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I have a client and a server, where the server needs to send a number of text files to the client.
The send file function receives the socket and the path of the file to send:
CHUNKSIZE = 1_000_000
def send_file(sock, filepath):
with open(filepath, 'rb') as f:
sock.sendall(f'{os.path.getsize(filepath)}'.encode() + b'\r\n')
# Send the file in chunks so large files can be handled.
while True:
data = f.read(CHUNKSIZE)
if not data:
break
sock.send(data)
And the receive file function receives the client socket and the path where to save the incoming file:
CHUNKSIZE = 1_000_000
def receive_file(sock, filepath):
with sock.makefile('rb') as file_socket:
length = int(file_socket.readline())
# Read the data in chunks so it can handle large files.
with open(filepath, 'wb') as f:
while length:
chunk = min(length, CHUNKSIZE)
data = file_socket.read(chunk)
if not data:
break
f.write(data)
length -= len(data)
if length != 0:
print('Invalid download.')
else:
print('Done.')
It works by sending the file size as the first line, then sending the text file line by line.
Both are invoked in loops in the client and the server, so that files are sent and saved one by one.
It works fine if I put a breakpoint and invoke these functions slowly. But If I let the program run uninterrupted, it fails when reading the size of the second file:
File "/home/stark/Work/test/networking.py", line 29, in receive_file
length = int(file_socket.readline())
ValueError: invalid literal for int() with base 10: b'00,1851,-34,-58,782,-11.91,13.87,-99.55,1730,-16,-32,545,-12.12,19.70,-99.55,1564,-8,-10,177,-12.53,24.90,-99.55,1564,-8,-5,88,-12.53,25.99,-99.55,1564,-8,-3,43,-12.53,26.54,-99.55,0,60,0\r\n'
Clearly a lot more data is being received by that length = int(file_socket.readline()) line.
My questions: why is that? Shouldn't that line read only the size given that it's always sent with a trailing \n?
How can I fix this so that multiple files can be sent in a row?
Thanks!
It seems like you're reusing the same connection and what happens is your file_socket being buffered means... you've actually recved more from your socket then you'd think with your read loop.
I.e. the receiver consumes more data from your socket and next time you attempt to readline() you end up reading rest of the previous file up to the new line contained therein or of the next length information.
This also means your initial problem actually is you've skipped a while. Effect of which is next read line is not an int you expected and hence the observed failure.
You can say:
with sock.makefile('rb', buffering=0) as file_socket:
instead to force the file like access being unbuffered. Or actually handle the receiving and buffering and parsing of incoming bytes (understanding where one file ends and the next one begins) on your own (instead of file like wrapper and readline).
You have to understand that socket communication is based on TCP/IP, does not matter if it's same machine (you use loopback in such cases) or different machines. So, you've got some IP addresses between which the connection is established. Going further, it involves accessing your network adapter, ie takes relatively long in comparison to accessing eg. RAM. Additionally, the adapter itself manages when to send particular data frames (lower ISO/OSI layers). Basically, in case of TCP there's ACK required, but on standard PC this is usually not some industrial, real-time ethernet.
So, in your code, you've got a while True loop without any sleep and you don't check what does sock.send returns. Even if something goes wrong with particular data frame, you ignore it and try to send next. On first glance it appears that something has been cached and receiver received what was flushed once connection was re-established.
So, first thing which you should do is check if sock.send indeed returned number of bytes sent. If not, I believe the frame should be re-sent. Another thing which I strongly recommend in such cases is think of some custom protocol (this is usually called application layer in context of OSI/ISO stack). For example, you might have 4 types of frames: START, FILESIZE, DATA, END, assign unique ID and start each frame with the identifier. Then, START is gonna be empty, FILESIZE gonna contain single uint16, DATA is gonna contain {FILE NUMBER, LINE NUMBER, LINE_LENGTH, LINE} and END is gonna be empty. Then, once you've got entire frame on the client, you can safely assemble the information you received.
The following code is for a python server that can receive a string.
import socket
TCP_IP = '127.0.0.1'
TCP_PORT = 8001
BUFFER_SIZE = 1024
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.bind((TCP_IP, TCP_PORT))
s.listen(1)
conn, addr = s.accept()
print 'Connection address:', addr
while 1:
length = conn.recv(1027)
data = conn.recv(int(length))
import StringIO
buff = StringIO.StringIO()
buff.write(data)
if not data: break
print "received data:", data
conn.send('Thanks') # echo
get_result(buff)
conn.close()
Can anyone help me to edit this code or create a similar one to be able to receive images instead of string?
First, your code actually can't receive a string. Sockets are byte streams, not message streams.
This line:
length = conn.recv(1027)
… will receive anywhere from 1 to 1027 bytes.
You need to loop around each recv and accumulate a buffer, like this:
def recvall(conn, length):
buf = b''
while len(buf) < length:
data = conn.recv(length - len(buf))
if not data:
return data
buf += data
return buf
Now you can make it work like this:
while True:
length = recvall(conn, 1027)
if not length: break
data = recvall(conn, int(length))
if not data: break
print "received data:", data
conn.send('Thanks') # echo
You can use StringIO or other techniques instead of concatenation for performance reasons, but I left that out because it's simpler and more concise this way, and understanding the code is more important than performance.
Meanwhile, it's worth pointing out that 1027 bytes is a ridiculous huge amount of space to use for a length prefix. Also, your sending code has to make sure to actually send 1027 bytes, no matter what. And your responses have to always be exactly 6 bytes long for this to work.
def send_string(conn, msg):
conn.sendall(str(len(msg)).ljust(1027))
conn.sendall(msg)
response = recvall(conn, 6)
return response
But at least now it is workable.
So, why did you think it worked?
TCP is a stream of bytes, not a stream of messages. There's no guarantee that a single send from one side will match up with the next recv on the other side. However, when you're running both sides on the same computer, sending relatively small buffers, and aren't loading the computer down too badly, they will often happen to match up 1-to-1. After all, each time you call recv, the other side has probably only had time to send one message, which is sitting in the OS's buffers all by itself, so the OS just gives you the whole thing. So, your code will appear to work in initial testing.
But if you send the message through a router to another computer, or if you wait long enough for the other side to make multiple send calls, or if your message is too big to fit into a single buffer, or if you just get unlucky, there could be 2-1/2 messages waiting in the buffer, and the OS will give you the whole 2-1/2 messages. And then your next recv will get the leftover 1/2 message.
So, how do you make this work for images? Well, it depends on what you mean by that.
You can read an image file into memory as a sequence of bytes, and call send_string on that sequence, and it will work fine. Then the other side can save that file, or interpret it as an image file and display it, or whatever it wants.
Alternatively, you can use something like PIL to parse and decompress an image file into a bitmap. Then, you encode the header data (width, height, pixel format, etc.) in some way (e.g., pickle it), send_string the header, then send_string the bitmap.
If the header has a fixed size (e.g., it's a simple structure that you can serialize with struct.pack), and contains enough information for the other side to figure out the length of the bitmap in bytes, you don't need to send_string each one; just use conn.sendall(serialized_header) then conn.sendall(bitmap).
I have simple tcp socket program and I would like to send strings in chunks of 10 bytes. The server will join the chunks.
However I'm not sure how to split a string into binary and how to send the chunks of binaries. Instead of sending 512 bytes at one time I want to send 10 byte several times.
I have found a module Pickle that can serialize data into bytestrings (?) but how do I apply socket.send() on this?
Server:
server_socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
server_socket.bind(("", my_port))
server_socket.listen(5)
client_socket, address = server_socket.accept()
data = client_socket.recv(512)
Client:
message = "some string I want to send in chunks"
client_socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
client_socket.connect((host, my_port))
client_socket.send(message)
client_socket.close()
First of all, your code is not actually sending 512 bytes at a time, it's receiving 512 bytes at a time.
Now, I think you're really asking two questions.
How do you send 10 bytes at a time over a TCP connection (you are using socket.SOCK_STREAM)
How do you send raw bytes using a Python socket.
Let's answer 2. first: If you call socket.send on a byte string, it should be sent out in binary as TCP payload.
For 1., the simplest approach would be to split the data into chunks (now that you know you're operating on strings, you can simply do that using the slice operations (see the Python tutorial on strings - e.g. s[0:10], s[10:20] etc). Next, you need to ensure these slices are sent individually. This could be done by calling socket.send, but the problem is, that your TCP/IP stack may group these into packets even if you don't want it to - you have after all asked it to provide you with a stream socket, socket.SOCK_STREAM. If you were writing to a file, what you'd do in this case is you'd flush the file, but this does not appear to be easy for Python sockets (see this question).
Now, I think the answer to that question, saying it's impossible, is not quite right. It appears that Scapy will let you send 10 byte TCP chunks (I got the chunks() function from here). I checked it in wireshark and tried it multiple times with consistent results, but I didn't check the implementation to make sure this is guaranteed to happen.
You should probably ask yourself why you want to send data in chunks of 10 bytes, rather than let TCP deal with what it was designed for, and consider using delimiters.
Anyway, here's the code using Scapy (fun fact: it looks like running this does not require root privileges):
client:
from scapy.all import *
import socket
host = '192.168.0.x' #replace with your IP
my_port = 3002
message = "some string I want to send in chunks"
def chunks(lst, n):
"Yield successive n-sized chunks from lst"
for i in xrange(0, len(lst), n):
yield lst[i:i+n]
client_socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
client_socket.connect((host, my_port))
ss=StreamSocket(client_socket,Raw)
for chunk in chunks(message, 10):
print "sending: " + chunk
ss.send(Raw(chunk) )
client_socket.close()
server:
import socket
my_port=3002
server_socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
server_socket.bind(("", my_port))
server_socket.listen(5)
client_socket, address = server_socket.accept()
while (True):
data = client_socket.recv(512)
if (data):
print data
else:
break
I'm doing some socket/select programming and one of my events is triggered by the incoming byte string of 'OK'. I'm using utf_8 to encode everything sent from the server and decoding it on the client. However, my client comparisons aren't working and my if statement never evaluates to true. Here is the code in question:
Server side:
def broadcast_string(self, data, omit_sock): # broadcasts data utf_8 encoded to all socks
for sock in self.descriptors:
if sock is not self.server and sock is not omit_sock:
sock.send(data.encode('utf_8'))
print(data)
def start_game(self): # i call this to send 'OK'
data = 'OK'
self.broadcast_string(data, 0)
self.new_round()
Client side:
else: # got data from server
if data.decode('utf_8') == 'OK': # i've tried substituting this with a var, no luck
self.playstarted = True
else:
sys.stdout.write(data.decode('utf_8') + "\n")
sys.stdout.flush()
if self.playstarted is True: # never reached because if statement never True
command = input("-->")
I've read this and I think I'm following it but apparently not. I've even done the examples using the python shell and have had them evaluate to True, but not when I run this program.
Thanks!
TCP sockets don't have message boundaries. As your last comment says you are getting multiple messages in one long string. You are reponsible for queuing up data until you have a complete message, and then processing it as one complete message.
Each time select says a socket has some data to read, append the data to a read buffer, then check to see if the buffer contains a complete message. If it does, extract just the message from the front of the buffer and process it. Continue until no more complete messages are found, then call select again. Note also you should only decode a complete message, since you might receive a partial UTF-8 multi-byte character otherwise.
Rough example using \n as a message terminator (no error handling):
tmp = sock.recv(1000)
readbuf += tmp
while b'\n' in readbuf:
msg,readbuf = readbuf.split(b'\n',1)
process(msg.decode('utf8'))
I'm trying to write a secure transfer file program using Python and AES and i've got a problem i don't totally understand. I send my file by parsing it with 1024 bytes chunks and sending them over but the server side who receive the data crashes ( I use AES CBC therefore my data length must be a multiple of 16 bytes ) and the error i get says that it is not.
I tried to print the length of the data sent by the client on the client side and the length of the data received on the server and it shows that the client is sending exactly 1024 bytes each time like it's supposed to, but the server side shows that at some point in time, a received packet is not and so less than 1024 bytes ( for example 743 bytes ).
I tried to put a time.sleep(0.5) between each socket send on the client side and it seems to work. Is it possible that it is some kind of socket buffer failure on the server side ? That too much data is being send too fast by the client and that it breaks somehow the socket buffer on the server side so the data is corrupted or vanish and the recv(1024) only receive a broken chunk? That's the only thing i could think of, but this may also be completely false, if anyone has an idea of why this is not working properly it would be great ;)
Following my idea i tried :
self.s.setsockopt(socket.SOL_SOCKET, socket.SO_RCVBUF, 32768000)
print socket.SO_RCVBUF
I tried to put a 32mbytes buffer on the server side but On Windows XP it shows 4098 on the print and on linux it shows only 8. I don't know how i must interpret this, the only thing i know is that it seems that it doesn't have a 32mbytes buffer so the code doesn't work.
Well it's been a really long post, i hope some of you had the courage to read it all to here ! i'm totally lost there so if anyone has any idea about this please share it :D
Thanks to Faisal my code is here :
Server Side: ( count is my filesize/1024 )
while 1:
txt=self.s.recv(1024)
if txt == " ":
break
txt = self.cipher.decrypt(txt)
if countbis == count:
txt = txt.rstrip()
tfile.write(txt)
countbis+=1
Client side :
while 1:
txt= tfile.read(1024)
if not txt:
self.s.send(" ")
break
txt += ' ' * (-len(txt) % 16)
txt = self.cipher.encrypt(txt)
self.s.send(txt)
Thanks in advance,
Nolhian
Welcome to network programming! You've just fallen into the same mistaken assumption that everyone makes the first time through in assuming that client sends & server recives should be symmetric. Unfortunately, this is not the case. The OS allows reception to occur in arbitrarily sized chunks. It's fairly easy to work around though, just buffer your data until the amount you've read in equals the amount you wish to receive. Something along the lines of this will do the trick:
buff=''
while len(buff) < 1024:
buff += s.recv( 1024 - len(buff) )
TCP is a stream protocol, it doesn't conserve message boundaries, as you have just discovered.
As others have pointed out you're probably processing an incomplete message. You need to either have fixed sized messages or have a delimiter (don't forget to escape your data!) so you know when a complete message has been received.
What TCP can guarantee is that all your data arrives, in the right order, at some point. (Unless something unexpected happens, by which it won't arrive.) But it's very possible that the data you send will still arrive in chunks. Much of it is because of limited send- and receive-buffers. What you should do is to continue doing your recv calls until you have enough data to process it. You might might have to call send multiple times; use its return value to keep track of how much data has been sent/buffered so far.
When you do print socket.SO_RCVBUF, you actually print the symbolic SO_RCVBUF contant (except that Python doesn't really have constants); the one used to tell setsockopt what you want to change. To get the current value, you should instead call getsockopt.
Not related to TCP (as that has been answered already), but appending to a string repeatedly will be rather inefficient if you're expecting to receive a lot. It might be better to append to a list and then turn the list into a string when you finished receiving by using ''.join(list).
For many applications, the complexities of TCP are neatly abstracted by Python's asynchat module.
Here is the nice snippet of code that I wrote some time ago, may be not the best , but it could be good example of big files transfer over the local network. http://setahost.com/sending-files-in-local-network-with-python/
As mentioned above
TCP is a stream protocol
You can try this code, where the data is your original data, you can read it from the file or user input
Sender
import socket as s
sock = s.socket(s.AF_INET, s.SOCK_STREAM)
sock.connect((addr,5000))
sock.sendall(data)
finish = t.time()
Receiver
import socket as s
sock = s.socket(s.AF_INET, s.SOCK_STREAM)
sock.setsockopt(s.SOL_SOCKET, s.SO_REUSEADDR, 1)
sock.bind(("", 5000))
sock.listen(1)
conn, _ = sock.accept()
pack = []
while True:
piece = conn.recv(8192)
if not piece:
break
pack.append(piece.decode())