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Node.js v6.0.0-nightly20160301d9f7a597e4 Documentation
Table of Contents
- 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)
- buf[index]
- buf.compare(otherBuffer)
- buf.copy(targetBuffer[, targetStart[, sourceStart[, sourceEnd]]])
- buf.entries()
- buf.equals(otherBuffer)
- buf.fill(value[, offset[, end]][, encoding])
- buf.indexOf(value[, byteOffset][, encoding])
- buf.includes(value[, byteOffset][, encoding])
- buf.keys()
- 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.values()
- 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
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. When creating a buffer from a string, this encoding will also correctly accept "URL and Filename Safe Alphabet" as specified in RFC 4648, Section 5.'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-elementUint32Array
with elements[1,2,3,4]
, not aUint32Array
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 buf.values()
, buf.keys()
, and
buf.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 aTypedArray
or anew 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])#
Creates a new Buffer containing the given JavaScript string str
. If
provided, the encoding
parameter identifies the strings character encoding.
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])#
Returns the actual byte length of a string. 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)#
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])#
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)#
Returns 'true' if obj
is a Buffer.
Class Method: Buffer.isEncoding(encoding)#
Returns true if the encoding
is a valid encoding argument, or false
otherwise.
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.toString('ascii'));
// Prints: Node.js
buf.compare(otherBuffer)#
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 ifotherBuffer
is the same asbuf
1
is returned ifotherBuffer
should come beforebuf
when sorted.-1
is returned ifotherBuffer
should come afterbuf
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]]])#
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.
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.entries()#
- Return: <Iterator>
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]
buf.equals(otherBuffer)#
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]][, encoding])#
Fills the Buffer with the specified value. If the offset
(defaults to 0
)
and end
(defaults to buf.length
) are not given the entire buffer will be
filled. The method returns a reference to the Buffer, so calls can be chained.
This is meant as a small simplification to creating a Buffer. Allowing the
creation and fill of the Buffer to be done on a single line:
const b = new Buffer(50).fill('h');
console.log(b.toString());
// Prints: hhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhh
encoding
is only relevant if value
is a string. Otherwise it is ignored.
value
is coerced to a uint32
value if it is not a String or Number.
The fill()
operation writes bytes into the Buffer dumbly. If the final write
falls in between a multi-byte character then whatever bytes fit into the buffer
are written.
Buffer(3).fill('\u0222');
// Prints: <Buffer c8 a2 c8>
buf.indexOf(value[, byteOffset][, encoding])#
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 by
default interpreted as UTF8. Buffers will use the entire Buffer (to compare a
partial Buffer use buf.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
const utf16Buffer = new Buffer('\u039a\u0391\u03a3\u03a3\u0395', 'ucs2');
utf16Buffer.indexOf('\u03a3', 0, 'ucs2');
// returns 4
utf16Buffer.indexOf('\u03a3', -4, 'ucs2');
// returns 6
buf.includes(value[, byteOffset][, encoding])#
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 buf.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.keys()#
- Return: <Iterator>
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
buf.length#
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.
var 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])#
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.
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])#
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.
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])#
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.
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])#
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.
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 1022
buf.readInt32BE(offset[, noAssert])#
buf.readInt32LE(offset[, noAssert])#
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.
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])#
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.
buf.readUInt8(offset[, noAssert])#
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.
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])#
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.
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])#
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.
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])#
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.
buf.slice([start[, end]])#
Returns a new Buffer that references the same memory as the original, but
offset and cropped by the start
and end
indices.
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]]])#
Decodes and returns a string from the Buffer data using the specified
character set encoding
.
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()#
- Return: <Object>
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.values()#
- Return: <Iterator>
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.write(string[, offset[, length]][, encoding])#
Writes string
to the Buffer at offset
using the given encoding
.
The length
parameter is the number of bytes to write. If the Buffer did not
contain enough space to fit the entire string, only a partial amount of the
string will be written however, it will not write only partially encoded
characters.
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])#
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.
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])#
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.
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.
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])#
Writes value
to the Buffer at the specified offset
. The value
must be a
valid signed 8-bit integer.
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.
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])#
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.
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.
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])#
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.
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.
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])#
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>
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.
buf.writeUInt8(value, offset[, noAssert])#
Writes value
to the Buffer at the specified offset
. The value
must be a
valid unsigned 8-bit integer.
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.
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])#
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.
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.
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])#
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.
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.
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])#
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>
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.
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.