/// <summary>
/// Hook a field by injecting a static "setter" method.
/// If target field is a static field, your setter should accept a value that is originally used to write the field.
/// If target field is not a static field, your setter should accept a object having the field followed by a value.
/// Your setter method should not have any return value.
/// </summary>
/// <param name="target field"></param>
/// <param name="hook method">your "setter"</param>
/// <param name="resolver">This is used to find every IL instruction that writes the field.</param>
/// <param name="hookName"></param>
static public void HookFieldWrite(FieldDefinition target, MethodDefinition hookMethod, ReferenceResolver resolver = null, string hookName = null)
{
if (hookName == null)
{
hookName = target.Name + "__hookwrite__" + hookMethod.Name;
}
if (resolver == null)
{
resolver = new ReferenceResolver();
resolver.ScanAssembly(target.DeclaringType.Module.Assembly);
}
var injectedMethod = InjectMethod(target.DeclaringType, hookMethod, hookName);
var references = resolver.FindAllReferences(target);
foreach (var reference in references)
{
if (reference.instruction.OpCode == OpCodes.Stfld || reference.instruction.OpCode == OpCodes.Stsfld)
{
reference.instruction.OpCode = OpCodes.Call;
reference.instruction.Operand = injectedMethod;
}
}
}
/// <summary>
/// Replace target method with your hook method.
/// To call the original method, just call hook method from the hook method.
/// </summary>
/// <param name="target method"></param>
/// <param name="hook method"></param>
/// <param name="resolver">This is used to find all instructions that call the target method.</param>
/// <param name="hook prefix">This will be used as the prefix of the original target method.</param>
static public void HookMethod(MethodDefinition targetMethod, MethodDefinition hookMethod, ReferenceResolver resolver = null, string hookPrefix = "__hooked__")
{
if (resolver == null)
{
resolver = new ReferenceResolver();
resolver.ScanAssembly(targetMethod.DeclaringType.Module.Assembly);
}
var injectedMethod = InjectMethod(targetMethod.DeclaringType, hookMethod);
injectedMethod.Attributes = targetMethod.Attributes;
if (!targetMethod.IsStatic && hookMethod.IsStatic)
{
// first argument is keyword "this"
injectedMethod.HasThis = true;
injectedMethod.Parameters.RemoveAt(0); // should not appear here
}
// rename original method
injectedMethod.Name = targetMethod.Name;
targetMethod.Name = hookPrefix + targetMethod.Name;
// replace the original method with the new one
resolver.ReplaceAllReferences(targetMethod, injectedMethod);
// process self-calls
for (int i = 0; i < injectedMethod.Body.Instructions.Count; ++i)
{
var ins = injectedMethod.Body.Instructions[i];
if (ins.OpCode == OpCodes.Call || ins.OpCode == OpCodes.Callvirt)
{
if ((ins.Operand as MethodReference).FullName == hookMethod.FullName)
{
ins.Operand = targetMethod;
}
}
}
}
