src: use MaybeStackBuffer on DoSend/Writev

instead of creating own buffer, use MaybeStackBuffer on DoSend to
take advantage of its destructor to free up memory, so buffer
never leaks memory - even if code in DoSend throws.

Use MaybeStackBuffer in Writev to take advantage of destructor
on MaybeStackBuffer to clear itself up, rather than Writev managing
resources itself.

PR-URL: https://github.com/nodejs/node/pull/8626
Reviewed-By: Anna Henningsen <anna@addaleax.net>

src/stream_base.cc

@@ -102,8 +102,7 @@ int StreamBase::Writev(const FunctionCallbackInfo<Value>& args) {
 
   size_t count = chunks->Length() >> 1;
 
-  uv_buf_t bufs_[16];
-  uv_buf_t* bufs = bufs_;
+  MaybeStackBuffer<uv_buf_t, 16> bufs(count);
 
   // Determine storage size first
   size_t storage_size = 0;
@@ -132,9 +131,6 @@ int StreamBase::Writev(const FunctionCallbackInfo<Value>& args) {
   if (storage_size > INT_MAX)
     return UV_ENOBUFS;
 
-  if (arraysize(bufs_) < count)
-    bufs = new uv_buf_t[count];
-
   WriteWrap* req_wrap = WriteWrap::New(env,
                                        req_wrap_obj,
                                        this,
@@ -174,11 +170,7 @@ int StreamBase::Writev(const FunctionCallbackInfo<Value>& args) {
     bytes += str_size;
   }
 
-  int err = DoWrite(req_wrap, bufs, count, nullptr);
-
-  // Deallocate space
-  if (bufs != bufs_)
-    delete[] bufs;
+  int err = DoWrite(req_wrap, *bufs, count, nullptr);
 
   req_wrap->object()->Set(env->async(), True(env->isolate()));
   req_wrap->object()->Set(env->bytes_string(),

src/udp_wrap.cc

@@ -275,13 +275,7 @@ void UDPWrap::DoSend(const FunctionCallbackInfo<Value>& args, int family) {
   SendWrap* req_wrap = new SendWrap(env, req_wrap_obj, have_callback);
   size_t msg_size = 0;
 
-  // allocate uv_buf_t of the correct size
-  // if bigger than 16 elements
-  uv_buf_t bufs_[16];
-  uv_buf_t* bufs = bufs_;
-
-  if (arraysize(bufs_) < count)
-    bufs = new uv_buf_t[count];
+  MaybeStackBuffer<uv_buf_t, 16> bufs(count);
 
   // construct uv_buf_t array
   for (size_t i = 0; i < count; i++) {
@@ -313,16 +307,12 @@ void UDPWrap::DoSend(const FunctionCallbackInfo<Value>& args, int family) {
   if (err == 0) {
     err = uv_udp_send(&req_wrap->req_,
                       &wrap->handle_,
-                      bufs,
+                      *bufs,
                       count,
                       reinterpret_cast<const sockaddr*>(&addr),
                       OnSend);
   }
 
-  // Deallocate space
-  if (bufs != bufs_)
-    delete[] bufs;
-
   req_wrap->Dispatched();
   if (err)
     delete req_wrap;