int trace_validate_incoming()

in src/samplers/tcp/bpf.c [283:314]

• 21 lines of code
• 5 McCabe index (conditional complexity)

int trace_validate_incoming(struct pt_regs *ctx, struct sock *sk, struct sk_buff *skb) {
    if (sk == NULL || skb == NULL)
        return 0;

    // read seq and rcv_nxt from kernel to bpf.
    u32 seq = 0;
    bpf_probe_read_kernel(&seq, sizeof(seq), ((const char *)skb) +
               offsetof(struct sk_buff, cb) +
               offsetof(struct tcp_skb_cb, seq));
    u32 rcv_nxt = 0;
    bpf_probe_read_kernel(&rcv_nxt, sizeof(rcv_nxt), ((const char *)sk) +
               offsetof(struct tcp_sock, rcv_nxt));

    int64_t distance = (int64_t)(seq) - (int64_t)(rcv_nxt);

    // Segment sequence before the expected one
    // which means this was a duplicated segment
    if (distance < 0) {
        // Increment duplicate counter
        int loc = 0;
        add_value(duplicate.lookup(&loc), 1);
    }

    // Segment sequence after the expected one
    // which means this segment was received out of order
    if (distance > 0) {
        // Increment out of order counter
        int loc = 0;
        add_value(ooo.lookup(&loc), 1);
    }
    return 0;
}