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• Linux: is here a read or recv from socket with timeout?

  - by osgx

  Hello How can I try to read data from socket with timeout? I know, select, pselect, poll, has a timeout field, but using of them disables "tcp fast-path" in tcp reno stack. The only idea I have is to use recv(fd, ..., MSG_DONTWAIT) in a loop

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• Strange client's address returned throug accept(..) function.

  - by Negai

  Hi everyone, I'm a socket programming newbie. Here's a snippet: struct sockaddr_storage client_addr; ... client_addr_size = sizeof(client_addr); client_socket = accept( server_socket, (struct sockaddr *)&client_addr, &client_addr_size ); ... result = inet_ntop( AF_INET, &((struct sockaddr_in *)&client_addr)->sin_addr, client_addr_str, sizeof(client_addr_str) ); Whenever the client connects the address I get is 0.0.0.0 regardless from the host. Can anybody explain, what I'm doing wrong? Thanks.

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• Python : How to close a UDP socket while is waiting for data in recv ?

  - by alexroat

  Hello, let's consider this code in python: import socket import threading import sys import select class UDPServer: def __init__(self): self.s=None self.t=None def start(self,port=8888): if not self.s: self.s=socket.socket(socket.AF_INET, socket.SOCK_DGRAM) self.s.bind(("",port)) self.t=threading.Thread(target=self.run) self.t.start() def stop(self): if self.s: self.s.close() self.t.join() self.t=None def run(self): while True: try: #receive data data,addr=self.s.recvfrom(1024) self.onPacket(addr,data) except: break self.s=None def onPacket(self,addr,data): print addr,data us=UDPServer() while True: sys.stdout.write("UDP server> ") cmd=sys.stdin.readline() if cmd=="start\n": print "starting server..." us.start(8888) print "done" elif cmd=="stop\n": print "stopping server..." us.stop() print "done" elif cmd=="quit\n": print "Quitting ..." us.stop() break; print "bye bye" It runs an interactive shell with which I can start and stop an UDP server. The server is implemented through a class which launches a thread in which there's a infinite loop of recv/*onPacket* callback inside a try/except block which should detect the error and the exits from the loop. What I expect is that when I type "stop" on the shell the socket is closed and an exception is raised by the recvfrom function because of the invalidation of the file descriptor. Instead, it seems that recvfrom still to block the thread waiting for data even after the close call. Why this strange behavior ? I've always used this patter to implements an UDP server in C++ and JAVA and it always worked. I've tried also with a "select" passing a list with the socket to the xread argument, in order to get an event of file descriptor disruption from select instead that from recvfrom, but select seems to be "insensible" to the close too. I need to have a unique code which maintain the same behavior on Linux and Windows with python 2.5 - 2.6. Thanks.

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• How to maintain a persistant network-connection between two applications over a network?

  - by John

  I was recently approached by my management with an interesting problem - where I am pretty sure I am telling my bosses the correct information but I really want to make sure I am telling them the correct stuff. I am being asked to develop some software that has this function: An application at one location is constantly processing real-time data every second and only generates data if the underlying data has changed in any way. On the event that the data has changed send the results to another box over a network Maintains a persistent connection between the both machines, altering the remote box if for some reason the network connection went down From what I understand, I imagine that I need to do some reading on doing some sort of TCP/IP socket-level stuff. That way if the connection is dropped the remote location will be aware that the data it has received may be stale. However management seems to be very convinced that this can be accomplished using SOAP. I was under the impression that SOAP is more or less a way for a client to initiate a procedure from a server and get some results via the HTTP protocol. Am I wrong in assuming this? I haven't been able to find much information on how SOAP might be able to solve a problem like this. I feel like a lot of people around my office are using SOAP as a buzzword and that has generated a bit of confusion over what SOAP actually is - and is capable of. Any thoughts on how to accomplish this task would be appreciated!

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• non blocking TCP-acceptor not reading from socket

  - by Abruzzo Forte e Gentile

  I have the code below implementing a NON-Blocking TCP acceptor. Clients are able to connect without any problem and the writing seems occurring as well, but the acceptor doesn't read anything from the socket and the call to read() blocks indefinitely. Am I using some wrong setting for the acceptor? Kind Regards AFG int main(){ create_programming_socket(); poll_programming_connect(); while(1){ poll_programming_read(); } } int create_programming_socket(){ int cnt = 0; p_listen_socket = socket( AF_INET, SOCK_STREAM, 0 ); if( p_listen_socket < 0 ){ return 1; } int flags = fcntl( p_listen_socket, F_GETFL, 0 ); if( fcntl( p_listen_socket, F_SETFL, flags | O_NONBLOCK ) == -1 ){ return 1; } bzero( (char*)&p_serv_addr, sizeof(p_serv_addr) ); p_serv_addr.sin_family = AF_INET; p_serv_addr.sin_addr.s_addr = INADDR_ANY; p_serv_addr.sin_port = htons( p_port ); if( bind( p_listen_socket, (struct sockaddr*)&p_serv_addr , sizeof(p_serv_addr) ) < 0 ) { return 1; } listen( p_listen_socket, 5 ); return 0; } int poll_programming_connect(){ int retval = 0; static socklen_t p_clilen = sizeof(p_cli_addr); int res = accept( p_listen_socket, (struct sockaddr*)&p_cli_addr, &p_clilen ); if( res > 0 ){ p_conn_socket = res; int flags = fcntl( p_conn_socket, F_GETFL, 0 ); if( fcntl( p_conn_socket, F_SETFL, flags | O_NONBLOCK ) == -1 ){ retval = 1; }else{ p_connected = true; } }else if( res == -1 && ( errno == EWOULDBLOCK || errno == EAGAIN ) ) { //printf( "poll_sock(): accept(c_listen_socket) would block\n"); }else{ retval = 1; } return retval; } int poll_programming_read(){ int retval = 0; bzero( p_buffer, 256 ); int numbytes = read( p_conn_socket, p_buffer, 255 ); if( numbytes > 0 ) { fprintf( stderr, "poll_sock(): read() read %d bytes\n", numbytes ); pkt_struct2_t tx_buf; int fred; int i; } else if( numbytes == -1 && ( errno == EWOULDBLOCK || errno == EAGAIN ) ) { //printf( "poll_sock(): read() would block\n"); } else { close( p_conn_socket ); p_connected = false; retval = 1; } return retval; }

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• How to write an Android SocketServer to listen on wifi

  - by xioxox

  I've written a thread using java.net.SocketServer to listen on a particular port. It works fine in the android simulator (using port forwarding). I'm planning to connect over wifi to this port when the app is being used. However, the SocketServer documentation says that if you don't supply an InetAddress, the server listens on localhost. Am I correct that if I do not supply the address, I will not be able to get a connection over wifi? How can I get the InetAddress of the wifi connection to pass to the SocketServer?

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• Flex: client / server messaging question (RPC or socket ?)

  - by Patrick

  hi, I'm building a Flex application, which is going to perform many server requests (let's say, that almost all interactions require an update from server). At the moment I'm using remote procedure calls for it. But I was wondering if using a socket would be better. In other terms, is maybe better to keep the connection alive rather then performing many calls in sequence ? For my demo app I only have 1 client. Is the number of clients connecting to the server a factor for this choice ? thanks

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• Ruby TCPSocket doesn't notice it when server is killed

  - by user303308

  I've this ruby code that connects to a TCP server (namely, netcat). It loops 20 times, and sends "ABCD ". If I kill netcat, it takes TWO iterations of the loop for an exception to be triggered. On the first loop after netcat is killed, no exception is triggered, and "send" reports that 5 bytes have been correctly written... Which in the end is not true, since of course the server never received them. Is there a way to work around this issue ? Right now I'm losing data : since I think it's been correctly transfered, I'm not replaying it. #!/usr/bin/env ruby require 'rubygems' require 'socket' sock = TCPSocket.new('192.168.0.10', 5443) sock.sync = true 20.times do sleep 2 begin count = sock.write("ABCD ") puts "Wrote #{count} bytes" rescue Exception => myException puts "Exception rescued : #{myException}" end end

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• BSD-Socket Options explanation needded

  - by khera-satinder

  I want detailed explanations for bsd-socket options so that I can use them in the right manner. Can anybody please provide me some document or link from where I can refer? Thanks, Satinder Singh [email protected]

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• How to handle server-client requests

  - by Layne

  Currently I'm working on a Server-Client system which will be the backbone of my application. I have to find the best way to send requests and handle them on the server-side. The server-side should be able to handle requests like this one: getPortfolio -i 2 -d all In an old project I decided to send such a request as string and the server application had to look up the first part of the string ("getPortfolio"). Afterwards the server application had to find the correct method in a map which linked the methods with the the first part of the string ("getPortfolio"). The second part ("-i 2 -d all") got passed as parameter and the method itself had to handle this string/parameter. I doubt that this is the best solution in order to handle many different requests. Rgds Layne

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• TCP/IP and UDP Questions and very small application for interview

  - by Shantanu Gupta

  I am going for an interview day after tomorrow where i will be asked vaious questions related to TCP/IP and UDP. As of now i have prepared theoritical knowledge about it. But now I am looking up for gaining some practicle knowledge related to how it works in a network. What all is going in vaious .NET classes. I want to create a very small application like a chat or something that can make me all these concepts very much clear. Could you please suggest some questions related to TCP/IP that you generally ask or that you might have faced. How communication is going from server to client. Right now I am studying TcpClient, TcpListener and UdpClient Class but I want to implement all of them so as to get aware about its working. Is Chat application a Tcp/IP application ? I would appreciate your help.

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• How do you make sure your pakcet is delivered to right client using public ip address

  - by TemporaryNickName

  So private IP addresses are 192.168.00 ~ 192.168.255.255 or 10.0.0.0 or 172.16.0.0 ~ 172.31.255.255 If I accepted a client to my serversocket, I can get the client's remoteIp address by using socket.getremotesocketaddress(); But I suspect the IP address that I'm getting from this method is only the public IP address and it must have more than one client using same public IP as this one (one like you see when you go on to the website www.whatismyip.com). So if I want to make sure that my packet is delivered to the right person using some IP address or otherthing that uniquely identifies a person, what should I have to do?

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• How do I detect server status in a port scanner java implementation

  - by akz

  I am writing a port scanner in Java and I want to be able to distinct the following 4 use cases: port is open port is open and server banner was read port is closed server is not live I have the following code: InetAddress address = InetAddress.getByName("google.com"); int[] ports = new int[]{21, 22, 23, 80, 443}; for (int i = 0; i < ports.length; i++) { int port = ports[i]; Socket socket = null; try { socket = new Socket(address, port); socket.setSoTimeout(500); System.out.println("port " + port + " open"); BufferedReader reader = new BufferedReader( new InputStreamReader(socket.getInputStream())); String line = reader.readLine(); if (line != null) { System.out.println(line); } socket.close(); } catch (SocketTimeoutException ex) { // port was open but nothing was read from input stream ex.printStackTrace(); } catch (ConnectException ex) { // port is closed ex.printStackTrace(); } catch (IOException e) { e.printStackTrace(); } finally { if (socket != null && !socket.isClosed()) { try { socket.close(); } catch (Exception e) { e.printStackTrace(); } } } } The problem is that I get a ConnectionException both when the port is closed and the server cannot be reached but with a different exception message: java.net.ConnectException: Connection timed out: connect when the connection was never established and java.net.ConnectException: Connection refused: connect when the port was closed so I cannot make the distinction between the two use cases without digging into the actual exception message. Same thing happens when I try a different approach for the socket creation. If I use: socket = new Socket(); socket.setSoTimeout(500); socket.connect(new InetSocketAddress(address, port), 1000); I have the same problem but with the SocketTimeoutException instead. I get a java.net.SocketTimeoutException: Read timed out if port was open but there was no banner to be read and java.net.SocketTimeoutException: connect timed out if server is not live or port is closed. Any ideas? Thanks in advance!

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• Is it ok to Swallow SocketExceptions in some situations?

  - by NoPyGod

  Let's say I've programmed an application which connects to a server using the Socket Class (TCP). If I encounter a SocketException while reading or writing, then obviously I have to do go ahead and run a disconnection routine to change the application's state to Disconnected. But what if I've started to Disconnect, and while I'm cleaning up, a SocketException occurs? The SocketException doesn't really mean anything to me, as I was going to shutdown the socket myself anyway.. so is it ok to swallow it? I really want to know what the best practice for this situation is.

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• Communicate between separate MPI-Programs

  - by Fyg

  I have the following problem: Program 1 has a huge amount of data, say 10GB. The data in question consists of large integer- and double-arrays. Program 2 has 1..n MPI processes that use tiles of this data to compute results. How can I send the data from program 1 to the MPI Processes? Using File I/O is out of question. The compute node has sufficient RAM.

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• c++ connect() keeps returning WSATIMEDOUT over internet but not localy

  - by KaiserJohaan

  Hello, For some reason, my chat application always gets WSATIMEDOUT when trying to connect to another person over the internet. int len_ip = GetWindowTextLength(GetDlgItem(hWnd,ID_EDIT_IP)); char ipBuffer[16]; SendMessage(GetDlgItem(hWnd,ID_EDIT_IP),WM_GETTEXT,16,(LPARAM)ipBuffer); long host_ip = inet_addr(ipBuffer); int initializeConnection(long host_ip, HWND hWnd) { // initialize winsock WSADATA wdata; int result = WSAStartup(MAKEWORD(2,2),&wdata); if (result != 0) { return 0; } // setup socket tcp_sock = socket(AF_INET,SOCK_STREAM,IPPROTO_TCP); if (tcp_sock == INVALID_SOCKET) { return 0; } // setup socket address SOCKADDR_IN tcp_sock_addr; tcp_sock_addr.sin_family = AF_INET; tcp_sock_addr.sin_port = SERVER_TCP_PORT; tcp_sock_addr.sin_addr.s_addr = host_ip; // connect to server if (connect(tcp_sock,(SOCKADDR*)&tcp_sock_addr,sizeof(tcp_sock_addr)) == SOCKET_ERROR) { return 0; } HRESULT hr = WSAGetLastError(); // set socket in asynchronous mode if (WSAAsyncSelect(tcp_sock,hWnd,SOCKET_TCP, FD_READ | FD_WRITE | FD_CONNECT | FD_CLOSE) == SOCKET_ERROR) { return 0; } return 1; } For some reason it works perfectly fine on local network between computers, but totally screws up over the internet. WSATIMEDOUT is always returned (not connection refused, so its not a port problem). It makes me believe something is wrong with the IP but why on earth can it work on local addresses (like 192.168.2.4) Any ideas? Cheers

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• "Can´t open socket or connection refused" with .NET

  - by HoNgOuRu

  Im getting a connection refused when I try to send some data to my server app using netcat. server side: IPAddress ip; ip = Dns.GetHostEntry("localhost").AddressList[0]; IPEndPoint ipFinal = new IPEndPoint(ip, 12345); Socket socket = new Socket(AddressFamily.InterNetworkV6, SocketType.Stream, ProtocolType.Tcp); socket.Bind(ipFinal); socket.Listen(100); Socket handler = socket.Accept(); ------> it stops here......nothing happens

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• How to change socket bind port of program? without source code.

  - by hunmr

  Hello everyone, PROBLEM: I have a program dummy.exe on windows. this program will bind to UDP port 5060, after started. but another program also want to bind port 5060. WHAT I HAVE DONE: using windbg to start dummy.exe, and set breakpoint on ws2_32!bind when the breakpoint hit, i changed the parameter (port value) with command ew this dummy.exe will bind to the new port, and worked well. QUESTION: How can i do that easily? write a simple windows debugger? Maybe i can hacking or modify the dummy.exe file, but how to do that? what's your way to achieve this? thanks

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• python streaming TCP server with RPC

  - by Noah

  I have written a little streaming mp3 server in python. So far all it does is accept a ServerSocket connection, and begin streaming all mp3 data in its queue to the request using socket.send(). I have implemented this to chunk in stream icy metadata, so the name of the playing song shows up in the client. I would like to add playlist management to the server, so that I can manipulate the playlist of the running server. I have a vague idea that xmlrpclib would be suited to doing this, but I'm confused about one thing: When I start the server it listens on port N. The python xmlrpclib examples involve creating a socket and listening for requests. So my question is should server listen on two ports; i.e., one for streaming client requests and one for xmlrpclib calls, or is there a way to do it by somehow delegating the request to the appropriate handler based on its type?

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• Why is ::connect() returning EHOSTUNREACH when ssh works fine?

  - by WilliamKF

  I am calling ::connect() in my application and it works fine in general, however, between two particular machines, from one to the other, it fails with EHOSTUNREACH which means "No route to host." If I can ssh with no problems, what might be going on here that ::connect() always fails for this particular machine pair?

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• Troubleshooting occasional timeout of select() in windows

  - by JonF

  I'm having an occasional problem with select() timing out on me. I have it set for twenty seconds. The system will handle 100's of transactions correctly, but occasionally one fails with the selet timing out. It does about 1 transaction every few seconds, opening and closing the tcp conncetion with each transaction. I thought the server my app was connecting to might have to many connection attempts pending, but no 4226 events are showing up in the logs One more point thing I noticed when using wireshark that I'm getting a SYN,RST in response to the SYN I am appearently sending. This only happens a few times over the first second or two, then I don't see any more activity in Wireshark

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• buffer size for socket connection in c++

  - by wyatt

  I'm trying to build a basic POP3 mail client in C/++, but I've run into a bit of an issue. Since you have to define the buffer size when building the program, but a message can be arbitrarily large, how do you, say, get the mail server to send it to you in parts? And if this isn't the correct means of solving the problem, what is? And while I'm here, can anyone confirm for me that RFC 2822 is still the current document defining email layout? Thanks

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• Writing Java code in Matlab?

  - by scooziexp

  Hi, I'm trying to use the Java commands pw.println() and br.readLine() in Matlab because I have set up a socket (input_socket2) between Matlab and a command-line program I want to control using Java classes BufferedReader and PrintWriter. Before the following snippet of code, I implemented another socket that goes between 2 computers. This works great and I also know that the following snippet of code successfully opens up a communication line between Matlab and the other program. However, Matlab throws an error at pw.println('noop'). I think it has something to do with syntax, but I'm not sure how to write the command in Matlab syntax then: try input_socket2 = Socket(host2,port2); input_stream2 = input_socket2.getInputStream; d_input_stream2 = DataInputStream(input_stream2); br = BufferedReader(InputStreamReader(input_stream2)); pw = PrintWriter(input_socket2.getOutputStream,true); pw.println('noop') br.read end Any ideas?

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• How to get server message correctly

  - by Leo

  Problem I send the message "12345" from the socket server to the client: myPrintWriter.println("12345"); After that I read this message on client: int c; while ((c = inputStream.read( )) != -1) { byte[] buffer2 = new byte[1]; buffer2[0] = (byte) c; String symbol = new String(buffer2 , "UTF-8"); String symbolCode = Integer.toString((int)buffer2[0]); Log.v(symbol, symbolCode); } Log.v("c == -1", "Disconnected"); What I see in log: With out.println("abcrefg"); Why? I think it's line termination symbol. I need to get string "12345" or any other and next strings correctly. Help me please.

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• Asynchronous IO in Java?

  - by thr

  What options for async io (socket-based) are there in java other then java.nio? Also does java.nio use threads in the backround (as I think .NET's async-socket-library does, maybe it's been changed) or is it "true" async io using a proper select call?

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