Programming :: Read DNS Informaton Using Sockets And C Libraries
Jun 9, 2010
I am using the API libpcap in order to filter the traffic of the port 53 from my PC ro other PCs, in other words the DNS traffic.I want to get more information about the DNS traffic that is being sent to the DNS server, in other words the queries. So far I have no idea how to read the information data or payload of the UDP package in order to read the content of the traffic for example if there is any PTR, A, MX, etc Resource Record.According to the RFC 1053 there is a header that is possible to use in order to easily get this info.
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Mar 20, 2010
I would like to learn how to program on Linux but I cant find any informaton on GCC. The manual is like a list that has no meaning to a novice. Are there any books out there that are not writen by Stallman? Is it more practical to learn it on another O.S and then transpose the information over to the Linux context?
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Nov 18, 2010
Is there any way to implement a simple ping script in C (unix)? I'm programming simple OpenWRT scripts.
I have found some examples of ping in C:
[URL]
However, nothing happens, nothing is sent.
When I look at the code, in the portion where the socket is created, I can see that the socket is not binding to any interface:
Code:
if ((sockfd = socket(AF_INET, SOCK_RAW, IPPROTO_ICMP)) == -1)
{
perror("socket");
exit(EXIT_FAILURE);
}
setsockopt(sockfd, IPPROTO_IP, IP_HDRINCL, &optval, sizeof(int));
Instead, it uses "setsockopt" to set some options.
My guess is that it is trying to send packets over the eth0 interface instead over the wl0 (wireless) interface (which is the one I want to use to send pings).
Now, my question is: Is there any other way to send pings in C by binding to an interface?
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Jul 25, 2010
I need to create a C/C++ program in Linux that succeeds in detecting how many tcp-sockets and what tcp-sockets are created by the other processes in the system in a particular time interval (e.g., the interval time this application is running in). Then, I'd need to get some information like local/remote port number and local/remote ip address of each of these sockets.
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Aug 27, 2010
I am struggling a little on how to best approach this problem. I have wrote a server program that runs via xinetd, that obviously spits out data at the client end. Fairly straightforward stuff?There is a point in my server code where I need to display an image/gui i.e something that runs on X11 that prompts a user to perform a task on the display connected at the the server side.So far I have written a test program that displays some text at the client end and then launches the browser at the server end. I have also set the following export. Code: export DISPLAY=:0 and then goes on to launch my web browser. Works great when ran locally on the server and when I remotely telnet in to the server and run the code.
However when I try to run the same piece of code as a xinetd service the export seems to have zero affect and the client terminal window displays errors associated with there not being a X11 server running.The code launches fine when I create a socket to serverip:6556 it just the ability to display gui programs to another display that does not seem to be working.
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Feb 1, 2011
Can someone help me with this problem,trying to send a packet,using tcp/ip,the packet should look like this:
Code:
field 1: SOCKS protocol version, 1 byte (0x05 for this version)
field 2: status, 1 byte:
0x00 = request granted
0x01 = general failure
0x02 = connection not allowed by ruleset
0x03 = network unreachable
0x04 = host unreachable
0x05 = connection refused by destination host
0x06 = TTL expired
0x07 = command not supported / protocol error
0x08 = address type not supported
field 3: reserved, must be 0x00
field 4: address type, 1 byte:
0x01 = IPv4 address
0x03 = Domain name
0x04 = IPv6 address
field 5: destination address of
4 bytes for IPv4 address
1 byte of name length followed by the name for Domain name
16 bytes for IPv6 address
field 6: network byte order port number, 2 bytes
and this is my code:
Code:
int domainLen = strlen(domain);
char reply[domainLen + 7];
reply[0] = 5; // version
reply[1] = 0; // succed
reply[2] = 0; // reserved
reply[3] = 3; // its a domain
reply[4] = domainLen;; // lenght of domain
for(int j = 0; j < domainLen; ++j)
{
reply[j + 5] = domain[j];
}
reply[5 + domainLen] = 80; // port
reply[20] = '�';
Send(reply, sizeof(reply));
domain is "www.google.com". Am I doing it right ? I dont know much about bits.
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Feb 25, 2011
I am doing a project where 2 clients connect to server and communicate (chat) and transfer data one after other using sockets. I have working code for this in C language. Now our main aim is to create a communication link where two clients transfer multiple streams data parallely. To be more precise i want to transfer images files and audio files parallel at same time, so is it possible to send data parallel using one socket connection?
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Jun 9, 2010
I have a problem creating my second socket in client file. the program was running well but when I try to add another socket to connect to the same server, I got a problem connecting to the first socket! it doesn't make sense. the original code was:
sockfd[i] = socket(AF_INET, SOCK_STREAM, 0);
if(sockfd[i] < 0) error("(MAIN) - Error openning socket 1");
port_num[i] = portno;
bzero((char*) &serv_addr[i], sizeof(serv_addr[i]));
[Code].....
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Feb 4, 2011
NextPendingConnection () returns a new socket with respect to a new client. This new QSocket is passed to the connect () function which connects it to a SLOT 'xyz' with SIGNAL 'readyRead()'. Now in the SLOT 'xyz' how I am supposed to automate the monitoring of ALL connected sockets to see whether some data is available on them? One pathetic way would be to run all the sockets through a for loop and check each one of them for the data. Secondly, I read up on QSocketNotifier() here: [URL]. But I am not sure if that is the correct thing.
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Nov 29, 2010
I am coding a http server which has to send the file(s) such as images, .avi files, .mpeg, that the client is going to request. I have been trying of sending files through sockets.
char info [256];
bzero(info, 256);
//memset(&info,0,sizeof(info));
read(socket, info, 255);
write(socket, HTTP, 255);
FILE *fl= fopen(info,"rb");
fseek(fl, 0, SEEK_END);
long len = ftell(fl);
printf("largo: %ld", len);
unsigned char *ret = (char*) malloc(len);
fseek(fl, 0, SEEK_SET);
fread(ret, 1, len, fl);
However, it's supposed to be shown in Mozilla Firefox (as the client). But it is not doing it, so.. It's just not getting the complete file.
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Apr 20, 2010
I have a problem passing a file descriptor from one process to another.
I have two processes A and B. Both are running in different network and
filesystem namespaces, so it is impossible to use unix domain sockets or
net sockets to pass a file descriptor from process A to process B.
The usage of STREAMS is also impossible, as you can see in
fixunix.com/unix/84093-streams-pipes-ioctl-i_sendfd.html
[quotation begin]
Linux doesn't have STREAMS, which are the System V way
of doing this task. ...
[quotation end]
Are there additional possibilities for file descriptor passing like
using named pipes or something like that or does anybody know
a good workaround for this problem ?
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Nov 30, 2010
I have written a server application which has select for both incoming new client connection requests and incoming data from client. I am able to process incoming connection requests and client data.
For example, server has 8 clients connected to it. If client 3 disconnects from server, how will server come to know this client has disconnected and to close its client socket fd gracefully? Does server's select get data on that client socket fd as 'close' data or any error code in recv() function that notifies server to close this client socket fd? Also if client disconnects abruptly without sending close request to server, how should server handle this? Does server get "EPIPE" error?
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Jul 8, 2011
Hi, is it possible to send a request to a http server without using sockets?
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Jul 12, 2011
I've created quite a predicament with my desktop installation and would prefer to be able to salvage it instead of having to reformat/re-install Ubuntu.
Quite a lot happened and here's my best recollection:
- My Ubuntu installation stopped working and I could not get the desktop to load.
- I backup up my entire home directory by creating a zip file along with other small zip files. I used Alt + Del + F1 to get the CLI to do this.
- I then did different things trying to get the desktop to load.
- I did a apt-get upgrade, to try and get it to work; this was not sucessful.
- Working through several dependency issues I finally got sudo apt-get ubuntu-desktop upgrade to work, but it did not finish completely. I started to get out of memory errors. I am assuming this was because too much hard drive space was taken up by the zip files I had created
-I could not boot and do anything properly after that. Every attempt to modify the filesystem (to free up space) results in an error "Read Only File System". The root file system was not being mounted and I would see root@none on the CL
- Looking on the boot loader I now have Ubuntu 9.10 2.6.24-generic installed
- I burnt a new installation of Ubuntu 10.4 LTS
- Using Live CD I tried to see if I could free up some space and get the system back to more stable state,
However this was NOT sucessful. I tried to mount my drive by sudo mount -t ext3 <dev> <dir> but I keep getting the following error: error while loading shared libraries: /lib/libsepol.so.1: cannot read file data: Input/output error
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Mar 31, 2011
Iam using socket programming in one of my problem. The scenario is like this.
=>one module is working as a socket server(process p1) is able to handle client sockets on that port.
=>one module is working as socket client (process p2) is connected to server socket and Tx/Rx data on this socket. This module has some more threads, based on received data from server socket it will connect to http on other thread and get information...
=>one more module is working as socket client (process p3) is also connected to server socket and doing some other transactions.
Here my problem is when in presence of p2, p3 http connection taking more time than the expected. If we wont start p3(means only one server-client socket) then http connection is fast enough.
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Apr 15, 2009
constructing a protocol where in it involves sending and receiving different files, so sending data over consists of file name, size of the file and content of the file, so while receiving can i use functions like strchr() to differentiate these fields for sockets? so to allocate memory for file to save i need to have its size.
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Jun 4, 2011
I've just upgraded to Fedora 15 and have been fiddling with the new systemd which replaces sysvinit. I googled quite a bit, but was really unable to find any real information about how it works and why it's better.
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Jul 24, 2010
I'm trying to add local sockets in my multi-threaded application in order to exchange data between threads. The only problem I got is that most of the information available on the net is related to internet oriented socket programming whileI want to perform local connections. got a thread that does the sniffing via libpcap. And I would like that thread to send each captured packet to a second thread that will analyse the packetof the thread implementations is written in separate .h file.Or maybe there is a more effective method of exchanging data between threads
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May 24, 2010
Im doing a project,in which i have to add a script in c++ inorder to merge two or pdf files page by page or based on some headindgs.SO anyone can please suggest me any open source pdf libraries in c++ which provide functions for merging and splitting.
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Feb 21, 2011
I am learning C++ and wish to include some Boost functions in my code. My machine is running Debian Linux with the pre-installed boost binarys.I have a couple of questions:How do I include the library in my C++ code as there are no cpp or h files only binary files (eg /usr/lib/libboost_regex-d.so and /usr/lib/libboost_regex-d.a)How do I comile the code. I am using DialogBlocks for creating forms using wxwidgets. The editor also compiles the code using the gcc compiler. Do I have to give an instruction to the compiler saying which file is requried and where to find it? If so, any ideas how this is done?
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Oct 13, 2010
I have question about the UNIX sockets. my goal is to connect multiple sockets from a single client to a single server and keep them open...I'm not sure if that is possible to create or not. Do you have any suggestion or an example of code?
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Aug 31, 2010
I write the network driver. Transmission of packets in user space I do through netlink socket`s. In user space there is a handling of packets and their transmission on other device (however, it isn't important).
Problem in that any time, packets through the driver in system, and is reverse, are transferred normally. But then there comes the moment when the kernel crash. If to look in syslog it seems to me that comes deadlock. Also I think that it is related with netlink socket`s.
I can't find the information on that anywhere how correctly to use netlink socket`s in kernel space. Can at you will any a reason into the account of synchronization of sockets and the driver in kernel space?
I can give the driver code if it is necessary.
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Oct 15, 2010
I am stuck with a problem to link static libraries with gcc. There is no problem with source files since I am able to compile in a machine where the static library is installed. I am compiling with the following: Code: :~/Emotion/pjproject-1.0.3/third_party 157% gcc -Wall -I/portaudio/include -o rec patest_record.c -L./lib -lportaudio-x86_64-unknown-linux-gnu
[Code]....
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Jan 30, 2010
So I decided to take my first steps into programming with C + gtk. So far I have doneI loaded eclipse and ensured I had the cdt package Created a new C/C++ project called "play" Added a new source file called "Playfullsrc.c" Added the following to paths and symbols (output of the command: pkg-config --cflags gtk+-2.0)
Code:
/usr/include/gtk-2.0
/usr/lib/gtk-2.0/include
/usr/include/atk-1.0
/usr/include/cairo
/usr/include/pango-1.0
/usr/include/pixman-1
/usr/include/freetype2
[Code]....
added "/usr/lib/libgtk-x11-2.0.so" to GCC C Linker Libaries (I have cheacked and this file exists) When I build the project I get the error message "cannot find -l/usr/lib/libgtk-x11-2.0.soplayline 0C/C++ Problem" I have been following this tutorial: [URL]
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Apr 4, 2010
I have 2 questions... I couldn't find answers by Googling (more precisely, by Blackling) and in GCC documents, so I'm asking here.
1. There are 2 flags for position independent code, -fpic and -fPIC. All the examples I read use -fPIC... so when is -fpic useful and what is the difference?
2. Some tutorials use "g++ -shared" while others use "ld" for the creation of the shared library. Why? Does it matter which method I use? Is there a difference? Why does nobody mention both options?
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Jan 6, 2010
I've been trying for days now to build my first FastCGI application using gcc.
This is the output:
Code:
I believe I wouldn't have to refer to the lib path, but I added the -L flag to be sure.
The directory /usr/lib includes (among others) these files:
Code:
I have tried to follow these instructions. The files in the tar.gz archive provided by FastCGI.com no longer corresponds to the instructions there, but I was still able to run the ./configure and make commands so I believe FastCGI is installed.
But why can not the library be properly linked to? Really hope you can help me out on this one!
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Apr 11, 2010
Just what it says in the title.
I can work in a 32-bit VirtualBox VM, but it's very inconvenient and I would rather work in my 64-bit desktop if that's not too difficult.
These are all the lib32 packages I have installed code...
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Oct 22, 2010
This post isn't really asking for a tutorial, but rather asking for some ideas. I've come up with a few ideas, but they seem cumbersome and unnecessary, so I was wondering if someone with more experience than me could out. Also, my explanations suck, but I'll try to do my best. So say I have an executable called X. At some point during its execution, X loads and uses (using dlopen and dlsym) a library called Y. In Y, there a bunch of functions that call the function called, for example, void *special_malloc (size_t). These functions come from another linked library (linked during compilation) called Z. Problem is, special_malloc contains some static variables within its scope, and when those variables are reset midway through a program, an invalid free occurs (special_malloc uses garbage collection). Now, what I want to happen is that whenever lib Z calls special_malloc, it instead calls the special_malloc defined in the executable X, so that these static variables are retained. Keep in mind that I have control of the Z library, meaning I can edit the source to fit my needs.
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Jul 21, 2010
I'm using debian and, though i'm new to c++, i'm writing a program using it which needs some HTTPs functionalities . I found these libcurl libraries could help me but I haven been able to use them from my program. I installed them (power trio configure -make -make install ) but i guess i'm doing something wrong ... i feel like i should copy or link them somehow in my project (besides the include sentences in my code). I hope you could give me a hand with this im quite lost
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Jun 1, 2009
Any good tutorial on sharing dynamically allocated objects across shared libraries in the same process and between shared libaries and main(). In particular, I need to know what creation and destruction sequences are valid when libraries are being loaded and unloaded. For example, is it valid to allocate an object from inside a shared library procedure, and then delete that pointer from a different module, especially in the case where the allocating module has already been unloaded.
I imagine there might be all kinds of problems with this. Although my preliminary tests seem to work most of the time, I get crashes from time to time, but I'm not sure if they're caused by memory management or by threading issues. I've been restructuring my code to use a global context object to manage object creation and destruction from main(), but I'd like to find a clear exposition of the specific issues I'm dealing with before I go too much further.
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