(Nodejs) Trying to read a file but not getting the output I expect

[noweare]

I am learning nodejs and I am just getting my feet wet with it.
For practice I am trying to read 2048 bytes from a file then put it in a buffer
and repeating until I have read the whole file.

In the code I print out 'hello' in the readmyFile function. I do see that repeatedly
but I do not see bytesRead or the contents of the buffer. I guess I need to learn
how to debug my code properly.

Thanks to anyone to help shed some light on this. JavaScript is challenging !
Btw : the file is Int8 which represent audio.

// read from file into buffer until contents have been read, then close file
const path = require('path');
const fsPromises = require('fs').promises;
const fs = require('fs');

let mypath = path.join(__dirname, 'files', 'myvoice.raw');
let fd = 0;
let interval = 0;
let count = 0;

const buffer = Buffer.alloc(2048); // Create a buffer to store the data

function closeFile() {
   fs.close(fd, (err) => {
        if (err) {
            console.error('Error closing file:', err);
        }
        else {
            clearInterval(interval);
            console.log('bytes read = 0, file closed');
            
        }
    })
}

//Open the file for reading
function openFile() {
    fs.open(mypath, 'r', (err, fd) => {
        if (err) {
            console.error('Error opening file:', err);
            return false; 
        }
        else {
            console.log(`fd : ${fd}`);
            //console.log(typeof(fd));
            //readmyFile();
            // return fd;
            //   interval = setInterval(readmyFile, 1000);
        }
  })
}


function readmyFile() {
    // Read 2048 bytes from the file each iteration
    console.log('hello');
    
    fs.read(fd, buffer, 0, 2048, -1, (err, bytesRead, buffer) => {
    if (err) {
        console.error('Error reading file:', err);
        return;
    }
    else {
        console.log('bytes read : ', bytesRead);
        console.log(buffer);
         if (bytesRead == 0){
                closeFile();
        }
    }
    })
}

// function begin(){
    
// }

 console.log('starting program');

 openFile();
 //setTimeout(begin, 2000);  //making sure  the file is opened before calling readmyFile
 interval = setInterval(readmyFile, 2000);

 

[ratwolf]

I am learning nodejs and I am just getting my feet wet with it.
For practice I am trying to read 2048 bytes from a file then put it in a buffer
and repeating until I have read the whole file.

In the code I print out 'hello' in the readmyFile function. I do see that repeatedly
but I do not see bytesRead or the contents of the buffer. I guess I need to learn
how to debug my code properly.

Thanks to anyone to help shed some light on this. JavaScript is challenging !
Btw : the file is Int8 which represent audio.

// read from file into buffer until contents have been read, then close file
const path = require('path');
const fsPromises = require('fs').promises;
const fs = require('fs');

let mypath = path.join(__dirname, 'files', 'myvoice.raw');
let fd = 0;
let interval = 0;
let count = 0;

const buffer = Buffer.alloc(2048); // Create a buffer to store the data

function closeFile() {
   fs.close(fd, (err) => {
        if (err) {
            console.error('Error closing file:', err);
        }
        else {
            clearInterval(interval);
            console.log('bytes read = 0, file closed');
           
        }
    })
}

//Open the file for reading
function openFile() {
    fs.open(mypath, 'r', (err, fd) => {
        if (err) {
            console.error('Error opening file:', err);
            return false;
        }
        else {
            console.log(`fd : ${fd}`);
            //console.log(typeof(fd));
            //readmyFile();
            // return fd;
            //   interval = setInterval(readmyFile, 1000);
        }
  })
}


function readmyFile() {
    // Read 2048 bytes from the file each iteration
    console.log('hello');
   
    fs.read(fd, buffer, 0, 2048, -1, (err, bytesRead, buffer) => {
    if (err) {
        console.error('Error reading file:', err);
        return;
    }
    else {
        console.log('bytes read : ', bytesRead);
        console.log(buffer);
         if (bytesRead == 0){
                closeFile();
        }
    }
    })
}

// function begin(){
   
// }

 console.log('starting program');

 openFile();
 //setTimeout(begin, 2000);  //making sure  the file is opened before calling readmyFile
 interval = setInterval(readmyFile, 2000);

You should try this: Update fd inside the callback and only start the interval once the file is successfully opened.

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

let mypath = path.join(__dirname, 'files', 'myvoice.raw');
let fd = null;
let interval = null;

const buffer = Buffer.alloc(2048); // Allocate 2048-byte buffer

function closeFile() {
    fs.close(fd, (err) => {
        if (err) {
            console.error('Error closing file:', err);
        } else {
            clearInterval(interval);
            console.log('bytes read = 0, file closed');
        }
    });
}

function readmyFile() {
    console.log('hello');

    fs.read(fd, buffer, 0, 2048, null, (err, bytesRead) => {
        if (err) {
            console.error('Error reading file:', err);
            return;
        }

        console.log('bytes read :', bytesRead);

        if (bytesRead === 0) {
            closeFile();
        } else {
            // Show a slice of buffer for readability
            console.log(buffer.slice(0, bytesRead));
        }
    });
}

function openFile() {
    fs.open(mypath, 'r', (err, fileDescriptor) => {
        if (err) {
            console.error('Error opening file:', err);
            return;
        }

        fd = fileDescriptor;
        console.log(`File opened, fd: ${fd}`);
        interval = setInterval(readmyFile, 500); // start reading after opening
    });
}

console.log('Starting program...');
openFile();

 

[noweare]

Yes, your suggestions worked. Thank you sir. Coming from a C background JS is so different. Getting my head around the asynchronous nature of JS makes it a lot different than C.

As it has been a couple of days since I posted this question, I read up on promises and async / await and used the promise version of the functions to get rid of using the interval timer.

Thank you for your help !