buffer: add .from(), .alloc() and .allocUnsafe()

Several changes:

* Soft-Deprecate Buffer() constructors
* Add `Buffer.from()`, `Buffer.alloc()`, and `Buffer.allocUnsafe()`
* Add `--zero-fill-buffers` command line option
* Add byteOffset and length to `new Buffer(arrayBuffer)` constructor
* buffer.fill('') previously had no effect, now zero-fills
* Update the docs

PR-URL: https://github.com/nodejs/node/pull/4682
Reviewed-By: Сковорода Никита Андреевич <chalkerx@gmail.com>
Reviewed-By: Stephen Belanger <admin@stephenbelanger.com>

3 files changed, 33 insertions, 5 deletions

diff --git a/src/node.cc b/src/node.cc
index 976237efe2..679643ebf8 100644
--- a/src/node.cc
+++ b/src/node.cc
@@ -955,7 +955,9 @@ Local<Value> WinapiErrnoException(Isolate* isolate,
 
 
 void* ArrayBufferAllocator::Allocate(size_t size) {
-  if (env_ == nullptr || !env_->array_buffer_allocator_info()->no_zero_fill())
+  if (env_ == nullptr ||
+      !env_->array_buffer_allocator_info()->no_zero_fill() ||
+      zero_fill_all_buffers)
     return calloc(size, 1);
   env_->array_buffer_allocator_info()->reset_fill_flag();
   return malloc(size);
@@ -3312,6 +3314,8 @@ static void PrintHelp() {
          "snapshots\n"
          "  --prof-process        process v8 profiler output generated\n"
          "                        using --prof\n"
+         "  --zero-fill-buffers   automatically zero-fill all newly allocated\n"
+         "                        Buffer and SlowBuffer instances\n"
          "  --v8-options          print v8 command line options\n"
 #if HAVE_OPENSSL
          "  --tls-cipher-list=val use an alternative default TLS cipher list\n"
@@ -3455,6 +3459,8 @@ static void ParseArgs(int* argc,
     } else if (strcmp(arg, "--prof-process") == 0) {
       prof_process = true;
       short_circuit = true;
+    } else if (strcmp(arg, "--zero-fill-buffers") == 0) {
+      zero_fill_all_buffers = true;
     } else if (strcmp(arg, "--v8-options") == 0) {
       new_v8_argv[new_v8_argc] = "--help";
       new_v8_argc += 1;
diff --git a/src/node_buffer.cc b/src/node_buffer.cc
index aecc6874d8..6720f2c937 100644
--- a/src/node_buffer.cc
+++ b/src/node_buffer.cc
@@ -48,7 +48,14 @@
   CHECK_NOT_OOB(end <= end_max);                                            \
   size_t length = end - start;
 
+#define BUFFER_MALLOC(length)                                               \
+  zero_fill_all_buffers ? calloc(length, 1) : malloc(length)
+
 namespace node {
+
+// if true, all Buffer and SlowBuffer instances will automatically zero-fill
+bool zero_fill_all_buffers = false;
+
 namespace Buffer {
 
 using v8::ArrayBuffer;
@@ -74,7 +81,6 @@ using v8::Uint8Array;
 using v8::Value;
 using v8::WeakCallbackInfo;
 
-
 class CallbackInfo {
  public:
   static inline void Free(char* data, void* hint);
@@ -210,7 +216,7 @@ MaybeLocal<Object> New(Isolate* isolate,
   // nullptr for zero-sized allocation requests.  Normalize by always using
   // a nullptr.
   if (length > 0) {
-    data = static_cast<char*>(malloc(length));
+    data = static_cast<char*>(BUFFER_MALLOC(length));
 
     if (data == nullptr)
       return Local<Object>();
@@ -256,7 +262,7 @@ MaybeLocal<Object> New(Environment* env, size_t length) {
 
   void* data;
   if (length > 0) {
-    data = malloc(length);
+    data = BUFFER_MALLOC(length);
     if (data == nullptr)
       return Local<Object>();
   } else {
@@ -419,7 +425,20 @@ void CreateFromArrayBuffer(const FunctionCallbackInfo<Value>& args) {
   if (!args[0]->IsArrayBuffer())
     return env->ThrowTypeError("argument is not an ArrayBuffer");
   Local<ArrayBuffer> ab = args[0].As<ArrayBuffer>();
-  Local<Uint8Array> ui = Uint8Array::New(ab, 0, ab->ByteLength());
+
+  size_t ab_length = ab->ByteLength();
+  size_t offset;
+  size_t max_length;
+
+  CHECK_NOT_OOB(ParseArrayIndex(args[1], 0, &offset));
+  CHECK_NOT_OOB(ParseArrayIndex(args[2], ab_length - offset, &max_length));
+
+  if (offset >= ab_length)
+    return env->ThrowRangeError("'offset' is out of bounds");
+  if (max_length > ab_length - offset)
+    return env->ThrowRangeError("'length' is out of bounds");
+
+  Local<Uint8Array> ui = Uint8Array::New(ab, offset, max_length);
   Maybe<bool> mb =
       ui->SetPrototype(env->context(), env->buffer_prototype_object());
   if (!mb.FromMaybe(false))
diff --git a/src/node_buffer.h b/src/node_buffer.h
index 2bcf245f39..2ecfab33a3 100644
--- a/src/node_buffer.h
+++ b/src/node_buffer.h
@@ -5,6 +5,9 @@
 #include "v8.h"
 
 namespace node {
+
+extern bool zero_fill_all_buffers;
+
 namespace Buffer {
 
 static const unsigned int kMaxLength =