Buffers
Pure Javascript is Unicode friendly but not nice to binary data. When dealing with TCP streams or the file system, it's necessary to handle octet streams. Node has several strategies for manipulating, creating, and consuming octet streams.
Raw data is stored in instances of the Buffer
class. A Buffer
is similar
to an array of integers but corresponds to a raw memory allocation outside
the V8 heap. A Buffer
cannot be resized.
The Buffer
object is global.
Converting between Buffers and JavaScript string objects requires an explicit encoding method. Here are the different string encodings;
'ascii'
- for 7 bit ASCII data only. This encoding method is very fast, and will strip the high bit if set. Note that this encoding converts a null character ('\0'
or'\u0000'
) into0x20
(character code of a space). If you want to convert a null character into0x00
, you should use'utf8'
.'utf8'
- Multi byte encoded Unicode characters. Many web pages and other document formats use UTF-8.'ucs2'
- 2-bytes, little endian encoded Unicode characters. It can encode only BMP(Basic Multilingual Plane, U+0000 - U+FFFF).'base64'
- Base64 string encoding.'binary'
- A way of encoding raw binary data into strings by using only the first 8 bits of each character. This encoding method is deprecated and should be avoided in favor ofBuffer
objects where possible. This encoding will be removed in future versions of Node.'hex'
- Encode each byte as two hexidecimal characters.
Table of Contents #
- new Buffer()
- new Buffer()
- new Buffer()
- buffer.write()
- buffer.toString()
- buffer[index]
- Buffer.isBuffer()
- Buffer.byteLength()
- buffer.length
- buffer.copy()
- buffer.slice()
- buffer.readUInt8()
- buffer.readUInt16LE()
- buffer.readUInt16BE()
- buffer.readUInt32LE()
- buffer.readUInt32BE()
- buffer.readInt8()
- buffer.readInt16LE()
- buffer.readInt16BE()
- buffer.readInt32LE()
- buffer.readInt32BE()
- buffer.readFloatLE()
- buffer.readFloatBE()
- buffer.readDoubleLE()
- buffer.readDoubleBE()
- buffer.writeUInt8()
- buffer.writeUInt16LE()
- buffer.writeUInt16BE()
- buffer.writeUInt32LE()
- buffer.writeUInt32BE()
- buffer.writeInt8()
- buffer.writeInt16LE()
- buffer.writeInt16BE()
- buffer.writeInt32LE()
- buffer.writeInt32BE()
- buffer.writeFloatLE()
- buffer.writeFloatBE()
- buffer.writeDoubleLE()
- buffer.writeDoubleBE()
- buffer.fill()
- INSPECT_MAX_BYTES
new Buffer(size) #
Allocates a new buffer of size
octets.
new Buffer(array) #
Allocates a new buffer using an array
of octets.
new Buffer(str, encoding='utf8') #
Allocates a new buffer containing the given str
.
buffer.write(string, offset=0, length=buffer.length-offset, encoding='utf8') #
Writes string
to the buffer at offset
using the given encoding. length
is
the number of bytes to write. Returns number of octets written. If buffer
did
not contain enough space to fit the entire string, it will write a partial
amount of the string. The method will not write partial characters.
Example: write a utf8 string into a buffer, then print it
buf = new Buffer(256);
len = buf.write('\u00bd + \u00bc = \u00be', 0);
console.log(len + " bytes: " + buf.toString('utf8', 0, len));
The number of characters written (which may be different than the number of
bytes written) is set in Buffer._charsWritten
and will be overwritten the
next time buf.write()
is called.
buffer.toString(encoding, start=0, end=buffer.length) #
Decodes and returns a string from buffer data encoded with encoding
beginning at start
and ending at end
.
See buffer.write()
example, above.
buffer[index] #
Get and set the octet at index
. The values refer to individual bytes,
so the legal range is between 0x00
and 0xFF
hex or 0
and 255
.
Example: copy an ASCII string into a buffer, one byte at a time:
str = "node.js";
buf = new Buffer(str.length);
for (var i = 0; i < str.length ; i++) {
buf[i] = str.charCodeAt(i);
}
console.log(buf);
// node.js
Buffer.isBuffer(obj) #
Tests if obj
is a Buffer
.
Buffer.byteLength(string, encoding='utf8') #
Gives 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:
str = '\u00bd + \u00bc = \u00be';
console.log(str + ": " + str.length + " characters, " +
Buffer.byteLength(str, 'utf8') + " bytes");
// ½ + ¼ = ¾: 9 characters, 12 bytes
buffer.length #
The size of the buffer in bytes. Note that this is not necessarily the size
of the contents. length
refers to the amount of memory allocated for the
buffer object. It does not change when the contents of the buffer are changed.
buf = new Buffer(1234);
console.log(buf.length);
buf.write("some string", "ascii", 0);
console.log(buf.length);
// 1234
// 1234
buffer.copy(targetBuffer, targetStart=0, sourceStart=0, sourceEnd=buffer.length) #
Does copy between buffers. The source and target regions can be overlapped.
Example: build two Buffers, then copy buf1
from byte 16 through byte 19
into buf2
, starting at the 8th byte in buf2
.
buf1 = new Buffer(26);
buf2 = new Buffer(26);
for (var i = 0 ; i < 26 ; i++) {
buf1[i] = i + 97; // 97 is ASCII a
buf2[i] = 33; // ASCII !
}
buf1.copy(buf2, 8, 16, 20);
console.log(buf2.toString('ascii', 0, 25));
// !!!!!!!!qrst!!!!!!!!!!!!!
buffer.slice(start, end=buffer.length) #
Returns a new buffer which references the
same memory as the old, but offset and cropped by the start
and end
indexes.
Modifying the new buffer slice will modify memory in the original buffer!
Example: build a Buffer with the ASCII alphabet, take a slice, then modify one byte from the original Buffer.
var buf1 = new Buffer(26);
for (var i = 0 ; i < 26 ; i++) {
buf1[i] = i + 97; // 97 is ASCII a
}
var buf2 = buf1.slice(0, 3);
console.log(buf2.toString('ascii', 0, buf2.length));
buf1[0] = 33;
console.log(buf2.toString('ascii', 0, buf2.length));
// abc
// !bc
buffer.readUInt8(offset, noAssert=false) #
Reads an unsigned 8 bit integer from the buffer at the specified offset.
Set noAssert
to true to skip validation of offset
. This means that offset
may be beyond the end of the buffer.
Example:
var buf = new Buffer(4);
buf[0] = 0x3;
buf[1] = 0x4;
buf[2] = 0x23;
buf[3] = 0x42;
for (ii = 0; ii < buf.length; ii++) {
console.log(buf.readUInt8(ii));
}
// 0x3
// 0x4
// 0x23
// 0x42
buffer.readUInt16LE(offset, noAssert=false) #
buffer.readUInt16BE(offset, noAssert=false) #
Reads an unsigned 16 bit integer from the buffer at the specified offset with specified endian format.
Set noAssert
to true to skip validation of offset
. This means that offset
may be beyond the end of the buffer.
Example:
var buf = new Buffer(4);
buf[0] = 0x3;
buf[1] = 0x4;
buf[2] = 0x23;
buf[3] = 0x42;
console.log(buf.readUInt16BE(0));
console.log(buf.readUInt16LE(0));
console.log(buf.readUInt16BE(1));
console.log(buf.readUInt16LE(1));
console.log(buf.readUInt16BE(2));
console.log(buf.readUInt16LE(2));
// 0x0304
// 0x0403
// 0x0423
// 0x2304
// 0x2342
// 0x4223
buffer.readUInt32LE(offset, noAssert=false) #
buffer.readUInt32BE(offset, noAssert=false) #
Reads an unsigned 32 bit integer from the buffer at the specified offset with specified endian format.
Set noAssert
to true to skip validation of offset
. This means that offset
may be beyond the end of the buffer.
Example:
var buf = new Buffer(4);
buf[0] = 0x3;
buf[1] = 0x4;
buf[2] = 0x23;
buf[3] = 0x42;
console.log(buf.readUInt32BE(0));
console.log(buf.readUInt32LE(0));
// 0x03042342
// 0x42230403
buffer.readInt8(offset, noAssert=false) #
Reads a signed 8 bit integer from the buffer at the specified offset.
Set noAssert
to true to skip validation of offset
. This means that offset
may be beyond the end of the buffer.
Works as buffer.readUInt8
, except buffer contents are treated as two's
complement signed values.
buffer.readInt16LE(offset, noAssert=false) #
buffer.readInt16BE(offset, noAssert=false) #
Reads a signed 16 bit integer from the buffer at the specified offset with specified endian format.
Set noAssert
to true to skip validation of offset
. This means that offset
may be beyond the end of the buffer.
Works as buffer.readUInt16*
, except buffer contents are treated as two's
complement signed values.
buffer.readInt32LE(offset, noAssert=false) #
buffer.readInt32BE(offset, noAssert=false) #
Reads a signed 32 bit integer from the buffer at the specified offset with specified endian format.
Set noAssert
to true to skip validation of offset
. This means that offset
may be beyond the end of the buffer.
Works as buffer.readUInt32*
, except buffer contents are treated as two's
complement signed values.
buffer.readFloatLE(offset, noAssert=false) #
buffer.readFloatBE(offset, noAssert=false) #
Reads a 32 bit float from the buffer at the specified offset with specified endian format.
Set noAssert
to true to skip validation of offset
. This means that offset
may be beyond the end of the buffer.
Example:
var buf = new Buffer(4);
buf[0] = 0x00;
buf[1] = 0x00;
buf[2] = 0x80;
buf[3] = 0x3f;
console.log(buf.readFloatLE(0));
// 0x01
buffer.readDoubleLE(offset, noAssert=false) #
buffer.readDoubleBE(offset, noAssert=false) #
Reads a 64 bit double from the buffer at the specified offset with specified endian format.
Set noAssert
to true to skip validation of offset
. This means that offset
may be beyond the end of the buffer.
Example:
var buf = new Buffer(8);
buf[0] = 0x55;
buf[1] = 0x55;
buf[2] = 0x55;
buf[3] = 0x55;
buf[4] = 0x55;
buf[5] = 0x55;
buf[6] = 0xd5;
buf[7] = 0x3f;
console.log(buf.readDoubleLE(0));
// 0.3333333333333333
buffer.writeUInt8(value, offset, noAssert=false) #
Writes value
to the buffer at the specified offset. Note, 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:
var buf = new Buffer(4);
buf.writeUInt8(0x3, 0);
buf.writeUInt8(0x4, 1);
buf.writeUInt8(0x23, 2);
buf.writeUInt8(0x42, 3);
console.log(buf);
// <Buffer 03 04 23 42>
buffer.writeUInt16LE(value, offset, noAssert=false) #
buffer.writeUInt16BE(value, offset, noAssert=false) #
Writes value
to the buffer at the specified offset with specified endian
format. Note, 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:
var buf = new Buffer(4);
buf.writeUInt16BE(0xdead, 0);
buf.writeUInt16BE(0xbeef, 2);
console.log(buf);
buf.writeUInt16LE(0xdead, 0);
buf.writeUInt16LE(0xbeef, 2);
console.log(buf);
// <Buffer de ad be ef>
// <Buffer ad de ef be>
buffer.writeUInt32LE(value, offset, noAssert=false) #
buffer.writeUInt32BE(value, offset, noAssert=false) #
Writes value
to the buffer at the specified offset with specified endian
format. Note, 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:
var buf = new Buffer(4);
buf.writeUInt32BE(0xfeedface, 0);
console.log(buf);
buf.writeUInt32LE(0xfeedface, 0);
console.log(buf);
// <Buffer fe ed fa ce>
// <Buffer ce fa ed fe>
buffer.writeInt8(value, offset, noAssert=false) #
Writes value
to the buffer at the specified offset. Note, 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.
Works as buffer.writeUInt8
, except value is written out as a two's complement
signed integer into buffer
.
buffer.writeInt16LE(value, offset, noAssert=false) #
buffer.writeInt16BE(value, offset, noAssert=false) #
Writes value
to the buffer at the specified offset with specified endian
format. Note, 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.
Works as buffer.writeUInt16*
, except value is written out as a two's
complement signed integer into buffer
.
buffer.writeInt32LE(value, offset, noAssert=false) #
buffer.writeInt32BE(value, offset, noAssert=false) #
Writes value
to the buffer at the specified offset with specified endian
format. Note, 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.
Works as buffer.writeUInt32*
, except value is written out as a two's
complement signed integer into buffer
.
buffer.writeFloatLE(value, offset, noAssert=false) #
buffer.writeFloatBE(value, offset, noAssert=false) #
Writes value
to the buffer at the specified offset with specified endian
format. Note, value
must be a valid 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:
var buf = new Buffer(4);
buf.writeFloatBE(0xcafebabe, 0);
console.log(buf);
buf.writeFloatLE(0xcafebabe, 0);
console.log(buf);
// <Buffer 4f 4a fe bb>
// <Buffer bb fe 4a 4f>
buffer.writeDoubleLE(value, offset, noAssert=false) #
buffer.writeDoubleBE(value, offset, noAssert=false) #
Writes value
to the buffer at the specified offset with specified endian
format. Note, value
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:
var buf = new Buffer(8);
buf.writeDoubleBE(0xdeadbeefcafebabe, 0);
console.log(buf);
buf.writeDoubleLE(0xdeadbeefcafebabe, 0);
console.log(buf);
// <Buffer 43 eb d5 b7 dd f9 5f d7>
// <Buffer d7 5f f9 dd b7 d5 eb 43>
buffer.fill(value, offset=0, end=buffer.length) #
Fills the buffer with the specified value. If the offset and end are not given it will fill the entire buffer.
var b = new Buffer(50);
b.fill("h");
INSPECT_MAX_BYTES #
How many bytes will be returned when buffer.inspect()
is called. This can
be overriden by user modules.
Documentation generated by mdoc.