strtok3

What is strtok3?

The strtok3 npm package is a streaming tokenizer for Buffer and string inputs in Node.js. It allows developers to parse through binary data or strings efficiently by defining tokenizers that can extract pieces of data sequentially. This is particularly useful for reading binary files or network streams where data structures are defined in terms of sequences or patterns of bytes.

What are strtok3's main functionalities?

Tokenizing fixed-length binary data

This feature allows for reading fixed-length binary data from a file. The example demonstrates reading a 32-bit unsigned integer from the beginning of a file.

const strtok3 = require('strtok3');
const { token } = require('strtok3/core');

async function parseBinaryFile(filePath) {
  const tokenizer = await strtok3.fromFile(filePath);
  const header = await tokenizer.readToken(token.UINT32_LE);
  console.log('Header:', header);
}

Tokenizing a stream of data

This feature is used for tokenizing data directly from a stream. The example shows how to read a size as a 32-bit unsigned integer and then read a buffer of that size from the stream.

const strtok3 = require('strtok3');
const { token } = require('strtok3/core');
const fs = require('fs');

const stream = fs.createReadStream('path/to/file');
const tokenizer = strtok3.fromStream(stream);

async function readData() {
  const size = await tokenizer.readToken(token.UINT32_LE);
  const data = await tokenizer.readToken(new token.BufferType(size));
  console.log('Data:', data.toString());
}

Other packages similar to strtok3

binary-parser

binary-parser is a package for building efficient binary data parsers. It is similar to strtok3 in that it helps parse binary data, but it uses a declarative approach to define the structure of the binary data instead of the imperative approach used by strtok3.

README

strtok3

A promise based streaming tokenizer for Node.js and browsers.

The strtok3 module provides several methods for creating a tokenizer from various input sources. Designed for:

• Seamless support in streaming environments.
• Efficiently decode binary data, strings, and numbers.
• Reading predefined or custom tokens.
• Offering tokenizers for reading from files, streams or Uint8Arrays.

Features

strtok3 can read from:

• Files, using a file path as input.
• Node.js streams.
• Buffer or Uint8Array.
• HTTP chunked transfer provided by @tokenizer/http.
• Amazon S3 chunks with @tokenizer/s3.

Installation

npm install strtok3

Compatibility

Starting with version 7, the module has migrated from CommonJS to pure ECMAScript Module (ESM). The distributed JavaScript codebase is compliant with the ECMAScript 2020 (11th Edition) standard.

[!NOTE] This module requires a Node.js ≥ 16 engine. It can also be used in a browser environment when bundled with a module bundler.

Support the Project

If you find this project useful and would like to support its development, consider sponsoring or contributing:

• Become a sponsor to Borewit

• Buy me a coffee:

  

API Documentation

strtok3 methods

Use one of the methods to instantiate an abstract tokenizer:

• fromFile¹
• fromStream¹
• fromWebStream
• fromBuffer

All methods return a Tokenizer, either directly or via a promise.

fromFile function

Creates a tokenizer from a local file.

function fromFile(sourceFilePath: string): Promise<FileTokenizer>

Parameter	Type	Description
sourceFilePath	string	Path to file to read from

[!NOTE]

• Only available for Node.js engines
• fromFile automatically embeds file-information

Returns, via a promise, a tokenizer which can be used to parse a file.

import * as strtok3 from 'strtok3';
import * as Token from 'token-types';

(async () => {

  const tokenizer = await strtok3.fromFile("somefile.bin");
         try {
    const myNumber = await tokenizer.readToken(Token.UINT8);
    console.log(`My number: ${myNumber}`);
  } finally {
    tokenizer.close(); // Close the file
  }
})();

fromStream function

Creates a tokenizer from a Node.js readable stream.

function fromStream(stream: Readable, options?: ITokenizerOptions): Promise<ReadStreamTokenizer>

Parameter	Optional	Type	Description
stream	no	Readable	Stream to read from
fileInfo	yes	IFileInfo	Provide file information

Returns a Promise providing a tokenizer.

[!NOTE]

• Only available for Node.js engines

fromWebStream function

Creates tokenizer from a WHATWG ReadableStream.

function fromWebStream(webStream: AnyWebByteStream, options?: ITokenizerOptions): ReadStreamTokenizer

Parameter	Optional	Type	Description
readableStream	no	ReadableStream	WHATWG ReadableStream to read from
fileInfo	yes	IFileInfo	Provide file information

Returns a Promise providing a tokenizer

import strtok3 from 'strtok3';
import * as Token from 'token-types';

strtok3.fromWebStream(readableStream).then(tokenizer => {
  return tokenizer.readToken(Token.UINT8).then(myUint8Number => {
    console.log(`My number: ${myUint8Number}`);
  });
});

fromBuffer() function

Create a tokenizer from memory (Uint8Array).

function fromBuffer(uint8Array: Uint8Array, options?: ITokenizerOptions): BufferTokenizer

Parameter	Optional	Type	Description
uint8Array	no	Uint8Array	Uint8Array or Buffer to read from
fileInfo	yes	IFileInfo	Provide file information

Returns a Promise providing a tokenizer.

import * as strtok3 from 'strtok3';

const tokenizer = strtok3.fromBuffer(buffer);

tokenizer.readToken(Token.UINT8).then(myUint8Number => {
  console.log(`My number: ${myUint8Number}`);
});

Tokenizer object

The tokenizer is an abstraction of a stream, file or Uint8Array, allowing reading or peeking from the stream. It can also be translated in chunked reads, as done in @tokenizer/http;

Key Features:

• Supports seeking within the stream using tokenizer.ignore().
• Offers peek methods to preview data without advancing the read pointer.
• Maintains the read position via tokenizer.position.

Tokenizer functions

Read methods advance the stream pointer, while peek methods do not.

There are two kind of functions:

1. read methods: used to read a token of Buffer from the tokenizer. The position of the tokenizer-stream will advance with the size of the token.
2. peek methods: same as the read, but it will not advance the pointer. It allows to read (peek) ahead.

readBuffer function

Read data from the tokenizer into provided "buffer" (Uint8Array). readBuffer(buffer, options?)

readBuffer(buffer: Uint8Array, options?: IReadChunkOptions): Promise<number>;

Parameter	Type	Description
buffer	Buffer | Uint8Array	Target buffer to write the data read to
options	IReadChunkOptions	An integer specifying the number of bytes to read

Return promise with number of bytes read. The number of bytes read maybe if less, mayBeLess flag was set.

peekBuffer function

Peek (read ahead), from tokenizer, into the buffer without advancing the stream pointer.

peekBuffer(uint8Array: Uint8Array, options?: IReadChunkOptions): Promise<number>;

Parameter	Type	Description
buffer	Buffer | Uint8Array	Target buffer to write the data read (peeked) to.
options	IReadChunkOptions	An integer specifying the number of bytes to read.

Return value Promise<number> Promise with number of bytes read. The number of bytes read maybe if less, mayBeLess flag was set.

readToken function

Read a token from the tokenizer-stream.

readToken<Value>(token: IGetToken<Value>, position: number = this.position): Promise<Value>

Parameter	Type	Description
token	IGetToken	Token to read from the tokenizer-stream.
position?	number	Offset where to begin reading within the file. If position is null, data will be read from the current file position.

Return value Promise<number>. Promise with number of bytes read. The number of bytes read maybe if less, mayBeLess flag was set.

peek function

Peek a token from the tokenizer.

peekToken<Value>(token: IGetToken<Value>, position: number = this.position): Promise<Value>

Parameter	Type	Description
token	IGetToken	Token to read from the tokenizer-stream.
position?	number	Offset where to begin reading within the file. If position is null, data will be read from the current file position.

Return a promise with the token value peeked from the tokenizer.

readNumber function

Peek a numeric token from the tokenizer.

readNumber(token: IToken<number>): Promise<number>

Parameter	Type	Description
token	IGetToken	Numeric token to read from the tokenizer-stream.

Returns a promise with the decoded numeric value from the tokenizer-stream.

ignore function

Advance the offset pointer with the token number of bytes provided.

ignore(length: number): Promise<number>

Parameter	Type	Description
ignore	number	Numeric of bytes to ignore. Will advance the tokenizer.position

Returns a promise with the decoded numeric value from the tokenizer-stream.

close function

Clean up resources, such as closing a file pointer if applicable.

Tokenizer attributes

• fileInfo

  Optional attribute describing the file information, see IFileInfo

• position

  Pointer to the current position in the tokenizer stream. If a position is provided to a read or peek method, is should be, at least, equal or greater than this value.

IReadChunkOptions interface

Each attribute is optional:

Attribute	Type	Description
length	number	Requested number of bytes to read.
position	number	Position where to peek from the file. If position is null, data will be read from the current file position. Position may not be less then tokenizer.position
mayBeLess	boolean	If and only if set, will not throw an EOF error if less then the requested mayBeLess could be read.

Example usage:

  tokenizer.peekBuffer(buffer, {mayBeLess: true});

IFileInfo interface

Provides optional metadata about the file being tokenized.

Attribute	Type	Description
size	number	File size in bytes
mimeType	number	MIME-type of file.
path	number	File path
url	boolean	File URL

Token object

The token is basically a description what to read form the tokenizer-stream. A basic set of token types can be found here: token-types.

A token is something which implements the following interface:

export interface IGetToken<T> {

  /**
   * Length in bytes of encoded value
   */
  len: number;

  /**
   * Decode value from buffer at offset
   * @param buf Buffer to read the decoded value from
   * @param off Decode offset
   */
  get(buf: Uint8Array, off: number): T;
}

The tokenizer reads token.len bytes from the tokenizer-stream into a Buffer. The token.get will be called with the Buffer. token.get is responsible for conversion from the buffer to the desired output type.

Working with Web-API readable stream

To convert a Web-API readable stream into a Node.js readable stream, you can use readable-web-to-node-stream to convert one in another.

import { fromWebStream } strtok3 from 'strtok3';
import { ReadableWebToNodeStream } from 'readable-web-to-node-stream';

(async () => {

  const response = await fetch(url);
  const readableWebStream = response.body; // Web-API readable stream
  const webStream = new ReadableWebToNodeStream(readableWebStream); // convert to Node.js readable stream

  const tokenizer = fromWebStream(webStream); // And we now have tokenizer in a web environment
})();

Dependencies

The diagram below illustrates the primary dependencies of strtok3:

graph TD;
  S(strtok3)-->P(peek-readable)
  S(strtok3)-->TO("@tokenizer/token")

• peek-readable: Manages reading operations with peeking capabilities, allowing data to be previewed without advancing the read pointer.
• @tokenizer/token: Provides token definitions and utilities used by strtok3 for interpreting binary data.

Licence

(The MIT License)

Copyright (c) 2024 Borewit

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the 'Software'), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED 'AS IS', WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

Footnotes

1. Only available when importing this module with Node.js ↩ ↩²