/// <summary>
/// Replaces the <paramref name="oldInstruction"/> with a set of new instructions.
/// </summary>
/// <param name="oldInstruction">The instruction currently being evaluated.</param>
/// <param name="hostMethod">The method that contains the target instruction.</param>
/// <param name="IL">The CilWorker that will be used to emit the method body instructions.</param>
protected override void Replace(Instruction oldInstruction, MethodDefinition hostMethod, CilWorker IL)
{
var targetField = (FieldReference) oldInstruction.Operand;
var fieldType = targetField.FieldType;
var isSetter = oldInstruction.OpCode == OpCodes.Stsfld || oldInstruction.OpCode == OpCodes.Stfld;
if (isSetter)
{
hostMethod.Body.InitLocals = true;
// Save the setter argument and box it if necessary
if (fieldType.IsValueType || fieldType is GenericParameter)
IL.Emit(OpCodes.Box, fieldType);
IL.Emit(OpCodes.Stloc, _currentArgument);
}
// There's no need to push the current object instance
// since the this pointer is pushed prior to the field call
if (hostMethod.IsStatic)
IL.Emit((OpCodes.Ldnull));
// Push the current method
var module = hostMethod.DeclaringType.Module;
// Push the current method onto the stack
IL.PushMethod(hostMethod, module);
// Push the current field onto the stack
IL.PushField(targetField, module);
// Push the host type onto the stack
IL.PushType(hostMethod.DeclaringType, module);
// Create the IFieldInterceptionContext instance
IL.Emit(OpCodes.Newobj, _fieldContextCtor);
IL.Emit(OpCodes.Stloc, _fieldContext);
var skipInterception = IL.Create(OpCodes.Nop);
// Obtain an interceptor instance
if (hostMethod.IsStatic)
{
IL.Emit(OpCodes.Ldloc, _fieldContext);
IL.Emit(OpCodes.Call, _getInterceptor);
}
else
{
IL.Emit(OpCodes.Ldarg_0);
IL.Emit(OpCodes.Isinst, _fieldInterceptionHostType);
IL.Emit(OpCodes.Brfalse, skipInterception);
IL.Emit(OpCodes.Ldarg_0);
IL.Emit(OpCodes.Isinst, _fieldInterceptionHostType);
IL.Emit(OpCodes.Callvirt, _getInstanceInterceptor);
}
// The field interceptor cannot be null
IL.Emit(OpCodes.Stloc, _fieldInterceptor);
IL.Emit(OpCodes.Ldloc, _fieldInterceptor);
IL.Emit(OpCodes.Brfalse, skipInterception);
// if (FieldInterceptor.CanIntercept(context) {
IL.Emit(OpCodes.Ldloc, _fieldInterceptor);
IL.Emit(OpCodes.Ldloc, _fieldContext);
IL.Emit(OpCodes.Callvirt, _canIntercept);
IL.Emit(OpCodes.Brfalse, skipInterception);
var isGetter = oldInstruction.OpCode == OpCodes.Ldsfld || oldInstruction.OpCode == OpCodes.Ldfld;
var endLabel = IL.Create(OpCodes.Nop);
//Call the interceptor instead of the getter or setter
if (isGetter)
{
IL.Emit(OpCodes.Ldloc, _fieldInterceptor);
IL.Emit(OpCodes.Ldloc, _fieldContext);
IL.Emit(OpCodes.Callvirt, _getValue);
IL.Emit(OpCodes.Unbox_Any, fieldType);
}
if (isSetter)
{
// Push the 'this' pointer for instance field setters
if (!hostMethod.IsStatic)
IL.Emit(OpCodes.Ldarg_0);
IL.Emit(OpCodes.Ldloc, _fieldInterceptor);
IL.Emit(OpCodes.Ldloc, _fieldContext);
IL.Emit(OpCodes.Ldloc, _currentArgument);
// Unbox the setter value
IL.Emit(OpCodes.Unbox_Any, fieldType);
IL.Emit(OpCodes.Callvirt, _setValue);
// Set the actual field value
IL.Emit(OpCodes.Unbox_Any, fieldType);
IL.Emit(oldInstruction.OpCode, targetField);
}
IL.Emit(OpCodes.Br, endLabel);
// }
IL.Append(skipInterception);
// else {
// Load the original field
if (!hostMethod.IsStatic)
IL.Emit(OpCodes.Ldarg_0);
if (isSetter)
{
IL.Emit(OpCodes.Ldloc, _currentArgument);
// Unbox the setter value
IL.Emit(OpCodes.Unbox_Any, fieldType);
}
IL.Emit(oldInstruction.OpCode, targetField);
// }
IL.Append(endLabel);
}
