Python client server communication

Question

I'm trying to send some data from the server to the client, but the client doesn't get all the data.

Server:

def handle( self ):       
        #self.request.setblocking( 0 )
        i = 10;
        while True:
            if( self.clientname == 'MasterClient' ):                
                try:                    
                    #ans = self.request.recv( 4096 )
                    #print( 'after recv' )   
                    """    Sendign data, testing purpose    """                 
                    while i:
                        mess = str( i );            
                        postbox['MasterClient'].put( self.creatMessage( 0, 0 , mess ) )
                        i = i - 1
                    while( postbox['MasterClient'].empty() != True ):                        
                        sendData = postbox['MasterClient'].get_nowait()                        

                        a = self.request.send( sendData )
                        print( a );
                        #dic = self.getMessage( sendData )
                        #print 'Sent:%s\n' % str( dic )                         
                except:                    
                    mess = str( sys.exc_info()[0] )
                    postbox['MasterClient'].put( self.creatMessage( 1, 0 , mess ) )
                    pass

Client:

def run( self ):        
        sock = socket.socket( socket.AF_INET, socket.SOCK_STREAM )        
        addr = ( self.ip, self.port )        
        #print addr
        sock.connect( addr )
        #sock.setblocking( 0 )
        while True:         
            try:   
                ans = sock.recv( 4096 )                
                dic = self.getMessage( ans )               
                self.recvMessageHandler( dic )  
                print 'Received:%s\n' % str( dic )       
            except:
               print "Unexpected error:", sys.exc_info()[0]

Where did I make the mistake?

Rakis · Accepted Answer · 2011-06-16 15:16:58Z

1

Reads are not symmetrical with writes when using TCP, very often the receiving OS will return much smaller chunks of data than the sending side sends out. A common solution is to prefix each send with a fixed-size integer that contains the length of the next message. The pattern for receiving a complete message then becomes:

bin  = sock.recv(4) # for 4-byte integer
mlen = struct.unpack('I', bin)[0]
msg  = ''
while len(msg) != mlen:
    chunk = sock.recv(4096) # 4096 is an arbitrary buffer size
    if not chunk:
        raise Exception("Connection lost")
    msg += chunk

answered Jun 16, 2011 at 15:16

Rakis

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Comments

Bryan · Accepted Answer · 2011-06-16 13:42:48Z

1

Make sure you are receiving all data as it's not guaranteed to be sent in a single chunk. For example:

data = ""
while True:
    chunk = sock.recv(4096)
    if not chunk:
        break
    data += chunk

answered Jun 16, 2011 at 13:42

Bryan

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