Add deeper TLS (ServerHello, ALPN); fix a QUIC/TCP false-positive bug

TLS: ServerHello now reports the negotiated version and cipher suite
alongside the existing ClientHello SNI support, plus ClientHello's
ALPN extension. ServerHello's version prefers the supported_versions
extension over legacy_version when present - TLS 1.3 always sets
legacy_version to 0x0303 for middlebox compatibility, so reading only
that field would misreport every real TLS 1.3 connection as 1.2.
Cipher suite names are hardcoded only for TLS 1.3's five suites (a
small closed set); everything else reports as raw hex rather than a
guessed name from a "common suites" list.

Live-verifying that against a real Cloudflare TLS 1.3 handshake
surfaced a real, unrelated bug in the QUIC dissector added earlier: it was also being tried against TCP port-443 payloads
(a side effect of the earlier L7Registry port-sharing fix), and
produced false "QUIC" labels on TLS ciphertext continuation fragments
- large encrypted records split across multiple TCP segments, each
fed to the parser independently since this project doesn't reassemble
by default, so a later fragment's effectively random bytes
occasionally passed as a plausible QUIC header.

Fixed in two layers: parse_quic() now enforces RFC 9000's real 20-byte
cap on connection ID lengths, closing most of the long-header false-
positive surface; and L7Dissector gained a transport() method
(defaulting to kAny, so every other dissector's behavior is unchanged)
so QuicDissector can declare itself UDP-only - necessary because the
length cap alone can't touch QUIC's short-header form, which by design
has no structural signal beyond one bit once header protection can't
be removed without connection state.

Re-verified against the identical live scenario afterward: zero false
QUIC labels on the same Cloudflare TCP handshake, and a repeat of the
earlier real HTTP/3 capture confirmed genuine QUIC still decodes
correctly on UDP.

1 files changed, 114 insertions, 1 deletions

diff --git a/tests/test_tls.cpp b/tests/test_tls.cpp
index 7a3ad27..bdb5300 100644
--- a/tests/test_tls.cpp
+++ b/tests/test_tls.cpp
@@ -22,7 +22,8 @@ void append_be16(std::vector<unsigned char>& out, std::uint16_t v) {
 // length instead of the real one (computed here, not via post-hoc
 // offset math into the finished buffer - equally fragile).
 std::vector<unsigned char> build_client_hello(const std::string& sni,
-                                               bool corrupt_sni_ext_len = false) {
+                                               bool corrupt_sni_ext_len = false,
+                                               std::vector<std::string> alpn_protocols = {}) {
     std::vector<unsigned char> body;
     body.push_back(0x03);
     body.push_back(0x03);                       // client_version: TLS 1.2
@@ -52,6 +53,20 @@ std::vector<unsigned char> build_client_hello(const std::string& sni,
         append_be16(extensions, ext_len);
         extensions.insert(extensions.end(), sni_ext_data.begin(), sni_ext_data.end());
     }
+    if (!alpn_protocols.empty()) {
+        std::vector<unsigned char> protocol_list;
+        for (const auto& proto : alpn_protocols) {
+            protocol_list.push_back(static_cast<unsigned char>(proto.size()));
+            protocol_list.insert(protocol_list.end(), proto.begin(), proto.end());
+        }
+        std::vector<unsigned char> alpn_ext_data;
+        append_be16(alpn_ext_data, static_cast<std::uint16_t>(protocol_list.size()));
+        alpn_ext_data.insert(alpn_ext_data.end(), protocol_list.begin(), protocol_list.end());
+
+        append_be16(extensions, kTlsExtensionAlpn);
+        append_be16(extensions, static_cast<std::uint16_t>(alpn_ext_data.size()));
+        extensions.insert(extensions.end(), alpn_ext_data.begin(), alpn_ext_data.end());
+    }
     append_be16(body, static_cast<std::uint16_t>(extensions.size()));
     body.insert(body.end(), extensions.begin(), extensions.end());
 
@@ -73,6 +88,47 @@ std::vector<unsigned char> build_client_hello(const std::string& sni,
     return record;
 }
 
+// Builds a real, well-formed TLS record containing a ServerHello.
+// `negotiated_version`, when set, adds a supported_versions extension
+// carrying that single 2-byte version - how a TLS 1.3 ServerHello
+// actually signals its real version, since legacy_version is always
+// 0x0303 there for middlebox compatibility.
+std::vector<unsigned char> build_server_hello(std::uint16_t cipher_suite,
+                                               std::optional<std::uint16_t> negotiated_version = {}) {
+    std::vector<unsigned char> body;
+    append_be16(body, 0x0303);            // legacy_version: always TLS 1.2 on the wire
+    body.insert(body.end(), 32, 0x00);    // random
+    body.push_back(0x00);                  // legacy_session_id_echo length: 0
+    append_be16(body, cipher_suite);
+    body.push_back(0x00);                  // legacy_compression_method: null
+
+    std::vector<unsigned char> extensions;
+    if (negotiated_version) {
+        append_be16(extensions, kTlsExtensionSupportedVersions);
+        append_be16(extensions, 2);
+        append_be16(extensions, *negotiated_version);
+    }
+    append_be16(body, static_cast<std::uint16_t>(extensions.size()));
+    body.insert(body.end(), extensions.begin(), extensions.end());
+
+    std::vector<unsigned char> handshake;
+    handshake.push_back(kTlsHandshakeTypeServerHello);
+    std::uint32_t hs_len = static_cast<std::uint32_t>(body.size());
+    handshake.push_back(static_cast<unsigned char>((hs_len >> 16) & 0xFF));
+    handshake.push_back(static_cast<unsigned char>((hs_len >> 8) & 0xFF));
+    handshake.push_back(static_cast<unsigned char>(hs_len & 0xFF));
+    handshake.insert(handshake.end(), body.begin(), body.end());
+
+    std::vector<unsigned char> record;
+    record.push_back(kTlsContentTypeHandshake);
+    record.push_back(0x03);
+    record.push_back(0x03);
+    append_be16(record, static_cast<std::uint16_t>(handshake.size()));
+    record.insert(record.end(), handshake.begin(), handshake.end());
+
+    return record;
+}
+
 }  // namespace
 
 TEST_CASE("parse_tls_client_hello extracts a real SNI extension") {
@@ -130,3 +186,60 @@ TEST_CASE("TlsSniDissector claims port 443 and its summary matches parse_tls_cli
     CHECK(summary->substr(0, 3) == "TLS");
     CHECK(summary->find("SNI=packeteer.test") != std::string::npos);
 }
+
+TEST_CASE("parse_tls_client_hello extracts ALPN protocols in order") {
+    auto record = build_client_hello("example.com", false, {"h2", "http/1.1"});
+    auto hello = parse_tls_client_hello(record);
+    REQUIRE(hello.has_value());
+    REQUIRE(hello->alpn_protocols.has_value());
+    REQUIRE(hello->alpn_protocols->size() == 2);
+    CHECK((*hello->alpn_protocols)[0] == "h2");
+    CHECK((*hello->alpn_protocols)[1] == "http/1.1");
+}
+
+TEST_CASE("parse_tls_client_hello leaves alpn_protocols unset when the extension is absent") {
+    auto record = build_client_hello("example.com");
+    auto hello = parse_tls_client_hello(record);
+    REQUIRE(hello.has_value());
+    CHECK_FALSE(hello->alpn_protocols.has_value());
+}
+
+TEST_CASE("parse_tls_server_hello extracts the negotiated cipher suite") {
+    auto record = build_server_hello(0x1301);  // TLS_AES_128_GCM_SHA256
+    auto hello = parse_tls_server_hello(record);
+    REQUIRE(hello.has_value());
+    CHECK(hello->cipher_suite == 0x1301);
+}
+
+TEST_CASE("parse_tls_server_hello uses legacy_version when there's no supported_versions extension") {
+    auto record = build_server_hello(0xC02F);  // a TLS 1.2-era cipher suite
+    auto hello = parse_tls_server_hello(record);
+    REQUIRE(hello.has_value());
+    CHECK(hello->negotiated_version == 0x0303);  // TLS 1.2
+}
+
+TEST_CASE("parse_tls_server_hello prefers supported_versions over legacy_version for TLS 1.3") {
+    auto record = build_server_hello(0x1301, std::uint16_t{0x0304});
+    auto hello = parse_tls_server_hello(record);
+    REQUIRE(hello.has_value());
+    CHECK(hello->negotiated_version == 0x0304);  // TLS 1.3, not the legacy 0x0303 on the wire
+}
+
+TEST_CASE("parse_tls_server_hello rejects a ClientHello handshake type") {
+    auto record = build_client_hello("example.com");
+    CHECK_FALSE(parse_tls_server_hello(record).has_value());
+}
+
+TEST_CASE("tls_cipher_suite_name names all five TLS 1.3 suites and falls back to hex otherwise") {
+    CHECK(tls_cipher_suite_name(0x1301) == "TLS_AES_128_GCM_SHA256");
+    CHECK(tls_cipher_suite_name(0x1305) == "TLS_AES_128_CCM_8_SHA256");
+    CHECK(tls_cipher_suite_name(0xC02F) == "0xc02f");
+}
+
+TEST_CASE("TlsSniDissector formats a ServerHello with version and cipher") {
+    TlsSniDissector dissector;
+    auto record = build_server_hello(0x1301, std::uint16_t{0x0304});
+    auto summary = dissector.summarize(record);
+    REQUIRE(summary.has_value());
+    CHECK(*summary == "TLS ServerHello version=TLS1.3 cipher=TLS_AES_128_GCM_SHA256");
+}