fartnet.c

// # compile this with 
// ./openwrt-sdk-19.07.7-ramips-mt76x8_gcc-7.5.0_musl.Linux-x86_64/staging_dir/toolchain-mipsel_24kc_gcc-7.5.0_musl/bin/mipsel-openwrt-linux-gcc fartnet.c -o fartnet
// # copy over the file:
// # at the pc, run:
// nc -l 9999 -w0 < fartnet
// # at the router, run:
// nc 192.168.2.116 9999 > fartnet
// chmod +x fartnet
// # next, kill everything that accesses the device node:
// kill -9 `ps w|grep watchdog_loop|grep -v grep|awk '{ print $1 }'`
// kill -9 `ps w|grep autopubmsg|grep -v grep|awk '{ print $1 }'`
// killall -9 pubmsg
// and run it!
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <netinet/in.h>

#define PORT    6454
#define MAXLINE 1024

int main()
{
    int sockfd;
    char buffer[MAXLINE];
    struct sockaddr_in servaddr, cliaddr;
      
    // Creating socket file descriptor
    if ( (sockfd = socket(AF_INET, SOCK_DGRAM, 0)) < 0 ) 
    {
        perror( "socket creation failed" );
        exit( EXIT_FAILURE );
    }
      
    memset( &servaddr, 0, sizeof(servaddr) );
    memset( &cliaddr, 0, sizeof(cliaddr) );

    // Server connection information
    servaddr.sin_family = AF_INET; // IPv4
    servaddr.sin_addr.s_addr = INADDR_ANY;
    servaddr.sin_port = htons( PORT );

    // Bind socket
    if ( bind(sockfd, (const struct sockaddr *)&servaddr, sizeof(servaddr)) < 0 )
    {
        perror("bind failed");
        exit(EXIT_FAILURE);
    }
      
    int len, n;
    FILE * fp;
     
    len = sizeof( cliaddr );

    // Serve forever
    while ( 1 )
    {
        n = recvfrom(
            sockfd,
            (char* )buffer, 
            MAXLINE, 
            MSG_WAITALL, 
            ( struct sockaddr* ) &cliaddr,
            &len
        );
        if ( n > 18 )
        {
            buffer[n] = '\0';
            
            fp = fopen("/dev/ws2812", "wb");            
            if( fp == NULL )
            {
                printf("Unable to open ws2812 device node.\n");
                exit(EXIT_FAILURE);
            }
            
            fwrite( ((char* )buffer)+18, sizeof( char ), n - 18, fp);
            fclose( fp );
        }
    }

    return 0;
}