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• Apache module, is it possible to have asynchronous processing

  - by prashant2361

  Hi, I have a requirement where I need to send continous updates to my clients. Client is browser in this case. We have some data which updates every sec, so once client connects to our server, we maintain a persistent connection and keep pushing data to the client. I am looking for suggestions of this implementation at the server end. Basically what I need is this: 1. client connects to server. I maintain the socket and metadata about the socket. metadata contains what updates need to be send to this client 2. server process now waits for new client connections 3. One other process will have the list of all the sockets opened and will go through each of them and send the updates if required. Can we do something like this in apache module: 1. apache process gets the new connection. It maintains the state for the connection. It keeps the state in some global memory and returns back to root process to signify that it is done so that it can accept the new connection 2. the apache process though has returned the status to root process but it is also executing parallely where it going through its global store and sending updates to the client, if any. So can a apache process do these things: 1. Have more than one connection associated with it 2. Asynchronously waiting for new connection and at the same time processing the previous connections? Regards Prashant

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• Is my objective possible using WCF (and is it the right way to do things?)

  - by David

  I'm writing some software that modifies a Windows Server's configuration (things like MS-DNS, IIS, parts of the filesystem). My design has a server process that builds an in-memory object graph of the server configuration state and a client which requests this object graph. The server would then serialize the graph, send it to the client (presumably using WCF), the server then makes changes to this graph and sends it back to the server. The server receives the graph and proceeds to make modifications to the server. However I've learned that object-graph serialisation in WCF isn't as simple as I first thought. My objects have a hierarchy and many have parametrised-constructors and immutable properties/fields. There are also numerous collections, arrays, and dictionaries. My understanding of WCF serialisation is that it requires use of either the XmlSerializer or DataContractSerializer, but DCS places restrictions on the design of my object-graph (immutable data seems right-out, it also requires parameter-less constructors). I understand XmlSerializer lets me use my own classes provided they implement ISerializable and have the de-serializer constructor. That is fine by me. I spoke to a friend of mine about this, and he advocates going for a Data Transport Object-only route, where I'd have to maintain a separate DataContract object-graph for the transport of data and re-implement my server objects on the client. Another friend of mine said that because my service only has two operations ("GetServerConfiguration" and "PutServerConfiguration") it might be worthwhile just skipping WCF entirely and implementing my own server that uses Sockets. So my questions are: Has anyone faced a similar problem before and if so, are there better approaches? Is it wise to send an entire object graph to the client for processing? Should I instead break it down so that the client requests a part of the object graph as it needs it and sends only bits that have changed (thus reducing concurrency-related risks?)? If sending the object-graph down is the right way, is WCF the right tool? And if WCF is right, what's the best way to get WCF to serialise my object graph?

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• Symbian: clear buffer of RSocket object

  - by Heinz

  Hi, I have to come back once again to sockets in Symbian. Code to set up a connection to a remote server looks as follows: TInetAddr serverAddr; TUint iPort=111; TRequestStatus iStatus; TSockXfrLength len; TInt res = iSocketSrv.Connect(); res = iSocket.Open(iSocketSrv,KAfInet,KSockStream, KProtocolInetTcp); res = iSocket.SetOpt(KSoTcpSendWinSize, KSolInetTcp, 0x10000); serverAddr.SetPort(iPort); serverAddr.SetAddress(INET_ADDR(11,11,179,154)); iSocket.Connect(serverAddr,iStatus); User::WaitForRequest(iStatus); Over the iSocket i receive packets of variable size. On very few occurences it happens that such a packet is corrupted. What I would like to do then is to clear all the data that is currently in the iSocket buffer and ready to be read. I have not seen any method of RSocket that allows me to clear the content of the buffer. Does anyone know how to do that? If possible, I would like to avoid using RecvOneOrMore() or similar recv function clear the buffer Thanks

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• Android, phone call audio stream via wlan

  - by moppel

  I am planning on developing my specific voip app for android. Here's the scenario: when a phone call occurs I want to hear the person who's calling on my local pc speakers and I want to speak to him via my own pc microphone / headset. So I need to send the audio stream of both me and the person I am talking to via the wlan network. Something like this: ... onCallStateChanged(int state, String phoneNumber){ while(state == PhoneListener.CALL_STATE_OFFHOOK){ //while phone call is happaning //send incoming speech via wlan to pc //receive audiostream from pc microphone and direct it to the phone call } } ... Is this possible with the current Android API? (Actually it should be since voip apps are available in the market) I did some research in the Android API and all I found was the AudioManager which has constant named public static final int STREAM_VOICE_CALL; //The audio stream for phone calls But I don't know how to use it our how it should give me access to the actual audiostreams which I can send via network. How do I manage to do this? The connection would be realised by TCP sockets.

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• How to stay DRY when using both Javascript and ERB templates (Rails)

  - by user94154

  I'm building a Rails app that uses Pusher to use web sockets to push updates to directly to the client. In javascript: channel.bind('tweet-create', function(tweet){ //when a tweet is created, execute the following code: $('#timeline').append("<div class='tweet'><div class='tweeter'>"+tweet.username+"</div>"+tweet.status+"</div>"); }); This is nasty mixing of code and presentation. So the natural solution would be to use a javascript template. Perhaps eco or mustache: //store this somewhere convenient, perhaps in the view folder: tweet_view = "<div class='tweet'><div class='tweeter'>{{tweet.username}}</div>{{tweet.status}}</div>" channel.bind('tweet-create', function(tweet){ //when a tweet is created, execute the following code: $('#timeline').append(Mustache.to_html(tweet_view, tweet)); //much cleaner }); This is good and all, except, I'm repeating myself. The mustache template is 99% identical to the ERB templates I already have written to render HTML from the server. The intended output/purpose of the mustache and ERB templates are 100% the same: to turn a tweet object into tweet html. What is the best way to eliminate this repetition? UPDATE: Even though I answered my own question, I really want to see other ideas/solutions from other people--hence the bounty!

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• Stream PDF to another local App

  - by Nathan

  Hi, I'm currently trying to optimize a small firefox extension that will grab a pdf off the current document and send it to a port that another local application is listening on. Right now it uses a terrifying hackjob of cache viewer. The way I'm getting it is loading the cache, searching through it using the current URL and grabbing the file and saving it to a temp directory. Then I stream the file in, delete the temp, and send it through the socket. Now, my new design, ideally I'd want to build it from scratch and cut out saving it to the local machine at all, and just stream it through the socket. I've been looking at doing something like, //check page to ensure its a pdf //init in/out streams //stream through sock //flush Now, this would be vastly superior to the 400 line hacked up mess I have now, but I'm new to building FF extensions, and after reading a lot about URIs and the file streaming and such I'm probably more confused than when I started trying to fix this three hours ago. I'm okay with sending things through the sockets and whatnot, I understand that, I'm mainly confused about what multitude of interfaces I want to use. Gah! Thanks! Also, long time reader, first time poster!

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• C socket programming: client send() but server select() doesn't see it

  - by Fantastic Fourier

  Hey all, I have a server and a client running on two different machines where the client send()s but the server doesn't seem to receive the message. The server employs select() to monitor sockets for any incoming connections/messages. I can see that when the server accepts a new connection, it updates the fd_set array but always returns 0 despite the client send() messages. The connection is TCP and the machines are separated by like one router so dropping packets are highly unlikely. I have a feeling that it's not select() but perhaps send()/sendto() from client that may be the problem but I'm not sure how to go about localizing the problem area. while(1) { readset = info->read_set; ready = select(info->max_fd+1, &readset, NULL, NULL, &timeout); } above is the server side code where the server has a thread that runs select() indefinitely. rv = connect(sockfd, (struct sockaddr *) &server_address, sizeof(server_address)); printf("rv = %i\n", rv); if (rv < 0) { printf("MAIN: ERROR connect() %i: %s\n", errno, strerror(errno)); exit(1); } else printf("connected\n"); sleep(3); char * somemsg = "is this working yet?\0"; rv = send(sockfd, somemsg, sizeof(somemsg), NULL); if (rv < 0) printf("MAIN: ERROR send() %i: %s\n", errno, strerror(errno)); printf("MAIN: rv is %i\n", rv); rv = sendto(sockfd, somemsg, sizeof(somemsg), NULL, &server_address, sizeof(server_address)); if (rv < 0) printf("MAIN: ERROR sendto() %i: %s\n", errno, strerror(errno)); printf("MAIN: rv is %i\n", rv); and this is the client side where it connects and sends messages and returns connected MAIN: rv is 4 MAIN: rv is 4 any comments or insightful insights are appreciated.

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• how to multithread on a python server

  - by user3732790

  HELP please i have this code import socket from threading import * import time HOST = '' # Symbolic name meaning all available interfaces PORT = 8888 # Arbitrary non-privileged port s = socket.socket(socket.AF_INET, socket.SOCK_STREAM) print ('Socket created') s.bind((HOST, PORT)) print ('Socket bind complete') s.listen(10) print ('Socket now listening') def listen(conn): odata = "" end = 'end' while end == 'end': data = conn.recv(1024) if data != odata: odata = data print(data) if data == b'end': end = "" print("conection ended") conn.close() while True: time.sleep(1) conn, addr = s.accept() print ('Connected with ' + addr[0] + ':' + str(addr[1])) Thread.start_new_thread(listen,(conn)) and i would like it so that when ever a person comes onto the server it has its own thread. but i can't get it to work please someone help me. :_( here is the error code: Socket created Socket bind complete Socket now listening Connected with 127.0.0.1:61475 Traceback (most recent call last): File "C:\Users\Myles\Desktop\test recever - Copy.py", line 29, in <module> Thread.start_new_thread(listen,(conn)) AttributeError: type object 'Thread' has no attribute 'start_new_thread' i am on python version 3.4.0 and here is the users code: import socket #for sockets import time s = socket.socket(socket.AF_INET, socket.SOCK_STREAM) print('Socket Created') host = 'localhost' port = 8888 remote_ip = socket.gethostbyname( host ) print('Ip address of ' + host + ' is ' + remote_ip) #Connect to remote server s.connect((remote_ip , port)) print ('Socket Connected to ' + host + ' on ip ' + remote_ip) while True: message = input("> ") #Set the whole string s.send(message.encode('utf-8')) print ('Message send successfully') data = s.recv(1024) print(data) s.close

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• Java Socket Returns True

  - by ikurtz

  I hope you can help. Im fairly new to progamming and Im playing around with java Sockets. The problem is the code below. for some reason commSocket = new Socket(hostName, portNumber); is returning true even when it has not connected with the server (server not implemented yet!). Any ideas regarding this situation? For hostName Im passing my local machine IP and for port a manually selected port. public void networkConnect(String hostName, int portNumber){ try { networkConnected = false; netMessage = "Attempting Connection"; NetworkMessage networkMessage = new NetworkMessage(networkConnected, netMessage); commSocket = new Socket(hostName, portNumber); // this returns true!! System.out.println(commSocket.isConnected()); networkConnected = true; netMessage = "Connected: "; System.out.println("hellooo"); } catch (UnknownHostException e){ System.out.println(e.getMessage()); } catch (IOException e){ System.out.println(e.getMessage()); } } Many thanks. EDIT: new Socket(.., ..); is blocking isnt it? i thought in that case if that was processed without exceptions then we have a true connection?

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• Socket Read In Multi-Threaded Application Returns Zero Bytes or EINTR (-1)

  - by user309670

  Hi. Am a c-coder for a while now - neither a newbie nor an expert. Now, I have a certain daemoned application in C on a PPC Linux. I use PHP's socket_connect as a client to connect to this service locally. The server uses epoll for concurrent connections via a Unix socket. A user submitted string is parsed for certain characters/words using strstr() and if found, spawns 4 joinable threads to different websites simultaneously. I use socket, connect, write and read, to interact with the said webservers via TCP on port 80 in each thread. All connections and writes seems successful. Reads to the webserver sockets fail however, with either (A) all 3 threads seem to hang, and only one thread returns -1 and errno is set to 104. The responding thread takes like 10 minutes - an eternity long:-(. *I read somewhere that the 104 (is EINTR) suggests that ...'the connection was reset by peer', or (B) 0 bytes from 3 threads, and only 1 of the 4 threads actually returns some data. Isn't the socket read/write thread-safe? Otherwise, use thread-safe (and reentrant) libc functions such as strtok_r, gethostbyname_r, etc. *I doubt that the said webhosts are actually resetting the connection, because when I run a single-threaded standalone (everything else equal) all things works perfectly right. There's a second problem too (oops), I can't write back to the client who connect to my epoll-ed Unix socket. My daemon application will hang and hog CPU 100% for ever. Yet nothing is written to the clients end. Am sure the client (a very typical PHP socket application) hasn't closed the connection whenever this is happening - no error(s) detected either. I cannot figure-out whatever is wrong even with Valgrind or GDB

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• Is it possible to have asynchronous processing

  - by prashant2361

  Hi, I have a requirement where I need to send continuous updates to my clients. Client is browser in this case. We have some data which updates every sec, so once client connects to our server, we maintain a persistent connection and keep pushing data to the client. I am looking for suggestions of this implementation at the server end. Basically what I need is this: 1. client connects to server. I maintain the socket and metadata about the socket. metadata contains what updates need to be send to this client 2. server process now waits for new client connections 3. One other process will have the list of all the sockets opened and will go through each of them and send the updates if required. Can we do something like this in Apache module: 1. Apache process gets the new connection. It maintains the state for the connection. It keeps the state in some global memory and returns back to root process to signify that it is done so that it can accept the new connection 2. the Apache process though has returned the status to root process but it is also executing in parallel where it going through its global store and sending updates to the client, if any. So can a Apache process do these things: 1. Have more than one connection associated with it 2. Asynchronously waiting for new connection and at the same time processing the previous connections? Regards Prashant

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• Proper way to scan a range of IP addresses

  - by Josh G

  Given a range of IP addresses entered by a user (through various means), I want to identify which of these machines have software running that I can talk to. Here's the basic process: Ping these addresses to find available machines Connect to a known socket on the available machines Send a message to the successfully established sockets Compare the response to the expected response Steps 2-4 are straight forward for me. What is the best way to implement the first step in .NET? I'm looking at the System.Net.NetworkInformation.Ping class. Should I ping multiple addresses simultaneously to speed up the process? If I ping one address at a time with a long timeout it could take forever. But with a small timeout, I may miss some machines that are available. Sometimes pings appear to be failing even when I know that the address points to an active machine. Do I need to ping twice in the event of the request getting discarded? To top it all off, when I scan large collections of addresses with the network cable unplugged, Ping throws a NullReferenceException in FreeUnmanagedResources(). !? Any pointers on the best approach to scanning a range of IPs like this?

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• webclient download problem!!!

  - by user472018

  Hello all, if this problem was discussed before,sorry for asking again.. I want to download an image from an url with using System.Net.WebClient class. When i try to download an image (ie. google logo).it does not occur any errors,but some images are occurring errors.I dont understand why this errors. how can i fix this problem? my Code is: WebClient client = new WebClient(); try { //Downloads the file from the given url to the given destination client.DownloadFile(urltxt.Text, filetxt.Text); return true; } catch (WebException w) { MessageBox.Show(w.ToString()); return false; } catch (System.Security.SecurityException) { MessageBox.Show("securityexeption"); return false; } catch (Exception) { MessageBox.Show("exception"); return false; } Errors are: System.Net.WebException:The underlying connection was closed:An unexpected error occurred on a recieve.--System.IO.IOException:Unable to read data from the transport connection:An existing connection was forcibly closed by the remote host.--System.Net.Sockets.SocketException:An existing connection was forcibly closed by the remote host...bla bla Thanks for your help.

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• one two-directed tcp socket OR two one-directed? (linux, high volume, low latency)

  - by osgx

  Hello I need to send (interchange) a high volume of data periodically with the lowest possible latency between 2 machines. The network is rather fast (e.g. 1Gbit or even 2G+). Os is linux. Is it be faster with using 1 tcp socket (for send and recv) or with using 2 uni-directed tcp sockets? The test for this task is very like NetPIPE network benchmark - measure latency and bandwidth for sizes from 2^1 up to 2^13 bytes, each size sent and received 3 times at least (in teal task the number of sends is greater. both processes will be sending and receiving, like ping-pong maybe). The benefit of 2 uni-directed connections come from linux: http://lxr.linux.no/linux+v2.6.18/net/ipv4/tcp_input.c#L3847 3847/* 3848 * TCP receive function for the ESTABLISHED state. 3849 * 3850 * It is split into a fast path and a slow path. The fast path is 3851 * disabled when: ... 3859 * - Data is sent in both directions. Fast path only supports pure senders 3860 * or pure receivers (this means either the sequence number or the ack 3861 * value must stay constant) ... 3863 * 3864 * When these conditions are not satisfied it drops into a standard 3865 * receive procedure patterned after RFC793 to handle all cases. 3866 * The first three cases are guaranteed by proper pred_flags setting, 3867 * the rest is checked inline. Fast processing is turned on in 3868 * tcp_data_queue when everything is OK. All other conditions for disabling fast path is false. And only not-unidirected socket stops kernel from fastpath in receive

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• one two-directed tcp socket of two one-directed? (linux, high volume, low latency)

  - by osgx

  Hello I need to send (interchange) a high volume of data periodically with the lowest possible latency between 2 machines. The network is rather fast (e.g. 1Gbit or even 2G+). Os is linux. Is it be faster with using 1 tcp socket (for send and recv) or with using 2 uni-directed tcp sockets? The test for this task is very like NetPIPE network benchmark - measure latency and bandwidth for sizes from 2^1 up to 2^13 bytes, each size sent and received 3 times at least (in teal task the number of sends is greater. both processes will be sending and receiving, like ping-pong maybe). The benefit of 2 uni-directed connections come from linux: http://lxr.linux.no/linux+v2.6.18/net/ipv4/tcp_input.c#L3847 3847/* 3848 * TCP receive function for the ESTABLISHED state. 3849 * 3850 * It is split into a fast path and a slow path. The fast path is 3851 * disabled when: ... 3859 * - Data is sent in both directions. Fast path only supports pure senders 3860 * or pure receivers (this means either the sequence number or the ack 3861 * value must stay constant) ... 3863 * 3864 * When these conditions are not satisfied it drops into a standard 3865 * receive procedure patterned after RFC793 to handle all cases. 3866 * The first three cases are guaranteed by proper pred_flags setting, 3867 * the rest is checked inline. Fast processing is turned on in 3868 * tcp_data_queue when everything is OK. All other conditions for disabling fast path is false. And only not-unidirected socket stops kernel from fastpath in receive

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• pyOpenSSL and the WantReadError

  - by directedition

  I have a socket server that I am trying to move over to SSL on python 2.5, but I've run into a snag with pyOpenSSL. I can't find any good tutorials on using it, so I'm operating largely on guesses. Here is how my server sets up the socket: ctx = SSL.Context(SSL.SSLv23_METHOD) ctx.use_privatekey_file ("mykey.pem") ctx.use_certificate_file("mycert.pem") sock = SSL.Connection(ctx, socket.socket(socket.AF_INET, socket.SOCK_STREAM)) sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1) addr = ('', int(8081)) sock.bind(addr) sock.listen(5) Here is how it accepts clients: sock.setblocking(0) while True: if len(select([sock], [], [], 0.25)[0]): client_sock, client_addr = sock.accept() client = ClientGen(client_sock) And here is how it sends/receives from the connected sockets: while True: (r, w, e) = select.select([sock], [sock], [], 0.25) if len(r): bytes = sock.recv(1024) if len(w): n_bytes = sock.send(self.message) It's compacted, but you get the general idea. The problem is, once the send/receive loop starts, it dies right away, before anything has been sent or received (that I can see anyway): Traceback (most recent call last): File "ClientGen.py", line 50, in networkLoop n_bytes = sock.send(self.message WantReadError The manual's description of the 'WantReadError' is very vague, saying it can come from just about anywhere. What am I doing wrong?

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• ZeroMQ REQ/REP on ipc:// and concurrency

  - by Metiu

  I implemented a JSON-RPC server using a REQ/REP 0MQ ipc:// socket and I'm experiencing strange behavior which I suspect is due to the fact that the ipc:// underlying unix socket is not a real socket, but rather a single pipe. From the documentation, one has to enforce strict zmq_send()/zmq_recv() alternation, otherwise the out-of-order zmq_send() will return an error. However, I expected the enforcement to be per-client, not per-socket. Of course with a Unix socket there is just one pipeline from multiple clients to the server, so the server won't know who it is talking with. Two clients could zmq_send() simultaneously and the server would see this as an alternation violation. The sequence could be: ClientA: zmq_send() ClientB: zmq_send() : will it block until the other send/receive completes? will it return -1? (I suspect it will with ipc:// due to inherent low-level problems, but with TCP it could distinguish the two clients) ClientA: zmq_recv() ClientB: zmq_recv() so what about tcp:// sockets? Will it work concurrently? Should I use some other locking mechanism to work around this?

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• How to hide helper functions from public API in c

  - by emge

  I'm working on a project and I need to create an API. I am using sockets to communicate between the server (my application) and the clients (the other applications using my API). This project is in c not C++ I come from a linux background and this is my first project using Windows, Visual Studio 2008, and dll libraries. I have communication working between the client and server, but I have some that is duplicated on both projects. I would like to create a library (probably a dll file), that both projects can link to so I don't have to maintain extra code. I also have to create the library that has the API that I need to make available for my clients. Within the API functions that I want public are the calls to these helper functions that are "duplicated code", I don't want to expose these functions to my client, but I do want my server to be able to use those functions. How can I do this? I will try to clarify with an example. This is what I started with. Server Project: int Server_GetPacket(SOCKET sd); int ReceiveAll(SOCKET sd, char *buf, int len); int VerifyLen(char *buf); Client Project: int Client_SendCommand(int command); int Client_GetData(int command, char *buf, int len); int ReceiveAll(SOCKET sd, char *buf, int len); int VerifyLen(char *buf); This is kind of what I would like to end up with: //Server Project: int Server_GetPacket(SOCKET sd); // library with public and private types // private API (not exposed to my client) int ReceiveAll(SOCKET sd, char *buf, int len); int VerifyLen(char *buf); // public API (header file available for client) int Client_SendCommand(int command); int Client_GetData(int command, char *buf, int len); Thanks any help would be appreciated.

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• How to Avoid Server Error 414 for Very Long QueryString Values

  - by Registered User

  I had a project that required posting a 2.5 million character QueryString to a web page. The server itself only parsed URI's that were 5,400 characters or less. After trying several different sets of code for WebRequest/WebResponse, WebClient, and Sockets, I finally found the following code that solved my problem: HttpWebRequest webReq; HttpWebResponse webResp = null; string Response = ""; Stream reqStream = null; webReq = (HttpWebRequest)WebRequest.Create(strURL); Byte[] bytes = Encoding.UTF8.GetBytes("xml_doc=" + HttpUtility.UrlEncode(strQueryString)); webReq.ContentType = "application/x-www-form-urlencoded"; webReq.Method = "POST"; webReq.ContentLength = bytes.Length; reqStream = webReq.GetRequestStream(); reqStream.Write(bytes, 0, bytes.Length); reqStream.Close(); webResp = (HttpWebResponse)webReq.GetResponse(); if (webResp.StatusCode == HttpStatusCode.OK) { StreamReader loResponseStream = new StreamReader(webResp.GetResponseStream(), Encoding.UTF8); Response = loResponseStream.ReadToEnd(); } webResp.Close(); reqStream = null; webResp = null; webReq = null;

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• Boost program will not working on Linux

  - by Martin Lauridsen

  Hi SOF, I have this program which uses Boost::Asio for sockets. I pretty much altered some code from the Boost examples. The program compiles and runs just like it should on Windows in VS. However, when I compile the program on Linux and run it, I get a Segmentation fault. I posted the code here The command I use to compile it is this: c++ -I/appl/htopopt/Linux_x86_64/NTL-5.4.2/include -I/appl/htopopt/Linux_x86_64/boost_1_43_0/include mpqs.cpp mpqs_polynomial.cpp mpqs_host.cpp -o mpqs_host -L/appl/htopopt/Linux_x86_64/NTL-5.4.2/lib -lntl -L/appl/htopopt/Linux_x86_64/gmp-4.2.1/lib -lgmp -lm -L/appl/htopopt/Linux_x86_64/boost_1_43_0/lib -lboost_system -lboost_thread -static -lpthread By commenting out code, I have found out that I get the Segmentation fault due to the following line: boost::asio::io_service io_service; Can anyone provide any assistance, as to what may be the problem (and the solution)? Thanks! Edit: I tried changing the program to a minimal example, using no other libraries or headers, just boost/asio.hpp: #define DEBUG 0 #include <boost/asio.hpp> int main(int argc, char* argv[]) { boost::asio::io_service io_service; return 0; } I also removed other library inclusions and linking on compilation, however this minimal example still gives me a segmentation fault.

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• queued view updates not happening when performSelector afterDelay:0 used

  - by JosephH

  Hi all, I have an app that performs some calculations based on data arriving on a socket or local user interaction. I want to show an 'activity spinner' whilst the calculation happens. spinner = [[UIActivityIndiactorView alloc] initWithActivityIndicatorStyle:UIActivityIndicatorViewStyleWhiteLarge]; [spinner setCenter:self.view.center]; [self.view addSubview:spinner]; [spinner startAnimating]; [self performSelector:@selector(doCalcs) withObject:nil afterDelay:0]; This works well, except in the case where the code is run as a result of a message arriving over the network. I'm using http://code.google.com/p/cocoaasyncsocket/ to handle sockets and the code is running in the onSocket:didReadData:withTag: method. 'doCalcs' takes a few seconds. The spinner doesn't appear whilst it's running. If I change afterDelay:0 to afterDelay:1 then the spinner does appear the whole time doCalcs is running, but with the downside that it takes an extra second. So it seems the code is all correct, but for whatever reason the spinner isn't getting a chance to get on screen before doCalcs runs. Any suggestions would be most welcome.

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• Listening UDP or switch to TCP in a MFC application

  - by Alexander.S

  I'm editing a legacy MFC application, and I have to add some basic network functionalities. The operating side has to receive a simple instruction (numbers 1,2,3,4...) and do something based on that. The clients wants the latency to be as fast as possible, so naturally I decided to use datagrams (UDP). But reading all sorts of resources left me bugged. I cannot listen to UDP sockets (CAsyncSocket) in MFC, it's only possible to call Receive which blocks and waits. Blocking the UI isn't really a smart. So I guess I could use some threading technique, but since I'm not all that experienced with MFC how should that be implemented? The other part of the question is should I do this, or revert to TCP, considering reliability and implementation issues. I know that UDP is unreliable, but just how unreliable is it really? I read that it is up to 50% faster, which is a lot for me. References I used: http://msdn.microsoft.com/en-us/library/09dd1ycd(v=vs.80).aspx

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• Fastest reliable way for Clojure (Java) and Ruby apps to communicate

  - by jkndrkn

  Hi There, We have cloud-hosted (RackSpace cloud) Ruby and Java apps that will interact as follows: Ruby app sends a request to Java app. Request consists of map structure containing strings, integers, other maps, and lists (analogous to JSON). Java app analyzes data and sends reply to Ruby App. We are interested in evaluating both messaging formats (JSON, Buffer Protocols, Thrift, etc.) as well as message transmission channels/techniques (sockets, message queues, RPC, REST, SOAP, etc.) Our criteria: Short round-trip time. Low round-trip-time standard deviation. (We understand that garbage collection pauses and network usage spikes can affect this value). High availability. Scalability (we may want to have multiple instances of Ruby and Java app exchanging point-to-point messages in the future). Ease of debugging and profiling. Good documentation and community support. Bonus points for Clojure support. What combination of message format and transmission method would you recommend? Why? I've gathered here some materials we have already collected for review: Comparison of various java serialization options Comparison of Thrift and Protocol Buffers (old) Comparison of various data interchange formats Comparison of Thrift and Protocol Buffers Fallacies of Protocol Buffers RPC features Discussion of RPC in the context of AMQP (Message-Queueing) Comparison of RPC and message-passing in distributed systems (pdf) Criticism of RPC from perspective of message-passing fan Overview of Avro from Ruby programmer perspective

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• Choosing approach for an IM client-server app

  - by John

  Update: totally re-wrote this to be more succint. I'm looking at a new application, one part of which will be very similar to standard IM clients, i.e text chat, ability to send attachments, maybe some real-time interaction like a multi-user whiteboard. It will be client-server, i.e all traffic goes through my central server. That means if I want to support cross-communication with other IM systems, I am still free to pick any protocol for my own client<--server communication - my server can use XMPP or whatever to talk to other systems. Clients are expected to include desktop apps, but probably also browser-based as well either through Flex/Silverlight or HTML/AJAX. I see 3 options for my own client-server communication layer: XMPP. The benefits are clients already exist as do open-source servers. However it requires the most up-front research/learning and also appears like it might raise legal issues due to GPL. Custom sockets. A server app makes connections with the clients, allowing any text/binary data to be sent very fast. However this approach requires building said server from scratch, and also makes a JS client tricky Servlets (or similar web server). Using tried and tested Java web-stack, clients send HTTP requests similar to AJAX-based websites. The benefit is the server is easy to write using well-established technologies, and easy to talk to. But what restrictions would this bring? Is it appropriate technology for real-time communication? Advice and suggests are welcome, especially what pros and cons surround using a web-server approach as compared to a socket-based approach.

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• Is a web-server (e.g servlets) a good solution for an IM server?

  - by John

  I'm looking at a new app, broadly speaking an IM application with a strong client-server model - all communications go through a server so they can be logged centrally. The server will be Java in some form, clients could at this point be anything from a .NET Desktop app to Flex/Silverlight, to a simple web-interface using JS/AJAX. I had anticipated doing the server using standard J2EE so I get a thread-safe, multi-user server for 'free'... to make things simple let's say using Servlets (but in practice SpringMVC would be likely). This all seemed very neat but I'm concerned if the stateless nature of Servlets is the best approach. If my memory of servlets (been a year or two) is right, each time a client sent a HTTP request, typically a new message entered by the user, the servlet could not assume it had the user/chat in memory and might have to get it from the DB... regardless it has to look it up. Then it either has to use some PUSH system to inform other members of the chat, or cache that there are new messages, for other clients who poll the server using AJAX or similar - and when they poll it again has to lookup the chat, including new messages, and send the new data. I'm wondering if a better system would be the server is running core Java, and implements a socket-based communication with clients. This allows much more immediate data transfer and is more flexible if say the IM client included some game you could play. But then you're writing a custom server and sockets don't sound very friendly to a browser-based client on current browsers. Am I missing some big piece of the puzzle here, it kind of feels like I am? Perhaps a better way to ask the question would simply be "if the client was browser-based using HTML/JS and had to run on IE7+,FF2+ (i.e no HTML5), how would you implement the server?" edit: if you are going to suggest using XMPP, I have been trying to get my head around this in another question, so please consider if that's a more appropriate place to discuss this specifically.

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