buffer: implement Uint8Array backed Buffer

With V8 4.4 removing the external array data API currently used by
Buffer, the new implementation uses the Uint8Array to back Buffer.

Buffers now have a maximum size of Smi::kMaxLength, as defined by V8.
Which is ~2 GB on 64 bit and ~1 GB on 32 bit.

The flag --use-old-buffer allows using the old Buffer implementation.
This flag will be removed once V8 4.4 has landed.

The two JS Buffer implementations have been split into two files for
simplicity.

Use getter to return expected .parent/.offset values for backwards
compatibility.

PR-URL: #1825
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>

Author: trevnorris

lib/buffer.js

@@ -69,8 +69,9 @@
       'lib/v8.js',
       'lib/vm.js',
       'lib/zlib.js',
-
       'lib/internal/child_process.js',
+      'lib/internal/buffer_old.js',
+      'lib/internal/buffer_new.js',
       'lib/internal/freelist.js',
       'lib/internal/smalloc.js',
       'lib/internal/socket_list.js',

lib/internal/buffer_new.js

@@ -231,6 +231,7 @@ namespace node {
   V(async_hooks_post_function, v8::Function)                                  \
   V(binding_cache_object, v8::Object)                                         \
   V(buffer_constructor_function, v8::Function)                                \
+  V(buffer_prototype_object, v8::Object)                                      \
   V(context, v8::Context)                                                     \
   V(domain_array, v8::Array)                                                  \
   V(fs_stats_constructor_function, v8::Function)                              \

lib/internal/buffer_old.js

@@ -5,6 +5,7 @@
 #include "node_http_parser.h"
 #include "node_javascript.h"
 #include "node_version.h"
+#include "node_internals.h"
 
 #if defined HAVE_PERFCTR
 #include "node_counters.h"
@@ -147,6 +148,8 @@ static uv_async_t dispatch_debug_messages_async;
 static Isolate* node_isolate = nullptr;
 static v8::Platform* default_platform;
 
+bool using_old_buffer = false;
+
 class ArrayBufferAllocator : public ArrayBuffer::Allocator {
  public:
   // Impose an upper limit to avoid out of memory errors that bring down
@@ -166,23 +169,17 @@ ArrayBufferAllocator ArrayBufferAllocator::the_singleton;
 
 
 void* ArrayBufferAllocator::Allocate(size_t length) {
-  if (length > kMaxLength)
-    return nullptr;
-  char* data = new char[length];
-  memset(data, 0, length);
-  return data;
+  return calloc(length, 1);
 }
 
 
 void* ArrayBufferAllocator::AllocateUninitialized(size_t length) {
-  if (length > kMaxLength)
-    return nullptr;
-  return new char[length];
+  return malloc(length);
 }
 
 
 void ArrayBufferAllocator::Free(void* data, size_t length) {
-  delete[] static_cast<char*>(data);
+  free(data);
 }
 
 
@@ -2836,6 +2833,11 @@ void SetupProcessObject(Environment* env,
     READONLY_PROPERTY(process, "traceDeprecation", True(env->isolate()));
   }
 
+  // --use-old_buffer
+  if (using_old_buffer) {
+    READONLY_PROPERTY(process, "useOldBuffer", True(env->isolate()));
+  }
+
   size_t exec_path_len = 2 * PATH_MAX;
   char* exec_path = new char[exec_path_len];
   Local<String> exec_path_value;
@@ -3067,6 +3069,7 @@ static void PrintHelp() {
          "  --track-heap-objects  track heap object allocations for heap "
          "snapshots\n"
          "  --v8-options          print v8 command line options\n"
+         "  --use-old-buffer      Revert to old Buffer implementation\n"
 #if defined(NODE_HAVE_I18N_SUPPORT)
          "  --icu-data-dir=dir    set ICU data load path to dir\n"
          "                          (overrides NODE_ICU_DATA)\n"
@@ -3204,6 +3207,10 @@ static void ParseArgs(int* argc,
 #endif
     } else if (strcmp(arg, "--expose-internals") == 0 ||
                strcmp(arg, "--expose_internals") == 0) {
+    } else if (strcmp(arg, "--use-old-buffer") == 0 ||
+               strcmp(arg, "--use_old_buffer") == 0) {
+      using_old_buffer = true;
+
       // consumed in js
     } else {
       // V8 option.  Pass through as-is.