
s.sendto("packet of data", 0, (HOST,PORT))
elif(recvpack[]="packet of data"):
pass # continue to next operations..
In the above receiving statement, if recvfrom() in not getting anydata, how to check recvpack and get back to next operations.. If socket.settimeout() or socket.setblocking() is the solution, how to use these..
If you don't mind a blocking call, I usually use settimeout to wait for a message. settimeout will raise an exception if it doesn't receive a message in time.
So basically you could do something like this:
s.settimeout(1)
try:
recvpack, payload = s.recvfrom(1024)
except error:
recvpack = None
if recvpack is not None:
...
Source : https://docs.python.org/2/library/socket.html#socket.socket.settimeout
I am writing a small python script in order to use it for checking haproxy. What the script does is to connect on haproxy socket and "poll" for stats.
#!/usr/bin/env python
import socket
import sys
my_socket = socket.socket( socket.AF_UNIX, socket.SOCK_STREAM )
try:
my_socket.connect( "/var/run/haproxy/haproxy.sock" )
except socket.error:
print "cant connect to socket"
sys.exit(1)
my_socket.send("show stat\n")
response = my_socket.recv(1024)
print response
What i wish to do is if there is no response from the socket, meaning if haproxy will not output the stats, to exit the script with exit code (1).Is it possible to somehow evaluate if an answer is received?
By default the socket will be in blocking mode and recv() will block until data is received or the connection is closed.
If you can assume that the proxy will respond within a certain amount of time you can set a timeout on the client socket. The timeout is the number of seconds to wait for a socket operation to complete. If the operation is not complete an exception is raised:
my_socket.settimeout(5.0) # 5 seconds. Set this after connecting.
try:
response = my_socket.recv(1024)
print response
except socket.timeout as exc:
print 'timed out waiting for response from proxy'
my_socket.close()
sys.exit(1)
That's one way and it's probably the easiest way. You could also look at the select() module which provides functions that will let your client wait for the socket to become readable, which indicates that there is data to be read, or that the socket has been closed. It really depends on what behaviour you want. Example using select():
import select
r, _, _ = select.select([my_socket], [], [], 5.0)
if r:
response = my_socket.recv(1024)
print response
else:
print 'Nothing received from proxy in 5 seconds'
my_socket.close()
sys.exit(1)
I am trying to have a client connect to my server, and have a stream of communication between them. The only reason the connection should break is due to network errors, or unless the client wants to stop talking.
The issue I am running into is keeping the handler in a tight loop, and parsing the JSON.
My server code is :
#!/usr/bin/env python
import SocketServer
import socket
import json
import time
class MyTCPServer(SocketServer.ThreadingTCPServer):
allow_reuse_address = True
class MyTCPServerHandler(SocketServer.BaseRequestHandler):
def handle(self):
while 1:
try:
networkData = (self.request.recv(1024).strip())
try:
jsonInputData = json.loads(networkData)
print jsonInputData
try:
if jsonInputData['type'] == 'SAY_HI':
print "HI"
except Exception, e:
print "no hi"
pass
try:
if jsonInputData['type'] == 'GO_AWAY':
print "Going away!"
except Exception, e:
print "no go away"
pass
except Exception, e:
pass
#time.sleep(0.001)
#print "JSON Error", e
except Exception, e:
#time.sleep(0.001)
pass
#print "No message", e
server = MyTCPServer(('192.168.1.115', 13373), MyTCPServerHandler)
server.serve_forever()
My client code is simple :
#!/usr/bin/env python
import socket
import json
import time
import sys
hostname = '192.168.1.103'
port = 13373
try:
sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
sock.connect((hostname,port))
except Exception, e:
print "Error, could not open socket: ", e
data = {'type':'SAY_HI'}
sock.send(json.dumps(data))
data = {'type':'SAY_BYE'}
sock.send(json.dumps(data))
Sometimes I'll see the messages being sent, "SAY_HI" and "SAY_BYE", but most of the times, no data is being displayed on the server side.
This question is really not clear, but calling self.request.recv(1024) is very likely not what you want to do. You're eliminating all of the nice application-level handling that TCP will happily do for you. If you change that to self.request.recv(8) or a similarly very small number (such that recv() returns whenever it receives data, and doesn't try to fill your buffer), you may get better results.
Ultimately this is super-simplistic change, even if it works, that will not work in a larger context. You will need to be handling exceptions from your json parser on the server side and waiting for more data until an entire well-formed message is received.
This is a hopelessly more complex subject than will be handled generally in any SO answer. If you're going to be doing any amount of raw sockets programming, you absolutely must own a copy of Unix Network Programming, Volume 1.