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• Java: How to manage UDP client-server state

  - by user92947

  I am trying to write a Java application that works similar to MapReduce. There is a server and several workers. Workers may come and go as they please and the membership to the group has a soft-state. To become a part of the group, the worker must send a UDP datagram to the server, but to continue to be part of the group, the worker must send the UDP datagram to the server every 5 minutes. In order to accommodate temporary errors, a worker is allowed to miss as many as two consecutive periodic UDP datagrams. So, the server must keep track of the current set of workers as well as the last time each worker had sent a UDP datagram. I've implemented a class called WorkerListener that implements Runnable and listens to UDP datagrams on a particular UDP port. Now, to keep track of active workers, this class may maintain a HashSet (or HashMap). When a datagram is received, the server may query the HashSet to check if it is a new member. If so, it can add the new worker to the group by adding an entry into the HashSet. If not, it must reset a "timer" for the worker, noting that it has just heard from the corresponding worker. I'm using the word timer in a generic sense. It doesn't have to be a clock of sorts. Perhaps this could also be implemented using int or long variables. Also, the server must run a thread that continuously monitors the timers for the workers to see that a client that times out on two consecutive datagram intervals, it is removed from the HashSet. I don't want to do this in the WorkerListener thread because it would be blocking on the UDP datagram receive() function. If I create a separate thread to monitor the worker HashSet, it would need to be a different class, perhaps WorkerRegistrar. I must share the HashSet with that thread. Mutual exclusion must also be implemented, then. My question is, what is the best way to do this? Pointers to some sample implementation would be great. I want to use the barebones JDK implementation, and not some fancy state maintenance API that takes care of everything, because I want this to be a useful demonstration for a class that I am teaching. Thanks

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• Spreading incoming batched data into a real-time stream

  - by pr1001

  I would like to display some events in 'real-time'. However, I must fetch the data from another source. I can request the last X minutes, though the source is updated approximately every 5 minutes. This means that there will be a delay between the most recent data retrieved and the point in time that I make the request. Second, because I will be receiving a batch of data, I don't want to just fire out all the events down a socket once my fetcher has retrieved it: I would like to spread out the events so that they are both accurately spaced amongst each other and in sync with their original occurrences (e.g. an event is always displayed 6 minutes after it actually happened). My thought is to fetch the data every 5 minutes from the source, knowing that I won't get the very latest data. The original data would be then queued to be sent down the socket 7.5 minutes from its original timestamp – that is, at least ~2.5 minutes from when its batch was fetched and at most 7.5 minutes since then. My question is this: is this the best way to approach the problem? Does this problem have any standard approaches or associated literature related to implementation best-practices and edge cases? I am a bit worried that the frequency of my fetches and the frequency in which the source is updated will get out of sync, leading to points where no data will be retrieved from the source. However, since my socket delay is greater than my fetch frequency, the subsequent fetch should retrieve newer data before the socket queue is empty. Is that correct? Am I missing something? Thanks!

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• Communicating with a remote host via HTTPS

  - by user619818

  I have developed a solution where a Java applet makes a socket connection to a port on a socket server (which happens to run on a web server). But a new client has implemented https within their LAN and so I am told communication must be via HTTPS. With standard socket communication you connect to a port on a host. But the clients HTTPS uses port 443. So will it be possible to connect to a socket server using a different port? I assume it must be possible? Any help would be much appreciated.

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• Serializing Data Structures in C

  - by src

  I've recently read three separate books on algorithms and data structures, tcp/ip socket programming, and programming with memory. The book about memory briefly discussed the topic of serializing data structures for the purposes of storing it to disk, or sending it across a network. I can't help but wonder why the the other two books didn't discuss serialization at all. After an unsuccessful web/book search I'm left wondering where I can find a good book/paper/tutorial on serializing data structures in C? Where or how did you learn it?

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• PHP, when to use iterators, how to buffer results?

  - by Jon L.

  When is it best to use Iterators in PHP, and how can they be implemented to best avoid loading all objects into memory simultaneously? Do any constructs exist in PHP so that we can queue up results of an operation for use with an Iterator, while again avoiding loading all objects into memory simultaneously? An example would be a curl HTTP request against a REST server In the case of an HTTP request that returns all results at once (a la curl), would we be better off to go with streaming results, and if so, are there any limitations or pitfalls to be aware of? If using streaming, is it better to replace curl with a PHP native stream/socket? My intention is to implement Iterators for a REST client, and separately a document ORM that I'm maintaining, but only if I can do so while gaining benefits from reduced memory usage, increased performance, etc. Thanks in advance for any responses :-)

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• Is ZeroMQ a good choice to make a Python app and a C# managed assembly work together?

  - by Alex Bausk

  I have a task that involves talking to a .NET-based API (namely AutoCAD) to retrieve data, send commands, and react to events. I want to separate the API operations and the proper program logic (largely already implemented in Python) by using natural tools for both: a C# DLL for the former and a Python app for the latter. To connect these two pieces, I began exchanging JSON in ZeroMQ messages. I'm at early development stages but having recently discovered that ZeroMQ does not guarantee message delivery/order, I have reservations about whether this is a feasible way to go. Right now my app is a very basic REQ/REP pair and I plan to handle reacting to events and executing different commands by adding some sort of 'recipient-function' field to my message format. The reason that I want to use ZMQ is that I might be able to scale the software into a larger, multi-user, distributed solution sometime. I am a lay programmer so I would ask for your advice about this architecture. Should I just go ahead with it and plan to deal with message reliability/ordering when problems appear? Should I consider developing some kind of a REST wrapper around ZMQ?

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• Network programming under windows: is WSA functions can be more complete than pSock functions [on hold]

  - by Kane

  I plan to make a set of classic socket functions to simplify their usages. Since i work under windows and linux indifferently i usually make it portable (it's not my first version of this set of functions), but i want to do something different this time and dedicate one version to windows, and one other to linux. With that i wonder for the windows version, if the WSA* functions can have any interest using them instead of the psock ones. I have found nothing about a comparison between them, so if any of you have any idea, suggestion, link or benchmark ?

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• How much overhead is there in persistent connections?

  - by nynex

  Ok so I'm musing over a little side project I want to start. Essentially its a multi-session web based FTP client. Multi-session in that you can log into several FTP servers at the same time and perform operations like moving a file from one FTP server to another. I'm doing this mainly to brush up on the new webdev technologies, particularly websockets. I'm using node.js + socket.io to keep a persistent bi-directional connection between the web browser and the web server. The web server will also have persistent connections to each FTP server the user has logged into. So if there are 100 concurrent users each logged into 5 ftp accounts, the web server will have 100 websocket connections + 500 ftp connections. Is servicing 600 connections a lot? I know it depends on the hardware resources of the server but is something like this doable on a budget? Are there more efficient means of doing something like this? I know its unlikely that this project will really get popular but I want it to scale well regardless. Thanks for any help, I've still got a lot to learn.

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• Pipe an infinite stream to internal loop?

  - by Sh3ljohn

  I've seen a lot of things about redirecting stdout to a TCP socket, but no real example of how to do it in practice, specifically when the output stream generated by the first "command" never ends. To talk about something concrete, let's take programs like servers that typically output their log endlessly to stdout (well, as long as they run). If you redirect the output to a log file on the disk, then this file is always open (therefore not readable by others?) and grows infinitely, which eventually is going to cause problems. This might be a nood question, but I don't know what it does or how to do it so. How to redirect the output of a command to the internal loop? I want to make sure that data is sent EVERY time something is written to stdout, and that the pipe won't wait for the command to end (never happens ideally!). Is that right? If 2 is true, is there a buffer system to send chunks of data once it reaches a certain size only? Could you give me concrete command line examples to do the above? Thanks in advance

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• copying same file name from client to server using tcp protocol with same size of file

  - by user3686570

  This is the client and server program where a client sends a file to server to save in the server. There is a issuse in that same file name is not getting copied on the server with same file size Please help me in this Client program import socket import sys s = socket.socket(socket.AF_INET, socket.SOCK_STREAM) s.connect(("localhost",9999)) path=raw_input("Please enter the complete PATH of your file : ") f=open (path, "rb") l = f.read(256) while (l): s.sendall(l) l = f.read(10000) s.close() Server Program import socket import sys s = socket.socket(socket.AF_INET, socket.SOCK_STREAM) s.bind(("localhost",9999)) s.listen(10) while True: s, address = s.accept() print address i=1 f = open( str(i),'wb') #open in binary #i=i+1 while (True): l=s.recv(256) #while (l): f.write(l) l=s.recv(256) print 'File recieve succesfully' f.close() #sc.close() s.close() Thanks in advance

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• Difference between a socket and a port

  - by cobie

  Could someone please explain quite clearly the difference between a port and a socket. I know that a port serves as a door into the network for an application process and that the application process uses a socket connection to the given port number to handle network communication but when you have multiple processes listening on a single port number, I am finding it difficult to understand the difference between the socket and the port and how they all fit together.

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• In what way I can implement packet filtering function in C++/C#?

  - by Network study

  Background: I am going to design a firewall-like application (with GUI) which will include several functions such as Packet sniffing and packet filtering. Both of the functions should be implemented to support different protocol levels including application, transport, network and link layer. I only know a little in C#.Net programming to perform the IP packet sniffing. It is also known that packet filtering requires the techniques in WFP or LSP and packet sniffing in application requires dll hooking. Questions: I am not sure which programming language(either C++ or C#) would be suitable for designing such an application described above. If I want to implement the packet filtering function, any libraries will be needed? edit01: Someone suggest that winDivert would be helpful, is it true?

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• C++ Program Flow: Sockets in an Object and the Main Function

  - by jfm429

  I have a rather tricky problem regarding C++ program flow using sockets. Basically what I have is this: a simple command-line socket server program that listens on a socket and accepts one connection at a time. When that connection is lost it opens up for further connections. That socket communication system is contained in a class. The class is fully capable of receiving the connections and mirroring the data received to the client. However, the class uses UNIX sockets, which are not object-oriented. My problem is that in my main() function, I have one line - the one that creates an instance of that object. The object then initializes and waits. But as soon as a connection is gained, the object's initialization function returns, and when that happens, the program quits. How do I somehow wait until this object is deleted before the program quits? Summary: main() creates instance of object Object listens Connection received Object's initialization function returns main() exits (!) What I want is for main() to somehow delay until that object is finished with what it's doing (aka it will delete itself) before it quits. Any thoughts?

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• Sockets and COBOL

  - by kati

  I have received a job at a hospital which still uses COBOL for all organizational work, the whole (now 20 Terabyte) database (Which was a homebrew in, guess what, COBOL) is filled with the data of every patient since the last 45 (or so) years. So that was my story. Now to my question: Currently, all sockets were (from what I've seen) implemented by COBOL programs writing their data into files. These files then were read out by C++ programs (That was an additional module added in the late 1980s) and using C++ sockets sent to the database. Now this solution has stopped working as they are moving the database from COBOL to COBOL, yes - they didn't use MySQL or so - they implemented a new database - again in COBOL. I asked the guy that worked there before me (hes around 70 now) why the hell someone would do that and he told me that he is so good at COBOL that he doesn't want to write it in any other language. So far so good now my question: How can I implement socket connections in COBOL? I need to create an interface to the external COBOL database located at, for example, 192.168.1.23:283.

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• Socket 1155 vs 2011 vs Haswell

  - by woody

  The title says it all. I am trying to decide between sockets and just cant pinpoint which to get based on pros and cons. The build this will go into will be my primary PC. It will be used for every day computing, coding, some multimedia and gaming. I have read that 1155 and 2011 will be dead within the new year and that Haswell will double the performance of Ivy Bridge. What is a general run down on the different sockets? Pros and Cons? More specifically what are the technical differences between the three?

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• AIX network parameters to close TCP sockets of unplugged devices

  - by ADD Geek

  Hi there We have an AIX box, running what we call in banking "ATM Switch" not the ATM networking switch, but the bank ATM driver. where we have some ATM machines connected to two server processes. The problem is, when we disconnect any of these machines, the netstat -na| grep <port number> command shows that the socket established for this disconnected device is still established, we have to manually send a command from the software to make the socket aware that it is not live anymore. Is there a parameter on tcp level to make this connection aware within a minute or two that this device is not connected anymore? we had the following parameters set with root privileges: no -o tcp_keepidle=1000 no -o tcp_keepcnt=2 no -o tcp_keepintvl=150 no -o tcp_finwait2=100 it was originally having the default values. but even after we changed these parameters and restarted the server processes, the problem was still there.

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• Transparent proxying leaves sockets with SYN_RCVD in MacOS X 10.6 Snow Leopard (and maybe FreeBSD)

  - by apenwarr

  I'm trying to create a transparent proxy on my MacOS machine in order to port the sshuttle ssh-based transproxy VPN from Linux. I think I almost have it working, but sadly, almost is not 100%. Short version is this. In one window, start something that listens on port 12300: $ while :; do nc -l 12300; done Now enable proxying: # sysctl -w net.inet.ip.forwarding=1 # sysctl -w net.inet.ip.fw.enable=1 # ipfw add 1000 fwd 127.0.0.1,12300 log tcp from any to any And now test it out: $ telnet localhost 9999 # any port number will do # this works; type stuff and you'll see it in the nc window $ telnet google.com 80 # any host/port will do # this *doesn't* work! After the latter experiment, I see lines like this in netstat: $ netstat -tn | grep ^tcp4 tcp4 0 0 66.249.91.104.80 192.168.1.130.61072 SYN_RCVD tcp4 0 0 192.168.1.130.61072 66.249.91.104.80 SYN_SENT The second socket belongs to my telnet program; the first is more suspicious. SYN_RCVD implies that my SYN packet was correctly captured by the firewall and taken in by the kernel, but apparently the SYNACK was never sent back to telnet, because it's still in SYN_SENT. On the other hand, if I kill the nc server, I get this: $ telnet google.com 80 Trying 66.249.81.104... telnet: connect to address 66.249.81.104: Connection refused telnet: Unable to connect to remote host ...which is as expected: my proxy server isn't running, so ipfw redirects my connection to port 12300, which has nobody listening on it, ie. connection refused. My uname says this: $ uname -a Darwin mean.local 10.2.0 Darwin Kernel Version 10.2.0: Tue Nov 3 10:37:10 PST 2009; root:xnu-1486.2.11~1/RELEASE_I386 i386 Does anybody see any different results? (I'm especially interested in Snow Leopard vs Leopard results, as there seem to be some internet rumours that transproxy is broken in Snow Leopard version) Any advice for how to fix?

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• connection to apache server switches sockets connection

  - by Newben

  I have just post a question but I post an other one because the problem is not the one I had in thought when asking the latter. So, I am running some rails app on osx, when I run rails s, everything works fine. If I shut down the apache server (mamp) and if I run rails s again, I have this message Can't connect to local MySQL server through socket '/Applications/MAMP/tmp/mysql/mysql.sock', which for sure is normal. For info, my mamp server is running, and the connection must pass through /Applications/MAMP/Library/bin/mysql, so I aliased it by setting in my bash profile : alias mysql="/Applications/MAMP/Library/bin/mysql" Now, when I launch a rails generate command type, I get this message : /$root/vendor/bundle/ruby/2.0.0/gems/mysql2-0.3.11/lib/mysql2/client.rb:44:in `connect': Can't connect to local MySQL server through socket '/tmp/mysql.sock' (2) (Mysql2::Error) So how it can be ?

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• Tips / techniques for high-performance C# server sockets

  - by McKenzieG1

  I have a .NET 2.0 server that seems to be running into scaling problems, probably due to poor design of the socket-handling code, and I am looking for guidance on how I might redesign it to improve performance. Usage scenario: 50 - 150 clients, high rate (up to 100s / second) of small messages (10s of bytes each) to / from each client. Client connections are long-lived - typically hours. (The server is part of a trading system. The client messages are aggregated into groups to send to an exchange over a smaller number of 'outbound' socket connections, and acknowledgment messages are sent back to the clients as each group is processed by the exchange.) OS is Windows Server 2003, hardware is 2 x 4-core X5355. Current client socket design: A TcpListener spawns a thread to read each client socket as clients connect. The threads block on Socket.Receive, parsing incoming messages and inserting them into a set of queues for processing by the core server logic. Acknowledgment messages are sent back out over the client sockets using async Socket.BeginSend calls from the threads that talk to the exchange side. Observed problems: As the client count has grown (now 60-70), we have started to see intermittent delays of up to 100s of milliseconds while sending and receiving data to/from the clients. (We log timestamps for each acknowledgment message, and we can see occasional long gaps in the timestamp sequence for bunches of acks from the same group that normally go out in a few ms total.) Overall system CPU usage is low (< 10%), there is plenty of free RAM, and the core logic and the outbound (exchange-facing) side are performing fine, so the problem seems to be isolated to the client-facing socket code. There is ample network bandwidth between the server and clients (gigabit LAN), and we have ruled out network or hardware-layer problems. Any suggestions or pointers to useful resources would be greatly appreciated. If anyone has any diagnostic or debugging tips for figuring out exactly what is going wrong, those would be great as well. Note: I have the MSDN Magazine article Winsock: Get Closer to the Wire with High-Performance Sockets in .NET, and I have glanced at the Kodart "XF.Server" component - it looks sketchy at best.

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• How to create sockets in google chrome extension ?

  - by Xinus

  Hello, I created small hello world extension for google chrome http://code.google.com/chrome/extensions/getstarted.html. I need to use sockets in extension for peer to peer communication using UDP. Is there any firefox Jslib equivalent in google chrome or how we can use other languages in google chrome extension? I doubt its possible in google chrome, looking at its documentation. ? Are there any other ways to achieve p2p communication in extension? Thanks

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• X.509 certificate based authentication with OpenSSL (without using sockets)

  - by hartem

  Hi, Is there an alternative in OpenSSL to SSL_set_connect_state()/SSL_set_accept_state() for X.509 certificate based authentication? The problem is that in my application the client and server do not communicate using sockets, and the establishment of direct connection between them is not possible. So what I want from OpenSSL is to 'expose' the intermediate SSL context establishment messages which I would then convey to the party at the other end. Thanks for your help!

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• FTP upload via sockets

  - by java2009

  Hello, how can I upload a file with sockets to a ftp server? I am reading something with "STOR" in RFC...It is the same how i transfer a file between two computers?A sample code would be helpfuly...thanks

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• Alternatives to "Raining Sockets"

  - by sanity

  I need to build a Java app with considerable IO requirements, supporting tens of thousands of concurrent TCP connections. I found a library called Raining Sockets which seems intended to make it easier to use Java's asynchronous NIO package, but the last update was 6 years ago. Are there other libraries, that are preferably still under active development, and with a public maven repository, that I should look at?

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• How to find cause and of the SocketException with message that an established connection was aborted

  - by cdpnet

  Hi All, I know the similar question may have been asked many times, but I want to represent the behavior I'm seeing and find if somebody can help predict the cause of this. I am writing a windows service which connects to other windows service over TCP. There are 100 user entities of this, and 5 connections per each. These users perform their tasks using their individual connections. The application goes on withough seeing this problem for 1 or 2 days. Or sometimes show the problem right after starting (-rarely). The best run I had was like 4 to 5 days without showing this exception. And after that application died or I had to stop it for various reasons. I want to know what can be causing this? Here is the stacktrace. System.IO.IOException: Unable to write data to the transport connection: An established connection was aborted by the software in your host machine. ---> System.Net.Sockets.SocketException: An established connection was aborted by the software in your host machine at System.Net.Sockets.Socket.Send(Byte[] buffer, Int32 offset, Int32 size, SocketFlags socketFlags) at System.Net.Sockets.NetworkStream.Write(Byte[] buffer, Int32 offset, Int32 size) --- End of inner exception stack trace --- at System.Net.Sockets.NetworkStream.Write(Byte[] buffer, Int32 offset, Int32 size) at System.Net.Security._SslStream.StartWriting(Byte[] buffer, Int32 offset, Int32 count, AsyncProtocolRequest asyncRequest) at System.Net.Security._SslStream.ProcessWrite(Byte[] buffer, Int32 offset, Int32 count, AsyncProtocolRequest asyncRequest) at System.Net.Security.SslStream.Write(Byte[] buffer, Int32 offset, Int32 count)

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• SocketException (Timeout) only when running as scheduled task

  - by BVartin

  I'm running a C# web-scrapper application (that I wrote) on a Windows Server 2003 instance under a user belonging to the local Administrator group. When I run it within a desktop/remote-desktop session the application runs successfully but when I schedule it to run under the same user/security-context outside of the desktop session, all socket connections timeout. The scheduled task calls a batch file which in-turn calls the application. The Windows Server 2003 instance has a very basic configuration and isn't even connected to a domain. I cannot find anything in any firewall or security configuration which is preventing this but maybe I have overlooked something, can anyone be of any assistance? System.Net.WebException: Unable to connect to the remote server --- System.Net.Sockets.SocketException: A connection attempt failed because the connected party did not properly respond after a period of time, or established connection failed because connected host has failed to respond X.X.X.X:443 at System.Net.Sockets.Socket.DoConnect(EndPoint endPointSnapshot, SocketAddress socketAddress) at System.Net.ServicePoint.ConnectSocketInternal(Boolean connectFailure, Socket s4, Socket s6, Socket& socket, IPAddress& address, ConnectSocketState state, IAsyncResult asyncResult, Int32 timeout, Exception& exception) --- End of inner exception stack trace --- at System.Net.HttpWebRequest.GetResponse()

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