// SPDX-License-Identifier: Apache-2.0
//
// ping -- ICMP echo, over a SchOS ping socket.
//
// This is a first-party program rather than toybox's ping, and the reason is
// worth recording because it is not "ours is better". toybox's ping reads its
// replies with recvmsg(2) and asks for the TTL through an IP_RECVTTL control
// message, and SchOS has neither: no recvmsg, no ancillary data. Both are owed
// -- recvmsg is item 1 of docs/plan/foundations.md, where it is wanted for
// SCM_RIGHTS -- and neither should be rushed to make one applet run.
//
// So this uses sendto/recvfrom, which the kernel does have, and proves the ICMP
// socket end to end in the meantime. When recvmsg lands, toybox's ping will
// work and this can go.
//
// A "ping socket" is socket(AF_INET, SOCK_DGRAM, IPPROTO_ICMP): the kernel owns
// the IP header and the caller reads and writes the ICMP message alone. See
// inet_icmp_recv_cb in kernel/net/inet.c.

#include "types.h"
#include "user.h"
#include "socket.h"

#define ICMP_ECHO        8
#define ICMP_ECHOREPLY   0
#define DEFAULT_COUNT    4
#define PAYLOAD          56          // what every other ping sends

struct icmphdr {
    uchar  type;
    uchar  code;
    ushort checksum;
    ushort id;
    ushort seq;
};

// lib/ is raw syscall stubs -- no libc, so not even memset. Everything here is
// hand-rolled for the same reason cmd/schinit is.
static void
zero(void *p, int n)
{
    char *b = p;
    while (n-- > 0) *b++ = 0;
}

static void
puts_(const char *s)
{
    int n = 0;
    while (s[n]) n++;
    write(1, (void *)s, n);
}

static void
putn_(int v)
{
    char buf[12];
    int i = 0, neg = 0;
    if (v < 0) { neg = 1; v = -v; }
    if (v == 0) buf[i++] = '0';
    while (v) { buf[i++] = (char)('0' + v % 10); v /= 10; }
    if (neg) buf[i++] = '-';
    while (i--) write(1, &buf[i], 1);
}

// The Internet checksum: one's complement of the one's complement sum of every
// 16-bit word. Computed over the ICMP message with the checksum field zeroed,
// which is why it is filled in last.
static ushort
cksum(const void *p, int n)
{
    const uchar *b = p;
    uint sum = 0;
    int i;

    for (i = 0; i + 1 < n; i += 2)
        sum += (uint)((b[i] << 8) | b[i + 1]);
    if (i < n)
        sum += (uint)(b[i] << 8);
    while (sum >> 16)
        sum = (sum & 0xFFFF) + (sum >> 16);
    return (ushort)(~sum & 0xFFFF);
}

static ushort
hton16(ushort v)
{
    return (ushort)((v >> 8) | (v << 8));
}

// Dotted quad to a network-byte-order address. Returns 0 on a malformed one,
// which is indistinguishable from 0.0.0.0 and is fine: nobody pings that.
static uint
parse_ip(const char *s, int *ok)
{
    uint out = 0;
    int part, i, digits;

    *ok = 0;
    for (i = 0; i < 4; i++) {
        part = 0; digits = 0;
        while (*s >= '0' && *s <= '9') {
            part = part * 10 + (*s - '0');
            if (part > 255) return 0;
            s++; digits++;
        }
        if (digits == 0) return 0;
        out |= (uint)part << (8 * i);       // little-endian host, so LSB first
        if (i < 3) {
            if (*s != '.') return 0;
            s++;
        }
    }
    if (*s != '\0') return 0;
    *ok = 1;
    return out;
}

static void
print_ip(uint addr)
{
    for (int i = 0; i < 4; i++) {
        putn_((int)((addr >> (8 * i)) & 0xFF));
        if (i < 3) puts_(".");
    }
}

int
main(int argc, char *argv[])
{
    char target[64];
    int count = DEFAULT_COUNT;
    int ok, sent = 0, recvd = 0;

    if (argc < 2) {
        puts_("usage: ping <host> [count]\n");
        exit();
    }

    // "localhost" without a resolver. The kernel has no DNS client reachable
    // from userland, and the one name worth special-casing is the one that
    // always means the same thing.
    const char *host = argv[1];
    if (host[0] == 'l' && host[1] == 'o' && host[2] == 'c' &&
        host[3] == 'a' && host[4] == 'l' && host[5] == 'h' &&
        host[6] == 'o' && host[7] == 's' && host[8] == 't' && host[9] == 0)
        host = "127.0.0.1";

    { int i = 0; while (host[i] && i < 63) { target[i] = host[i]; i++; } target[i] = 0; }

    uint addr = parse_ip(target, &ok);
    if (!ok) {
        puts_("ping: not a dotted-quad address: ");
        puts_(argv[1]);
        puts_("\nping: there is no resolver yet; use an address\n");
        exit();
    }

    if (argc > 2) {
        count = 0;
        for (const char *p = argv[2]; *p >= '0' && *p <= '9'; p++)
            count = count * 10 + (*p - '0');
        if (count <= 0) count = DEFAULT_COUNT;
    }

    int fd = socket(AF_INET, SOCK_DGRAM, IPPROTO_ICMP);
    if (fd < 0) {
        puts_("ping: socket: ");
        putn_(fd);
        puts_("\n");
        exit();
    }

    puts_("PING ");
    print_ip(addr);
    puts_(" ");
    putn_(PAYLOAD);
    puts_(" bytes of data.\n");

    ushort id = (ushort)getpid();

    for (int seq = 1; seq <= count; seq++) {
        char out[sizeof(struct icmphdr) + PAYLOAD];
        struct icmphdr *ih = (struct icmphdr *)out;

        zero(out, (int)sizeof(out));
        ih->type = ICMP_ECHO;
        ih->code = 0;
        ih->id   = hton16(id);
        ih->seq  = hton16((ushort)seq);
        for (int i = 0; i < PAYLOAD; i++)
            out[sizeof(*ih) + i] = (char)('a' + (i % 26));
        ih->checksum = 0;
        // The checksum is stored as it is computed: cksum() already works in
        // network order, so byte-swapping it here would send a wrong one.
        ih->checksum = hton16(cksum(out, (int)sizeof(out)));

        struct sockaddr_in sa;
        zero(&sa, (int)sizeof(sa));
        sa.sin_family = AF_INET;
        sa.sin_port   = 0;
        sa.sin_addr   = addr;

        int t0 = uptime();
        int n = sendto(fd, out, (int)sizeof(out), 0,
                       (struct sockaddr *)&sa, sizeof(sa));
        if (n < 0) {
            puts_("ping: sendto: ");
            putn_(n);
            puts_("\n");
            break;
        }
        sent++;

        // Wait for a reply, but not forever. uptime() counts 10 ms ticks, so
        // 100 of them is one second -- the same timeout every ping uses.
        char in[256];
        int got = -1, waited = 0;
        struct sockaddr_in from;
        int fromlen = sizeof(from);

        while (waited < 100) {
            got = recvfrom(fd, in, (int)sizeof(in), 0,
                           (struct sockaddr *)&from, &fromlen);
            if (got > 0) break;
            sleep(1);
            waited = uptime() - t0;
        }

        if (got <= 0) {
            puts_("Request timeout for icmp_seq ");
            putn_(seq);
            puts_("\n");
            continue;
        }

        struct icmphdr *rh = (struct icmphdr *)in;
        if (rh->type != ICMP_ECHOREPLY || hton16(rh->id) != id) {
            puts_("ping: reply for somebody else, ignored\n");
            continue;
        }

        recvd++;
        putn_(got);
        puts_(" bytes from ");
        print_ip(from.sin_addr);
        puts_(": icmp_seq=");
        putn_((int)hton16(rh->seq));
        puts_(" time=");
        putn_((uptime() - t0) * 10);
        puts_(" ms\n");

        if (seq < count)
            sleep(100);                 // one second between packets
    }

    close(fd);

    puts_("--- ");
    print_ip(addr);
    puts_(" ping statistics ---\n");
    putn_(sent);
    puts_(" packets transmitted, ");
    putn_(recvd);
    puts_(" received, ");
    putn_(sent ? (sent - recvd) * 100 / sent : 0);
    puts_("% packet loss\n");

    exit();
}