Introduction to first-chunk-stream

Efficient streaming and handling of large data chunks are crucial for performance-optimized Node.js applications. The first-chunk-stream module allows developers to easily manipulate the first chunk of a stream, providing unique opportunities for data processing and transformation. In this blog post, we will introduce various APIs of first-chunk-stream and demonstrate their usage through code snippets and a detailed application example.

APIs of first-chunk-stream

Creating a First Chunk Stream

You can create a first chunk stream using the firstChunk function. It takes a callback function which is invoked with the first chunk of the stream:

  const firstChunk = require('first-chunk-stream');
  
  const stream = someReadableStream().pipe(firstChunk({ chunkLength: 10 }, (chunk, enc, cb) => {
      // Processing the first chunk
      cb(null, chunk);
  }));

Modifying the First Chunk

This API allows you to modify the first chunk before passing it to the downstream:

  const modifiedStream = someReadableStream().pipe(firstChunk({ chunkLength: 10 }, (chunk, enc, cb) => {
      const modifiedChunk = Buffer.from('Modified: ' + chunk.toString());
      cb(null, modifiedChunk);
  }));

Add Custom Header to a File Stream

Example of adding a custom header to a file stream using first-chunk-stream:

  const fs = require('fs');
  const firstChunk = require('first-chunk-stream');
  
  const readStream = fs.createReadStream('input.txt');
  const writeStream = fs.createWriteStream('output.txt');
  
  readStream
    .pipe(firstChunk({ chunkLength: 0 }, (chunk, enc, cb) => {
        cb(null, Buffer.from('Custom Header\n') + chunk);
    }))
    .pipe(writeStream);

Checking Data Format

Check data format such as magic numbers in files:

  const firstChunk = require('first-chunk-stream');
  
  someReadableStream()
    .pipe(firstChunk({ chunkLength: 8 }, (chunk, enc, cb) => {
        if (chunk.toString('hex', 0, 4) !== '89504e47') {
            return cb(new Error('Not a PNG file'));
        }
        cb(null, chunk);
    }));

Application Example

Let’s create an example: a simple application that reads a text file, adds a header to it, and writes the result to a new file.

  const fs = require('fs');
  const firstChunk = require('first-chunk-stream');
  
  const addHeaderToFile = (inputFile, outputFile, header, callback) => {
      const readStream = fs.createReadStream(inputFile);
      const writeStream = fs.createWriteStream(outputFile);
    
      readStream
          .pipe(firstChunk({ chunkLength: 0 }, (chunk, enc, cb) => {
              cb(null, Buffer.from(header + '\n') + chunk);
          }))
          .pipe(writeStream)
          .on('finish', callback);
  };

  addHeaderToFile('input.txt', 'output.txt', 'Custom Header', () => {
      console.log('Header added successfully');
  });

This application reads input.txt, adds ‘Custom Header’ as the first line, and writes the resulting content to output.txt.

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