Implement pr #33796 CheckTransaction consensus validation function

src/BitcoinKernel.Core/Abstractions/Transaction.cs

@@ -1,6 +1,7 @@
 using System;
 using System.Runtime.InteropServices;
 using BitcoinKernel.Core.Exceptions;
+using BitcoinKernel.Core.TransactionValidation;
 using BitcoinKernel.Interop;
 
 namespace BitcoinKernel.Core.Abstractions;
@@ -158,6 +159,24 @@ public Transaction Copy()
         return new Transaction(copyHandle);
     }
 
+    /// <summary>
+    /// Validates this transaction against consensus rules.
+    /// </summary>
+    /// <returns>A TxValidationState containing the validation result.</returns>
+    public TxValidationState Validate()
+    {
+        return TransactionValidator.CheckTransaction(this);
+    }
+
+    /// <summary>
+    /// Checks if this transaction is valid according to consensus rules.
+    /// </summary>
+    /// <returns>True if the transaction is valid, false otherwise.</returns>
+    public bool IsValid()
+    {
+        return TransactionValidator.IsValid(this);
+    }
+
     internal IntPtr Handle => _handle;
 
     public void Dispose()

src/BitcoinKernel.Core/TransactionValidation/TransactionValidator.cs

@@ -0,0 +1,46 @@
+using BitcoinKernel.Core.Abstractions;
+using BitcoinKernel.Core.Exceptions;
+using BitcoinKernel.Interop;
+
+namespace BitcoinKernel.Core.TransactionValidation;
+
+/// <summary>
+/// Provides transaction validation functionality for consensus checks.
+/// </summary>
+public static class TransactionValidator
+{
+    /// <summary>
+    /// Checks if a transaction is valid according to consensus rules.
+    /// This is more efficient than CheckTransaction() when you only need a boolean result.
+    /// </summary>
+    /// <param name="transaction">The transaction to validate.</param>
+    /// <returns>True if the transaction is valid, false otherwise.</returns>
+    /// <exception cref="ArgumentNullException">Thrown when transaction is null.</exception>
+    public static bool IsValid(Transaction transaction)
+    {
+        ArgumentNullException.ThrowIfNull(transaction);
+        return NativeMethods.CheckTransaction(transaction.Handle, out nint statePtr) == 1;
+    }
+
+    /// <summary>
+    /// Performs context-free consensus checks on a transaction and returns detailed validation state.
+    /// Use this when you need to know why a transaction is invalid.
+    /// For simple validation, use IsValid() instead.
+    /// </summary>
+    /// <param name="transaction">The transaction to validate.</param>
+    /// <returns>A TxValidationState containing the validation result.</returns>
+    /// <exception cref="ArgumentNullException">Thrown when transaction is null.</exception>
+    /// <exception cref="TransactionException">Thrown when validation fails to execute.</exception>
+    public static TxValidationState CheckTransaction(Transaction transaction)
+    {
+        ArgumentNullException.ThrowIfNull(transaction);
+
+        IntPtr statePtr;
+        int result = NativeMethods.CheckTransaction(transaction.Handle, out statePtr);
+
+        if (statePtr == IntPtr.Zero)
+            throw new TransactionException("Failed to create validation state");
+
+        return new TxValidationState(statePtr);
+    }
+}

src/BitcoinKernel.Core/TransactionValidation/TxValidationState.cs

@@ -0,0 +1,75 @@
+using BitcoinKernel.Interop;
+using BitcoinKernel.Interop.Enums;
+
+namespace BitcoinKernel.Core.TransactionValidation;
+
+/// <summary>
+/// Represents the validation state of a transaction after consensus checks.
+/// </summary>
+public sealed class TxValidationState : IDisposable
+{
+    private IntPtr _handle;
+    private bool _disposed;
+
+    internal TxValidationState(IntPtr handle)
+    {
+        _handle = handle != IntPtr.Zero
+            ? handle
+            : throw new ArgumentException("Invalid validation state handle", nameof(handle));
+    }
+
+    /// <summary>
+    /// Gets the validation mode (VALID, INVALID, or INTERNAL_ERROR).
+    /// </summary>
+    public ValidationMode Mode
+    {
+        get
+        {
+            ThrowIfDisposed();
+            return NativeMethods.TxValidationStateGetValidationMode(_handle);
+        }
+    }
+
+    /// <summary>
+    /// Gets the detailed validation result indicating why the transaction was invalid.
+    /// </summary>
+    public TxValidationResult Result
+    {
+        get
+        {
+            ThrowIfDisposed();
+            return NativeMethods.TxValidationStateGetTxValidationResult(_handle);
+        }
+    }
+
+    /// <summary>
+    /// Returns true if the transaction is valid.
+    /// </summary>
+    public bool IsValid => Mode == ValidationMode.VALID;
+
+    /// <summary>
+    /// Returns true if the transaction is invalid.
+    /// </summary>
+    public bool IsInvalid => Mode == ValidationMode.INVALID;
+
+    /// <summary>
+    /// Returns true if an internal error occurred during validation.
+    /// </summary>
+    public bool IsError => Mode == ValidationMode.INTERNAL_ERROR;
+
+    private void ThrowIfDisposed()
+    {
+        if (_disposed)
+            throw new ObjectDisposedException(nameof(TxValidationState));
+    }
+
+    public void Dispose()
+    {
+        if (!_disposed && _handle != IntPtr.Zero)
+        {
+            NativeMethods.TxValidationStateDestroy(_handle);
+            _handle = IntPtr.Zero;
+            _disposed = true;
+        }
+    }
+}

src/BitcoinKernel.Interop/Enums/TxValidationResult.cs

@@ -0,0 +1,23 @@
+namespace BitcoinKernel.Interop.Enums
+{
+    /// <summary>
+    /// A granular "reason" why a transaction was invalid.
+    /// Mirrors consensus/validation.h: enum class TxValidationResult.
+    /// </summary>
+    public enum TxValidationResult : uint
+    {
+        UNSET = 0,
+        CONSENSUS = 1,
+        INPUTS_NOT_STANDARD = 2,
+        NOT_STANDARD = 3,
+        MISSING_INPUTS = 4,
+        PREMATURE_SPEND = 5,
+        WITNESS_MUTATED = 6,
+        WITNESS_STRIPPED = 7,
+        CONFLICT = 8,
+        MEMPOOL_POLICY = 9,
+        NO_MEMPOOL = 10,
+        RECONSIDERABLE = 11,
+        UNKNOWN = 12
+    }
+}

src/BitcoinKernel.Interop/NativeMethods.cs

@@ -377,6 +377,13 @@ public static extern int TransactionToBytes(
         [DllImport(LibName, CallingConvention = CallingConvention.Cdecl, EntryPoint = "btck_transaction_destroy")]
         public static extern void TransactionDestroy(IntPtr transaction);
 
+        /// <summary>
+        /// Run consensus/tx_check::CheckTransaction on a transaction and return the filled state.
+        /// Returns 1 if valid, 0 if invalid.
+        /// </summary>
+        [DllImport(LibName, CallingConvention = CallingConvention.Cdecl, EntryPoint = "btck_check_transaction")]
+        public static extern int CheckTransaction(IntPtr tx, out IntPtr out_state);
+
         /// <summary>
         /// Gets the script pubkey from a transaction output.
         /// Returns a pointer to btck_ScriptPubkey.
@@ -404,6 +411,28 @@ public static extern int TransactionToBytes(
 
         #endregion
 
+        #region TxValidationState Operations
+
+        /// <summary>
+        /// Gets the validation mode from a transaction validation state.
+        /// </summary>
+        [DllImport(LibName, CallingConvention = CallingConvention.Cdecl, EntryPoint = "btck_tx_validation_state_get_validation_mode")]
+        public static extern ValidationMode TxValidationStateGetValidationMode(IntPtr state);
+
+        /// <summary>
+        /// Gets the transaction validation result from a transaction validation state.
+        /// </summary>
+        [DllImport(LibName, CallingConvention = CallingConvention.Cdecl, EntryPoint = "btck_tx_validation_state_get_tx_validation_result")]
+        public static extern TxValidationResult TxValidationStateGetTxValidationResult(IntPtr state);
+
+        /// <summary>
+        /// Destroys a transaction validation state.
+        /// </summary>
+        [DllImport(LibName, CallingConvention = CallingConvention.Cdecl, EntryPoint = "btck_tx_validation_state_destroy")]
+        public static extern void TxValidationStateDestroy(IntPtr state);
+
+        #endregion
+
         #region ScriptPubkey Operations
 
         /// <summary>