node_buffer.h

// Copyright Joyent, Inc. and other Node contributors.
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#ifndef NODE_BUFFER_H_
#define NODE_BUFFER_H_

#include <node.h>
#include <node_object_wrap.h>
#include <v8.h>
#include <assert.h>

namespace node {

/* A buffer is a chunk of memory stored outside the V8 heap, mirrored by an
 * object in javascript. The object is not totally opaque, one can access
 * individual bytes with [] and slice it into substrings or sub-buffers
 * without copying memory.
 *
 * // return an ascii encoded string - no memory is copied
 * buffer.asciiSlice(0, 3)
 */

/*
   The C++ API for Buffer changed radically between v0.2 and v0.3, in fact
   it was the reason for bumping the version. In v0.2 JavaScript Buffers and
   C++ Buffers were in one-to-one correspondence via ObjectWrap. We found
   that it was faster to expose the C++ Buffers to JavaScript as a
   "SlowBuffer" which is used as a private backend to pure JavaScript
   "Buffer" objects - a 'Buffer' in v0.3 might look like this:

   { _parent: s,
     _offset: 520,
     length: 5 }

   Migrating code C++ Buffer code from v0.2 to v0.3 is difficult. Here are
   some tips:
    - buffer->data() calls should become Buffer::Data(buffer) calls.
    - buffer->length() calls should become Buffer::Length(buffer) calls. 
    - There should not be any ObjectWrap::Unwrap<Buffer>() calls. You should
      not be storing pointers to Buffer objects at all - as they are
      now considered internal structures. Instead consider making a
      JavaScript reference to the buffer.

   See the source code node-png as an example of a module which successfully
   compiles on both v0.2 and v0.3 while making heavy use of the C++ Buffer
   API.

 */


class Buffer : public ObjectWrap {
 public:

  static bool HasInstance(v8::Handle<v8::Value> val);

  static inline char* Data(v8::Handle<v8::Object> obj) {
    return (char*)obj->GetIndexedPropertiesExternalArrayData();
  }

  static inline char* Data(Buffer *b) {
    return Buffer::Data(b->handle_);
  }

  static inline size_t Length(v8::Handle<v8::Object> obj) {
    return (size_t)obj->GetIndexedPropertiesExternalArrayDataLength();
  }

  static inline size_t Length(Buffer *b) {
    return Buffer::Length(b->handle_);
  }


  ~Buffer();

  typedef void (*free_callback)(char *data, void *hint);

  // C++ API for constructing fast buffer
  static v8::Handle<v8::Object> New(v8::Handle<v8::String> string);

  static void Initialize(v8::Handle<v8::Object> target);
  static Buffer* New(size_t length); // public constructor
  static Buffer* New(char *data, size_t len); // public constructor
  static Buffer* New(char *data, size_t length,
                     free_callback callback, void *hint); // public constructor

  private:
  static v8::Persistent<v8::FunctionTemplate> constructor_template;

  static v8::Handle<v8::Value> New(const v8::Arguments &args);
  static v8::Handle<v8::Value> BinarySlice(const v8::Arguments &args);
  static v8::Handle<v8::Value> AsciiSlice(const v8::Arguments &args);
  static v8::Handle<v8::Value> Base64Slice(const v8::Arguments &args);
  static v8::Handle<v8::Value> Utf8Slice(const v8::Arguments &args);
  static v8::Handle<v8::Value> Ucs2Slice(const v8::Arguments &args);
  static v8::Handle<v8::Value> BinaryWrite(const v8::Arguments &args);
  static v8::Handle<v8::Value> Base64Write(const v8::Arguments &args);
  static v8::Handle<v8::Value> AsciiWrite(const v8::Arguments &args);
  static v8::Handle<v8::Value> Utf8Write(const v8::Arguments &args);
  static v8::Handle<v8::Value> Ucs2Write(const v8::Arguments &args);
  static v8::Handle<v8::Value> ByteLength(const v8::Arguments &args);
  static v8::Handle<v8::Value> MakeFastBuffer(const v8::Arguments &args);
  static v8::Handle<v8::Value> Fill(const v8::Arguments &args);
  static v8::Handle<v8::Value> Copy(const v8::Arguments &args);

  Buffer(v8::Handle<v8::Object> wrapper, size_t length);
  void Replace(char *data, size_t length, free_callback callback, void *hint);

  size_t length_;
  char* data_;
  free_callback callback_;
  void* callback_hint_;
};


}  // namespace node buffer

#endif  // NODE_BUFFER_H_