How to calculate the MD5 checksum of a file with Node.js

  • Node.js
  • Gabriele Romanato

The MD5 checksum is a sequence of 32 hexadecimal characters that represents a unique fingerprint of the contents of a file. It is commonly used to verify the integrity of files, ensuring that they have not been modified. In Node.js, calculating the MD5 checksum of a file is a simple operation thanks to the built-in crypto module. In this article we will see how to calculate the MD5 hash of a file using Node.js and the crypto module.

To calculate the MD5 checksum, we will use the crypto module (to generate the hash) and the fs module to read the file. Both of these modules are already included in Node.js, so there is no need to install additional dependencies.

We define a function called calculateMD5 that will accept as a parameter the path of the file to process. The function will read the file content and generate the MD5 checksum.


const crypto = require('crypto');
const fs = require('fs');

function calculateMD5(filePath) {
  return new Promise((resolve, reject) => {
    // Create an MD5 hash instance
    const hash = crypto.createHash('md5');

    // Create a file read stream
    const stream = fs.createReadStream(filePath);

    // Update the hash with data as we read it from the stream
    stream.on('data', (chunk) => {
      hash.update(chunk);
    });

    // When the stream is finished, resolve the promise with the final hash
    stream.on('end', () => {
      const md5Checksum = hash.digest('hex');
      resolve(md5Checksum);
    });

    // Handle errors
    stream.on('error', (err) => {
      reject(err);
    });
  });
}

This function uses a stream to read the file piece by piece and progressively updates the MD5 hash. When the reading is complete (stream.on('end')), the function returns the checksum in hexadecimal format.

In detail:

  1. Creating the hash instance: crypto.createHash('md5') creates an MD5 hash object.
  2. Reading the file via stream: fs.createReadStream(filePath) reads the file without loading everything into memory, making the process more efficient.
  3. Calculating the hash: every time we receive a chunk of data from the file, we update the hash with hash.update(chunk).
  4. Finalizing the hash: when the reading is complete, we call hash.digest('hex') to get the MD5 value in hexadecimal format.

Conclusion

This method is also efficient for large files, as it reads the data incrementally without having to load the entire file into memory. Using this approach with Node.js, we can quickly calculate the MD5 checksum of a file to verify its integrity.

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