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  • Dynamically find other hosts in a LAN in Java

    - by Federico Cristina
    A while ago I developed a little LAN chat app. in Java which allows chatting with other hosts, send images, etc. Although it was created just for fun, now it's being used where I work. Currently, there is no "chat server" on the app. where each client registers, updates it's status, etc. (I liked the idea of symmetric design and not depending on a server running on some other machine). Instead, each host is a client/server which has a hosts.properties file with the hostname of the other hosts, and - for instance - broadcasts to each one of them when sending a massive message/image/whatever. In the beginning there were just a couple of hosts, so this hosts.properties file wasn't an issue. But as the amount of users increased, the need of updating that file was a bit daunting. So now I've decided to get rid of it, and each time the app. starts, dynammically find the other active hosts. However, I cannot find the correct way of implement this. I've tried starting different threads, each one of them searching for other hosts in a known range of IP addresses. Something like this (simplified for the sake of readability): /** HostsLocator */ public static void searchForHosts(boolean waitToEnd) { for (int i=0; i < MAX_IP; i+= MAX_IP / threads) { HostsLocator detector = new HostsLocator(i, i+(MAX_IP / threads - 1)); // range: from - to new Thread(detector).start(); } } public void run() { for (int i=from; i<=to; i++) findHosts( maskAddress + Integer.toString(i) ); } public static boolean findHosts(String IP) { InetAddress address = InetAddress.getByName(IP); if ( address.isReachable(CONNECTION_TIME_OUT) ) // host found! } However: With a single thread and a low value in CONNECTION_TIME_OUT (500ms) I get wrong Host Not Found status for for hosts actually active. With a high value in CONNECTION_TIME_OUT (5000ms) and only one single thread takes forever to end With several threads I've also found problems similar like the first one, due to collisions. So... I guess there's a better way of solving this problem but I couldn't find it. Any advice? Thanks!

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  • Algorithm for non-contiguous netmask match

    - by Gianluca
    Hi, I have to write a really really fast algorithm to match an IP address to a list of groups, where each group is defined using a notation like 192.168.0.0/252.255.0.255. As you can see, the bitmask can contain zeros even in the middle, so the traditional "longest prefix match" algorithms won't work. If an IP matches two groups, it will be assigned to the group containing most 1's in the netmask. I'm not working with many entries (let's say < 1000) and I don't want to use a data structure requiring a large memory footprint (let's say 1-2 MB), but it really has to be fast (of course I can't afford a linear search). Do you have any suggestion? Thanks guys. UPDATE: I found something quite interesting at http://www.cse.usf.edu/~ligatti/papers/grouper-conf.pdf, but it's still too memory-hungry for my utopic use case

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  • length of captured packets more than MTU

    - by kumar
    Hi, I m running iperf between two machines (linux) and I can observe the mtu of both the interfaces connected is 1500. I ran tcpdump to capture packets and I observed some packets have "length as 2962"....how come this is possible with mtu as only 1500? Please clarify. Thanks! Note: flags field is set as DF. and proto is TCP

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  • Is it possible to have more than P2P on iPhone with Bluetooth

    - by Ricardo Ferreira
    Hi all, This seems like a straightforward google search answer, but after a while, I still can't be 100% sure of this. I've found Z2Live (http://www.z2live.com/), which is basically a layer above GameKit and they too use only P2P with Bluetooth. So I just want to be sure if I can only have P2P with Bluetooth or if I can have like 4 iPhones all connected to a server (who will also be a client) using Bluetooth. Thanks in advance.

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  • Serialization of Mouse cursors over network

    - by Ehtsham
    hi I am working a client/server application in C#. My server Capture current Mouse Cursors and send these to client so that Cursor of the cleint also chage accordingly.I can detect windows Cursors and serialize them over binaryformatter. it works fine but but problem is there are many cursors that can not be detected like mspaint cursors so i have to take its handler and create the cursor and its x nad y hotspots and add them in an arraylist and serialize it over network but after 10 to 15 minute it thorws exception "Error HRESULT E_FAIL has been returned from a call to a COM Compeonet" and cleint throws the exception of "method of invocation" Can anybody guid me what going wrong ort some better way to do like this Some code is here IntPtr curInfo = GetCurrentCursor(); Cursor cur; Icon ic; byte cursor = 0; if (curInfo != null && curInfo.ToInt32() != 0) { cur = CheckForCusrors(curInfo); try { if (!isLinuxClient) { if (cur == null) { PlatformInvokeUSER32.GetIconInfo(curInfo, out temp); ic = Icon.FromHandle(curInfo); //bitmap = ic.ToBitmap(); ArrayList ar = new ArrayList(); ar.Add(ic); ar.Add(temp.xHotspot); ar.Add(temp.yHotspot); b.Serialize(stm, ar); } else { ArrayList ar = new ArrayList(); ar.Add(cur); b.Serialize(stm, ar); } } public Cursor CheckForCusrors(IntPtr hCur) { if (hCur == Cursors.AppStarting.Handle) return Cursors.AppStarting; else if (hCur == Cursors.Arrow.Handle) return Cursors.Arrow; . . . else if (hCur == Cursors.PanWest.Handle) return Cursors.PanWest; return null; } `

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  • How to test for secure SMTP mail service on a mail server

    - by Vinay S Shenoy
    I'm working on a project to auto-configure a user's email server settings in Java. I am extracting the mail server from his email address and looking up the MX records of that mail server using the DirContext class with com.sun.jndi.dns.DnsContextFactory. Then I'm opening a Socket to each server and testing them using a HELO command and checking the responses. My problem is that this works only when I test it with the unsecure SMTP port 25. How can I use it with the secure port 465? I tried using Secure Sockets by using SSLSocketFactory sslsocketfactory = (SSLSocketFactory)SSLSocketFactory.getDefault(); SSLSocket socket = (SSLSocket)sslsocketfactory.createSocket(mailserver, STANDARD_SMTP_PORT); But all connections get a timeout exception as follows alt1.gmail-smtp-in.l.google.com. java.net.ConnectException: Operation timed out Please help.

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  • What alternative is there to writing a TCP/IP data relay?

    - by LoudNPossiblyRight
    I am about to write a tcp/ip data relay - application that passes a one way stream of data from one host/port to another host/port. Initially it will be generic, but later on i will customize it to the need of a specific business request. I am guessing that something generic already exists out there so my question is: Has anyone used a third party (preferably open source) data relay in a production environment, if so what is, and do you recommend it? Any platform is fine. Thanks.

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  • For distributed applications, which to use, ASIO vs. MPI?

    - by Rhubarb
    I am a bit confused about this. If you're building a distributed application, which in some cases may perform parallel operations (although not necessarily mathematical), should you use ASIO or something like MPI? I take it MPI is a higher level than ASIO, but it's not clear where in the stack one would begin.

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  • Using a Cyc Image in Windows

    - by nrhine1
    Hi, I am trying to use a Microtheory for a research project I am working on, and am having trouble getting my saved Image of constants I create to work correctly. I save the image after creating the constants using (write-image "world\MyImage") and then going to the \server\run\ directory and using run-cyc-32bit.bat -w "world\MyImage" It loads the server correctly, but not with my constants. I found the above command at the reference page here. Thank you for any help

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  • socket timeout and remove O_NONBLOCK option

    - by juxstapose
    Hello, I implemented a socket timeout and retry but in order to do it I had to set the socket as a non-blocking socket. However, I need the socket to block. This was my attempt at a solution to these two problems. This is not working. Subsequent send calls block but never send any data. When I connect without the select and the timeout, subsequent send calls work normally. References: C: socket connection timeout How to reset a socket back to blocking mode (after I set it to nonblocking mode)? Code: fd_set fdset; struct timeval tv; fcntl(dsock, F_SETFL, O_NONBLOCK); tv.tv_sec = theDeviceTimeout; tv.tv_usec = 0; int retries=0; logi(theLogOutput, LOG_INFO, "connecting to device socket num retrys: %i", theDeviceRetry); for(retries=0;retries<theDeviceRetry;retries++) { connect(dsock, (struct sockaddr *)&daddr, sizeof daddr); FD_ZERO(&fdset); FD_SET(dsock, &fdset); if (select(dsock + 1, NULL, &fdset, NULL, &tv) == 1) { int so_error; socklen_t slen = sizeof so_error; getsockopt(dsock, SOL_SOCKET, SO_ERROR, &so_error, &slen); if (so_error == 0) { logi(theLogOutput, LOG_INFO, "connected to socket on port %i on %s", theDevicePort, theDeviceIP); break; } else { logi(theLogOutput, LOG_WARN, "connect to %i failed on ip %s because %s retries %i", theDevicePort, theDeviceIP, strerror(errno), retries); logi(theLogOutput, LOG_WARN, "failed to connect to device %s", strerror(errno)); logi(theLogOutput, LOG_WARN, "error: %i %s", so_error, strerror(so_error)); continue; } } } int opts; opts = fcntl(dsock,F_GETFL); logi(theLogOutput, LOG_DEBUG, "clearing nonblock option %i retries %i", opts, retries); opts ^= O_NONBLOCK; fcntl(dsock, F_SETFL, opts);

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  • warcraft3 packet infromation [closed]

    - by ajay009ajay
    Hello All, I have made a program which is fetching data from server to and game to server. I want to keep these record in my file. But my problem is this is not in good format that i can read easily. I am reading all data as "Byte" (from java). Can anybody explain header or data info of packet. so I can read it in human manner Huh thanks.

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  • How to reliably identify users across Internet?

    - by amn
    I know this is a big one. In fact, it may be used for some SO community wiki. Anyways, I am running a website that DOES NOT use explicit authentication of users. It's public as in open to everybody. However, due to the nature of the service, some users need to be locked out due to misbehavior. I am currently blocking IP addresses, but I am aware of the supposed fact that many people purposefully reset their DHCP client cache to have their ISP assign them new addresses. Is that a fact? I think it certainly is a lucrative possibility for some people who want to circumvent being denied access. So IPs turn out to be a suboptimal way of dealing with this. But there is nothing else, is it? MAC addresses don't survive on WAN (change from hop to hop?), and even if they did - these can also be spoofed, although I think less easily than IP renewal. Cookies and even Flash cookies are out of the question, because there are tons of "tutorials" how to wipe these, and those intent on wreaking havoc on Internet are well aware and well equipped against such rudimentary measures I would employ. Is there anything else to lean on? I was thinking heuristical profiling - collecting available data from client-side and forming some key with it, but have not gone as far as to implementing it - is it an option?

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  • Google App Engine - How to implement the activity stream in a social network

    - by spidee
    I want some ideas on the best practice to implement an activity stream for a social network im building in app engine (PYTHON) I first want to keep a log for all activities of each user - so that we have a history. i.e. someone became a friend, added a picture, changed their address etc. This way we have a users history available should we need it. Also mean we can remove friendship joins, change user data but have a historical log. I also want to stream a users activity to their friends. for this only the last X activities need to be kept - that is in the scenario that messages are sent to friends when an activity occurs. Its pretty straight forward designing a history log - ie: when, what, where. The complication comes as to how we notify friends of a user as to their activity. In our app friendships are not mutual - ie they are based on the twitter following model. Some accounts could have thousands of followers. What is the best approach to model this. using a many to many join table and doing a costly query - using a feed class that fired a copy of the activity to all the subscribers - maybe into mcache? As their maybe a need to fire thousands of messages i would imagine a cron job would need to be used. Any help ideas thoughts on this Thx

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  • A smart UDP protocol analyzer?

    - by ripper234
    Is there a "smart" UDP protocol analyzer that can help me reverse engineer a message based protocol? I'm using Wireshark to do the sniffing, but if there's a tool that can detect regularities in the protocol (repeated strings, bits of the protocol that are CRC/Checksum or length, ...) and aid the process that would help.

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  • How do you learn a class hierarchy quickly?

    - by rsteckly
    Hi, Something I don't enjoy about programming is learning a new API. For example, right now I'm trying to learn Windows Identity Foundation. Its frustrating because I'm going to spend the bulk of the time learning how a few classes work and actually only write several lines of code. In .NET, there are so many types that I seem to spend more time hunting around in msdn for a class than writing code. It also interrupts my workflow while I'm working because I have to type a little bit than look something up. Obviously, I don't have to do this for the basic classes. Whenever new things come though there is definitely some looking up to do. Then I often don't reuse that class enough to really review it or bring it into action. I'm wondering if anybody out there has a found a way to memorize (or look up more efficiently) these object model hierarchies?

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  • Pure functional bottom up tree algorithm

    - by Axel Gneiting
    Say I wanted to write an algorithm working on an immutable tree data structure that has a list of leaves as its input. It needs to return a new tree with changes made to the old tree going upwards from those leaves. My problem is that there seems to be no way to do this purely functional without reconstructing the entire tree checking at leaves if they are in the list, because you always need to return a complete new tree as the result of an operation and you can't mutate the existing tree. Is this a basic problem in functional programming that only can be avoided by using a better suited algorithm or am I missing something?

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  • How to handle building and parsing HTTP URL's / URI's / paths in Perl

    - by Robert S. Barnes
    I have a wget like script which downloads a page and then retrieves all the files linked in img tags on that page. Given the URL of the original page and the the link extracted from the img tag in that page I need to build the URL for the image file I want to retrieve. Currently I use a function I wrote: sub build_url { my ( $base, $path ) = @_; # if the path is absolute just prepend the domain to it if ($path =~ /^\//) { ($base) = $base =~ /^(?:http:\/\/)?(\w+(?:\.\w+)+)/; return "$base$path"; } my @base = split '/', $base; my @path = split '/', $path; # remove a trailing filename pop @base if $base =~ /[[:alnum:]]+\/[\w\d]+\.[\w]+$/; # check for relative paths my $relcount = $path =~ /(\.\.\/)/g; while ( $relcount-- ) { pop @base; shift @path; } return join '/', @base, @path; } The thing is, I'm surely not the first person solving this problem, and in fact it's such a general problem that I assume there must be some better, more standard way of dealing with it, using either a core module or something from CPAN - although via a core module is preferable. I was thinking about File::Spec but wasn't sure if it has all the functionality I would need.

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  • Hebbian learning

    - by Bane
    I have asked another question on Hebbian learning before, and I guess I got a good answer which I accepted, but, the problem is that I now realize that I've mistaken about Hebbian learning completely, and that I'm a bit confused. So, could you please explain how it can be useful, and what for? Because the way Wikipedia and some other pages describe it - it doesn't make sense! Why would we want to keep increasing the weight between the input and the output neuron if the fire together? What kind of problems can it be used to solve, because when I simulate it in my head, it certainly can't do the basic AND, OR, and other operations (say you initialize the weights at zero, the output neurons never fire, and the weights are never increased!)

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  • Deciphering Encoding: Packet Analyzation Tools

    - by Zombies
    I am looking for better tools than wireshark for this. The problem with wireshark is that it does not format the data layer (which is the only part I am looking at) cleanly for me to compare the different packets and attempt to understand the third party encoding (which is closed source). Specifically, what are some good tools for viewing data, and not tcp/udp header information? Particularly, a tool that formats the data for comparison. To be very specific: I would like a program that compares multiple (not just 2) files in hex.

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  • How to create a language these days?

    - by Mike
    I need to get around to writing that programming language I've been meaning to write. How do you kids do it these days? I've been out of the loop for over a decade; are you doing it any differently now than we did back in the pre-internet, pre-windows days? You know, back when "real" coders coded in C, used the command line, and quibbled over which shell was superior? Just to clarify, I mean, not how do you DESIGN a language (that I can figure out fairly easily) but how do you build the compiler and standard libraries and so forth? What tools do you kids use these days?

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