loratap-example.c

#include "loratap.h"
#include <string.h>
#include <stdio.h>
#include <arpa/inet.h>

#define LINKTYPE_LORA_LORATAP 270

typedef struct pcap_hdr_s {
    uint32_t magic_number;   /* magic number */
    uint16_t version_major;  /* major version number */
    uint16_t version_minor;  /* minor version number */
    int32_t  thiszone;       /* GMT to local correction */
    uint32_t sigfigs;        /* accuracy of timestamps */
    uint32_t snaplen;        /* max length of captured packets, in octets */
    uint32_t network;        /* data link type */
} pcap_hdr_t;

typedef struct pcaprec_hdr_s {
    uint32_t ts_sec;         /* timestamp seconds */
    uint32_t ts_usec;        /* timestamp microseconds */
    uint32_t incl_len;       /* number of octets of packet saved in file */
    uint32_t orig_len;       /* actual length of packet */
} pcaprec_hdr_t;


void dumpLoraTapHeader(loratap_header_t header) {
    printf("LoRaTap packet header\n");
    printf("Packet RSSI: %d\n", header.rssi.packet_rssi);
    printf("RSSI: %d\n", header.rssi.current_rssi);
    printf("SNR: %d\n", header.rssi.snr);
    printf("Frequency: %u\n", ntohl(header.channel.frequency));
    printf("SF: %2u\n", header.channel.sf);
}

void writeFakePcap(const char *outputfile, int payloadsize, unsigned char *payload) {
    FILE * captureFile;
    pcap_hdr_t file_header;
    loratap_header_t loratap_packet_header;
    pcaprec_hdr_t pcap_packet_header;
    
    /* Create pcap with header */
    captureFile = fopen(outputfile, "w");
    file_header.magic_number = 0xa1b2c3d4;
    file_header.version_major = 2;
    file_header.version_minor = 4;
    file_header.thiszone = 0;
    file_header.sigfigs = 0;
    file_header.snaplen = 255;
    file_header.network = LINKTYPE_LORA_LORATAP;
    fwrite(&file_header, sizeof(pcap_hdr_t), 1, captureFile);

    /* Write packet */
    pcap_packet_header.ts_sec = 0;
    pcap_packet_header.ts_usec = 0;
    pcap_packet_header.incl_len = payloadsize + sizeof(loratap_header_t);
    pcap_packet_header.orig_len = payloadsize + sizeof(loratap_header_t);
    loratap_packet_header.lt_version = 0;
    loratap_packet_header.lt_length = htons(sizeof(loratap_header_t));
    loratap_packet_header.channel.frequency = htonl(868100000);
    loratap_packet_header.channel.bandwidth = 1;
    loratap_packet_header.channel.sf = 7;
    loratap_packet_header.rssi.packet_rssi = 0;
    loratap_packet_header.rssi.current_rssi = 0;
    loratap_packet_header.rssi.max_rssi = 255;
    loratap_packet_header.rssi.snr = 0;
    loratap_packet_header.sync_word = 0x34; // LoRaWAN
    dumpLoraTapHeader(loratap_packet_header);
    fwrite(&pcap_packet_header, sizeof(pcaprec_hdr_t), 1, captureFile);
    fwrite(&loratap_packet_header, sizeof(loratap_header_t), 1, captureFile);
    fwrite(payload, payloadsize, 1, captureFile);
    fclose(captureFile);
}

int main() {
    unsigned char buffer[] = "Hello LoraTap";
    writeFakePcap("loratap.pcap", strlen(buffer), buffer);
}