CONNECT packet must have at least 7 bytes.

[andycheng-jiuluomall]

Describe your question

testapi.suzhoujiding.com host => localhost

PacketFormatterAdapter.TryDecode

if (formatter.ProtocolVersion == MqttProtocolVersion.Unknown)
{
formatter.DetectProtocolVersion(receivedMqttPacket);
}

public void DetectProtocolVersion(ReceivedMqttPacket receivedMqttPacket)
{
var protocolVersion = ParseProtocolVersion(receivedMqttPacket);
UseProtocolVersion(protocolVersion);
}

[andycheng-jiuluomall]

when i use 'mqtt'

[andycheng-jiuluomall]

when i use mqtts
in "ReceiveConnectPacket"
zhe buffer info is "Tls Client Hello"

then i use the next code to read the buffer

namespace MQTTS_Packet_Analyzer
{
    class Program
    {
        static void Main(string[] args)
        {
            // Your MQTTS packet body (hexadecimal string)
            string hexData1 = "16 03 01 00 E1 01 00 00 DD 03 03 D1 64 DE A7 23 D5 A2 12 12 B9 C1 40 1F 61 95 35 88 A2 48 27 26 17 11 27 E3 EB A5 CA 2B B8 69 7F 20 1C 57 DC 30 28 8E 57 E8 8C 2E 06 E2 DE EA E7 D1 D9 D7 18 3A E3 A8 2A 7E 9E 43 9F 23 8A 93 32 46 00 24 13 01 13 02 13 03 C0 2F C0 2B C0 30 C0 2C C0 27 CC A9 CC A8 C0 09 C0 13 C0 0A C0 14 00 9C 00 9D 00 2F 00 35 01 00 00 70 00 17 00 00 FF 01 00 01 00 00 0A 00 08 00 06 00 1D 00 17 00 18 00 0B 00 02 01 00 00 23 00 00 00 0D 00 14 00 12 04 03 08 04 04 01 05 03 08 05 05 01 08 06 06 01 02 01 00 33 00 26 00 24 00 1D 00 20 13 90 A0 CA 41 3F 0A D3 C4 91 8A 3A 6E 85 19 6A 9C D8 6F 05 4A 3E 88 67 89 C3 05 DE F5 B3 08 73 00 2D 00 02 01 01 00 2B 00 05 04 03 04 03 03";

            string hexData2 = "16 03 01 02 00 01 00 01 FC 03 03 52 D1 56 B5 BE 0D 72 1B B0 9B 44 9A 01 0E 92 42 57 F3 00 E5 0A A6 6E 6E E0 75 D7 69 26 70 A8 02 20 A0 5D 2C 8C FD 8C 7C 5F FC 00 67 8D 88 6A 32 01 05 59 C9 7A 48 B2 09 92 E0 58 87 22 BD 4C 80 55 00 24 13 01 13 02 13 03 C0 2F C0 2B C0 30 C0 2C C0 27 CC A9 CC A8 C0 09 C0 13 C0 0A C0 14 00 9C 00 9D 00 2F 00 35 01 00 01 8F 00 00 00 1D 00 1B 00 00 18 74 65 73 74 61 70 69 2E 73 75 7A 68 6F 75 6A 69 64 69 6E 67 2E 63 6F 6D 00 17 00 00 FF 01 00 01 00 00 0A 00 08 00 06 00 1D 00 17 00 18 00 0B 00 02 01 00 00 23 00 00 00 0D 00 14 00 12 04 03 08 04 04 01 05 03 08 05 05 01 08 06 06 01 02 01 00 33 00 26 00 24 00 1D 00 20 87 BA E1 AE 28 77 3B 9C A7 A6 71 4E 29 3E 1F 39 CF DF 58 01 27 39 F0 77 9D 12 2A 19 0F 3F E8 43 00 2D 00 02 01 01 00 2B 00 05 04 03 04 03 03 00 15 00 FA 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00";

            // Parse TLS Client Hello packet
            var parser = new TlsClientHelloParser(HexStringToByteArray(hexData1.Replace(" ", "")));
            parser.Parse();

            // Output parsing results
            parser.PrintResult();
            parser = new TlsClientHelloParser(HexStringToByteArray(hexData2.Replace(" ", "")));
            parser.Parse();
            parser.PrintResult();
        }

        /// <summary>
        /// Convert hexadecimal string to byte array
        /// </summary>
        public static byte[] HexStringToByteArray(string hex)
        {
            int length = hex.Length;
            byte[] bytes = new byte[length / 2];
            for (int i = 0; i < length; i += 2)
            {
                bytes[i / 2] = Convert.ToByte(hex.Substring(i, 2), 16);
            }
            return bytes;
        }
    }

    /// <summary>
    /// TLS Client Hello packet parser
    /// </summary>
    public class TlsClientHelloParser
    {
        private byte[] _data;
        private int _offset; // Parsing offset
        private Dictionary<string, string> _result = new Dictionary<string, string>();

        // Cipher suite mapping (common ones)
        private readonly Dictionary<ushort, string> _cipherSuites = new Dictionary<ushort, string>
        {
            { 0x1301, "TLS_AES_128_GCM_SHA256" },
            { 0x1302, "TLS_AES_256_GCM_SHA384" },
            { 0x1303, "TLS_CHACHA20_POLY1305_SHA256" },
            { 0xC02F, "TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384" },
            { 0xC02B, "TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256" },
            { 0xC030, "TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384" },
            { 0xC02C, "TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256" },
            { 0x009C, "TLS_RSA_WITH_AES_128_GCM_SHA256" },
            { 0x009D, "TLS_RSA_WITH_AES_256_GCM_SHA384" },
            { 0x002F, "TLS_RSA_WITH_AES_128_CBC_SHA" },
            { 0x0035, "TLS_RSA_WITH_AES_256_CBC_SHA" }
        };

        public TlsClientHelloParser(byte[] data)
        {
            _data = data;
            _offset = 0;
        }

        /// <summary>
        /// Parse the entire Client Hello packet
        /// </summary>
        public void Parse()
        {
            // 1. Parse TLS Record Layer Header (5 bytes)
            ParseRecordLayerHeader();

            // 2. Parse Handshake Protocol Header
            ParseHandshakeHeader();

            // 3. Parse Client Hello core content
            ParseClientHello();
        }

        /// <summary>
        /// Parse TLS Record Layer Header
        /// Format: Content Type(1) + Version(2) + Length(2)
        /// </summary>
        private void ParseRecordLayerHeader()
        {
            // Content Type
            byte contentType = _data[_offset++];
            _result["Content Type"] = contentType switch
            {
                0x16 => "Handshake",
                0x17 => "Application Data",
                0x18 => "Change Cipher Spec",
                _ => $"Unknown (0x{contentType:X2})"
            };

            // TLS Version (Major + Minor)
            byte verMajor = _data[_offset++];
            byte verMinor = _data[_offset++];
            _result["TLS Record Layer Version"] = $"TLS {verMajor}.{verMinor} (0x{verMajor:X2}{verMinor:X2})";

            // Record Layer Length (Big-endian)
            ushort recordLength = (ushort)((_data[_offset++] << 8) | _data[_offset++]);
            _result["Record Layer Data Length"] = $"{recordLength} bytes";
        }

        /// <summary>
        /// Parse Handshake Protocol Header
        /// Format: Handshake Type(1) + Length(3)
        /// </summary>
        private void ParseHandshakeHeader()
        {
            // Handshake Type
            byte handshakeType = _data[_offset++];
            _result["Handshake Type"] = handshakeType switch
            {
                0x01 => "Client Hello",
                0x02 => "Server Hello",
                _ => $"Unknown (0x{handshakeType:X2})"
            };

            // Handshake Message Length (3 bytes big-endian)
            int handshakeLength = (_data[_offset++] << 16) | (_data[_offset++] << 8) | _data[_offset++];
            _result["Handshake Message Length"] = $"{handshakeLength} bytes";
        }

        /// <summary>
        /// Parse Client Hello core fields
        /// </summary>
        private void ParseClientHello()
        {
            // 1. Client Hello Version (2 bytes)
            byte chVerMajor = _data[_offset++];
            byte chVerMinor = _data[_offset++];
            _result["Client Hello Version"] = $"TLS {chVerMajor}.{chVerMinor} (0x{chVerMajor:X2}{chVerMinor:X2})";

            // 2. Random Number (32 bytes)
            byte[] random = new byte[32];
            Array.Copy(_data, _offset, random, 0, 32);
            _offset += 32;
            _result["Random Number (Random)"] = BitConverter.ToString(random).Replace("-", " ");

            // 3. Session ID Length + Session ID
            byte sessionIdLen = _data[_offset++];
            byte[] sessionId = new byte[sessionIdLen];
            if (sessionIdLen > 0)
            {
                Array.Copy(_data, _offset, sessionId, 0, sessionIdLen);
                _offset += sessionIdLen;
                _result["Session ID"] = BitConverter.ToString(sessionId).Replace("-", " ");
            }
            else
            {
                _result["Session ID"] = "Empty";
            }

            // 4. Cipher Suites Length + Cipher Suites List
            ushort cipherSuitesLen = (ushort)((_data[_offset++] << 8) | _data[_offset++]);
            int cipherSuiteCount = cipherSuitesLen / 2;
            List<string> cipherSuiteList = new List<string>();

            for (int i = 0; i < cipherSuiteCount; i++)
            {
                ushort suiteCode = (ushort)((_data[_offset++] << 8) | _data[_offset++]);
                string suiteName = _cipherSuites.ContainsKey(suiteCode)
                    ? _cipherSuites[suiteCode]
                    : $"Unknown (0x{suiteCode:X4})";
                cipherSuiteList.Add($"{suiteName} (0x{suiteCode:X4})");
            }
            _result["Number of Cipher Suites"] = cipherSuiteCount.ToString();
            _result["Cipher Suites List"] = string.Join(", ", cipherSuiteList);

            // 5. Compression Methods Length + Compression Method
            byte compressionMethodsLen = _data[_offset++];
            byte compressionMethod = _data[_offset++];
            _result["Compression Method"] = compressionMethod switch
            {
                0x00 => "No Compression",
                _ => $"Unknown (0x{compressionMethod:X2})"
            };

            // 6. Extensions Length + Parse SNI (Server Name Indication)
            ushort extensionsLen = (ushort)((_data[_offset++] << 8) | _data[_offset++]);
            int extensionsStart = _offset;

            while (_offset < extensionsStart + extensionsLen)
            {
                // Extension Type (2 bytes)
                ushort extType = (ushort)((_data[_offset++] << 8) | _data[_offset++]);
                // Extension Length (2 bytes)
                ushort extLen = (ushort)((_data[_offset++] << 8) | _data[_offset++]);

                if (extType == 0x0000) // SNI Extension Type
                {
                    ParseSNIExtension(extLen);
                    break; // Exit after finding SNI, continue if need to parse other extensions
                }
                else
                {
                    _offset += extLen; // Skip other extensions
                }
            }
        }

        /// <summary>
        /// Parse SNI (Server Name Indication) Extension
        /// </summary>
        private void ParseSNIExtension(int extLen)
        {
            int sniStart = _offset;
            // SNI List Length (2 bytes)
            ushort sniListLen = (ushort)((_data[_offset++] << 8) | _data[_offset++]);

            while (_offset < sniStart + extLen)
            {
                // Name Type (1 byte)
                byte nameType = _data[_offset++];
                // Name Length (2 bytes)
                ushort nameLen = (ushort)((_data[_offset++] << 8) | _data[_offset++]);
                // Name Content
                byte[] nameBytes = new byte[nameLen];
                Array.Copy(_data, _offset, nameBytes, 0, nameLen);
                _offset += nameLen;

                if (nameType == 0x00) // Hostname Type
				{
					string serverName = Encoding.ASCII.GetString(nameBytes);
					_result["Server Name (SNI)"] = serverName;
				}
			}
		}

		/// <summary>
		/// Print parsing results
		/// </summary>
		public void PrintResult()
		{
			Console.WriteLine("=== MQTTS (TLS Client Hello) Packet Parsing Results ===");
			foreach (var kv in _result)
			{
				Console.WriteLine($"{kv.Key}: {kv.Value}");
			}
			Console.WriteLine("======================================================");
		}
	}
}

the result is next

=== MQTTS (TLS Client Hello) Packet Parsing Results ===
Content Type: Handshake
TLS Record Layer Version: TLS 3.1 (0x0301)
Record Layer Data Length: 512 bytes
Handshake Type: Client Hello
Handshake Message Length: 508 bytes
Client Hello Version: TLS 3.3 (0x0303)
Random Number (Random): 52 D1 56 B5 BE 0D 72 1B B0 9B 44 9A 01 0E 92 42 57 F3 00 E5 0A A6 6E 6E E0 75 D7 69 26 70 A8 02
Session ID: A0 5D 2C 8C FD 8C 7C 5F FC 00 67 8D 88 6A 32 01 05 59 C9 7A 48 B2 09 92 E0 58 87 22 BD 4C 80 55
Number of Cipher Suites: 18
Cipher Suites List: TLS_AES_128_GCM_SHA256 (0x1301), TLS_AES_256_GCM_SHA384 (0x1302), TLS_CHACHA20_POLY1305_SHA256 (0x1303), TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (0xC02F), TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256 (0xC02B), TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384 (0xC030), TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256 (0xC02C), Unknown (0xC027) (0xC027), Unknown (0xCCA9) (0xCCA9), Unknown (0xCCA8) (0xCCA8), Unknown (0xC009) (0xC009), Unknown (0xC013) (0xC013), Unknown (0xC00A) (0xC00A), Unknown (0xC014) (0xC014), TLS_RSA_WITH_AES_128_GCM_SHA256 (0x009C), TLS_RSA_WITH_AES_256_GCM_SHA384 (0x009D), TLS_RSA_WITH_AES_128_CBC_SHA (0x002F), TLS_RSA_WITH_AES_256_CBC_SHA (0x0035)
Compression Method: No Compression
Server Name (SNI): testapi.suzhoujiding.com
======================================================

So I wonder if the parsing of the TLS packet header is not considered in the MQTTnet code.
or i miss some important config setting also like "CA" and the other