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  • Waiting for data via select not working

    - by BSchlinker
    I'm currently working on a project which involves multiple clients connected to a server and waiting for data. I'm using select and monitoring the connection for incoming data. However, the client just continues to print nothing, acting as if select has discovered incoming data. Perhaps I'm attacking this wrong? For the first piece of data the server does send, it is displayed correctly. However, the server then disconnects and the client continues to spew blank lines. FD_ZERO(&readnet); FD_SET(sockfd, &readnet); while(1){ rv = select(socketdescrip, &readnet, NULL, NULL, &timeout); if (rv == -1) { perror("select"); // error occurred in select() } else if (rv == 0) { printf("Connection timeout! No data after 10 seconds.\n"); } else { // one or both of the descriptors have data if (FD_ISSET(sockfd, &readnet)) { numbytes = recv(sockfd, buf, sizeof buf, 0); printf("Data Received\n"); buf[numbytes] = '\0'; printf("client: received '%s'\n",buf); sleep(10); } } }

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  • Trying to packetize TCP with non-blocking IO is hard! Am I doing something wrong?

    - by Ricket
    Oh how I wish TCP was packet-based like UDP is! But alas, that's not the case, so I'm trying to implement my own packet layer. Here's the chain of events so far (ignoring writing packets) Oh, and my Packets are very simply structured: two unsigned bytes for length, and then byte[length] data. (I can't imagine if they were any more complex, I'd be up to my ears in if statements!) Server is in an infinite loop, accepting connections and adding them to a list of Connections. PacketGatherer (another thread) uses a Selector to figure out which Connection.SocketChannels are ready for reading. It loops over the results and tells each Connection to read(). Each Connection has a partial IncomingPacket and a list of Packets which have been fully read and are waiting to be processed. On read(): Tell the partial IncomingPacket to read more data. (IncomingPacket.readData below) If it's done reading (IncomingPacket.complete()), make a Packet from it and stick the Packet into the list waiting to be processed and then replace it with a new IncomingPacket. There are a couple problems with this. First, only one packet is being read at a time. If the IncomingPacket needs only one more byte, then only one byte is read this pass. This can of course be fixed with a loop but it starts to get sorta complicated and I wonder if there is a better overall way. Second, the logic in IncomingPacket is a little bit crazy, to be able to read the two bytes for the length and then read the actual data. Here is the code, boiled down for quick & easy reading: int readBytes; // number of total bytes read so far byte length1, length2; // each byte in an unsigned short int (see getLength()) public int getLength() { // will be inaccurate if readBytes < 2 return (int)(length1 << 8 | length2); } public void readData(SocketChannel c) { if (readBytes < 2) { // we don't yet know the length of the actual data ByteBuffer lengthBuffer = ByteBuffer.allocate(2 - readBytes); numBytesRead = c.read(lengthBuffer); if(readBytes == 0) { if(numBytesRead >= 1) length1 = lengthBuffer.get(); if(numBytesRead == 2) length2 = lengthBuffer.get(); } else if(readBytes == 1) { if(numBytesRead == 1) length2 = lengthBuffer.get(); } readBytes += numBytesRead; } if(readBytes >= 2) { // then we know we have the entire length variable // lazily-instantiate data buffers based on getLength() // read into data buffers, increment readBytes // (does not read more than the amount of this packet, so it does not // need to handle overflow into the next packet's data) } } public boolean complete() { return (readBytes > 2 && readBytes == getLength()+2); } Basically I need feedback on my code. Please suggest any improvements. Even overhauling my entire system would be okay, if you have suggestions for how better to implement the whole thing. Book recommendations are welcome too; I love books. I just get the feeling that something isn't quite right.

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  • Best way to parse XMPP-like XML streams?

    - by codethief
    I am working on a server application which receives data over a TCP socket in an XMPP-like XML format, i.e. every child of the <root> element essentially represents one separate request (stanza). The connection is closed as soon as </root> is received. I do know that I must use a stream parser like SAX, somehow. Though, for convenience, I'd prefer to have a tree-like interface to access each stanza's child elements. (The data sent with every request is not large so I think it makes sense to read each stanza as a whole.) What's the best way to realize that in Python (preferably v3)? This is the code I'd like to build it in. Feel free to point me in a totally different direction to solve this issue. import socketserver import settings class MyServer(socketserver.ThreadingMixIn, socketserver.TCPServer): pass class MyRequestHandler(socketserver.StreamRequestHandler): def handle(self): pass if __name__ == '__main__': server = MyServer((settings.host, settings.port), MyRequestHandler) server.serve_forever()

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  • Issuing multiple requests using HTTP/1.1 Pipelining

    - by Robert S. Barnes
    When using HTTP/1.1 Pipelining what does the standard say about issuing multiple requests without waiting for each request to complete? What do servers do in practice? I ask because I once tried writing a client which would issue a batch of GET requests for multiple files and remember getting errors. I wasn't sure if it was due to me incorrectly issuing the GET's or needing to wait for each individual request to finish before issuing the next GET.

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  • how works applications which blocks web sites?

    - by noisy
    I know only one low-level way of blocking websites - hosts file. However, it is obvious that main stream programs has some other way of achieving this. I have an idea for new model of this kind of program, but without possibility of blocking sites it is useless :(

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  • Is there any reason for a blocking call to winsock send() function on Vista to return immediately ?

    - by ivymike
    Hi All, Is there any reason for a blocking call to winsock's send() function on Vista to return immediately ? It works with expected delay on XP and below. I'm wondering if this has got anything to do with auto-tuning feature of Vista. Code: char *pBuffer; // pointer to data int bytes; // total size int i = 0, j=0; while (i < bytes) { j = send(m_sock, pBuffer+i, bytes-i, 0); i+=j; } Thanks, Pavan

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  • Please suggest other ways of communicating between server & client.

    - by Geo
    I'm writing a TCP chat server ( programming language does not mather ). It's a school project for my nephew, so it won't be released, and all questions I'm asking are just for my knowledge :). . Some of the things it will support: chatting between users ( doh ), it will be multithreaded sending each other files I know I could easily get away with all the stuff above if I go with serialization, and just send objects from client to server and back. But, if I do that, it will be limited to a specific programming language ( meaning clients written in other programming languages may not be able to deserialize the objects ). What would be the way to go so that other clients written in other languages could be supported? One way to go, off the top of my head, would be to go in this direction: the server & the client communicate by sending messages & chunks ( in lieu of other names ). Here's what I mean by this: every time the client/server wants to send something ( text message or file ) it will first send a simple text message ( newline terminated ) with the number of the chunks it will send. Example: command 4,20,30,40,50 Where command would be something like instant-message or file,4 would be the number of chunks to be sent, 20 would be the size in bytes of the first chunk, 30 of the 2nd, and so forth. after the message was sent, the client/server will start sending chunks ( of sizes mentioned in the sent message ). What do you think about implementing the client/server communication this way? What better options are there?

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  • client-server application design

    - by nelly
    Hi, i want to create a client-server application using sockets on .net platform and being new to networking programming and i have a dilemma. The client will send data to server often and also the server will notify clients often. What is the best way to design it? should the server keep a thread to communicate with each client until it quits or just the clients send data to the server and it update the clients regularly(few seconds) or none of those? Some help would be great. Thanks guys.

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  • How can I get the "Latency" of a process that has a TCP connection open?

    - by Dave
    Hello, I am looking to get the "Latency" field of a TCP connection. I notice windows Resource Monitor has this field, and I was wondering if there was a way I can find it. Preferrably without using WMI. If you are unsure what field I am talking about, open Task Manager, goto the Performance tab and hit the Resource Monitor button. Once Resource Monitor is open, expand the TCP Connections area and you will see a Latency field. Is there anyway to access this programatically? Thanks!

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  • Need a good website URL to test against

    - by Zombies
    I need a URL to just test basic http connectivity. It needs to be consistent and: Always be up Never change drastically due to IP or user agent. (IE: 301 Location redirect/ huge difference in content... minor would be tolerable) The URL itself has a consistent content-length. (IE: it doesn't vary from by 2kb at most, ever) A few examples, yet none match all 3 criteria: One example of always up: www.google.com (yet it 301 redirects based on IP location). Another good one is http://www.google.com/webhp?hl=en. but the problem there is that based on a given holiday, the content-length can really vary.

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  • deleting a file in java while uploading it in other thread

    - by user369507
    i'm trying to build a semi file sharing program, when each computer acts both as a server and as a client. I give multiple threads the option to DL the file from my system. also, i've got a user interface that can recieve a delete message. my problem is that i want that the minute a delete message receieved, i wait for all the threads that are DL the file to finish DL, and ONLY than excute file.delete(). what is the best way to do it? I thought about some database that holds and iterate and check if the thread is active, but it seems clumsy. is there a better way? thanks

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  • JAVA: How do I accept input during a certain period of time only

    - by sebrock
    Im trying to do a simple game where I continually need input from players. This needs to happen during a certain time period only. Everything that is sent after that will be discarded. After the time period a new game starts. So: Start game Wait for input from all players during 10 seconds 10 secs no more input Calculate the winner and do some stuff Goto 1. I was thinking using a timer and timertask to keep track of time and maybe use a boolean variable that changes from "open" to "closed" after 10 seconds? Please give me some advise on this.

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  • tool to find out distance in terms of no. of hops in unix

    - by mawia
    Hi! all, I am writing an application for video streaming.In the application server is required to know the distance of the client from it self in terms of hop number.My question is,is there any tool/method other than traceroute available in unix environment to find it? I also need to find out the geographical location of the client.So is their any tool/method for this as well? Any help in this regard will be highly appreciated. Thanks in advance. Mawia

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  • Listening Port Permanently. if file is on my stream, Get file. How to?

    - by Phsika
    i writed 2 client and server program. client dend file also server listen port and than get file.But i need My server App must listen on 51124 port permanently. if any file on my stream, show my message "there is a file on your stream" and than show me savefile dialog. But my server app in "Infinite loop". 1) listen 51124 port every time 2) do i have a file on my stream, show me a messagebox. private void Form1_Load(object sender, EventArgs e) { TcpListener Dinle = new TcpListener(51124); try { Dinle.Start(); Socket Baglanti = Dinle.AcceptSocket(); if (!Baglanti.Connected) { MessageBox.Show("No Connection!"); } else { while (true) { byte[] Dizi = new byte[250000]; Baglanti.Receive(Dizi, Dizi.Length, 0); string Yol; saveFileDialog1.Title = "Save File"; saveFileDialog1.ShowDialog(); Yol = saveFileDialog1.FileName; FileStream Dosya = new FileStream(Yol, FileMode.Create); Dosya.Write(Dizi, 0, Dizi.Length - 20); Dosya.Close(); listBox1.Items.Add("dosya indirildi"); listBox1.Items.Add("Dosya Boyutu=" + Dizi.Length.ToString()); listBox1.Items.Add("Indirilme Tarihi=" + DateTime.Now); listBox1.Items.Add("--------------------------------"); } } } catch (Exception) { throw; } } My Algorithm: if(AnyFileonStream()==true) { GetFile() //Also continue to listening 51124 port... } How can i do that?

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  • how to customize the filter when following a stream in wireshark?

    - by jim
    when selecting a packet and choosing to follow the stream, wireshark automatically sets a filter that looks something like this: (ip.addr eq 10.2.3.8 and ip.addr eq 10.2.255.255) and (udp.port eq 999 and udp.port eq 899). i'd like to be able to set that myself when following the stream, but have not been able to identify where to do that. setting the display filter has no effect. in fact, after following the stream, whatever display filter is currently set will be replaced by the follow stream formatted filter. is customizing the follow stream filter even possible? thanks

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  • OS-independent Inter-program communication between Python and C

    - by Gyppo
    I have very little idea what I'm doing here, I've never done anything like this before, but a friend and I are writing competing chess programs and they need to be able to communicate to each other. He'll be writing mainly in C, the bulk of mine will be in Python, and I can see a few options: Alternately write to a temp file, or successive temp files. As the communication won't be in any way bulky this could work, but seems like an ugly work-around to me, the programs will have to keep checking for change/new files, it just seems ugly. Find some way of manipulating pipes i.e. mine.py| ./his . This seems like a bit of a dead end. Use sockets. But I don't know what I'd be doing, so could someone give me a pointer to some reading material? I'm not sure if there are OS-independent, language independent methods. Would there have to be some kind of supervisor server program to administrate? Use some kind of HTML protocol, which seems like overkill. I don't mind the programs having to run on the same machine. What do people recommend, and where can I start reading?

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  • Are there any lightweight analogues to CORBA/RPC for embedded programs?

    - by Mtr
    I am writing embedded applications for different hardware (avr, arm7, tms55xx…) and different rtoses (freeRTOS, rtx, dsp/bios). And every second of them needs to communicate with PC or another digital device. Sometimes interactions logic is very advanced. So I'm interesting in common methodology (like state-machine programming style), protocol specification or library, that could simplify developing such things.

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  • API for configuring static IP addresses in an android application

    - by awoodland
    Is it possible to set the IP address of an interface in Android within an application? I can query the available interfaces and their current addresses using java.net.NetworkInterface, but this doesn't provide a facility to change these. Did I just miss something somewhere or is it not allowed? I was hoping to be able to make my application either change or add an alias to one or more of the existing interfaces at runtime on an "off the shelf" device. (2.1/2.2). Ideally I'd like to do this for both IPv4 and v6 addresses.

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