strtok3

A promise based streaming tokenizer for Node.js and browsers. This node module is a successor of strtok2.

The strtok3 contains a few methods to turn different input into a tokenizer. Designed to

• Support a streaming environment
• Decoding of binary data, strings and numbers in mind
• Read predefined or custom tokens.
• Optimized tokenizers for reading from file, stream or buffer.

It can read from:

• A file (taking a file path as an input)
• A Node.js stream.
• A Buffer
• HTTP chunked transfer provided by @tokenizer/http.

Installation

npm install --save strtok3

Usage

Use one of the methods to instantiate an abstract tokenizer:

• strtok3.fromFile
• strtok3.fromStream
• strtok3.fromBuffer

strtok3 methods

All of the strtok3 methods return a tokenizer, either directly or via a promise.

Method strtok3.fromFile()

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

const strtok3 = require('strtok3');
const Token = require('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
  } 
})();

Method strtok3.fromStream()

Create tokenizer from a node.js readable stream.

Returns a tokenizer, via a Promise, which can be used to parse a buffer.

const strtok3 = require('strtok3');
const Token = require('token-types');

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

Method strtok3.fromBuffer()

Returns a tokenizer which can be used to parse the provided buffer.

const strtok3 = require('strtok3');
    
const tokenizer = strtok3.fromBuffer(buffer);

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

Tokenizer

The tokenizer allows us to read or peek from the tokenizer-stream. The tokenizer-stream is an abstraction of a stream, file or Buffer. It can also be translated in chunked reads, as done in @tokenizer/http;

What is the difference with Nodejs.js stream?

• The tokenizer-stream supports jumping / seeking in a the tokenizer-stream using tokenizer.ignore()
• In addition to read methods, it has peek methods, to read a ahead and check what is coming.

The tokenizer.position keeps tracks of

Tokenizer attributes

Attribute tokenizer.fileSize

Optional attribute of the total file or stream length in bytes

Attribute tokenizer.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.

Tokenizer methods

There are to groups of methods

• 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.
• peek methods: same as the read, but it will not advance the pointer. It allows to read (peek) ahead.

Method tokenizer.readBuffer()

Read buffer from stream. readBuffer(buffer, offset?, length?, position?, maybeless?)

Return value Promise<number> Promise with number of bytes read

Method tokenizer.peekBuffer()

Peek (read ahead) buffer from tokenizer peekBuffer(buffer, offset?, length?, position?, maybeless?)

Return value Promise<number> Promise with number of bytes read

Method tokenizer.readToken()

Read a token from the tokenizer-stream. readToken(token, position?, maybeless?)

Return value Promise<T>. Promise with token value read from the tokenizer-stream.

Method tokenizer.peekToken()

Peek a token from the tokenizer-stream. peekToken(token, position?, maybeless?)

Return value Promise<T> Promise with token value peeked from the tokenizer-stream.

Method tokenizer.readNumber()

Peek a numeric token from the tokenizer-stream. readNumber(token)

Return value Promise<number> Promise with number peeked from the tokenizer-stream.

Method tokenizer.ignore()

Peek a numeric token from the tokenizer-stream. ignore(length)

Return value Promise<number> Promise with number peeked from the tokenizer-stream.

Method tokenizer.close()

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

Token

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: Buffer, 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.

Browser compatibility

To exclude fs based dependencies, you can use a submodule-import from 'strtok3/lib/core'.

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.

Example submodule-import:

const strtok3core = require('strtok3/lib/core'); // Submodule-import to prevent Node.js specific dependencies
const {ReadableWebToNodeStream} = require('readable-web-to-node-stream');

(async () => {

  const response = await fetch(url);
  const readableWebStream = response.body; // Web-API readable stream
  const nodeStream = new ReadableWebToNodeStream(readableWebStream); // convert to Node.js readable stream
  
  const tokenizer = strtok3core.fromStream(nodeStream); // And we now have tokenizer in a web environment
})();