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/node#23938
Reviewed-By: James M Snell <[email protected]>
Reviewed-By: Daniel Bevenius <[email protected]>

Author: addaleax

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

@@ -256,7 +256,10 @@ 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>();
@@ -287,7 +290,10 @@ 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);
@@ -325,7 +331,11 @@ 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);
@@ -365,7 +375,11 @@ 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, true).ToLocal(&obj))
     return handle_scope.Escape(obj);

src/node_errors.h

@@ -17,6 +17,7 @@ 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)                                   \
@@ -55,6 +56,8 @@ 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`")    \
@@ -73,8 +76,11 @@ namespace node {
   inline v8::Local<v8::Value> code(v8::Isolate* isolate) {                   \
     return code(isolate, message);                                           \
   }                                                                          \
+  inline void THROW_ ## code(v8::Isolate* isolate) {                         \
+    isolate->ThrowException(code(isolate, message));                         \
+  }                                                                          \
   inline void THROW_ ## code(Environment* env) {                             \
-    env->isolate()->ThrowException(code(env->isolate(), message));           \
+    THROW_ ## code(env->isolate());                                          \
   }
   PREDEFINED_ERROR_MESSAGES(V)
 #undef V