Add NTP and DHCP L7 dissectors

NTP decodes the fixed header's version/mode/stratum - the timestamp
fields need NTP era/fraction fixed-point math to render meaningfully
and add nothing a one-line summary needs, so they're left alone.

DHCP decodes RFC 2131's BOOTP fixed header + magic cookie, then walks
the TLV options bounds-safely for option 53 (message type), plus
yiaddr when the server has assigned one. It's the first dissector
needing two well-known ports (67 server, 68 client) rather than one;
registering at just 67 still matches both directions since
l7_summarize() already falls back from dst_port to src_port.

Verified live: NTP against a real pool.ntp.org query on wlp1s0 (a
genuine stratum-2 reply came back). DHCP over loopback with a
synthetic-but-wire-format-real DISCOVER/OFFER exchange rather than a
real lease renewal, to avoid disrupting this machine's actual network
state - caught a test-setup mistake in the process (both packets
sent from the same ephemeral port instead of the OFFER actually
originating from port 67), not a dissector bug.

1 files changed, 64 insertions, 0 deletions

diff --git a/tests/test_ntp.cpp b/tests/test_ntp.cpp
new file mode 100644
index 0000000..2c93302
--- /dev/null
+++ b/tests/test_ntp.cpp
@@ -0,0 +1,64 @@
+#include <doctest/doctest.h>
+
+#include <vector>
+
+#include "packeteer/l7/ntp.hpp"
+
+using namespace packeteer::net;
+
+namespace {
+
+std::vector<unsigned char> ntp_client_request() {
+    std::vector<unsigned char> bytes(48, 0);
+    bytes[0] = (4 << 3) | 3;  // version 4, mode 3 (client)
+    bytes[1] = 0;             // stratum: not applicable on a client request
+    return bytes;
+}
+
+std::vector<unsigned char> ntp_server_reply() {
+    std::vector<unsigned char> bytes(48, 0);
+    bytes[0] = (4 << 3) | 4;  // version 4, mode 4 (server)
+    bytes[1] = 2;             // stratum 2
+    return bytes;
+}
+
+}  // namespace
+
+TEST_CASE("parse_ntp decodes a client request") {
+    auto ntp = parse_ntp(ntp_client_request());
+    REQUIRE(ntp.has_value());
+    CHECK(ntp->version == 4);
+    CHECK(ntp->mode == 3);
+}
+
+TEST_CASE("parse_ntp decodes a server reply with its stratum") {
+    auto ntp = parse_ntp(ntp_server_reply());
+    REQUIRE(ntp.has_value());
+    CHECK(ntp->mode == 4);
+    CHECK(ntp->stratum == 2);
+}
+
+TEST_CASE("parse_ntp rejects a payload shorter than the fixed header") {
+    std::vector<unsigned char> bytes(20, 0);
+    CHECK_FALSE(parse_ntp(bytes).has_value());
+}
+
+TEST_CASE("NtpDissector claims port 123 and includes stratum for client/server modes") {
+    NtpDissector dissector;
+    CHECK(dissector.port() == kNtpPort);
+
+    auto summary = dissector.summarize(ntp_server_reply());
+    REQUIRE(summary.has_value());
+    CHECK(*summary == "NTP v4 server stratum=2");
+}
+
+TEST_CASE("NtpDissector omits stratum for non-client/server modes") {
+    NtpDissector dissector;
+    std::vector<unsigned char> bytes(48, 0);
+    bytes[0] = (4 << 3) | 5;  // mode 5: broadcast
+    bytes[1] = 1;
+
+    auto summary = dissector.summarize(bytes);
+    REQUIRE(summary.has_value());
+    CHECK(summary->find("stratum") == std::string::npos);
+}