radio_sniff.cpp

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// Copyright (C) 2026 Douglas Quigg (dstroy0) <dquigg123@gmail.com>
// SPDX-License-Identifier: AGPL-3.0-or-later
 
/**
 * @file radio_sniff.cpp
 * @brief Receive-only radio channel sniffer -> pcap capture records (see radio_sniff.h).
 */
 
#include "services/radio_sniff/radio_sniff.h"
 
#if DETWS_ENABLE_RADIO_SNIFF
 
namespace
{
void wr16le(uint8_t *p, uint16_t v)
{
    p[0] = (uint8_t)v;
    p[1] = (uint8_t)(v >> 8);
}
void wr32le(uint8_t *p, uint32_t v)
{
    p[0] = (uint8_t)v;
    p[1] = (uint8_t)(v >> 8);
    p[2] = (uint8_t)(v >> 16);
    p[3] = (uint8_t)(v >> 24);
}
} // namespace
 
uint32_t detws_radiosniff_i2f32(int32_t dbm)
{
    if (dbm == 0)
        return 0;
    uint32_t sign = 0;
    uint32_t mag;
    if (dbm < 0)
    {
        sign = 0x80000000u;
        mag = (uint32_t)(-(int64_t)dbm);
    }
    else
        mag = (uint32_t)dbm;
    int e = 31;
    while (!((mag >> e) & 1u))
        e--; // highest set bit
    uint32_t exp = (uint32_t)(127 + e);
    uint32_t mant = (e >= 23) ? ((mag >> (e - 23)) & 0x7FFFFFu) : ((mag << (23 - e)) & 0x7FFFFFu);
    return sign | (exp << 23) | mant;
}
 
size_t detws_radiosniff_global(uint8_t *out, size_t cap)
{
    return det_pcap_global_header(out, cap, DET_DLT_IEEE802_15_4_TAP);
}
 
size_t detws_radiosniff_tap_record(uint8_t *out, size_t cap, const uint8_t *frame, size_t flen, int32_t rssi_dbm,
                                   uint16_t channel, uint32_t ts_sec, uint32_t ts_usec)
{
    if (!out || !frame || flen == 0)
        return 0;
    size_t caplen = RADIO_SNIFF_TAP_LEN + flen;
    size_t total = DET_PCAP_REC_HDR_LEN + caplen;
    if (cap < total)
        return 0;
 
    // pcap record header.
    det_pcap_record_header(out, cap, ts_sec, ts_usec, (uint32_t)caplen, (uint32_t)caplen);
    uint8_t *p = out + DET_PCAP_REC_HDR_LEN;
 
    // 802.15.4 TAP header: version(1)=0, reserved(1)=0, length(2 LE) = whole TAP block.
    p[0] = 0;
    p[1] = 0;
    wr16le(p + 2, RADIO_SNIFF_TAP_LEN);
    // TLV: Received Signal Strength (type 1, len 4), float32 dBm.
    wr16le(p + 4, 1);
    wr16le(p + 6, 4);
    wr32le(p + 8, detws_radiosniff_i2f32(rssi_dbm));
    // TLV: Channel Assignment (type 3, len 3 -> padded to 4): channel number(2 LE) + page(1).
    wr16le(p + 12, 3);
    wr16le(p + 14, 3);
    wr16le(p + 16, channel);
    p[18] = 0; // channel page 0
    p[19] = 0; // pad
 
    // The raw MAC frame.
    uint8_t *f = p + RADIO_SNIFF_TAP_LEN;
    for (size_t i = 0; i < flen; i++)
        f[i] = frame[i];
    return total;
}
 
#endif // DETWS_ENABLE_RADIO_SNIFF