BulkPrintingAPI/MAXClient/Client.cs

using ExtensionMethods;
using MAX.Models;
using Microsoft.Extensions.Logging;
using System;
using System.Net.Sockets;
using System.Security.Cryptography;
using System.Text;
using System.Threading;
using System.Threading.Tasks;
using System.Xml;

namespace MAX
{
    public class Client : IDisposable
    {
        private ILogger _logger;
        private string _host;
        private int _port;
        private int _vendorId;
        private string _serialNumber;
        private int _userId;
        private string _username;
        private string _password;
        private bool _logResponses;

        private TcpClient _connection = null;
        private NetworkStream _connectionStream = null;
        private TripleDES _des = null;

        private bool _disposed = false;

        public Client(ILogger logger, bool logResponses, string host, int port, int vendorId, string serialNumber, int userId, string username, string password)
        {
            _logger = logger;
            _host = host;
            _port = port;
            _vendorId = vendorId;
            _serialNumber = serialNumber;
            _userId = userId;
            _username = username;
            _password = password;
            _logResponses = logResponses;

            ConnectTimeout = 10000;
            ReceiveTimeout = 10000;
            SendTimeout = 10000;
        }

        public Client(ILogger logger, bool logResponses, string host, int port, LoginCredentials credentials)
            : this(logger, logResponses, host, port, credentials.Vendor.Id, credentials.Vendor.SerialNumber,
                  credentials.User.Id, credentials.User.Username, credentials.Password)
        {
        }

        public void Close()
        {
            Dispose(true);
        }

        public async Task<User> ConnectAsync()
        {
            if (_connection != null)
                throw new Exception("Already connected");

            _connection = new TcpClient(AddressFamily.InterNetwork);
            _connection.ReceiveTimeout = ReceiveTimeout;
            _connection.SendTimeout = SendTimeout;

            // Connect to the server
            try
            {
                using (var cancellationSource = new CancellationTokenSource(ConnectTimeout))
                {
                    await _connection.ConnectAsync(_host, _port).WithCancellation(cancellationSource.Token).ConfigureAwait(false);
                }
            }
            catch (OperationCanceledException)
            {
                throw new Exception("Connect timeout");
            }
            _connectionStream = _connection.GetStream();

            // Device authentication
            await WriteMessageAsync(new MessageBuilder()
                .Append("Hi ")
                .Append(_serialNumber)
                .Append("|V")
                .Append(_vendorId)
                .Append("|123451234512345||||||")).ConfigureAwait(false);

            var response = ExpectResponse(await ReadMessageAsync().ConfigureAwait(false), "Hi");

            // Request server RSA key
            //
            // WARNING:
            //
            // The protocol does not do any form of server authentication so this step is
            // trivially vulnerable to a man-in-the-middle attack where an intermediary 
            // intercepts this request and sends their own RSA key while keeping the server RSA
            // key to themselves.
            await WriteMessageAsync(new MessageBuilder().Append("PK")).ConfigureAwait(false);
            response = await ReadMessageAsync().ConfigureAwait(false);

            // Key exchange
            _des = TripleDES.Create();
            _des.IV = new byte[8];
            await WriteMessageAsync(new MessageBuilder()
                .Append("3D ")
                .Append(EncryptRSA(response, BitConverter.ToString(_des.Key).Replace("-", "")))).ConfigureAwait(false);

            response = ExpectResponse(await ReadMessageAsync().ConfigureAwait(false), "OK");

            // User authentication
            await WriteMessageAsync(new MessageBuilder()
                .Append("User ")
                .Append(Encrypt(new StringBuilder()
                    .Append(_userId)
                    .Append("|")
                    .Append(_username)
                    .Append("|")
                    .Append(_password).ToString()))).ConfigureAwait(false);

            response = ExpectResponse(Decrypt(await ReadMessageAsync().ConfigureAwait(false)), "OK");

            var parts = response.Split('|');
            var user = new User()
            {
                Id = _userId,
                Username = _username,
                FirstName = parts[4],
                Surname = parts[3],
                Enabled = ParseBool(parts[6], "User.Enabled(6)", response),
                Level = (User.UserLevel)ParseInt(parts[1], "User.Level(1)", response),
                System = ParseInt(parts[2], "User.System(2)", response),
                LastLogin = ParseDateTime(parts[5], "User.LastLogin(5)", response)
            };

            if (user.Level == User.UserLevel.CustomUser)
            {
                user.CanPrintOffline = ParseBool(parts[7], "User.CanPrintOffline(7)", response);
                user.OfflinePrintValue = ParseDecimal(parts[8], "User.OfflinePrintValue(8)", response);
                user.CanPrintOnline = ParseBool(parts[9], "User.CanPrintOnline(9)", response);
                user.OnlinePrintValue = ParseDecimal(parts[10], "User.OnlinePrintValue(10)", response);
                user.CanReprintOffline = ParseBool(parts[11], "User.CanReprintOffline(11)", response);
                user.OfflineReprintValue = ParseDecimal(parts[12], "User.OfflineReprintValue(12)", response);
                user.CanReprintOnline = ParseBool(parts[13], "User.CanReprintOnline(13)", response);
                user.OnlineReprintValue = ParseDecimal(parts[14], "User.OnlineReprintValue(14)", response);
                user.BulkExport = ParseBool(parts[15], "User.BulkExport(15)", response);
                user.BulkExportMaxValue = ParseDecimal(parts[16], "User.BulkExportMaxValue(16)", response);
                user.BulkOrder = ParseBool(parts[17], "User.BulkOrder(17)", response);
                user.BulkOrderMaxValue = ParseDecimal(parts[18], "User.BulkOrderMaxValue(18)", response);
                user.BulkViewPins = ParseBool(parts[19], "User.BulkViewPins(19)", response);
                user.BulkReExport = ParseBool(parts[20], "User.BulkReExport(20)", response);
            }

            return user;
        }

        public int ConnectTimeout { get; set; }

        protected virtual void Dispose(bool disposing)
        {
            if (_disposed)
                return;

            _disposed = true;

            // No unmanaged resources are disposed so we don't need the full finalisation pattern.
            if (disposing)
            {
                if (_des != null)
                {
                    _des.Dispose();
                    _des = null;
                }
                if (_connectionStream != null)
                {
                    _connectionStream.Dispose();
                    _connectionStream = null;
                }
                if (_connection != null)
                {
                    _connection.Dispose();
                    _connection = null;
                }
            }
        }

        public void Dispose()
        {
            Dispose(true);
        }

        private string Decrypt(string cipherText)
        {
            var response = Utils.TripleDESDecrypt(cipherText, _des);
            if (_logResponses)
            {
                _logger.LogDebug("Decrypted response for {0}: {1}", LoginCredentials.Format(_userId, _username, _vendorId, _serialNumber), response);
            }
            return response;
        }

        private string Encrypt(string plainText)
        {
            return Utils.TripleDESEncrypt(plainText, _des);
        }

        private string EncryptRSA(string publicKey, string plainText)
        {
            RSAParameters parameters = new RSAParameters();

            var xml = new XmlDocument();
            xml.LoadXml(publicKey);
            if (! xml.DocumentElement.Name.Equals("RSAKeyValue"))
                throw new Exception("Invalid RSA key");

            foreach (XmlNode node in xml.DocumentElement.ChildNodes)
            {
                switch (node.Name)
                {
                    case "Modulus": parameters.Modulus = Convert.FromBase64String(node.InnerText); break;
                    case "Exponent": parameters.Exponent = Convert.FromBase64String(node.InnerText); break;
                    case "P": parameters.P = Convert.FromBase64String(node.InnerText); break;
                    case "Q": parameters.Q = Convert.FromBase64String(node.InnerText); break;
                    case "DP": parameters.DP = Convert.FromBase64String(node.InnerText); break;
                    case "DQ": parameters.DQ = Convert.FromBase64String(node.InnerText); break;
                    case "InverseQ": parameters.InverseQ = Convert.FromBase64String(node.InnerText); break;
                    case "D": parameters.D = Convert.FromBase64String(node.InnerText); break;
                }
            }

            using (var rsa = RSA.Create())
            {
                rsa.ImportParameters(parameters);
                var blockSize = rsa.KeySize / 8 - 42;
                var offset = 0;
                var input = Encoding.UTF32.GetBytes(plainText);
                StringBuilder output = new StringBuilder();
                while (offset < input.Length)
                {
                    var length = input.Length - offset;
                    if (length > blockSize)
                        length = blockSize;
                    var block = new byte[length];
                    Array.Copy(input, offset, block, 0, length);
                    var cipherText = rsa.Encrypt(block, RSAEncryptionPadding.OaepSHA1);
                    Array.Reverse(cipherText);
                    output.Append(Convert.ToBase64String(cipherText));
                    offset += length;
                }
                return output.ToString();
            }
        }

        public async Task<Account> GetAccountAsync()
        {
            await WriteMessageAsync(new MessageBuilder().Append("Acc")).ConfigureAwait(false);
            var response = ExpectResponse(Decrypt(await ReadMessageAsync().ConfigureAwait(false)), "OK");
            var parts = response.Split('|');
            return new Account()
            {
                Id = ParseInt(parts[1], "Account.Id(1)", response),
                Name = parts[2],
                Balance = ParseDecimal(parts[3], "Account.Balance(3)", response),
                Status = (Account.AccountStatus)ParseInt(parts[4], "Account.AccountStatus(4)", response),
                Reference = parts[5],
                Warehouse = new Warehouse()
                {
                    Id = ParseInt(parts[6], "Account.Warehouse.Id(6)", response),
                    Name = parts[7]
                }
            };
        }

        public async Task<ProductCatalogue> GetProductCatalogueAsync(Account account)
        {
            var encryptedWarehouseName = Encrypt(account.Warehouse.Name);
            await WriteMessageAsync(new MessageBuilder()
                .Append("Pdt ")
                .Append(encryptedWarehouseName)).ConfigureAwait(false);
            var response = ExpectResponse(Decrypt(await ReadMessageAsync().ConfigureAwait(false)), "OK");

            var parts = response.Split('|');
            var count = ParseInt(parts[1], "Products.Count(1)", response);

            var catalogue = new ProductCatalogue();
            
            var listCommand = new MessageBuilder().Append("List ")
                .Append(encryptedWarehouseName).GetBytes();
            for (var i = 0; i < count; i++)
            {
                await _connectionStream.WriteAsync(listCommand, 0, listCommand.Length).ConfigureAwait(false);
                response = ExpectResponse(Decrypt(await ReadMessageAsync().ConfigureAwait(false)), "OK");

                parts = response.Split('|');
                int networkId = ParseInt(parts[4], "Product.NetworkId(4)", response);
                Network network;
                if (! catalogue.NetworkMap.TryGetValue(networkId, out network))
                {
                    network = catalogue.AddNetwork(networkId, parts[5]);
                }

                catalogue.AddProduct(
                    network: network,
                    id: ParseInt(parts[1], "Product.Id(1)", response),
                    faceValue: ParseDecimal(parts[2], "Product.FaceValue(2)", response),
                    description: parts[3],
                    voucherType: (Batch.Vouchertype)ParseInt(parts[6], "Product.VoucherType(6)", response),
                    discountPercentage: ParseDecimal(parts[7], "Product.DiscountPercentage(7)", response)
                );
            }

            return catalogue;
        }

        private void ThrowParseError(string value, string valueName, string valueType, string fullResponse)
        {
            _logger.LogError(
                "Failed to parse value: valueType={0} valueName={1} value={2} fullResponse={3} {4}",
                valueType,
                valueName,
                value,
                fullResponse,
                LoginCredentials.Format(_userId, _username, _vendorId, _serialNumber)
            );
            throw new Exception(String.Format("Invalid value for {0}", valueName));
        }

        private bool ParseBool(string value, string valueName, string fullResponse)
        {
            bool ret;
            if (! bool.TryParse(value, out ret))
            {
                ThrowParseError(value, valueName, "bool", fullResponse);
            }
            return ret;
        }

        private DateTime ParseDateTime(string value, string valueName, string fullResponse)
        {
            DateTime ret;
            if (!DateTime.TryParse(value, out ret))
            {
                ThrowParseError(value, valueName, "DateTime", fullResponse);
            }
            return ret;
        }

        private decimal ParseDecimal(string value, string valueName, string fullResponse)
        {
            decimal ret;
            if (!decimal.TryParse(value, out ret))
            {
                double fallback;
                if (!double.TryParse(value, out fallback))
                {
                    ThrowParseError(value, valueName, "decimal", fullResponse);
                }
                return (decimal)fallback;
            }
            return ret;
        }

        private int ParseInt(string value, string valueName, string fullResponse)
        {
            int ret;
            if (!int.TryParse(value, out ret))
            {
                ThrowParseError(value, valueName, "int", fullResponse);
            }
            return ret;
        }

        public async Task<OrderResponse> PlaceOrderAsync(int accountId, Product product, int quantity,
            string customerReference, string internalReference, Guid? orderGuid, byte[] key)
        {
            if (key.Length != 24)
            {
                throw new ArgumentException("24 byte key expected", nameof(key));
            }

            _logger.LogDebug(
                "Placing order for {0}: date={1} quantity={2} productId={3} productDescription={4} networkId={5} networkName={6} customerRef={7} internalRef={8}",
                LoginCredentials.Format(_userId, _username, _vendorId, _serialNumber),
                DateTimeOffset.UtcNow,
                quantity,
                product.Id,
                product.Description,
                product.Network.Id,
                product.Network.Name,
                customerReference,
                internalReference
            );

            await WriteMessageAsync(new MessageBuilder()
                .Append("Order ")
                .Append(Encrypt(new StringBuilder()
                    .Append(product.Id)
                    .Append("|")
                    .Append(quantity)
                    .Append("|")
                    .Append(customerReference)
                    .Append("|2|") // EncType: 0:None, 1:DES, 2:Triple DES
                    .Append(BitConverter.ToString(key, 0, 8).Replace("-", ""))
                    .Append("|")
                    .Append(BitConverter.ToString(key, 8, 8).Replace("-", ""))
                    .Append("|")
                    .Append(BitConverter.ToString(key, 16, 8).Replace("-", ""))
                    .Append("|")
                    .Append(internalReference)
                    .ToString()))).ConfigureAwait(false);

            var response = ExpectResponse(Decrypt(await ReadMessageAsync().ConfigureAwait(false)), "OK");

            _logger.LogDebug("Order response for {0} customerRef={1} internalRef={2}: {3}",
                LoginCredentials.Format(_userId, _username, _vendorId, _serialNumber),
                customerReference,
                internalReference,
                response
            );

            var parts = response.Split('|');
            return new OrderResponse()
            {
                Batch = new Batch()
                {
                    Id = ParseInt(parts[1], "Batch.Id(1)", response),
                    OrderReference = parts[2],
                    RequestedQuantity = ParseInt(parts[3], "Batch.RequestQuantity(3)", response),
                    DeliveredQuantity = ParseInt(parts[4], "Batch.DeliveredQuantity(4)", response),
                    Cost = ParseDecimal(parts[5], "Batch.Cost(5)", response),
                    InternalReference = internalReference,
                    OrderGuid = orderGuid,
                    AccountId = accountId,
                    VendorId = _vendorId,
                    ProductId = product.Id,
                    ProductDescription = product.Description,
                    VoucherType = product.VoucherType,
                    FaceValue = product.FaceValue,
                    DiscountPercentage = product.DiscountPercentage,
                    NetworkId = product.Network.Id,
                    NetworkName = product.Network.Name,
                    OrderDate = DateTimeOffset.UtcNow,
                    OrderedById = _userId,
                    ReadyForDownload = false
                },
                RemainingBalance = ParseDecimal(parts[6], "Batch.RemainingBalance(6)", response)
            };
        }

        private async Task<byte[]> ReadBytesAsync(int count)
        {
            int totalBytesRead = 0;
            byte[] buffer = new byte[count];
            while (totalBytesRead < count)
            {
                int bytesRead = await _connectionStream.ReadAsync(buffer, totalBytesRead, count - totalBytesRead).ConfigureAwait(false);
                if (bytesRead == 0)
                    throw new Exception("Connection closed unexpectedly");
                totalBytesRead += bytesRead;
            }
            return buffer;
        }

        private async Task<string> ReadMessageAsync()
        {
            byte[] buffer = await ReadBytesAsync(2).ConfigureAwait(false);
            int size = buffer[0] * 256 + buffer[1];
            if (size <= 0)
            {
                throw new Exception("Invalid message size");
            }
            var response = Encoding.ASCII.GetString(await ReadBytesAsync(size).ConfigureAwait(false));
            if (_logResponses)
            {
                _logger.LogDebug("Response for {0}: {1}", LoginCredentials.Format(_userId, _username, _vendorId, _serialNumber), response);
            }
            return response;
        }

        public int ReceiveTimeout { get; set; }

        public int SendTimeout { get; set; }

        private string ExpectResponse(string response, string prefix)
        {
            if (response.StartsWith("ER"))
            {
                var parts = response.Split('|');
                int errorCode;
                if ((parts.Length < 2) || ! int.TryParse(parts[1], out errorCode))
                {
                    errorCode = -1;
                }
                var message = parts.Length >= 3 ? parts[2] : String.Format("Malformed server error: {0}", response);
                _logger.LogError("MAX Error for {0}: {1} (code {2})",
                    LoginCredentials.Format(_userId, _username, _vendorId, _serialNumber), message, errorCode);
                throw new MAXException(errorCode, message);
            }
            else if (! response.StartsWith(prefix))
            {
                _logger.LogError("Invalid MAX response for {0}: {1}",
                    LoginCredentials.Format(_userId, _username, _vendorId, _serialNumber),
                    response);
                throw new Exception(String.Format("Invalid server response: {0}", response));
            }
            return response;
        }

        private async Task WriteMessageAsync(MessageBuilder message)
        {
            byte[] data = message.GetBytes();
            await _connectionStream.WriteAsync(data, 0, data.Length).ConfigureAwait(false);
        }
    }
}