Have you ever wanted to push a value to a HTTP page and don’t care about the result? Well, you can do it in pure C, but be prepared – it is not as trivial as you might think. Here is how to do it.
Includes
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| #include <stdio.h>
#include <errno.h>
#include <string.h>
#include <time.h> |
Distinguish Windows from Unix/Linux
We need to include winsock if we compile under Windows – otherwise use Unix/Linux headers for networking operations.
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| #ifdef _WIN32
#include <winsock.h>
#include <io.h>
#else
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netdb.h>
#define closesocket(s) close(s)
#endif |
Defining the port to connect to
The default port to connect to is 80. You can change it here if you need to.
The push_value Function
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| void push_value( char *host, char *path, char *value ) { |
Variable Declarations
This is the place to save the actual date string to. It’s length is limited to 15 characters – 14 for the date string and one for the terminating \0 at the end.
The actual HTTP Request is being written to this variable.
These are needed to create the socket/connection.
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| struct sockaddr_in server;
struct hostent *host_info;
unsigned long addr;
int sock; |
Windows needs Winsock initialisation
Windows TCP initialisation has to be done only if compiled under Windows.
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| #ifdef _WIN32
short wVersReq;
WSADATA wsaData;
wVersReq = MAKEWORD( 1, 1 );
if( WSAStartup( wVersReq, &wsaData ) != 0 ) {
fprintf( stderr,
"Failed to init windows sockets\n" );
return;
}
#endif |
Get actual date
strftime creates the actual date into datum, it uses the format given (“%Y%m%d%H%M%S”) and the current time from time(NULL).
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| tt = time(NULL);
strftime( datum,
sizeof( datum ),
"%Y%m%d%H%M%S",
localtime(&tt) ); |
Create a socket
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| sock = socket( PF_INET, SOCK_STREAM, 0 );
if( sock < 0 ) {
perror( "failed to create socket" );
return;
} |
Create struct for connection partner
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| memset( &server, 0, sizeof( server ) );
if( ( addr = inet_addr( host ) ) != INADDR_NONE ) { |
host is a numerical IP Address. Nothing special has to be done.
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| memcpy( (char *) &server.sin_addr,
&addr, sizeof( addr ) );
} else { |
host is a domain name. Convert this domain name into a numerical IP Address.
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| host_info = gethostbyname( host );
if( NULL == host_info ) {
fprintf( stderr,
"unknown server: %s\n",
host );
return;
}
memcpy( (char *) &server.sin_addr,
host_info->h_addr,
host_info->h_length );
} |
Set server parameters.
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| server.sin_family = AF_INET;
server.sin_port = htons( HTTP_PORT ); |
Create connection with partner
Time to get together. Creating connection to server.
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| if( connect( sock, (struct sockaddr*) &server,
sizeof( server ) ) < 0 ) {
perror( "can't connect to server" );
return;
} |
Create HTTP 1.0 request with given value value and current time datum.
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| sprintf( request,
"GET %s?value=%s&time=%s HTTP/1.0\n\n",
path,
value,
datum); |
Send created HTTP request to server. Ignore response, as it is not needed (see specification).
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| send( sock, request, sizeof( request ), 0 ); |
Close socket, we don’t need it anymore – “fire and forget”.
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| closesocket( sock );
} |
Call push_value
This is a small main function that gets the host, path and value from the command line and calls the push_value function. Originally for testing purpose only, but I left it in for you to test it on your own.
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| int main( int argc, char **argv ) {
if( argc < 3 ) {
fprintf( stderr, "usage: %s host path value",
argv[0] );
return -1;
}
push_value( argv[1], argv[2], argv[3] );
return 0;
} |
Conclusion
With a shell script it would have been a lot easier. Given the above C programme we could create an equivalent bash shell script to do that:
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| #!/bin/sh
if [ $# -lt 3 ]; then
echo "usage: $0 host path value"
exit -1
fi
TIME=$(date +%Y%m%d%H%M%S)
wget -q -O /dev/null "http://$1:80$2?value=$3&time=$TIME" |
On the other hand this shell script takes about twice the time to complete than the C programme. Decide for yourself if it’s worth the cost.
If you like you can download the C Source Code or the Bash Script. Compile the C programme with gcc -o pushclient pushclient.c.
November 15th, 2009 at 03:01
Pero bash usa wget sin wget y sin usar otro programa en bash seria aun mas tardado de realizar