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buffer: do proper error propagation in addon methods #23939

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buffer: do proper error propagation in addon methods 
- Always fulfill the `MaybeLocal<>` contract by scheduling an
  exception when returning an empty value. This was previously
  inconsistent, with no way to know whether an exception was
  be scheduled or not in case of failure.
- Make sure that memory is released exactly once in case of
  failure. Previously, some exit conditions would have leaked
  memory or attempted to free it multiple times.

This should not really affect how `Buffer`s are created by
addons in practice, due to the low frequency with which
these errors would typically occur.
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@addaleax
addaleax committed Oct 28, 2018
commit 5b67c335d1cf54fc2ff058c577f7f7d1b53c4a97
48 changes: 25 additions & 23 deletions src/node_buffer.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -243,8 +243,10 @@ MaybeLocal<Object> New(Isolate* isolate,
if (length > 0) {
data = static_cast<char*>(BufferMalloc(length));

if (data == nullptr)
if (data == nullptr) {
THROW_ERR_MEMORY_ALLOCATION_FAILED(isolate);
return Local<Object>();
}

actual = StringBytes::Write(isolate, data, length, string, enc);
CHECK(actual <= length);
Expand Down Expand Up @@ -283,14 +285,17 @@ MaybeLocal<Object> New(Environment* env, size_t length) {

// V8 currently only allows a maximum Typed Array index of max Smi.
if (length > kMaxLength) {
env->isolate()->ThrowException(ERR_BUFFER_TOO_LARGE(env->isolate()));
return Local<Object>();
}

void* data;
if (length > 0) {
data = BufferMalloc(length);
if (data == nullptr)
if (data == nullptr) {
THROW_ERR_MEMORY_ALLOCATION_FAILED(env);
return Local<Object>();
}
} else {
data = nullptr;
}
Expand All @@ -300,14 +305,10 @@ MaybeLocal<Object> New(Environment* env, size_t length) {
data,
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@refack refack Oct 28, 2018

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suggestion: std::move(data) to indicate transfer of ownership.

length,
ArrayBufferCreationMode::kInternalized);
MaybeLocal<Uint8Array> ui = Buffer::New(env, ab, 0, length);

if (ui.IsEmpty()) {
// Object failed to be created. Clean up resources.
free(data);
}

return scope.Escape(ui.FromMaybe(Local<Uint8Array>()));
Local<Object> obj;
if (Buffer::New(env, ab, 0, length).ToLocal(&obj))
return scope.Escape(obj);
return Local<Object>();
}


Expand All @@ -327,15 +328,18 @@ MaybeLocal<Object> Copy(Environment* env, const char* data, size_t length) {

// V8 currently only allows a maximum Typed Array index of max Smi.
if (length > kMaxLength) {
env->isolate()->ThrowException(ERR_BUFFER_TOO_LARGE(env->isolate()));
return Local<Object>();
}

void* new_data;
if (length > 0) {
CHECK_NOT_NULL(data);
new_data = node::UncheckedMalloc(length);
if (new_data == nullptr)
if (new_data == nullptr) {
THROW_ERR_MEMORY_ALLOCATION_FAILED(env);
return Local<Object>();
}
memcpy(new_data, data, length);
} else {
new_data = nullptr;
Expand All @@ -346,14 +350,10 @@ MaybeLocal<Object> Copy(Environment* env, const char* data, size_t length) {
new_data,
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@refack refack Oct 28, 2018

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possibly here

length,
ArrayBufferCreationMode::kInternalized);
MaybeLocal<Uint8Array> ui = Buffer::New(env, ab, 0, length);

if (ui.IsEmpty()) {
// Object failed to be created. Clean up resources.
free(new_data);
}

return scope.Escape(ui.FromMaybe(Local<Uint8Array>()));
Local<Object> obj;
if (Buffer::New(env, ab, 0, length).ToLocal(&obj))
return scope.Escape(obj);
return Local<Object>();
}


Expand All @@ -380,6 +380,8 @@ MaybeLocal<Object> New(Environment* env,
EscapableHandleScope scope(env->isolate());

if (length > kMaxLength) {
env->isolate()->ThrowException(ERR_BUFFER_TOO_LARGE(env->isolate()));
callback(data, hint);
return Local<Object>();
}

Expand All @@ -391,11 +393,11 @@ MaybeLocal<Object> New(Environment* env,
ab->Neuter();
MaybeLocal<Uint8Array> ui = Buffer::New(env, ab, 0, length);

if (ui.IsEmpty()) {
return Local<Object>();
}

CallbackInfo::New(env->isolate(), ab, callback, data, hint);

if (ui.IsEmpty())
return MaybeLocal<Object>();

return scope.Escape(ui.ToLocalChecked());
}

Expand Down