buffer: throw exception when creating from non-Node.js Context

Throw an exception instead of crashing when attempting to create
`Buffer` objects from a Context that is not associated with
a Node.js `Environment`.

Possible alternatives for the future might be just returning
a plain `Uint8Array`, or working on providing `Buffer` for all
`Context`s.

PR-URL: nodejs#23938
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Daniel Bevenius <daniel.bevenius@gmail.com>

doc/api/errors.md

@@ -613,6 +613,19 @@ An attempt was made to register something that is not a function as an
 The type of an asynchronous resource was invalid. Note that users are also able
 to define their own types if using the public embedder API.
 
+<a id="ERR_BUFFER_CONTEXT_NOT_AVAILABLE"></a>
+### ERR_BUFFER_CONTEXT_NOT_AVAILABLE
+
+An attempt was made to create a Node.js `Buffer` instance from addon or embedder
+code, while in a JS engine Context that is not associated with a Node.js
+instance. The data passed to the `Buffer` method will have been released
+by the time the method returns.
+
+When encountering this error, a possible alternative to creating a `Buffer`
+instance is to create a normal `Uint8Array`, which only differs in the
+prototype of the resulting object. `Uint8Array`s are generally accepted in all
+Node.js core APIs where `Buffer`s are; they are available in all Contexts.
+
 <a id="ERR_BUFFER_OUT_OF_BOUNDS"></a>
 ### ERR_BUFFER_OUT_OF_BOUNDS
 

src/node_buffer.cc

@@ -271,7 +271,10 @@ MaybeLocal<Object> New(Isolate* isolate, size_t length) {
   EscapableHandleScope handle_scope(isolate);
   Local<Object> obj;
   Environment* env = Environment::GetCurrent(isolate);
-  CHECK_NOT_NULL(env);  // TODO(addaleax): Handle nullptr here.
+  if (env == nullptr) {
+    THROW_ERR_BUFFER_CONTEXT_NOT_AVAILABLE(isolate);
+    return MaybeLocal<Object>();
+  }
   if (Buffer::New(env, length).ToLocal(&obj))
     return handle_scope.Escape(obj);
   return Local<Object>();
@@ -314,7 +317,10 @@ MaybeLocal<Object> New(Environment* env, size_t length) {
 MaybeLocal<Object> Copy(Isolate* isolate, const char* data, size_t length) {
   EscapableHandleScope handle_scope(isolate);
   Environment* env = Environment::GetCurrent(isolate);
-  CHECK_NOT_NULL(env);  // TODO(addaleax): Handle nullptr here.
+  if (env == nullptr) {
+    THROW_ERR_BUFFER_CONTEXT_NOT_AVAILABLE(isolate);
+    return MaybeLocal<Object>();
+  }
   Local<Object> obj;
   if (Buffer::Copy(env, data, length).ToLocal(&obj))
     return handle_scope.Escape(obj);
@@ -364,7 +370,11 @@ MaybeLocal<Object> New(Isolate* isolate,
                        void* hint) {
   EscapableHandleScope handle_scope(isolate);
   Environment* env = Environment::GetCurrent(isolate);
-  CHECK_NOT_NULL(env);  // TODO(addaleax): Handle nullptr here.
+  if (env == nullptr) {
+    callback(data, hint);
+    THROW_ERR_BUFFER_CONTEXT_NOT_AVAILABLE(isolate);
+    return MaybeLocal<Object>();
+  }
   Local<Object> obj;
   if (Buffer::New(env, data, length, callback, hint).ToLocal(&obj))
     return handle_scope.Escape(obj);
@@ -403,7 +413,11 @@ MaybeLocal<Object> New(Environment* env,
 MaybeLocal<Object> New(Isolate* isolate, char* data, size_t length) {
   EscapableHandleScope handle_scope(isolate);
   Environment* env = Environment::GetCurrent(isolate);
-  CHECK_NOT_NULL(env);  // TODO(addaleax): Handle nullptr here.
+  if (env == nullptr) {
+    free(data);
+    THROW_ERR_BUFFER_CONTEXT_NOT_AVAILABLE(isolate);
+    return MaybeLocal<Object>();
+  }
   Local<Object> obj;
   if (Buffer::New(env, data, length).ToLocal(&obj))
     return handle_scope.Escape(obj);

src/node_errors.h

@@ -21,6 +21,7 @@ namespace node {
 // a `Local<Value>` containing the TypeError with proper code and message
 
 #define ERRORS_WITH_CODE(V)                                                  \
+  V(ERR_BUFFER_CONTEXT_NOT_AVAILABLE, Error)                                 \
   V(ERR_BUFFER_OUT_OF_BOUNDS, RangeError)                                    \
   V(ERR_BUFFER_TOO_LARGE, Error)                                             \
   V(ERR_CANNOT_TRANSFER_OBJECT, TypeError)                                   \
@@ -64,6 +65,8 @@ namespace node {
 // Errors with predefined static messages
 
 #define PREDEFINED_ERROR_MESSAGES(V)                                         \
+  V(ERR_BUFFER_CONTEXT_NOT_AVAILABLE,                                        \
+    "Buffer is not available for the current Context")                       \
   V(ERR_CANNOT_TRANSFER_OBJECT, "Cannot transfer object of unsupported type")\
   V(ERR_CLOSED_MESSAGE_PORT, "Cannot send data on closed MessagePort")       \
   V(ERR_CONSTRUCT_CALL_REQUIRED, "Cannot call constructor without `new`")    \

test/addons/non-node-context/binding.cc

@@ -1,4 +1,5 @@
 #include <node.h>
+#include <node_buffer.h>
 #include <assert.h>
 
 namespace {
@@ -15,6 +16,17 @@ using v8::Script;
 using v8::String;
 using v8::Value;
 
+inline void MakeBufferInNewContext(
+    const v8::FunctionCallbackInfo<v8::Value>& args) {
+  Isolate* isolate = args.GetIsolate();
+  Local<Context> context = Context::New(isolate);
+  Context::Scope context_scope(context);
+
+  // This should throw an exception, rather than actually do anything.
+  MaybeLocal<Object> buf = node::Buffer::Copy(isolate, "foo", 3);
+  assert(buf.IsEmpty());
+}
+
 inline void RunInNewContext(
     const v8::FunctionCallbackInfo<v8::Value>& args) {
   Isolate* isolate = args.GetIsolate();
@@ -41,13 +53,8 @@ inline void RunInNewContext(
 inline void Initialize(Local<Object> exports,
                        Local<Value> module,
                        Local<Context> context) {
-  Isolate* isolate = context->GetIsolate();
-  Local<String> key = String::NewFromUtf8(
-      isolate, "runInNewContext", NewStringType::kNormal).ToLocalChecked();
-  Local<Function> value = FunctionTemplate::New(isolate, RunInNewContext)
-                   ->GetFunction(context)
-                   .ToLocalChecked();
-  assert(exports->Set(context, key, value).IsJust());
+  NODE_SET_METHOD(exports, "runInNewContext", RunInNewContext);
+  NODE_SET_METHOD(exports, "makeBufferInNewContext", MakeBufferInNewContext);
 }
 
 }  // anonymous namespace

test/addons/non-node-context/test-make-buffer.js

@@ -0,0 +1,22 @@
+'use strict';
+
+const common = require('../../common');
+const assert = require('assert');
+const {
+  makeBufferInNewContext
+} = require(`./build/${common.buildType}/binding`);
+
+// Because the `Buffer` function and its protoype property only (currently)
+// exist in a Node.js instance’s main context, trying to create buffers from
+// another context throws an exception.
+
+try {
+  makeBufferInNewContext();
+} catch (exception) {
+  assert.strictEqual(exception.constructor.name, 'Error');
+  assert(!(exception.constructor instanceof Error));
+
+  assert.strictEqual(exception.code, 'ERR_BUFFER_CONTEXT_NOT_AVAILABLE');
+  assert.strictEqual(exception.message,
+                     'Buffer is not available for the current Context');
+}