stream_base: always use Base template class

First cast the pointer to the child Base class before casting to the
parent class to make sure it returns the correct pointer.

PR-URL: https://github.com/nodejs/node/pull/6184
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Anna Henningsen <anna@addaleax.net>

src/stream_base-inl.h

@@ -77,8 +77,13 @@ void StreamBase::AddMethods(Environment* env,
 template <class Base>
 void StreamBase::GetFD(Local<String> key,
                        const PropertyCallbackInfo<Value>& args) {
-  StreamBase* wrap = Unwrap<Base>(args.Holder());
+  Base* handle = Unwrap<Base>(args.Holder());
 
+  // Mimic implementation of StreamBase::GetFD() and UDPWrap::GetFD().
+  if (handle == nullptr)
+    return args.GetReturnValue().Set(-1);
+
+  StreamBase* wrap = static_cast<StreamBase*>(handle);
   if (!wrap->IsAlive())
     return args.GetReturnValue().Set(UV_EINVAL);
 
@@ -89,8 +94,13 @@ void StreamBase::GetFD(Local<String> key,
 template <class Base>
 void StreamBase::GetBytesRead(Local<String> key,
                               const PropertyCallbackInfo<Value>& args) {
-  StreamBase* wrap = Unwrap<Base>(args.Holder());
+  Base* handle = Unwrap<Base>(args.Holder());
+
+  // The handle instance hasn't been set. So no bytes could have been read.
+  if (handle == nullptr)
+    return args.GetReturnValue().Set(0);
 
+  StreamBase* wrap = static_cast<StreamBase*>(handle);
   // uint64_t -> double. 53bits is enough for all real cases.
   args.GetReturnValue().Set(static_cast<double>(wrap->bytes_read_));
 }
@@ -99,8 +109,12 @@ void StreamBase::GetBytesRead(Local<String> key,
 template <class Base>
 void StreamBase::GetExternal(Local<String> key,
                              const PropertyCallbackInfo<Value>& args) {
-  StreamBase* wrap = Unwrap<Base>(args.Holder());
+  Base* handle = Unwrap<Base>(args.Holder());
 
+  if (handle == nullptr)
+    return args.GetReturnValue().SetUndefined();
+
+  StreamBase* wrap = static_cast<StreamBase*>(handle);
   Local<External> ext = External::New(args.GetIsolate(), wrap);
   args.GetReturnValue().Set(ext);
 }
@@ -109,8 +123,12 @@ void StreamBase::GetExternal(Local<String> key,
 template <class Base,
           int (StreamBase::*Method)(const FunctionCallbackInfo<Value>& args)>
 void StreamBase::JSMethod(const FunctionCallbackInfo<Value>& args) {
-  StreamBase* wrap = Unwrap<Base>(args.Holder());
+  Base* handle = Unwrap<Base>(args.Holder());
+
+  if (handle == nullptr)
+    return args.GetReturnValue().SetUndefined();
 
+  StreamBase* wrap = static_cast<StreamBase*>(handle);
   if (!wrap->IsAlive())
     return args.GetReturnValue().Set(UV_EINVAL);