bitcoin-bufferlist (Bitcoin BufferList)

A Node.js Buffer Writer and Reader for Bitcoin apps

bitcoin-bufferlist is a storage object for collections of Node Buffers, exposing them with the main Buffer readable API.

The original buffers are kept intact and copies are only done as necessary. Any reads that require the use of a single original buffer will return a slice of that buffer only (which references the same memory as the original buffer). Reads that span buffers perform concatenation as required and return the results transparently.

This module is heavily inspired from rvagg/bl but without the callback and streaming interface, and with added Bitcoin-related functions such as writeUInt8/16LE/32LE/64LE, readUInt64LE, and write/readVarInt

const BufferList = require('bitcoin-bufferlist')

var bl = new BufferList()
bl.append(new Buffer('abcd'))
bl.append(new Buffer('efg'))
bl.append(new Buffer('j'))
bl.append(new Buffer([ 0x3, 0x4 ]))
bl.append('hi')                     // bl will also accept & convert Strings
bl.append('00aa', 'hex')                     // bl will also accept & convert hex Strings
bl.append(0xff)                     // bl will also accept & convert Numbers
bl.append([118, 169])  // bl will also accept & convert Arrays

console.log(bl.length) // 12

console.log(bl.slice(0, 10).toString('ascii')) // 'abcdefghij'
console.log(bl.slice(3, 10).toString('ascii')) // 'defghij'
console.log(bl.slice(3, 6).toString('ascii'))  // 'def'
console.log(bl.slice(3, 8).toString('ascii'))  // 'defgh'
console.log(bl.slice(5, 10).toString('ascii')) // 'fghij'

// or just use toString!
console.log(bl.toString())               // 'abcdefghij\u0003\u0004'
console.log(bl.toString('ascii', 3, 8))  // 'defgh'
console.log(bl.toString('ascii', 5, 10)) // 'fghij'

// other standard Buffer readables
console.log(bl.readUInt16LE(10)) // 0x0403

API

• new BufferList([s])
• bl.length
• bl.append(buffer)
• bl.writePad(string, length, encoding)
• bl.get(index)
• bl.slice([ start[, end ] ])
• bl.copy(dest, [ destStart, [ srcStart [, srcEnd ] ] ])
• bl.toString([encoding, [ start, [ end ]]])

bl.readUInt32LE(), bl.readUInt32BE(), bl.readUInt16LE(), bl.readUInt16BE(), bl.readUInt8(), bl.readVarInt(offset),

bl.writeUInt32LE(), bl.writeUInt32BE(), bl.writeUInt16LE(), bl.writeUInt16BE(), bl.writeUInt8(), bl.writeVarInt(n),

new BufferList([ callback | buffer | buffer array ])

The constructor takes an optional callback, if supplied, the callback will be called with an error argument followed by a reference to the bl instance, when bl.end() is called (i.e. from a piped stream). This is a convenient method of collecting the entire contents of a stream, particularly when the stream is chunky, such as a network stream.

Normally, no arguments are required for the constructor, but you can initialise the list by passing in a single Buffer object or an array of Buffer object.

new is not strictly required, if you don't instantiate a new object, it will be done automatically for you so you can create a new instance simply with:

var bl = require('bl')
var myinstance = bl()

// equivilant to:

var BufferList = require('bl')
var myinstance = new BufferList()

bl.length

Get the length of the list in bytes. This is the sum of the lengths of all of the buffers contained in the list, minus any initial offset for a semi-consumed buffer at the beginning. Should accurately represent the total number of bytes that can be read from the list.

bl.append(buffer)

append(buffer) adds an additional buffer or BufferList to the internal list.

bl.writePad(string, length, encoding)

writePad(string, length, encoding) writes a string padded with zeros so that the total length equals length

bl.get(index)

get() will return the byte at the specified index.

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

slice() returns a new Buffer object containing the bytes within the range specified. Both start and end are optional and will default to the beginning and end of the list respectively.

If the requested range spans a single internal buffer then a slice of that buffer will be returned which shares the original memory range of that Buffer. If the range spans multiple buffers then copy operations will likely occur to give you a uniform Buffer.

bl.copy(dest, [ destStart, [ srcStart [, srcEnd ] ] ])

copy() copies the content of the list in the dest buffer, starting from destStart and containing the bytes within the range specified with srcStart to srcEnd. destStart, start and end are optional and will default to the beginning of the dest buffer, and the beginning and end of the list respectively.

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

toString() will return a string representation of the buffer. The optional start and end arguments are passed on to slice(), while the encoding is passed on to toString() of the resulting Buffer. See the Buffer#toString() documentation for more information.

bl.readUInt64LE(), bl.readUInt64BE(), bl.readUInt32LE(), bl.readUInt32BE() bl.readUInt16LE(), bl.readUInt16BE(), bl.readUInt8()

All of the standard byte-reading methods of the Buffer interface are implemented and will operate across internal Buffer boundaries transparently.

See the Buffer documentation for how these work.

bl.writeUInt64LE(), bl.writeUInt64BE(), bl.writeUInt32LE(), bl.writeUInt32BE(), bl.writeIntU16LE(), bl.writeUInt16BE(), bl.writeUInt8()

All of the standard byte-writing methods of the Buffer. At the moment you cannot set an offset, and can only append the bytes.

See the Buffer documentation for how these work.

bl.readVarInt(offset)

returns a { res: res, offset: offset } object

bl.writeVarInt(n)