xref: /napi_generator/examples/napitutorials/doc/apiguide/buffer.md

# Buffer

Class `Napi::Buffer` inherits from class [`Napi::Uint8Array`][].

The `Napi::Buffer` class creates a projection of raw data that can be consumed by
script.

## Methods

### New

Allocates a new `Napi::Buffer` object with a given length.

```cpp
static Napi::Buffer<T> Napi::Buffer::New(napi_env env, size_t length);
```

- `[in] env`: The environment in which to create the `Napi::Buffer` object.
- `[in] length`: The number of `T` elements to allocate.

Returns a new `Napi::Buffer` object.

### New

> When `NODE_API_NO_EXTERNAL_BUFFERS_ALLOWED` is defined, this method is not available.
> See [External Buffer][] for more information.

Wraps the provided external data into a new `Napi::Buffer` object.

The `Napi::Buffer` object does not assume ownership for the data and expects it to be
valid for the lifetime of the object. Since the `Napi::Buffer` is subject to garbage
collection this overload is only suitable for data which is static and never
needs to be freed.
This factory method will not provide the caller with an opportunity to free the
data when the `Napi::Buffer` gets garbage-collected. If you need to free the
data retained by the `Napi::Buffer` object please use other variants of the
`Napi::Buffer::New` factory method that accept `Napi::Finalizer`, which is a
function that will be invoked when the `Napi::Buffer` object has been
destroyed.

```cpp
static Napi::Buffer<T> Napi::Buffer::New(napi_env env, T* data, size_t length);
```

- `[in] env`: The environment in which to create the `Napi::Buffer` object.
- `[in] data`: The pointer to the external data to expose.
- `[in] length`: The number of `T` elements in the external data.

Returns a new `Napi::Buffer` object.

### New

> When `NODE_API_NO_EXTERNAL_BUFFERS_ALLOWED` is defined, this method is not available.
> See [External Buffer][] for more information.

Wraps the provided external data into a new `Napi::Buffer` object.

The `Napi::Buffer` object does not assume ownership for the data and expects it
to be valid for the lifetime of the object. The data can only be freed once the
`finalizeCallback` is invoked to indicate that the `Napi::Buffer` has been released.

```cpp
template <typename Finalizer>
static Napi::Buffer<T> Napi::Buffer::New(napi_env env,
                     T* data,
                     size_t length,
                     Finalizer finalizeCallback);
```

- `[in] env`: The environment in which to create the `Napi::Buffer` object.
- `[in] data`: The pointer to the external data to expose.
- `[in] length`: The number of `T` elements in the external data.
- `[in] finalizeCallback`: The function to be called when the `Napi::Buffer` is
  destroyed. It must implement `operator()`, accept an Napi::Env, a `T*` (which is the
  external data pointer), and return `void`.

Returns a new `Napi::Buffer` object.

### New

> When `NODE_API_NO_EXTERNAL_BUFFERS_ALLOWED` is defined, this method is not available.
> See [External Buffer][] for more information.

Wraps the provided external data into a new `Napi::Buffer` object.

The `Napi::Buffer` object does not assume ownership for the data and expects it to be
valid for the lifetime of the object. The data can only be freed once the
`finalizeCallback` is invoked to indicate that the `Napi::Buffer` has been released.

```cpp
template <typename Finalizer, typename Hint>
static Napi::Buffer<T> Napi::Buffer::New(napi_env env,
                     T* data,
                     size_t length,
                     Finalizer finalizeCallback,
                     Hint* finalizeHint);
```

- `[in] env`: The environment in which to create the `Napi::Buffer` object.
- `[in] data`: The pointer to the external data to expose.
- `[in] length`: The number of `T` elements in the external data.
- `[in] finalizeCallback`: The function to be called when the `Napi::Buffer` is
  destroyed. It must implement `operator()`, accept an Napi::Env, a `T*` (which is the
  external data pointer) and `Hint*`, and return `void`.
- `[in] finalizeHint`: The hint to be passed as the second parameter of the
  finalize callback.

Returns a new `Napi::Buffer` object.

### NewOrCopy

Wraps the provided external data into a new `Napi::Buffer` object. When the
[external buffer][] is not supported, allocates a new `Napi::Buffer` object and
copies the provided external data into it.

The `Napi::Buffer` object does not assume ownership for the data and expects it to be
valid for the lifetime of the object. Since the `Napi::Buffer` is subject to garbage
collection this overload is only suitable for data which is static and never
needs to be freed.

This factory method will not provide the caller with an opportunity to free the
data when the `Napi::Buffer` gets garbage-collected. If you need to free the
data retained by the `Napi::Buffer` object please use other variants of the
`Napi::Buffer::New` factory method that accept `Napi::Finalizer`, which is a
function that will be invoked when the `Napi::Buffer` object has been
destroyed.

```cpp
static Napi::Buffer<T> Napi::Buffer::NewOrCopy(napi_env env, T* data, size_t length);
```

- `[in] env`: The environment in which to create the `Napi::Buffer` object.
- `[in] data`: The pointer to the external data to expose.
- `[in] length`: The number of `T` elements in the external data.

Returns a new `Napi::Buffer` object.

### NewOrCopy

Wraps the provided external data into a new `Napi::Buffer` object. When the
[external buffer][] is not supported, allocates a new `Napi::Buffer` object and
copies the provided external data into it and the `finalizeCallback` is invoked
immediately.

The `Napi::Buffer` object does not assume ownership for the data and expects it
to be valid for the lifetime of the object. The data can only be freed once the
`finalizeCallback` is invoked to indicate that the `Napi::Buffer` has been released.

```cpp
template <typename Finalizer>
static Napi::Buffer<T> Napi::Buffer::NewOrCopy(napi_env env,
                                               T* data,
                                               size_t length,
                                               Finalizer finalizeCallback);
```

- `[in] env`: The environment in which to create the `Napi::Buffer` object.
- `[in] data`: The pointer to the external data to expose.
- `[in] length`: The number of `T` elements in the external data.
- `[in] finalizeCallback`: The function to be called when the `Napi::Buffer` is
  destroyed. It must implement `operator()`, accept an Napi::Env, a `T*` (which is the
  external data pointer), and return `void`.

Returns a new `Napi::Buffer` object.

### NewOrCopy

Wraps the provided external data into a new `Napi::Buffer` object. When the
[external buffer][] is not supported, allocates a new `Napi::Buffer` object and
copies the provided external data into it and the `finalizeCallback` is invoked
immediately.

The `Napi::Buffer` object does not assume ownership for the data and expects it to be
valid for the lifetime of the object. The data can only be freed once the
`finalizeCallback` is invoked to indicate that the `Napi::Buffer` has been released.

```cpp
template <typename Finalizer, typename Hint>
static Napi::Buffer<T> Napi::Buffer::NewOrCopy(napi_env env,
                                               T* data,
                                               size_t length,
                                               Finalizer finalizeCallback,
                                               Hint* finalizeHint);
```

- `[in] env`: The environment in which to create the `Napi::Buffer` object.
- `[in] data`: The pointer to the external data to expose.
- `[in] length`: The number of `T` elements in the external data.
- `[in] finalizeCallback`: The function to be called when the `Napi::Buffer` is
  destroyed. It must implement `operator()`, accept an Napi::Env, a `T*` (which is the
  external data pointer) and `Hint*`, and return `void`.
- `[in] finalizeHint`: The hint to be passed as the second parameter of the
  finalize callback.

Returns a new `Napi::Buffer` object.

### Copy

Allocates a new `Napi::Buffer` object and copies the provided external data into it.

```cpp
static Napi::Buffer<T> Napi::Buffer::Copy(napi_env env, const T* data, size_t length);
```

- `[in] env`: The environment in which to create the `Napi::Buffer` object.
- `[in] data`: The pointer to the external data to copy.
- `[in] length`: The number of `T` elements in the external data.

Returns a new `Napi::Buffer` object containing a copy of the data.

### Constructor

Initializes an empty instance of the `Napi::Buffer` class.

```cpp
Napi::Buffer::Buffer();
```

### Constructor

Initializes the `Napi::Buffer` object using an existing Uint8Array.

```cpp
Napi::Buffer::Buffer(napi_env env, napi_value value);
```

- `[in] env`: The environment in which to create the `Napi::Buffer` object.
- `[in] value`: The Uint8Array reference to wrap.

### Data

```cpp
T* Napi::Buffer::Data() const;
```

Returns a pointer the external data.

### Length

```cpp
size_t Napi::Buffer::Length() const;
```

Returns the number of `T` elements in the external data.

[`Napi::Uint8Array`]: ./typed_array_of.md
[External Buffer]: ./external_buffer.md