Userland: Add an extremely simple NTP client

This only queries a single NTP server, only does a point-to-point
request, doens't do any filtering, doesn't display the response
in any useful format, and is generally very bare-bones.

But maybe, over time it can learn to query more servers, do
filtering, run as a service that keeps state over time to
improve filtering, adjust system time, and maybe learn to
run as an NTP server then.

Userland/ntpquery.cpp

@@ -0,0 +1,149 @@
+/*
+ * Copyright (c) 2020, Nico Weber <thakis@chromium.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#define _GNU_SOURCE
+#include <LibCore/ArgsParser.h>
+#include <arpa/inet.h>
+#include <endian.h>
+#include <netdb.h>
+#include <netinet/in.h>
+#include <stdio.h>
+#include <string.h>
+#include <sys/socket.h>
+#include <sys/time.h>
+
+struct [[gnu::packed]] NtpPacket {
+    uint8_t li_vn_mode;
+    uint8_t stratum;
+    int8_t poll;
+    int8_t precision;
+
+    uint32_t root_delay;
+    uint32_t root_dispersion;
+    uint32_t reference_id;
+
+    uint64_t reference_timestamp;
+    uint64_t origin_timestamp;
+    uint64_t receive_timestamp;
+    uint64_t transmit_timestamp;
+};
+
+static_assert(sizeof(NtpPacket) == 48);
+
+int main(int argc, char** argv)
+{
+    if (pledge("stdio inet dns", nullptr) < 0) {
+        perror("pledge");
+        return 1;
+    }
+
+    // FIXME: Request serenityos.pool.ntp.org here https://manage.ntppool.org/manage/vendor
+    // and then use that as the default value.
+    // Until then, explicitly pass this as `ntpquery pool.ntp.org`.
+    const char* host = nullptr;
+
+    Core::ArgsParser args_parser;
+    args_parser.add_positional_argument(host, "NTP server", "host", Core::ArgsParser::Required::Yes);
+    args_parser.parse(argc, argv);
+
+    auto* hostent = gethostbyname(host);
+    if (!hostent) {
+        fprintf(stderr, "Lookup failed for '%s'\n", host);
+        return 1;
+    }
+
+    if (pledge("stdio inet", nullptr) < 0) {
+        perror("pledge");
+        return 1;
+    }
+    unveil(nullptr, nullptr);
+
+    int fd = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);
+    if (fd < 0) {
+        perror("socket");
+        return 1;
+    }
+
+    struct timeval timeout {
+        5, 0
+    };
+    if (setsockopt(fd, SOL_SOCKET, SO_RCVTIMEO, &timeout, sizeof(timeout)) < 0) {
+        perror("setsockopt");
+        return 1;
+    }
+
+    sockaddr_in peer_address;
+    memset(&peer_address, 0, sizeof(peer_address));
+    peer_address.sin_family = AF_INET;
+    peer_address.sin_port = htons(123);
+    peer_address.sin_addr.s_addr = *(const in_addr_t*)hostent->h_addr_list[0];
+
+    NtpPacket packet;
+    memset(&packet, 0, sizeof(packet));
+    packet.li_vn_mode = (4 << 3) | 3; // Version 4, client connection.
+
+    // The server will copy the transmit_timestamp to origin_timestamp in the reply.
+    timeval t;
+    gettimeofday(&t, nullptr);
+    packet.transmit_timestamp = htobe64(ntp_timestamp_from_timeval(t));
+
+    ssize_t rc;
+    rc = sendto(fd, &packet, sizeof(packet), 0, (const struct sockaddr*)&peer_address, sizeof(peer_address));
+    if (rc < 0) {
+        perror("sendto");
+        return 1;
+    }
+    if ((size_t)rc < sizeof(packet)) {
+        fprintf(stderr, "incomplete packet send\n");
+        return 1;
+    }
+
+    socklen_t peer_address_size = sizeof(peer_address);
+    rc = recvfrom(fd, &packet, sizeof(packet), 0, (struct sockaddr*)&peer_address, &peer_address_size);
+    if (rc < 0) {
+        perror("recvfrom");
+        return 1;
+    }
+    if ((size_t)rc < sizeof(packet)) {
+        fprintf(stderr, "incomplete packet recv\n");
+        return 1;
+    }
+
+    printf("NTP response from %s:\n", inet_ntoa(peer_address.sin_addr));
+    printf("Leap Information: %d\n", packet.li_vn_mode >> 6);
+    printf("Version Number: %d\n", (packet.li_vn_mode >> 3) & 7);
+    printf("Mode: %d\n", packet.li_vn_mode & 7);
+    printf("Stratum: %d\n", packet.stratum);
+    printf("Poll: %d\n", packet.stratum);
+    printf("Precision: %d\n", packet.precision);
+    printf("Root delay: %#x\n", ntohl(packet.root_delay));
+    printf("Root dispersion: %#x\n", ntohl(packet.root_dispersion));
+    printf("Reference ID: %#x\n", ntohl(packet.reference_id));
+    printf("Reference timestamp: %#016llx\n", be64toh(packet.reference_timestamp));
+    printf("Origin timestamp:    %#016llx\n", be64toh(packet.origin_timestamp));
+    printf("Receive timestamp:   %#016llx\n", be64toh(packet.receive_timestamp));
+    printf("Transmit timestamp:  %#016llx\n", be64toh(packet.transmit_timestamp));
+}