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• Linux network stack : adding protocols with an LKM and dev_add_pack

  - by agent0range

  Hello, I have recently been trying to familiarize myself with the Linux Networking stack and device drivers (have both similarly named O'Reilly books) with the eventual goal of offloading UDP. I have already implemented UDP on the NIC but now the hard part... Rather than ask for assistance on this larger goal I was hoping someone could clarify for me a particular snippet I found that is part of a LKM which registeres a new protocol (OTP) that acts as a filter between the device driver and network stack. http://www.phrack.org/archives/55/p55_0x0c_Building%20Into%20The%20Linux%20Network%20Layer_by_lifeline%20&%20kossak.txt (Note: this Phrack article contains three different modules, code for the OTP is at the bottom of the page) In the init function of his example he has: otp_proto.type = htons(ETH_P_ALL); otp_proto.func = otp_func; dev_add_pack(&otp_proto); which (if I understand correctly) should register otp_proto as a packet sniffer and put it into the ptype_all data structure. My question is about the dev_add_pack. Is it the case that the protocol being registered as a filter will always be placed at this layer between L2 and the device driver? Or, for instance could I make such a filtering occur between the application and transport layers (analyze socket parameters) using the same process? I apologize if this is confusing - I am having some trouble wrapping my head around the bigger picture when it comes to modules altering kernel stack functionality. Thanks

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• Boost::Asio - Remove the "null"-character in the end of tcp packets.

  - by shump

  I'm trying to make a simple msn client mostly for fun but also for educational purposes. And I started to try some tcp package sending and receiving using Boost Asio as I want cross-platform support. I have managed to send a "VER"-command and receive it's response. However after I send the following "CVR"-command, Asio casts an "End of file"-error. After some further researching I found by packet sniffing that my tcp packets to the messenger server got an extra "null"-character (Ascii code: 00) at the end of the message. This means that my VER-command gets an extra character in the end which I don't think the messenger server like and therefore shuts down the connection when I try to read the CVR response. This is how my package looks when sniffing it, (it's Payload): (Hex:) 56 45 52 20 31 20 4d 53 4e 50 31 35 20 43 56 52 30 0a 0a 00 (Char:) VER 1 MSNP15 CVR 0... and this is how Adium(chat client for OS X)'s package looks: (Hex:) 56 45 52 20 31 20 4d 53 4e 50 31 35 20 43 56 52 30 0d 0a (Char:) VER 1 MSNP15 CVR 0.. So my question is if there is any way to remove the null-character in the end of each package, of if I've misunderstood something and used Asio in a wrong way. My write function (slightly edited) looks lite this: int sendVERMessage() { boost::system::error_code ignored_error; char sendBuf[] = "VER 1 MSNP15 CVR0\r\n"; boost::asio::write(socket, boost::asio::buffer(sendBuf), boost::asio::transfer_all(), ignored_error); if(ignored_error) { cout << "Failed to send to host!" << endl; return 1; } cout << "VER message sent!" << endl; return 0; } And here's the main documentation on the msn protocol I'm using. Hope I've been clear enough.

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• GUI Agent accepts statuses from Daemon and shows it using progress indicator

  - by Pavel

  Hi to all! My application is a GUI agent, which communicate with daemon through the unix domain socket, wrapped in CFSocket.... So there are main loop and added CFRunLoop source. Daemon sends statuses and agent shows it with a progress indicator. When there are any data on socket, callback function begin to work and at this time I have to immediately show the new window with progress indicator and increase counter. //this function initiate the runloop for listening socket - (int) AcceptDaemonConnection:(ConnectionRef)conn { int err = 0; conn->fSockCF = CFSocketCreateWithNative(NULL, (CFSocketNativeHandle) conn->fSockFD, kCFSocketAcceptCallBack, ConnectionGotData, NULL); if (conn->fSockCF == NULL) err = EINVAL; if (err == 0) { conn->fRunLoopSource = CFSocketCreateRunLoopSource(NULL, conn->fSockCF, 0); if (conn->fRunLoopSource == NULL) err = EINVAL; else CFRunLoopAddSource(CFRunLoopGetCurrent(), conn->fRunLoopSource, kCFRunLoopDefaultMode); CFRelease(conn->fRunLoopSource); } return err; } // callback function void ConnectionGotData(CFSocketRef s, CFSocketCallBackType type, CFDataRef address, const void * data, void * info) { #pragma unused(s) #pragma unused(address) #pragma unused(info) assert(type == kCFSocketAcceptCallBack); assert( (int *) data != NULL ); assert( (*(int *) data) != -1 ); TStatusUpdate status; int nativeSocket = *(int *) data; status = [agg AcceptPacket:nativeSocket]; // [stWindow InitNewWindow] inside [agg SendUpdateStatus:status.percent]; } AcceptPacket function receives packet from the socket and trying to show new window with progress indicator. Corresponding function is called, but nothing happens... I think, that I have to make work the main application loop with interrupting CFSocket loop... Or send a notification? No idea....

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• How do I use Spreadsheet::WriteExcel to create a chart from numeric log data?

  - by yaohung

  I used csv2xls.pl to convert a text log into .xls format, and then I create a chart as in the following: my $chart3 = $workbook->add_chart( type => 'line' , embedded => 1); # Configure the series. $chart3->add_series( categories => '=Sheet1!$B$2:$B$64', values => '=Sheet1!$C$2:$C$64', name => 'Test data series 1', ); # Add some labels. $chart3->set_title( name => 'Bridge Rate Analysis' ); $chart3->set_x_axis( name => 'Packet Size ' ); $chart3->set_y_axis( name => 'BVI Rate' ); # Insert the chart into the main worksheet. $worksheet->insert_chart( 'G2', $chart3 ); I can see the chart in the .xls file. However, all the data are in text format, not numeric, so the chart looks wrong. How do I convert text into number before applying this create-chart function? Also, how do I sort the .xls file before creating the chart?

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• Publishing WCF .NET 3.5 to IIS 5.1

  - by Adam

  I've been developing a WCF web service using .NET 3.5 with IIS7 and it works perfectly on my local computer. I tried publishing it to a server running IIS 5.1 and even though I can view the WSDL in my browser, the client application doesn't seem to be connecting to it correctly. I launched a packet sniffing app (Charles Proxy) and the response for the first message comes back to the client empty (0 bytes). Every message after the first one times out. The WCF service is part of a larger application that uses ASP .NET 3.5. That application has been working fine on IIS 5.1 for awhile now so I think it's something specific to WCF. I also tried throwing an exception in the SVC file to see if it made it that far and the exception never got thrown so I have a feeling it's something more low level that's not working. Any thoughts? Is there anything I need to install on the IIS5 server? If so how am I still able to view the WSDL in my browser?

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• DNS protocol message example

  - by virtual-lab

  hello there, I am trying to figure out how to send out DNS messages from an application socket adapter to a DNSBL. I spent the last two days understanding the basics, including experimenting with WireShark to catch an example of message exchanged. Now I would like to query the DNS without using dig or host command (I'm using Ubuntu); how can I perform this action at low level, without the help of these tools in wrapping the request in a proper DNS message format? How the message should be post it? Hex or String? Thanks in advance for any help. Regards Alessandro Ilardo Comment added I am investigating on JDev and Oracle SOA. The platform provides a Socket Adapter which simply apply a transformation (XSLT) and send the message straight to the socket. How the payload parameters (ex. the host I'm looking up) are wrapped within the message is left to the developer. So basically I have an idea on how the all DNS message is structured, but rather than put everything on JDev stright away I'd like to make some tests on my own just to make sure I got a valid message format. So, I am not using any specific language (I don't even understand why they moved my question from serverfault) and I don't want to use any tools which would hide part of the message, such as the header. I know they work well btw. I guess this stuff has something to do with packet injection. Someone suggested me to use telnet, but I've only used for SMTP or HTTP, I haven't got a clue on how it works for DNS request. Does it make more sense now?

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• Is this a good starting point for iptables in Linux?

  - by sbrattla

  Hi, I'm new to iptables, and i've been trying to put together a firewall which purpose is to protect a web server. The below rules are the ones i've put together so far, and i would like to hear if the rules makes sense - and wether i've left out anything essential? In addition to port 80, i also need to have port 3306 (mysql) and 22 (ssh) open for external connections. Any feedback is highly appreciated! #!/bin/sh # Clear all existing rules. iptables -F # ACCEPT connections for loopback network connection, 127.0.0.1. iptables -A INPUT -i lo -j ACCEPT # ALLOW established traffic iptables -A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT # DROP packets that are NEW but does not have the SYN but set. iptables -A INPUT -p tcp ! --syn -m state --state NEW -j DROP # DROP fragmented packets, as there is no way to tell the source and destination ports of such a packet. iptables -A INPUT -f -j DROP # DROP packets with all tcp flags set (XMAS packets). iptables -A INPUT -p tcp --tcp-flags ALL ALL -j DROP # DROP packets with no tcp flags set (NULL packets). iptables -A INPUT -p tcp --tcp-flags ALL NONE -j DROP # ALLOW ssh traffic (and prevent against DoS attacks) iptables -A INPUT -p tcp --dport ssh -m limit --limit 1/s -j ACCEPT # ALLOW http traffic (and prevent against DoS attacks) iptables -A INPUT -p tcp --dport http -m limit --limit 5/s -j ACCEPT # ALLOW mysql traffic (and prevent against DoS attacks) iptables -A INPUT -p tcp --dport mysql -m limit --limit 25/s -j ACCEPT # DROP any other traffic. iptables -A INPUT -j DROP

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• TCP Socket.Connect is generating false positives

  - by Mark

  I'm experiencing really weird behavior with the Socket.Connect method in C#. I am attempting a TCP Socket.Connect to a valid IP but closed port and the method is continuing as if I have successfully connected. When I packet sniffed what was going on I saw that the app was receiving RST packets from the remote machine. Yet from the tracing that is in place it is clear that the connect method is not throwing an exception. Any ideas what might be causing this? The code that is running is basically this IPEndPoint iep = new IPEndPoint(System.Net.IPAddress.Parse(m_ipAddress), m_port); Socket tcpSocket = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp); tcpSocket.Connect(iep); To add to the mystery... when running this code in a stand alone console application, the result is as expected – the connect method throws an exception. However, when running it in the Windows Service deployment we have the connect method does not throw an exception. Edit in response to Mystere Man's answer How would the exception be swallowed? I have a Trace.WriteLine right above the .Connect method and a Trace.WriteLine right under it (not shown in the code sample for readability). I know that both traces are running. I also have a try catch around the whole thing which also does a Trace.Writeline and I don't see that in the log files anywhere. I have also enabled the internal socket tracing as you suggested. I don't see any exceptions. I see what appears to be successful connections. I am trying to identify differences between the windows service app and the diagnostic console app I made. I am running out of ideas though End edit Thanks

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• Using awk to return only certain chunks of data

  - by Koriar

  I'm not 100% certain how to phrase my question simply, so I apologize if this has been answered somewhere and I was just unable to find it. What I have are debug logs with authentication packets in them along with a bunch of other output. I need to search through about 2 million lines of logs to find every packet that contains a certain mac address. The packets look something like this (slightly censored): -----------------[ header ]----------------- Event: Authd-Response (1900) Sequence: -54 Timestamp: 1969-12-31 19:30:00 (0) ---------------[ attributes ]--------------- Auth-Result = Auth-Accept Service-Profile-SID = 53 Service-Profile-SID = 49 RADIUS-Access-Accept-Attr/WiMAX-Capability = 0x(numbers) Session-Timeout = 3600 Service-Profile-SID = 4 Service-Profile-SID = 29 Chargeable-User-Identity = "(Numbers)" User-Password = "(the MAC address I'm looking for)" -------------------------------------------- However there are about 10 different possible types with different possible lengths. They all start with the header line and end with the all-dashes line. I've had success using awk to get the code blocks themselves using this: awk '/-----------------\[ header \]-----------------/,/--------------------------------------------/' filename.txt But I was hoping to be able to use it to return only the packets which contain the MAC address that I need. I've been trying to figure this out for a few days now and I'm pretty stuck. I could try and write a bash script, but I could swear that I've used awk to do something like this before...

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• Cannot connect to Github?

  - by user2973438

  so I tried to push some updates onto my repo on github via terminal on Mac OSX 10.8.4 and it doesn't work. I've been getting the same error many times: Lillys-MacBook-Air:Yuewei Lilly$ git push origin master error: Failed connect to github.com:443; Operation timed out while accessing https://github.com/lillybeans/Yuewei.git/info/refs?service=git-receive-pack fatal: HTTP request failed Some background: I've pushed many projects onto github before using terminal (when I was in Canada). I am currently in Shanghai, China, could it be the GFW? But when I was in Beijing, I was able to push projects onto github still. when I do ping github.com: Lillys-MacBook-Air:Yuewei Lilly$ ping github.com PING github.com (192.30.252.131): 56 data bytes Request timeout for icmp_seq 0 Request timeout for icmp_seq 1 ping: sendto: No route to host Request timeout for icmp_seq 2 ping: sendto: Host is down Request timeout for icmp_seq 3 ping: sendto: Host is down Request timeout for icmp_seq 4 ping: sendto: Host is down Request timeout for icmp_seq 5 ping: sendto: Host is down Request timeout for icmp_seq 6 ping: sendto: Host is down Request timeout for icmp_seq 7 ^C --- github.com ping statistics --- 9 packets transmitted, 0 packets received, 100.0% packet loss Lillys-MacBook-Air:Yuewei Lilly$ I have ShadowSocks (proxy) turned on. Without it I can't access github.com via browser, with it, I can. also when I do "git remote -v" I see both my pull and push remote repos correctly listed. Thank you in advance!

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• Creating Binary Block from struct

  - by MOnsDaR

  I hope the title is describing the problem, i'll change it if anyone has a better idea. I'm storing information in a struct like this: struct AnyStruct { AnyStruct : testInt(20), testDouble(100.01), testBool1(true), testBool2(false), testBool3(true), testChar('x') {} int testInt; double testDouble; bool testBool1; bool testBool2; bool testBool3; char testChar; std::vector<char> getBinaryBlock() { //how to build that? } } The struct should be sent via network in a binary byte-buffer with the following structure: Bit 00- 31: testInt Bit 32- 61: testDouble most significant portion Bit 62- 93: testDouble least significant portion Bit 94: testBool1 Bit 95: testBool2 Bit 96: testBool3 Bit 97-104: testChar According to this definition the resulting std::vector should have a size of 13 bytes (char == byte) My question now is how I can form such a packet out of the different datatypes I've got. I've already read through a lot of pages and found datatypes like std::bitset or boost::dynamic_bitset, but neither seems to solve my problem. I think it is easy to see, that the above code is just an example, the original standard is far more complex and contains more different datatypes. Solving the above example should solve my problems with the complex structures too i think. One last point: The problem should be solved just by using standard, portable language-features of C++ like STL or Boost (

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• Android: sending xml as document object, POST method

  - by juro

  i am new at programming and i need some help with that please =/ web service is already written but not by me. so all i have to do is send xml as document object by post method through web service. my code: public class send extends application { @Override public void onCreate(Bundle icicle) { super.onCreate(icicle); HttpClient httpclient = new DefaultHttpClient(); HttpPost httppost = new HttpPost("http://app.local/test/"); try { DocumentBuilderFactory documentBuilderFactory = DocumentBuilderFactory.newInstance(); DocumentBuilder documentBuilder = documentBuilderFactory.newDocumentBuilder(); Document document = documentBuilder.newDocument(); Element rootElement = document.createElement("packet"); rootElement.setAttribute("version", "1.2"); document.appendChild(rootElement); Element em = document.createElement("imei"); em.appendChild(document.createTextNode("000000000000000")); rootElement.appendChild(em); em = document.createElement("username"); em.appendChild(document.createTextNode("5555")); rootElement.appendChild(em); HttpResponse response = httpclient.execute(httppost); } catch (Exception e) { System.out.println("XML Pasing Excpetion = " + e); } } }

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• What's the cleanest way to do byte-level manipulation?

  - by Jurily

  I have the following C struct from the source code of a server, and many similar: // preprocessing magic: 1-byte alignment typedef struct AUTH_LOGON_CHALLENGE_C { // 4 byte header uint8 cmd; uint8 error; uint16 size; // 30 bytes uint8 gamename[4]; uint8 version1; uint8 version2; uint8 version3; uint16 build; uint8 platform[4]; uint8 os[4]; uint8 country[4]; uint32 timezone_bias; uint32 ip; uint8 I_len; // I_len bytes uint8 I[1]; } sAuthLogonChallenge_C; // usage (the actual code that will read my packets): sAuthLogonChallenge_C *ch = (sAuthLogonChallenge_C*)&buf[0]; // where buf is a raw byte array These are TCP packets, and I need to implement something that emits and reads them in C#. What's the cleanest way to do this? My current approach involves [StructLayout(LayoutKind.Sequential, Pack = 1)] unsafe struct foo { ... } and a lot of fixed statements to read and write it, but it feels really clunky, and since the packet itself is not fixed length, I don't feel comfortable using it. Also, it's a lot of work. However, it does describe the data structure nicely, and the protocol may change over time, so this may be ideal for maintenance. What are my options? Would it be easier to just write it in C++ and use some .NET magic to use that?

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• Generic that takes only numeric types (int double etc)?

  - by brandon

  In a program I'm working on, I need to write a function to take any numeric type (int, short, long etc) and shove it in to a byte array at a specific offset. There exists a Bitconverter.GetBytes() method that takes the numeric type and returns it as a byte array, and this method only takes numeric types. So far I have: private void AddToByteArray<T>(byte[] destination, int offset, T toAdd) where T : struct { Buffer.BlockCopy(BitConverter.GetBytes(toAdd), 0, destination, offset, sizeof(toAdd)); } So basically my goal is that, for example, a call to AddToByteArray(array, 3, (short)10) would take 10 and store it in the 4th slot of array. The explicit cast exists because I know exactly how many bytes I want it to take up. There are cases where I would want a number that is small enough to be a short to really take up 4 bytes. On the flip side, there are times when I want an int to be crunched down to just a single byte. I'm doing this to create a custom network packet, if that makes any ideas pop in to your heads. If the where clause of a generic supported something like "where T : int || long || etc" I would be ok. (And no need to explain why they don't support that, the reason is fairly obvious) Any help would be greatly appreciated! Edit: I realize that I could just do a bunch of overloads, one for each type I want to support... but I'm asking this question because I want to avoid precisely that :)

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• [php,mysql] insert only adds upto 1000 records and ignoresall records after that.

  - by user560559

  Hello i have a large database where the client stores personal messages and fire email notifications [if allowed by the users]. certain users have the option of sending messages to their entire network of friends. some users have over 5000 friends in their network so if they select the whole network they'll be sending messages to over 5000 friends and system will store all the messages into a table. the problem is this that it does not insert more than 1000 records and ignores all inserts after the first 1000. i have increased the packet size, bulk_insert_buffer_size but still no luck. since the system stores some of the info in another table for reports, every insert returns its new message id. due to this i can not use the "insert into table (column1,column2) values (value1,value2) , (value1,value2)....etc." table engine is innodb, mysql version is 5.1.3 and is hosted on amazon web services. all i want is to fix this issue of inserting more than 1000 records at a time. as mentioned earlier, it works fine but only up to 1000 records and simply ignores all the records after that. i'm using php foreach(){} to insert message for each friend and if email is available, send notification to the user. this foreach(){} also inserts the same record in another table [with only 3 columns] for generating reports. thank you in advance for all the help and support. WMA.

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• Which are the most useful techniques for faster Bluetooth?

  - by Mike Howard

  Hi. I'm adding peer-to-peer bluetooth using GameKit to an iPhone shoot-em-up, so speed is vital. I'm sending about 40 messages a second each way, most of them with the faster GKSendDataUnreliable, all serializing with NSCoding. In testing between a 3G and 3GS, this is slowing the 3G down a lot more than I'd like. I'm wondering where I should concentrate my efforts to speed it up. How much slower is GKSendDataReliable? For the few packets that have to get there, would it be faster to send a GKSendDataUnreliable and have the peer send an acknowledgement so I can send again if I don't get the Ack within, say, 100ms? How much faster would it be to create the NSData instance using a regular C array rather than archiving with the NSCoding protocol? Is this serialization process (for about a dozen floats) just as slow as you'd expect from an object creation/deallocation overhead, or is something particularly slow happening? I heard that (for example) sending four seperate sets of data is much, much slower, than sending one piece of data four times the size. Would I make a significant saving by sending separate packets of data that wouldn't always go together in the same packet when they happen at the same time? Are there any other bluetooth performance secrets I've missed? Thanks for your help.

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• iPhone: Which are the most useful techniques for faster Bluetooth?

  - by Mike Howard

  Hi. I'm adding peer-to-peer bluetooth using GameKit to an iPhone shoot-em-up, so speed is vital. I'm sending about 40 messages a second each way, most of them with the faster GKSendDataUnreliable, all serializing with NSCoding. In testing between a 3G and 3GS, this is slowing the 3G down a lot more than I'd like. I'm wondering where I should concentrate my efforts to speed it up. How much slower is GKSendDataReliable? For the few packets that have to get there, would it be faster to send a GKSendDataUnreliable and have the peer send an acknowledgement so I can send again if I don't get the Ack within, say, 100ms? How much faster would it be to create the NSData instance using a regular C array rather than archiving with the NSCoding protocol? Is this serialization process (for about a dozen floats) just as slow as you'd expect from an object creation/deallocation overhead, or is something particularly slow happening? I heard that (for example) sending four seperate sets of data is much, much slower, than sending one piece of data four times the size. Would I make a significant saving by sending separate packets of data that wouldn't always go together in the same packet when they happen at the same time? Are there any other bluetooth performance secrets I've missed? Thanks for your help.

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• Insert only adds upto 1000 records and ignoresall records after that.

  - by user560559

  i have a large database where the client stores personal messages and fire email notifications [if allowed by the users]. certain users have the option of sending messages to their entire network of friends. some users have over 5000 friends in their network so if they select the whole network they'll be sending messages to over 5000 friends and system will store all the messages into a table. the problem is this that it does not insert more than 1000 records and ignores all inserts after the first 1000. i have increased the packet size, bulk_insert_buffer_size but still no luck. since the system stores some of the info in another table for reports, every insert returns its new message id. due to this i can not use the "insert into table (column1,column2) values (value1,value2) , (value1,value2)....etc." table engine is innodb, mysql version is 5.1.3 and is hosted on amazon web services. all i want is to fix this issue of inserting more than 1000 records at a time. as mentioned earlier, it works fine but only up to 1000 records and simply ignores all the records after that. i'm using php foreach(){} to insert message for each friend and if email is available, send notification to the user. this foreach(){} also inserts the same record in another table [with only 3 columns] for generating reports.

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• TCP/IP RST being sent differently in different browsers.

  - by Brian

  On Mac OS X (10.6), if I start a YouTube video download and pull the Ethernet cable for 5 or so seconds, then plug it back in, I get varying results depending on the browser. With Opera and Chrome, after I plug the cable back in the video continues to load. But with Safari and Firefox, it never does. Using Wireshark to look at the traffic, I found that Opera and Chrome simply ACK the first packet from YouTube after the cable has been plugged back in, but Safari and Firefox set the RST flag (0x4) in the TCP header and no more traffic follows. I can put a HUB in between the machine and the internet connection, the problem goes away and all four browsers continue loading the video when the cable is plugged back into the HUB. Again, looking at the Wireshark logs, it's evident that the machine doesn't see the Mulitcast connection close and there is simply a delay in the packets flowing through. So it seems that if Safari and Firefox sees a Multicast connection close, and then later see data on that same connection, they will send a RST. My question is why? What is the correct course of action, and why are 2/4 browsers doing it one way, while the other 2/4 are doing it another way? Is there somewhere in the code that I can see where this is happening in Firefox, for instance? Thank you very much.

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• How to detect a Socket disconnection?

  - by AngryHacker

  I've implemented a task using the async Sockets pattern in Silverlight 3. I started with Michael Schwarz's implementation and built on top of that. So basically, my Silverlight app establishes a persistent socket connection to a device and then data flows both ways as necessary between the device and the Silverlight app. One thing I am struggling with is how to detect disconnection. I could think of 2 approaches: Keep-Alive. I know this can be done at the Sockets level, but I am not sure how to do this in an async model. How would the Socket class let me know there has been a disconnection. Manual keep alive. Basically, I am having the Silverlight app send a dummy packet every 20 seconds or so. If it fails, I'd assume disconnection. However, incredibly, SocketAsyncEventArgs.SocketError always reports success, even if I simply unplug the device that the Silverlight app is connected to. I am not sure whether this is a bug or what or perhaps I need to upgrade to SL4. Any ideas, direction or implementation would be appreciated.

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• How to filter and intercept Linux packets by using net_dev_add() API?

  - by Khajavi

  I'm writing ethernet network driver for linux. I want to receive packets, edit and resend them. I know how to edit the packet in packet_interceptor function, but how can I drop incoming packets in this function?? #include <linux/netdevice.h> #include <linux/skbuff.h> #include <linux/ip.h> #include <net/sock.h> struct packet_type my_proto; int packet_interceptor(struct sk_buff *skb, struct net_device *dev, struct packet_type *pt, struct net_device *orig_dev) { // I dont want certain packets go to upper in net_devices for further processing. // How can I drop sk_buff here?! return 0; } static int hello_init( void ) { printk(KERN_INFO "Hello, world!\n"); my_proto.type = htons(ETH_P_ALL); my_proto.dev = NULL; my_proto.func = packet_interceptor; dev_add_pack(&my_proto); return 0; } static void hello_exit(void) { dev_remove_pack(&my_proto); printk(KERN_INFO "Bye, world\n"); } module_init(hello_init); module_exit(hello_exit);

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• Ensure that my C# desktop application is making requests to my ASP .NET MVC action?

  - by Mathias Lykkegaard Lorenzen

  I've seen questions that are almost identical to this one, except minor but important differences that I would like to get detailed. Let's say that I have a controller and an action method in MVC which therefore accepts requests on the following URL: http://example.com/api/myapimethod?data=some-data-here. This URL is then being called regularly by 1000 clients or more spread out in the public. The reason for this is crowdsourcing. The clients around the globe help feed a global cache on my server, which makes it faster for the rest of the clients to fetch the data. Now, if I'm sneaky (and I am), I can go into Fiddler, Ethereal, Wireshark or any other packet sniffing tool and figure out which requests the program is making. By figuring that out, I can also replicate them, and fill the service with false corrupted data. What is the best approach to ensuring that the data received in my ASP .NET MVC action method is actually from the desktop client application, and not some falsely generated data that the user invented? Since it is all based on crowdsourcing, would it be a good idea for my users to be able to "vote" if some data is falsified, and then let an automatic cleanup commence if there are enough votes? I do not have access to a tool like SmartAssembly, so unfortunately my .NET program is fully decompilable. I realize this might be impossible to accomplish in an error-proof manner, but I would like to know where my best chances are.

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• Java: Cleaing up connection reset (but not by peer).

  - by Zombies

  There seems to be some confusion as well contradicting statements on various SO answers: http://stackoverflow.com/questions/585599/whats-causing-my-java-net-socketexception-connection-reset . You can see here that the accepted answer states that the connecteion was closed by other side. But this is not true, closing a connection doesn't cause a connection reset. It is cauesed by "an underlying TCP/IP error." What I want to know is if a SocketException: Connection reset means really besides "unerlying TCP/IP Error." What really causes this? As I doubt it has anything to do with the connection being closed (since closing a connection isn't an exception worthy flag, and reading from a closed connection is, but that isn't an "underlying TCP/IP error." My hypothesis is this Connection reset is caused from a server's failure to acknowledge an ACK packet (either wholly or just improperly as per TCP/IP). And that a SocketTimeoutException is generated only when no data is generated to be read (since this is thrown during a read after a certain duration, and read is waiting for data, but is not concerned with ACK packets). In other words, read() throws SocketTimeoutException if it didn't read any bytes of actual data (DATA LAYER) in its allotted time.

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• Detecting TCP dropout over an unreliable network

  - by yx

  I am doing some experimentation over an unreliable radio network (home brewed) using very rudimentary java socket programming to transfer messages back and forth between the end nodes. The setup is as follows: Node A --- Relay Node --- Node B One problem I am constantly running into is that somehow the connection drops out and neither Node A or B knows that the link is dead, and yet continues to transmit data. The TCP connection does not time out either. I have added in a heartbeat message that causes a timeout after a while, but I still would like to know what is the underlying cause of why TCP does not time out. Here are the options I am enabling when setting up a socket: channel.socket().setKeepAlive(false); channel.socket().setTrafficClass(0x08); // for max throughput This behavior is strange since it is totally different than when I have a wired network. On a wired network, I can simulate a disconnected connection by pulling out the ethernet cord, however, once I plug the cord back in, the connection becomes restablished and messages begin to be passed through once more. On the radio network, the connection is never reestablished and once it silently dies, the messages never resume. Is there some other unknown java implentation or setting for a socket that I can use, also, why am I seeing this behavior in the first place? And yes, before anyone says anything, I know TCP is not the preffered choice over an unreliable network, but in this case I wanted to ensure no packet loss.

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• SYN receives RST,ACK very frequently

  - by user1289508

  Hi Socket Programming experts, I am writing a proxy server on Linux for SQL Database server running on Windows. The proxy is coded using bsd sockets and in C, and it is working just fine. When I use a database client (written in JAVA, and running on a Linux box) to fire queries (with a concurrency of 100 or more) directly to the Database server, not experiencing connection resets. But through my proxy I am experiencing many connection resets. Digging deeper I came to know that connection from 'DB client' to 'Proxy' always succeeds but when the 'Proxy' tries to connect to the DB server the connection fails, due to the SYN packet getting RST,ACK. That was to give some background. The question is : Why does sometimes SYN receives RST,ACK? 'DB client(linux)' to 'Server(windows)' ---- Works fine 'DB client(linux) to 'Proxy(Linux)' to 'Server(windows)' ----- problematic I am aware that this can happen in "connection refused" case but this definitely is not that one. SYN flooding might be another scenario, but that does not explain fine behavior while firing to Server directly. I am suspecting some socket option setting may be required, that the client does before connecting and my proxy does not. Please put some light on this. Any help (links or pointers) is most appreciated. Additional info: Wrote a C client that does concurrent connections, which takes concurrency as an argument. Here are my observations: - At 5000 concurrency and above, some connects failed with 'connection refused'. - Below 2000, it works fine. But the actual problem is observed even at a concurrency of 100 or more. Note: The problem is time dependent sometimes it never comes at all and sometimes it is very frequent and DB client (directly to server) works fine at all times .

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