mirror of https://github.com/nodejs/node.git synced 2024-11-30 23:43:09 +01:00

Shigeki Ohtsu 64e294adb2 doc: fix heading level error in Buffer doc

tools/doc/html.js in make doc throws an error in checking a heading
level in the markdown file.

PR-URL: https://github.com/nodejs/node/pull/4537
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

2016-01-05 10:13:21 -08:00

39 KiB

Raw Blame History

Buffer

Stability: 2 - Stable

Prior to the introduction of TypedArray in ECMAScript 2015 (ES6), the JavaScript language had no mechanism for reading or manipulating streams of binary data. The Buffer class was introduced as part of the Node.js API to make it possible to interact with octet streams in the context of things like TCP streams and file system operations.

Now that TypedArray has been added in ES6, the Buffer class implements the Uint8Array API in a manner that is more optimized and suitable for Node.js' use cases.

Instances of the Buffer class are similar to arrays of integers but correspond to fixed-sized, raw memory allocations outside the V8 heap. The size of the Buffer is established when it is created and cannot be resized.

The Buffer class is a global within Node.js, making it unlikely that one would need to ever use require('buffer').

const buf1 = new Buffer(10);
  // creates a buffer of length 10

const buf2 = new Buffer([1,2,3]);
  // creates a buffer containing [01, 02, 03]

const buf3 = new Buffer('test');
  // creates a buffer containing ASCII bytes [74, 65, 73, 74]

const buf4 = new Buffer('tést', 'utf8');
  // creates a buffer containing UTF8 bytes [74, c3, a9, 73, 74]

Buffers and Character Encodings

Buffers are commonly used to represent sequences of encoded characters such as UTF8, UCS2, Base64 or even Hex-encoded data. It is possible to convert back and forth between Buffers and ordinary JavaScript string objects by using an explicit encoding method.

const buf = new Buffer('hello world', 'ascii');
console.log(buf.toString('hex'));
  // prints: 68656c6c6f20776f726c64
console.log(buf.toString('base64'));
  // prints: aGVsbG8gd29ybGQ=

The character encodings currently supported by Node.js include:

'ascii' - for 7-bit ASCII data only. This encoding method is very fast and will strip the high bit if set.
'utf8' - Multibyte encoded Unicode characters. Many web pages and other document formats use UTF-8.
'utf16le' - 2 or 4 bytes, little-endian encoded Unicode characters. Surrogate pairs (U+10000 to U+10FFFF) are supported.
'ucs2' - Alias of 'utf16le'.
'base64' - Base64 string encoding.
'binary' - A way of encoding the buffer into a one-byte (latin-1) encoded string. The string 'latin-1' is not supported. Instead, pass 'binary' to use 'latin-1' encoding.
'hex' - Encode each byte as two hexadecimal characters.

Buffers and TypedArray

Buffers are also Uint8Array TypedArray instances. However, there are subtle incompatibilities with the TypedArray specification in ECMAScript 2015. For instance, while ArrayBuffer#slice() creates a copy of the slice, the implementation of Buffer#slice() creates a view over the existing Buffer without copying, making Buffer#slice() far more efficient.

It is also possible to create new TypedArray instances from a Buffer with the following caveats:

The Buffer instances's memory is copied to the TypedArray, not shared.
The Buffer's memory is interpreted as an array of distinct elements, and not as a byte array of the target type. That is, new Uint32Array(new Buffer([1,2,3,4])) creates a 4-element Uint32Array with elements [1,2,3,4], not a Uint32Array with a single element [0x1020304] or [0x4030201].

It is possible to create a new Buffer that shares the same allocated memory as a TypedArray instance by using the TypeArray objects .buffer property:

const arr = new Uint16Array(2);
arr[0] = 5000;
arr[1] = 4000;

const buf1 = new Buffer(arr); // copies the buffer
const buf2 = new Buffer(arr.buffer); // shares the memory with arr;

console.log(buf1);
  // Prints: <Buffer 88 a0>, copied buffer has only two elements
console.log(buf2);
  // Prints: <Buffer 88 13 a0 0f>

arr[1] = 6000;
console.log(buf1);
  // Prints: <Buffer 88 a0>
console.log(buf2);
  // Prints: <Buffer 88 13 70 17>

Note that when creating a Buffer using the TypeArray's .buffer, it is not currently possible to use only a portion of the underlying ArrayBuffer. To create a Buffer that uses only a part of the ArrayBuffer, use the buf.slice() function after the Buffer is created:

const arr = new Uint16Array(20);
const buf = new Buffer(arr.buffer).slice(0, 16);
console.log(buf.length);
  // Prints: 16

Buffers and ES6 iteration

Buffers can be iterated over using the ECMAScript 2015 (ES6) for..of syntax:

const buf = new Buffer([1, 2, 3]);

for (var b of buf)
  console.log(b)

// Prints:
//   1
//   2
//   3

Additionally, the buffer.values(), buffer.keys(), and buffer.entries() methods can be used to create iterators.

Class: Buffer

The Buffer class is a global type for dealing with binary data directly. It can be constructed in a variety of ways.

new Buffer(array)

array Array

Allocates a new Buffer using an array of octets.

const buf = new Buffer([0x62,0x75,0x66,0x66,0x65,0x72]);
  // creates a new Buffer containing ASCII bytes
  // ['b','u','f','f','e','r']

new Buffer(buffer)

buffer {Buffer}

Copies the passed buffer data onto a new Buffer instance.

const buf1 = new Buffer('buffer');
const buf2 = new Buffer(buf1);

buf1[0] = 0x61;
console.log(buf1.toString());
  // 'auffer'
console.log(buf2.toString());
  // 'buffer' (copy is not changed)

new Buffer(arrayBuffer)

arrayBuffer - The .buffer property of a TypedArray or a new ArrayBuffer()

When passed a reference to the .buffer property of a TypedArray instance, the newly created Buffer will share the same allocated memory as the TypedArray.

const arr = new Uint16Array(2);
arr[0] = 5000;
arr[1] = 4000;

const buf = new Buffer(arr.buffer); // shares the memory with arr;

console.log(buf);
  // Prints: <Buffer 88 13 a0 0f>

// changing the TypdArray changes the Buffer also
arr[1] = 6000;

console.log(buf);
  // Prints: <Buffer 88 13 70 17>

new Buffer(size)

size Number

Allocates a new Buffer of size bytes. The size must be less than or equal to the value of require('buffer').kMaxLength (on 64-bit architectures, kMaxLength is (2^31)-1). Otherwise, a RangeError is thrown. If a size less than 0 is specified, a zero-length Buffer will be created.

Unlike ArrayBuffers, the underlying memory for Buffer instances created in this way is not initialized. The contents of a newly created Buffer are unknown and could contain sensitive data. Use buf.fill(0) to initialize a Buffer to zeroes.

const buf = new Buffer(5);
console.log(buf);
  // <Buffer 78 e0 82 02 01>
  // (octets will be different, every time)
buf.fill(0);
console.log(buf);
  // <Buffer 00 00 00 00 00>

new Buffer(str[, encoding])

str String - string to encode.
encoding String - encoding to use, Optional.

Creates a new Buffer containing the given JavaScript string str. If provided, the encoding parameter identifies the strings character encoding. If not provided, encoding defaults to 'utf8'.

const buf1 = new Buffer('this is a tést');
console.log(buf1.toString());
  // prints: this is a tést
console.log(buf1.toString('ascii'));
  // prints: this is a tC)st

const buf2 = new Buffer('7468697320697320612074c3a97374', 'hex');
console.log(buf2.toString());
  // prints: this is a tést

Class Method: Buffer.byteLength(string[, encoding])

string String
encoding String, Optional, Default: 'utf8'
Return: Number

Returns the actual byte length of a string. If not specified, encoding defaults to 'utf8'. This is not the same as String.prototype.length since that returns the number of characters in a string.

Example:

const str = '\u00bd + \u00bc = \u00be';

console.log(`${str}: ${str.length} characters, ` +
            `${Buffer.byteLength(str, 'utf8')} bytes`);

// ½ + ¼ = ¾: 9 characters, 12 bytes

Class Method: Buffer.compare(buf1, buf2)

buf1 {Buffer}
buf2 {Buffer}

Compares buf1 to buf2 typically for the purpose of sorting arrays of Buffers. This is equivalent is calling buf1.compare(buf2).

const arr = [Buffer('1234'), Buffer('0123')];
arr.sort(Buffer.compare);

Class Method: Buffer.concat(list[, totalLength])

list {Array} List of Buffer objects to concat
totalLength {Number} Total length of the Buffers in the list when concatenated

Returns a new Buffer which is the result of concatenating all the Buffers in the list together.

If the list has no items, or if the totalLength is 0, then a new zero-length Buffer is returned.

If totalLength is not provided, it is calculated from the Buffers in the list. This, however, adds an additional loop to the function, so it is faster to provide the length explicitly.

Example: build a single Buffer from a list of three Buffers:

const buf1 = new Buffer(10).fill(0);
const buf2 = new Buffer(14).fill(0);
const buf3 = new Buffer(18).fill(0);
const totalLength = buf1.length + buf2.length + buf3.length;

console.log(totalLength);
const bufA = Buffer.concat([buf1, buf2, buf3], totalLength);
console.log(bufA);
console.log(bufA.length);

// 42
// <Buffer 00 00 00 00 ...>
// 42

Class Method: Buffer.isBuffer(obj)

obj Object
Return: Boolean

Returns 'true' if obj is a Buffer.

Class Method: Buffer.isEncoding(encoding)

encoding {String} The encoding string to test

Returns true if the encoding is a valid encoding argument, or false otherwise.

buffer.entries()

Creates and returns an iterator of [index, byte] pairs from the Buffer contents.

const buf = new Buffer('buffer');
for (var pair of buf.entries()) {
  console.log(pair);
}
// prints:
//   [0, 98]
//   [1, 117]
//   [2, 102]
//   [3, 102]
//   [4, 101]
//   [5, 114]

buffer.keys()

Creates and returns an iterator of Buffer keys (indices).

const buf = new Buffer('buffer');
for (var key of buf.keys()) {
  console.log(key);
}
// prints:
//   0
//   1
//   2
//   3
//   4
//   5

buffer.values()

Creates and returns an iterator for Buffer values (bytes). This function is called automatically when the Buffer is used in a for..of statement.

const buf = new Buffer('buffer');
for (var value of buf.values()) {
  console.log(value);
}
// prints:
//   98
//   117
//   102
//   102
//   101
//   114

for (var value of buf) {
  console.log(value);
}
// prints:
//   98
//   117
//   102
//   102
//   101
//   114

buf[index]

The index operator [index] can be used to get and set the octet at position index in the Buffer. The values refer to individual bytes, so the legal value range is between 0x00 and 0xFF (hex) or 0 and 255 (decimal).

Example: copy an ASCII string into a Buffer, one byte at a time:

const str = "Node.js";
const buf = new Buffer(str.length);

for (var i = 0; i < str.length ; i++) {
  buf[i] = str.charCodeAt(i);
}

console.log(buf);
  // Prints: Node.js

buf.compare(otherBuffer)

otherBuffer {Buffer}

Compares two Buffer instances and returns a number indicating whether buf comes before, after, or is the same as the otherBuffer in sort order. Comparison is based on the actual sequence of bytes in each Buffer.

0 is returned if otherBuffer is the same as buf
1 is returned if otherBuffer should come before buf when sorted.
-1 is returned if otherBuffer should come after buf when sorted.

const buf1 = new Buffer('ABC');
const buf2 = new Buffer('BCD');
const buf3 = new Buffer('ABCD');

console.log(buf1.compare(buf1));
  // Prints: 0
console.log(buf1.compare(buf2));
  // Prints: -1
console.log(buf1.compare(buf3));
  // Prints: 1
console.log(buf2.compare(buf1));
  // Prints: 1
console.log(buf2.compare(buf3));
  // Prints: 1

[buf1, buf2, buf3].sort(Buffer.compare);
  // produces sort order [buf1, buf3, buf2]

buf.copy(targetBuffer[, targetStart][, sourceStart][, sourceEnd])

targetBuffer Buffer object - Buffer to copy into
targetStart Number, Optional, Default: 0
sourceStart Number, Optional, Default: 0
sourceEnd Number, Optional, Default: buffer.length

Copies data from a region of this Buffer to a region in the target Buffer even if the target memory region overlaps with the source. If undefined, the targetStart and sourceStart parameters default to 0 while sourceEnd defaults to buffer.length.

Returns the number of bytes copied.

Example: build two Buffers, then copy buf1 from byte 16 through byte 19 into buf2, starting at the 8th byte in buf2.

const buf1 = new Buffer(26);
const buf2 = new Buffer(26).fill('!');

for (var i = 0 ; i < 26 ; i++) {
  buf1[i] = i + 97; // 97 is ASCII a
}

buf1.copy(buf2, 8, 16, 20);
console.log(buf2.toString('ascii', 0, 25));
  // Prints: !!!!!!!!qrst!!!!!!!!!!!!!

Example: Build a single Buffer, then copy data from one region to an overlapping region in the same Buffer

const buf = new Buffer(26);

for (var i = 0 ; i < 26 ; i++) {
  buf[i] = i + 97; // 97 is ASCII a
}

buf.copy(buf, 0, 4, 10);
console.log(buf.toString());

// efghijghijklmnopqrstuvwxyz

buf.equals(otherBuffer)

otherBuffer {Buffer}

Returns a boolean indicating whether this and otherBuffer have exactly the same bytes.

const buf1 = new Buffer('ABC');
const buf2 = new Buffer('414243', 'hex');
const buf3 = new Buffer('ABCD');

console.log(buf1.equals(buf2));
  // Prints: true
console.log(buf1.equals(buf3));
  // Prints: false

buf.fill(value[, offset][, end])

value
offset Number, Optional
end Number, Optional

Fills the Buffer with the specified value. If the offset (defaults to 0) and end (defaults to buffer.length) are not given it will fill the entire Buffer. The method returns a reference to the Buffer so calls can be chained.

const b = new Buffer(50).fill('h');
console.log(b.toString());
  // Prints: hhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhh

buf.indexOf(value[, byteOffset])

value String, Buffer or Number
byteOffset Number, Optional, Default: 0
Return: Number

Operates similar to Array#indexOf() in that it returns either the starting index position of value in Buffer or -1 if the Buffer does not contain value. The value can be a String, Buffer or Number. Strings are interpreted as UTF8. Buffers will use the entire Buffer (to compare a partial Buffer use Buffer#slice()). Numbers can range from 0 to 255.

const buf = new Buffer('this is a buffer');

buf.indexOf('this');
  // returns 0
buf.indexOf('is');
  // returns 2
buf.indexOf(new Buffer('a buffer'));
  // returns 8
buf.indexOf(97); // ascii for 'a'
  // returns 8
buf.indexOf(new Buffer('a buffer example'));
  // returns -1
buf.indexOf(new Buffer('a buffer example').slice(0,8));
  // returns 8

buf.includes(value[, byteOffset][, encoding])

value String, Buffer or Number
byteOffset Number, Optional, Default: 0
encoding String, Optional, Default: 'utf8'

Operates similar to Array#includes(). The value can be a String, Buffer or Number. Strings are interpreted as UTF8 unless overridden with the encoding argument. Buffers will use the entire Buffer (to compare a partial Buffer use Buffer#slice()). Numbers can range from 0 to 255.

The byteOffset indicates the index in buf where searching begins.

const buf = new Buffer('this is a buffer');

buf.includes('this');
  // returns true
buf.includes('is');
  // returns true
buf.includes(new Buffer('a buffer'));
  // returns true
buf.includes(97); // ascii for 'a'
  // returns true
buf.includes(new Buffer('a buffer example'));
  // returns false
buf.includes(new Buffer('a buffer example').slice(0,8));
  // returns true
buf.includes('this', 4);
  // returns false

buf.length

Number

Returns the amount of memory allocated for the Buffer in number of bytes. Note that this does not necessarily reflect the amount of usable data within the Buffer. For instance, in the example below, a Buffer with 1234 bytes is allocated, but only 11 ASCII bytes are written.

const buf = new Buffer(1234);

console.log(buf.length);
  // Prints: 1234

buf.write('some string', 0, 'ascii');
console.log(buf.length);
  // Prints: 1234

While the length property is not immutable, changing the value of length can result in undefined and inconsistent behavior. Applications that wish to modify the length of a Buffer should therefore treat length as read-only and use buf.slice to create a new Buffer.

const buf = new Buffer(10);
buf.write('abcdefghj', 0, 'ascii');
console.log(buf.length);
  // Prints: 10
buf = buf.slice(0,5);
console.log(buf.length);
  // Prints: 5

buf.readDoubleBE(offset[, noAssert])

buf.readDoubleLE(offset[, noAssert])

offset Number
noAssert Boolean, Optional, Default: false
Return: Number

Reads a 64-bit double from the Buffer at the specified offset with specified endian format (readDoubleBE() returns big endian, readDoubleLE() returns little endian).

Setting noAssert to true skips validation of the offset. This allows the offset to be beyond the end of the Buffer. When not specified, noAssert defaults to false.

const buf = new Buffer([1,2,3,4,5,6,7,8]);

buf.readDoubleBE();
  // Returns: 8.20788039913184e-304
buf.readDoubleLE();
  // Returns: 5.447603722011605e-270
buf.readDoubleLE(1);
  // throws RangeError: Index out of range

buf.readDoubleLE(1, true); // Warning: reads passed end of buffer!
  // Segmentation fault! don't do this!

buf.readFloatBE(offset[, noAssert])

buf.readFloatLE(offset[, noAssert])

offset Number
noAssert Boolean, Optional, Default: false
Return: Number

Reads a 32-bit float from the Buffer at the specified offset with specified endian format (readFloatBE() returns big endian, readFloatLE() returns little endian).

Setting noAssert to true skips validation of the offset. This allows the offset to be beyond the end of the Buffer. When not specified, noAssert defaults to false.

const buf = new Buffer([1,2,3,4]);

buf.readFloatBE();
  // Returns: 2.387939260590663e-38
buf.readFloatLE();
  // Returns: 1.539989614439558e-36
buf.readFloatLE(1);
  // throws RangeError: Index out of range

buf.readFloatLE(1, true); // Warning: reads passed end of buffer!
  // Segmentation fault! don't do this!

buf.readInt8(offset[, noAssert])

offset Number
noAssert Boolean, Optional, Default: false
Return: Number

Reads a signed 8-bit integer from the Buffer at the specified offset.

Setting noAssert to true skips validation of the offset. This allows the offset to be beyond the end of the Buffer. When not specified, noAssert defaults to false.

Integers read from the Buffer are interpreted as two's complement signed values.

const buf = new Buffer([1,-2,3,4]);

buf.readInt8(0);
  // returns 1
buf.readInt8(1);
  // returns -2

buf.readInt16BE(offset[, noAssert])

buf.readInt16LE(offset[, noAssert])

offset Number
noAssert Boolean, Optional, Default: false
Return: Number

Reads a signed 16-bit integer from the Buffer at the specified offset with the specified endian format (readInt16BE() returns big endian, readInt16LE() returns little endian).

Setting noAssert to true skips validation of the offset. This allows the offset to be beyond the end of the Buffer. When not specified, noAssert defaults to false.

Integers read from the Buffer are interpreted as two's complement signed values.

const buf = new Buffer([1,-2,3,4]);

buf.readInt16BE();
  // returns 510
buf.readInt16LE(1);
  // returns -511

buf.readInt32BE(offset[, noAssert])

buf.readInt32LE(offset[, noAssert])

offset Number
noAssert Boolean, Optional, Default: false
Return: Number

Reads a signed 32-bit integer from the Buffer at the specified offset with the specified endian format (readInt32BE() returns big endian, readInt32LE() returns little endian).

Setting noAssert to true skips validation of the offset. This allows the offset to be beyond the end of the Buffer. When not specified, noAssert defaults to false.

Integers read from the Buffer are interpreted as two's complement signed values.

const buf = new Buffer([1,-2,3,4]);

buf.readInt32BE();
  // returns 33424132
buf.readInt32LE(1);
  // returns 67370497

buf.readIntBE(offset, byteLength[, noAssert])

buf.readIntLE(offset, byteLength[, noAssert])

offset {Number} 0 <= offset <= buf.length
byteLength {Number} 0 < byteLength <= 6
noAssert {Boolean} Default: false
Return: {Number}

Reads byteLength number of bytes from the Buffer at the specified offset and interprets the result as a two's complement signed value. Supports up to 48 bits of accuracy. For example:

const buf = new Buffer(6);
buf.writeUInt16LE(0x90ab, 0);
buf.writeUInt32LE(0x12345678, 2);
buf.readIntLE(0, 6).toString(16);  // Specify 6 bytes (48 bits)
// Returns: '1234567890ab'

buf.readIntBE(0, 6).toString(16);
// Returns: -546f87a9cbee

Setting noAssert to true skips validation of the offset. This allows the offset to be beyond the end of the Buffer. When not specified, noAssert defaults to false.

buf.readUInt8(offset[, noAssert])

offset Number
noAssert Boolean, Optional, Default: false
Return: Number

Reads an unsigned 8-bit integer from the Buffer at the specified offset.

Setting noAssert to true skips validation of the offset. This allows the offset to be beyond the end of the Buffer. When not specified, noAssert defaults to false.

const buf = new Buffer([1,-2,3,4]);

buf.readUInt8(0);
  // returns 1
buf.readUInt8(1);
  // returns 254

buf.readUInt16BE(offset[, noAssert])

buf.readUInt16LE(offset[, noAssert])

offset Number
noAssert Boolean, Optional, Default: false
Return: Number

Reads an unsigned 16-bit integer from the Buffer at the specified offset with specified endian format (readInt32BE() returns big endian, readInt32LE() returns little endian).

Setting noAssert to true skips validation of the offset. This allows the offset to be beyond the end of the Buffer. When not specified, noAssert defaults to false.

Example:

const buf = new Buffer([0x3, 0x4, 0x23, 0x42]);

buf.readUInt16BE(0);
  // Returns: 0x0304
buf.readUInt16LE(0);
  // Returns: 0x0403
buf.readUInt16BE(1);
  // Returns: 0x0423
buf.readUInt16LE(1);
  // Returns: 0x2304
buf.readUInt16BE(2);
  // Returns: 0x2342
buf.readUInt16LE(2);
  // Returns: 0x4223

buf.readUInt32BE(offset[, noAssert])

buf.readUInt32LE(offset[, noAssert])

offset Number
noAssert Boolean, Optional, Default: false
Return: Number

Reads an unsigned 32-bit integer from the Buffer at the specified offset with specified endian format (readInt32BE() returns big endian, readInt32LE() returns little endian).

Setting noAssert to true skips validation of the offset. This allows the offset to be beyond the end of the Buffer. When not specified, noAssert defaults to false.

Example:

const buf = new Buffer([0x3, 0x4, 0x23, 0x42]);

buf.readUInt32BE(0);
  // Returns: 0x03042342
console.log(buf.readUInt32LE(0));
  // Returns: 0x42230403

buf.readUIntBE(offset, byteLength[, noAssert])

buf.readUIntLE(offset, byteLength[, noAssert])

offset {Number} 0 <= offset <= buf.length
byteLength {Number} 0 < byteLength <= 6
noAssert {Boolean} Default: false
Return: {Number}

Reads byteLength number of bytes from the Buffer at the specified offset and interprets the result as an unsigned integer. Supports up to 48 bits of accuracy. For example:

const buf = new Buffer(6);
buf.writeUInt16LE(0x90ab, 0);
buf.writeUInt32LE(0x12345678, 2);
buf.readUIntLE(0, 6).toString(16);  // Specify 6 bytes (48 bits)
// Returns: '1234567890ab'

buf.readUIntBE(0, 6).toString(16);
// Returns: ab9078563412

Setting noAssert to true skips validation of the offset. This allows the offset to be beyond the end of the Buffer. When not specified, noAssert defaults to false.

buf.slice([start[, end]])

start Number, Optional, Default: 0
end Number, Optional, Default: buffer.length

Returns a new Buffer that references the same memory as the original, but offset and cropped by the start (defaults to 0) and end (defaults to buffer.length) indexes.

Note that modifying the new Buffer slice will modify the memory in the original Buffer because the allocated memory of the two objects overlap.

Example: build a Buffer with the ASCII alphabet, take a slice, then modify one byte from the original Buffer.

const buf1 = new Buffer(26);

for (var i = 0 ; i < 26 ; i++) {
  buf1[i] = i + 97; // 97 is ASCII a
}

const buf2 = buf1.slice(0, 3);
buf2.toString('ascii', 0, buf2.length);
  // Returns: 'abc'
buf1[0] = 33;
buf2.toString('ascii', 0, buf2.length);
  // Returns : '!bc'

Specifying negative indexes causes the slice to be generated relative to the end of the Buffer rather than the beginning.

const buf = new Buffer('buffer');

buf.slice(-6, -1).toString();
  // Returns 'buffe', equivalent to buf.slice(0, 5)
buf.slice(-6, -2).toString();
  // Returns 'buff', equivalent to buf.slice(0, 4)
buf.slice(-5, -2).toString();
  // Returns 'uff', equivalent to buf.slice(1, 4)

buf.toString([encoding][, start][, end])

encoding String, Optional, Default: 'utf8'
start Number, Optional, Default: 0
end Number, Optional, Default: buffer.length

Decodes and returns a string from the Buffer data using the specified character set encoding. If encoding is undefined or null, then encoding defaults to 'utf8'. The start and end parameters default to 0 and buffer.length when undefined.

const buf = new Buffer(26);
for (var i = 0 ; i < 26 ; i++) {
  buf[i] = i + 97; // 97 is ASCII a
}
buf.toString('ascii');
  // Returns: 'abcdefghijklmnopqrstuvwxyz'
buf.toString('ascii',0,5);
  // Returns: 'abcde'
buf.toString('utf8',0,5);
  // Returns: 'abcde'
buf.toString(undefined,0,5);
  // Returns: 'abcde', encoding defaults to 'utf8'

buf.toJSON()

Returns a JSON representation of the Buffer instance. JSON.stringify implicitly calls this function when stringifying a Buffer instance.

Example:

const buf = new Buffer('test');
const json = JSON.stringify(buf);

console.log(json);
// Prints: '{"type":"Buffer","data":[116,101,115,116]}'

const copy = JSON.parse(json, (key, value) => {
    return value && value.type === 'Buffer'
      ? new Buffer(value.data)
      : value;
  });

console.log(copy.toString());
// Prints: 'test'

buf.write(string[, offset][, length][, encoding])

string String - data to be written to buffer
offset Number, Optional, Default: 0
length Number, Optional, Default: buffer.length - offset
encoding String, Optional, Default: 'utf8'

Writes string to the Buffer at offset using the given encoding. When undefined, offset defaults to 0, and encoding defaults to 'utf8'. The length parameter is the number of bytes to write, when undefined length defaults to buffer.length - offset. If the Buffer did not contain enough space to fit the entire string, only a partial amount of the string will be written however, the will not write only partially encoded characters. The return value indicates the number of octets written.

const buf = new Buffer(256);
const len = buf.write('\u00bd + \u00bc = \u00be', 0);
console.log(`${len} bytes: ${buf.toString('utf8', 0, len)}`);
  // Prints: 12 bytes: ½ + ¼ = ¾

buf.writeDoubleBE(value, offset[, noAssert])

buf.writeDoubleLE(value, offset[, noAssert])

value Number
offset Number
noAssert Boolean, Optional, Default: false

Writes value to the Buffer at the specified offset with specified endian format (writeDoubleBE() writes big endian, writeDoubleLE() writes little endian). The value argument must be a valid 64-bit double.

Set noAssert to true to skip validation of value and offset. This means that value may be too large for the specific function and offset may be beyond the end of the Buffer leading to the values being silently dropped. This should not be used unless you are certain of correctness. Defaults to false.

Example:

const buf = new Buffer(8);
buf.writeDoubleBE(0xdeadbeefcafebabe, 0);

console.log(buf);
  // Prints: <Buffer 43 eb d5 b7 dd f9 5f d7>

buf.writeDoubleLE(0xdeadbeefcafebabe, 0);

console.log(buf);
  // Prints: <Buffer d7 5f f9 dd b7 d5 eb 43>

buf.writeFloatBE(value, offset[, noAssert])

buf.writeFloatLE(value, offset[, noAssert])

value Number
offset Number
noAssert Boolean, Optional, Default: false

Writes value to the Buffer at the specified offset with specified endian format (writeFloatBE() writes big endian, writeFloatLE() writes little endian). Behavior is unspecified if value is anything other than a 32-bit float.

Example:

const buf = new Buffer(4);
buf.writeFloatBE(0xcafebabe, 0);

console.log(buf);
  // Prints: <Buffer 4f 4a fe bb>

buf.writeFloatLE(0xcafebabe, 0);

console.log(buf);
  // Prints: <Buffer bb fe 4a 4f>

buf.writeInt8(value, offset[, noAssert])

value Number
offset Number
noAssert Boolean, Optional, Default: false

Writes value to the Buffer at the specified offset. The value must be a valid signed 8-bit integer.

The value is interpreted and written as a two's complement signed integer.

const buf = new Buffer(2);
buf.writeInt8(2, 0);
buf.writeInt8(-2, 1);
console.log(buf);
  // Prints: <Buffer 02 fe>

buf.writeInt16BE(value, offset[, noAssert])

buf.writeInt16LE(value, offset[, noAssert])

value Number
offset Number
noAssert Boolean, Optional, Default: false

Writes value to the Buffer at the specified offset with specified endian format (writeInt16BE() writes big endian, writeInt16LE() writes little endian). The value must be a valid signed 16-bit integer.

The value is interpreted and written as a two's complement signed integer.

const buf = new Buffer(4);
buf.writeInt16BE(0x0102,0);
buf.writeInt16LE(0x0304,2);
console.log(buf);
  // Prints: <Buffer 01 02 04 03>

buf.writeInt32BE(value, offset[, noAssert])

buf.writeInt32LE(value, offset[, noAssert])

value Number
offset Number
noAssert Boolean, Optional, Default: false

Writes value to the Buffer at the specified offset with specified endian format (writeInt32BE() writes big endian, writeInt32LE() writes little endian). The value must be a valid signed 32-bit integer.

The value is interpreted and written as a two's complement signed integer.

const buf = new Buffer(8);
buf.writeInt32BE(0x01020304,0);
buf.writeInt32LE(0x05060708,4);
console.log(buf);
  // Prints: <Buffer 01 02 03 04 08 07 06 05>

buf.writeIntBE(value, offset, byteLength[, noAssert])

buf.writeIntLE(value, offset, byteLength[, noAssert])

value {Number} Bytes to be written to Buffer
offset {Number} 0 <= offset <= buf.length
byteLength {Number} 0 < byteLength <= 6
noAssert {Boolean} Default: false
Return: {Number}

Writes value to the Buffer at the specified offset and byteLength. Supports up to 48 bits of accuracy. For example:

const buf1 = new Buffer(6);
buf1.writeUIntBE(0x1234567890ab, 0, 6);
console.log(buf1);
  // Prints: <Buffer 12 34 56 78 90 ab>

const buf2 = new Buffer(6);
buf2.writeUIntLE(0x1234567890ab, 0, 6);
console.log(buf2);
  // Prints: <Buffer ab 90 78 56 34 12>

buf.writeUInt8(value, offset[, noAssert])

value Number
offset Number
noAssert Boolean, Optional, Default: false

Writes value to the Buffer at the specified offset. The value must be a valid unsigned 8-bit integer.

Example:

const buf = new Buffer(4);
buf.writeUInt8(0x3, 0);
buf.writeUInt8(0x4, 1);
buf.writeUInt8(0x23, 2);
buf.writeUInt8(0x42, 3);

console.log(buf);
  // Prints: <Buffer 03 04 23 42>

buf.writeUInt16BE(value, offset[, noAssert])

buf.writeUInt16LE(value, offset[, noAssert])

value Number
offset Number
noAssert Boolean, Optional, Default: false

Writes value to the Buffer at the specified offset with specified endian format (writeUInt16BE() writes big endian, writeUInt16LE() writes little endian). The value must be a valid unsigned 16-bit integer.

Example:

const buf = new Buffer(4);
buf.writeUInt16BE(0xdead, 0);
buf.writeUInt16BE(0xbeef, 2);

console.log(buf);
  // Prints: <Buffer de ad be ef>

buf.writeUInt16LE(0xdead, 0);
buf.writeUInt16LE(0xbeef, 2);

console.log(buf);
  // Prints: <Buffer ad de ef be>

buf.writeUInt32BE(value, offset[, noAssert])

buf.writeUInt32LE(value, offset[, noAssert])

value Number
offset Number
noAssert Boolean, Optional, Default: false

Writes value to the Buffer at the specified offset with specified endian format (writeUInt32BE() writes big endian, writeUInt32LE() writes little endian). The value must be a valid unsigned 32-bit integer.

Example:

const buf = new Buffer(4);
buf.writeUInt32BE(0xfeedface, 0);

console.log(buf);
  // Prints: <Buffer fe ed fa ce>

buf.writeUInt32LE(0xfeedface, 0);

console.log(buf);
  // Prints: <Buffer ce fa ed fe>

buf.writeUIntBE(value, offset, byteLength[, noAssert])

buf.writeUIntLE(value, offset, byteLength[, noAssert])

value {Number} Bytes to be written to Buffer
offset {Number} 0 <= offset <= buf.length
byteLength {Number} 0 < byteLength <= 6
noAssert {Boolean} Default: false
Return: {Number}

Writes value to the Buffer at the specified offset and byteLength. Supports up to 48 bits of accuracy. For example:

const buf = new Buffer(6);
buf.writeUIntBE(0x1234567890ab, 0, 6);
console.log(buf);
  // Prints: <Buffer 12 34 56 78 90 ab>

buffer.INSPECT_MAX_BYTES

Number, Default: 50

Returns the maximum number of bytes that will be returned when buffer.inspect() is called. This can be overridden by user modules. See util.inspect() for more details on buffer.inspect() behavior.

Note that this is a property on the buffer module as returned by require('buffer'), not on the Buffer global or a Buffer instance.

Class: SlowBuffer

Returns an un-pooled Buffer.

In order to avoid the garbage collection overhead of creating many individually allocated Buffers, by default allocations under 4KB are sliced from a single larger allocated object. This approach improves both performance and memory usage since v8 does not need to track and cleanup as many Persistent objects.

In the case where a developer may need to retain a small chunk of memory from a pool for an indeterminate amount of time, it may be appropriate to create an un-pooled Buffer instance using SlowBuffer then copy out the relevant bits.

// need to keep around a few small chunks of memory
const store = [];

socket.on('readable', () => {
  var data = socket.read();
  // allocate for retained data
  var sb = new SlowBuffer(10);
  // copy the data into the new allocation
  data.copy(sb, 0, 0, 10);
  store.push(sb);
});

Use of SlowBuffer should be used only as a last resort after a developer has observed undue memory retention in their applications.

39 KiB Raw Blame History

Buffer

Buffers and Character Encodings

Buffers and TypedArray

Buffers and ES6 iteration

Class: Buffer

new Buffer(array)

new Buffer(buffer)

new Buffer(arrayBuffer)

new Buffer(size)

new Buffer(str[, encoding])

Class Method: Buffer.byteLength(string[, encoding])

Class Method: Buffer.compare(buf1, buf2)

Class Method: Buffer.concat(list[, totalLength])

Class Method: Buffer.isBuffer(obj)

Class Method: Buffer.isEncoding(encoding)

buffer.entries()

buffer.keys()

buffer.values()

buf[index]

buf.compare(otherBuffer)

buf.copy(targetBuffer[, targetStart][, sourceStart][, sourceEnd])

buf.equals(otherBuffer)

buf.fill(value[, offset][, end])

buf.indexOf(value[, byteOffset])

buf.includes(value[, byteOffset][, encoding])

buf.length

buf.readDoubleBE(offset[, noAssert])

buf.readDoubleLE(offset[, noAssert])

buf.readFloatBE(offset[, noAssert])

buf.readFloatLE(offset[, noAssert])

buf.readInt8(offset[, noAssert])

buf.readInt16BE(offset[, noAssert])

buf.readInt16LE(offset[, noAssert])

buf.readInt32BE(offset[, noAssert])

buf.readInt32LE(offset[, noAssert])

buf.readIntBE(offset, byteLength[, noAssert])

buf.readIntLE(offset, byteLength[, noAssert])

buf.readUInt8(offset[, noAssert])

buf.readUInt16BE(offset[, noAssert])

buf.readUInt16LE(offset[, noAssert])

buf.readUInt32BE(offset[, noAssert])

buf.readUInt32LE(offset[, noAssert])

buf.readUIntBE(offset, byteLength[, noAssert])

buf.readUIntLE(offset, byteLength[, noAssert])

buf.slice([start[, end]])

buf.toString([encoding][, start][, end])

buf.toJSON()

buf.write(string[, offset][, length][, encoding])

buf.writeDoubleBE(value, offset[, noAssert])

buf.writeDoubleLE(value, offset[, noAssert])

buf.writeFloatBE(value, offset[, noAssert])

buf.writeFloatLE(value, offset[, noAssert])

buf.writeInt8(value, offset[, noAssert])

buf.writeInt16BE(value, offset[, noAssert])

buf.writeInt16LE(value, offset[, noAssert])

buf.writeInt32BE(value, offset[, noAssert])

buf.writeInt32LE(value, offset[, noAssert])

buf.writeIntBE(value, offset, byteLength[, noAssert])

buf.writeIntLE(value, offset, byteLength[, noAssert])

buf.writeUInt8(value, offset[, noAssert])

buf.writeUInt16BE(value, offset[, noAssert])

buf.writeUInt16LE(value, offset[, noAssert])

buf.writeUInt32BE(value, offset[, noAssert])

buf.writeUInt32LE(value, offset[, noAssert])

buf.writeUIntBE(value, offset, byteLength[, noAssert])

buf.writeUIntLE(value, offset, byteLength[, noAssert])

buffer.INSPECT_MAX_BYTES

Class: SlowBuffer

39 KiB

Raw Blame History