CODEWITHSUNDEEP
pythonsockets
user1003967
user1003967

Reputation: 167

Python socket Recv not working properly could someone explain

i am trying to create a gui client for my command line server. However, i am running into some annoying problems i cant seem to fix.

I'm not 100 % sure of what the actual problem is as sometimes the code will work, other times it wont. I think the main problem is that originally i tried the 

while 1:
    self.data = s.recv(1024)
    if not self.data():
          break
    else:
          print self.data()

Then i was sending to it with this 

  for f in files:
      s.send(f)

Each f was a string of a filename. I expected it to come out on the recv side as one file name recieved for each recv call but instead on one recv call i got a big chunk of filenames i assume 1024 chars worth

Which made it impossible to check for the end of the data and thus the loop never exited.

This is the code i have now

def get_data(self,size = 1024):

    self.alldata = ""
    while 1:

        while gtk.events_pending():
             gtk.main_iteration()

        self.recvdata = self.s.recv(size)
        self.alldata += self.recvdata
        if self.alldata.find("\r\n\r\nEOF"):
           print "recieved end message"
           self.rdata = self.alldata[:self.alldata.find("\r\n\r\nEOF")]
           break



    print "All data Recieved: " + str(len(self.rdata)) + "Bytes"
    print "All data :\n" + self.rdata + "\n-------------------------------------------------"  

    self.infiles = self.rdata.split("-EOS-")
    for nf in self.infiles:
        if len(nf) > 2:
            self.add_message(self.incomingIcon,nf)

At the minute im trying to get the client to read correctly from the server. What i want to happen is when the command list is typed in and sent to the client the server sends back the data and each file is appended to the list store

some times this works ok, other times only one of 1200 files gets returned, if it executes ok, if i try to type another command and send it , the whole gtk window geys out and the program becomes unresponsive.

Sorry i cant explain this question better, ive tried alot of different solutions all of which give different errors.

if someone could explain the recv command and why it may be giving the errors this is how im sending data to the client

if(commands[0] == 'list'):
    whatpacketshouldlooklike=""
    print "[Request] List files ", address
    fil = list_files(path)
    for f in fil:
         sdata =  f  
         whatpacketshouldlooklike += sdata + "-EOS-"
         newSock.send(sdata +"-EOS-")
         #print "sent: " + sdata
         newSock.send("\r\n\r\nEOF")
    whatpacketshouldlooklike += "\r\n\r\nEOF"
    print "---------------------------------"
    print whatpacketshouldlooklike
    print "---------------------------------"

Upvotes: 5

Views: 8553

Answers (4)

Alexander Lubyagin
Alexander Lubyagin

Reputation: 1494

My source code:

def readReliably(s,n):
    buf = bytearray(n)
    view = memoryview(buf)
    sz = 0
    while sz < n:
        k = s.recv_into(view[sz:],n-sz)
        sz += k
    # print 'readReliably()',sz
    return sz,buf

def writeReliably(s,buf,n):
    sz = 0
    while sz < n:
        k = s.send(buf[sz:],n-sz)
        sz += k
    # obj = s.makefile(mode='w')
    # obj.flush()
    # print 'writeReliably()',sz
    return sz

Usage of these functions:

# Server
s = socket.socket(socket.AF_INET,socket.SOCK_STREAM)
s.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
s.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEPORT, 1)
s.setsockopt(socket.IPPROTO_TCP, socket.TCP_NODELAY, 1)
s.bind((host,port))
s.listen(10) # unaccepted connections
while True:
  sk,skfrom = s.accept()
  sz,buf = io.readReliably(sk,4)
  a = struct.unpack("4B",buf)
  print repr(a)
  # ...
  io.writeReliably(sk,struct.pack("4B",*[0x01,0x02,0x03,0x04]))

See also official docs about recv_into(...), https://docs.python.org/2/library/socket.html#socket.socket.recv_into

Upvotes: 0

Jo&#227;o Pinto
Jo&#227;o Pinto

Reputation: 5619

There are different problems with your code.

Let's start with the fundamental that some people already commented, there is no relation between sends() and recv(), you do not control which part of the data is returned on a recv(call), you need some kind of protocol, on your case it could be just as simple as terminating command strings with "\n", and checking for "\n" on the server to consume the data.

Now other problems:

  • You are using send without checking it's return size, a send() does not guarantee that the data is completely written, if you need that please use sendall().
  • By using recv(1024) in a blocking socket (default), your server code may wait for 1024 bytes to be received, this will not allow you to process messages until you get the full chunk, you need to use a non blocking socket, and the select module.

Upvotes: 2

schlamar
schlamar

Reputation: 9509

Use an abstraction layer (Pyro, XML-RPC, zeromq) or define your own protocol to distinguish messages.

For example as own protocol you can send the length of a message as a "header" before each string. In this case you should use the struct module to parse the length into a binary format. Ask again, if you want to go this way, but I strongly recommend choosing one of the mentioned abstraction layers.

Upvotes: 2

stonemetal
stonemetal

Reputation: 6208

The problem you had in the first part is that sockets are stream based not message based. You need to come up with a message abstraction to layer on top of the stream. This way the other end of the pipe knows what is going on(how much data to expect as a part of one command) and isn't guessing at what is supposed to happen.

Upvotes: 3

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