Using fs Library in Lambda

• Using fs Library in Lambda
  • Documenting the issues I faced while using fs library in lambda
    • Reading any file in lambda
  • Reference

Documenting the issues I faced while using fs library in lambda

Here I have considered below template as reference for all my use cases below, // Your Code Here is the part that I will be referring to here on forward

const fs = require('fs');
const fsp = require('fs').promises;
exports.handler = async (event) => {

    // Your Code Here

    const response = {
        statusCode: 200,
        body: JSON.stringify('Hello from Lambda!'),
    };
    return response;
};

Reading any file in lambda

• Failed Code

  var test = fs.readFile("test.txt", function(err, data){
      console.log(data.toString(), err);
  });
  console.log(test);
  

• Successful Code

  console.log(fs.readFileSync("test.txt"));
  console.log(fs.readFileSync('test2.txt', 'utf8'));
  

  If the encoding option is specified then this function returns a string. Otherwise it returns a buffer.

• Successful Code

  console.log(await fsp.readFile('test2.txt', 'utf8'));
  console.log(await fsp.readFile("test.txt"));
  

  fs.writeFileSync("/tmp/test.txt","Hey text.txt");
  console.log((await fs.readFileSync("/tmp/test.txt")).toString());
  fsp.writeFile("/tmp/test2.txt","Hey text2.txt")
  console.log(await fsp.readFile('/tmp/test2.txt', 'utf8'));
  

So What’s The Difference? readFileSync() is synchronous and blocks execution until finished. These return their results as return values. readFile() are asynchronous and return immediately (mostly undefined) while they function in the background. You pass a callback function which gets called when they finish.

Reference

• fs Promises API
• Difference Between readFile() and readFileSync()