bl

# bl *(BufferList)* [![NPM](https://nodei.co/npm/bl.svg?style=flat&data=n,v&color=blue)](https://nodei.co/npm/bl/) **A Node.js Buffer list collector, reader and streamer thingy.** **bl** is a storage object for collections of Node Buffers, exposing them with the main Buffer readable API. Also works as a duplex stream so you can collect buffers from a stream that emits them and emit buffers to a stream that consumes them! 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. ## Installation ```bash npm install bl ``` ## Basic Usage ```js import { BufferList } from 'bl' const bl = new BufferList() bl.append(Buffer.from('abcd')) bl.append(Buffer.from('efg')) bl.append('hi') // bl will also accept & convert Strings bl.append(Buffer.from('j')) bl.append(Buffer.from([ 0x3, 0x4 ])) 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' console.log(bl.indexOf('def')) // 3 console.log(bl.indexOf('asdf')) // -1 // 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.readUInt16BE(10)) // 0x0304 console.log(bl.readUInt16LE(10)) // 0x0403 ``` ### Node.js Streams Collect the contents of a stream: ```js import { BufferListStream } from 'bl' import { pipeline } from 'node:stream/promises' import { Readable } from 'node:stream' const response = await fetch('https://raw.githubusercontent.com/rvagg/bl/master/README.md') const bl = new BufferListStream() await pipeline(Readable.fromWeb(response.body), bl) console.log(bl.toString()) ``` Or use it as a readable stream to pipe to an output: ```js import BufferListStream from 'bl' import { pipeline } from 'node:stream/promises' import fs from 'node:fs' const bl = new BufferListStream() bl.append(Buffer.from('abcd')) bl.append(Buffer.from('efg')) bl.append(Buffer.from('hi')) bl.append(Buffer.from('j')) await pipeline(bl, fs.createWriteStream('gibberish.txt')) ``` ## API * <a href="#ctor"><code>new BufferList([ buf ])</code></a> * <a href="#isBufferList"><code>BufferList.isBufferList(obj)</code></a> * <a href="#length"><code>bl.length</code></a> * <a href="#append"><code>bl.append(buffer)</code></a> * <a href="#prepend"><code>bl.prepend(buffer)</code></a> * <a href="#get"><code>bl.get(index)</code></a> * <a href="#indexOf"><code>bl.indexOf(value[, byteOffset][, encoding])</code></a> * <a href="#slice"><code>bl.slice([ start[, end ] ])</code></a> * <a href="#shallowSlice"><code>bl.shallowSlice([ start[, end ] ])</code></a> * <a href="#copy"><code>bl.copy(dest, [ destStart, [ srcStart [, srcEnd ] ] ])</code></a> * <a href="#duplicate"><code>bl.duplicate()</code></a> * <a href="#consume"><code>bl.consume(bytes)</code></a> * <a href="#toString"><code>bl.toString([encoding, [ start, [ end ]]])</code></a> * <a href="#readXX"><code>bl.readDoubleBE()</code>, <code>bl.readDoubleLE()</code>, <code>bl.readFloatBE()</code>, <code>bl.readFloatLE()</code>, <code>bl.readBigInt64BE()</code>, <code>bl.readBigInt64LE()</code>, <code>bl.readBigUInt64BE()</code>, <code>bl.readBigUInt64LE()</code>, <code>bl.readInt32BE()</code>, <code>bl.readInt32LE()</code>, <code>bl.readUInt32BE()</code>, <code>bl.readUInt32LE()</code>, <code>bl.readInt16BE()</code>, <code>bl.readInt16LE()</code>, <code>bl.readUInt16BE()</code>, <code>bl.readUInt16LE()</code>, <code>bl.readInt8()</code>, <code>bl.readUInt8()</code></a> * <a href="#ctorStream"><code>new BufferListStream([ callback ])</code></a> * <a href="#getBuffers"><code>bl.getBuffers()</code></a> -------------------------------------------------------- <a name="ctor"></a> ### new BufferList([ Buffer | Buffer array | BufferList | BufferList array | String ]) 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` objects. ```js import { BufferList } from 'bl' const bl = new BufferList() ``` -------------------------------------------------------- <a name="isBufferList"></a> ### BufferList.isBufferList(obj) Determines if the passed object is a `BufferList`. It will return `true` if the passed object is an instance of `BufferList` **or** `BufferListStream` and `false` otherwise. N.B. this won't return `true` for `BufferList` or `BufferListStream` instances created by versions of this library before this static method was added. -------------------------------------------------------- <a name="length"></a> ### 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. -------------------------------------------------------- <a name="append"></a> ### bl.append(Buffer | Buffer array | BufferList | BufferList array | String) `append(buffer)` adds an additional buffer or BufferList to the internal list. `this` is returned so it can be chained. -------------------------------------------------------- <a name="prepend"></a> ### bl.prepend(Buffer | Buffer array | BufferList | BufferList array | String) `prepend(buffer)` adds an additional buffer or BufferList at the beginning of the internal list. `this` is returned so it can be chained. -------------------------------------------------------- <a name="get"></a> ### bl.get(index) `get()` will return the byte at the specified index. -------------------------------------------------------- <a name="indexOf"></a> ### bl.indexOf(value[, byteOffset][, encoding]) `indexOf()` method returns the first index at which a given element can be found in the BufferList, or -1 if it is not present. -------------------------------------------------------- <a name="slice"></a> ### 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. -------------------------------------------------------- <a name="shallowSlice"></a> ### bl.shallowSlice([ start, [ end ] ]) `shallowSlice()` returns a new `BufferList` 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. No copies will be performed. All buffers in the result share memory with the original list. -------------------------------------------------------- <a name="copy"></a> ### 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. -------------------------------------------------------- <a name="duplicate"></a> ### bl.duplicate() `duplicate()` performs a **shallow-copy** of the list. The internal Buffers remains the same, so if you change the underlying Buffers, the change will be reflected in both the original and the duplicate. This method is needed if you want to call `consume()` or `pipe()` and still keep the original list. Example: ```js import BufferListStream from 'bl' const bl = new BufferListStream() bl.append('hello') bl.append(' world') bl.append('\n') bl.duplicate().pipe(process.stdout, { end: false }) console.log(bl.toString()) ``` -------------------------------------------------------- <a name="consume"></a> ### bl.consume(bytes) `consume()` will shift bytes *off the start of the list*. The number of bytes consumed don't need to line up with the sizes of the internal Buffers - initial offsets will be calculated accordingly in order to give you a consistent view of the data. -------------------------------------------------------- <a name="toString"></a> ### 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()](http://nodejs.org/docs/latest/api/buffer.html#buffer_buf_tostring_encoding_start_end) documentation for more information. -------------------------------------------------------- <a name="readXX"></a> ### bl.readDoubleBE(), bl.readDoubleLE(), bl.readFloatBE(), bl.readFloatLE(), bl.readBigInt64BE(), bl.readBigInt64LE(), bl.readBigUInt64BE(), bl.readBigUInt64LE(), bl.readInt32BE(), bl.readInt32LE(), bl.readUInt32BE(), bl.readUInt32LE(), bl.readInt16BE(), bl.readInt16LE(), bl.readUInt16BE(), bl.readUInt16LE(), bl.readInt8(), 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 <code>[Buffer](http://nodejs.org/docs/latest/api/buffer.html)</code> documentation for how these work. -------------------------------------------------------- <a name="ctorStream"></a> ### new BufferListStream([ callback | Buffer | Buffer array | BufferList | BufferList array | String ]) **BufferListStream** is a Node **[Duplex Stream](http://nodejs.org/docs/latest/api/stream.html#stream_class_stream_duplex)**, so it can be read from and written to like a standard Node stream. You can also `pipe()` to and from a **BufferListStream** instance. 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` objects. N.B. For backwards compatibility reasons, `BufferListStream` is the **default** export when you `import from 'bl'`: ```js import { BufferListStream } from 'bl' // equivalent to: import BufferListStream from 'bl' ``` -------------------------------------------------------- <a name="getBuffers"></a> ### bl.getBuffers() `getBuffers()` returns the internal list of buffers. ## Migrating from v6 v7 is a modernisation release: * **ESM-only**: CommonJS `require('bl')` is no longer supported. Use `import` instead. * **`new` is required**: `BufferListStream()` and `BufferList()` can no longer be called without `new`. * **Zero runtime dependencies**: `readable-stream`, `buffer`, and `inherits` have been removed. `BufferListStream` now uses Node's built-in `node:stream` Duplex directly. * **Node.js >= 20**: Browser bundling is no longer a supported use case. If you need buffer accumulation in the browser, consider working with `Uint8Array` directly. ## Contributors **bl** is brought to you by the following hackers: * [Rod Vagg](https://github.com/rvagg) * [Matteo Collina](https://github.com/mcollina) * [Jarett Cruger](https://github.com/jcrugzz) <a name="license"></a> ## License & copyright Copyright (c) 2013-2026 bl contributors (listed above). bl is licensed under the MIT license. All rights not explicitly granted in the MIT license are reserved. See the included LICENSE.md file for more details.