then-read-stream

A promise based asynchronous stream reader, which makes reading from a stream easy.

Allows to read from a Readable Stream similar as you would read from a file.

Usage

The then-read-stream contains one class: StreamReader. The constructor of the StreamReader if provided with the stream.Readable you want to read from.

Examles:

In the following example we read the first 16 bytes from a stream and store them in our buffer.

var stream_reader = require("then-read-stream");

var readThisStream = ... // Some stream of type stream.Readable
var streamReader = new stream_reader.StreamReader(readThisStream);

var buffer = new Buffer(16);

return streamReader.read(buf, 0, 16)
  .then( function(bytesRead) {
    // If all went well, buf contains the promised 16 bytes of data read
  })
  .catch( function(err) {
    if(err === stream_reader.StreamReader.EndOfStream) {
      // Rejected, end of the stream has been reached
    }
  })

With peek you can read ahead:

return streamReader.peek(buffer, 0, 1)
  .then( function(bytesRead) {
    if(bytesRead !== 2 || buffer[0] !== 0xFF){
      throw new Error('Stream should start with 0xFF');
    }
    // Read 16 bytes, start at the same offset as peek, so the first byte will be 0xFF
    return streamReader.peek(buffer, 0, 16);
  })

If you have to skip a part of the data, you can use ignore:

return streamReader.ignore(16)
  .then( function(bytesIgnored) {
    if(bytesIgnored<16){
      console.log('Remaing stream length was %s, expected 16', bytesIgnored)
    }
  })

TypeScript:

TypeScript definitions are build in. No need to install additional modules.

import {StreamReader} from "then-read-stream";

const readThisStream = ... // Some stream of type stream.Readable
const streamReader = new StreamReader(readThisStream);

const buf = new Buffer(16);
  
return streamReader.read(buf, 0, 16).then((bytesRead) => {
    // If all went well, buf contains the promised 16 bytes of data read
  }).catch((err) => {
    if(err === StreamReader.EndOfStream) {
      // Rejected, end of the stream has been reached
    }
  })