[Resolved]Python socket not receiving anything
Question: I'm trying to receive a variable length stream from a camera with python, but
get weird behaviour. This is Python 2.6.4 (r264:75706) on linux(Ubuntu 9.10)

The message is supposed to come with a static header followed by the size, and
rest of the stream. here is the code

    
    
    from socket import *
    import array
    import select
    
    HOST = '169.254.0.10'
    PORT = 10001
    BUFSIZ = 1024
    ADDR = (HOST, PORT)
    
    tcpCliSock = socket(AF_INET, SOCK_STREAM)
    tcpCliSock.connect(ADDR)
    tcpCliSock.setblocking(0)
    
    def dump(x):
        dfile = open('dump','w')
        dfile.write(x)
        dfile.close
    
    
    data='I'
    tcpCliSock.send(data)
    tcpCliSock.shutdown(1)
    ready_to_read, ready_to_write, in_error = select.select(
    		[tcpCliSock], 
    		[], 
    		[], 
    		30)
    if ready_to_read == []:
    	print "sokadens"
    data=''
    while len(data)<10:
    	chunk = tcpCliSock.recv(1024)
    	print 'recv\'d %d bites'%len(data)
    	data=data+chunk
    index=data.find('##IMJ')
    if index == -1:
    	dump(data)
    	raise RuntimeError, "imahe get error"
    datarr = array.array('B',data)
    size=datarr[6]+datarr[7]<<8+datarr[8]<<16+datarr[9]<<24
    ready_to_read, ready_to_write, in_error = select.select(
    		[tcpCliSock], 
    		[], 
    		[], 
    		30)
    if ready_to_read == []:
    	print "sokadens"
    while len(data)<size:
    	chunk = tcpCliSock.recv(1024)
    	data=data+chunk	
    
    outfile=open('resim.jpg','w')
    outfile.write(data[10:])
    outfile.close
    
    tcpCliSock.close()
    

with this code I either get stuck in a "recv\'d 0 bites" loop(which happens
rarely) or this:

    
    
    `recv'd 0 bites`
    Traceback (most recent call last):
      File "client.py", line 44, in <module>
        raise RuntimeError, "imahe get error"
    RuntimeError: imahe get error
    

which is totally weird(receive 0 bytes but get out of the loop). The dumped
data is erroneous, which is expected in that situation

Edit 1: the device is supposed to send a JPEG image, preceded by a 10-byte
header. When(if) I get past the first loop, I need to check this header for
correctness and size info. The program terminates with wrong data error, and
the dump file is a bunch of binary garbage, so I have no Idea what I received
at the end. I am pretty sure the device at the other side is trying to send
the correct data.

Edit 2: I found the cause of the problem. You can consider this closed.


Answer: You don't really know how many bytes you received, since your code is:

    
    
    data=''
    while len(data)<10:
            chunk = tcpCliSock.recv(1024)
            print 'recv\'d %d bites'%len(data)
            data=data+chunk
    

i.e., you're receiving bytes in `chunk`, but what you're printing is
`len(data)` before you update `data`. So of course it will print 0 the first
time, always -- then it will update `data` and exit if the `chunk` was at
least 10 bytes.

This info is not sufficient to debug your problem, but printing len(chunk),
and len(data) upon exiting the loop, can't hurt the attempt to understand
what's going on. Also, what's in `dump` when you exit with the `imahe get
error` message?

