Nodejs Javascript TypedArray to Buffer to String and Back Again

Question

I'm trying to implement a serialization and deserialization of a repeating set of floats, using TypedArray to string (for saving across wire/disk), But it's not making it round trip

Answer 1

I got it working by using the ArrayBuffer to Buffer methods provided on the linked issue, the issue is I think I was treating them as arbitrary Typed Arrays rather than the native Uint8Array that I guess Buffers use. Here's the working version.

var recordsPerWrite = 1;
var ab = new ArrayBuffer(8 + 8 + 8 * recordsPerWrite);
var f64ry = new Float64Array(ab);

var records_added = 1;


var i1 = records_added * 0;
var i2 = records_added * 1;
var i3 = records_added * 2;
////////////////////////////
var timestamp = 1.1;
var price = 2.2;
var amount = 3.3;

f64ry[i1] = timestamp;
f64ry[i2] = price;
f64ry[i3] = amount;

console.log(f64ry[i1], f64ry[i2],f64ry[i3]);


    var buffer = toBuffer(ab);
    var st = buffer.toString('base64');
    console.log("ST '" + st + "'");

    var buffer2 = new Buffer(st, 'base64');

    var ab2 = toArrayBuffer(buffer2);
    var f64ry2 = new Float64Array(ab2);


function toArrayBuffer(buffer) {
    var ab = new ArrayBuffer(buffer.length);
    var view = new Uint8Array(ab);
    for (var i = 0; i < buffer.length; ++i) {
        view[i] = buffer[i];
    }
    return ab;
}
function toBuffer(ab) {
    var buffer = new Buffer(ab.byteLength);
    var view = new Uint8Array(ab);
    for (var i = 0; i < buffer.length; ++i) {
        buffer[i] = view[i];
    }
    return buffer;
}

timestamp2 = f64ry2[i1];
price2 = f64ry2[i2];
amount2 = f64ry2[i3];

console.log("IN " + timestamp, price, amount);
console.log("OUT " + timestamp2, price2, amount2);

OUTPUT

SOURCE: 1.1 2.2 3.3
CLONE: undefined undefined undefined  //expected 1.1 2.2 3.3

I am using the approach linked here: Convert a binary NodeJS Buffer to JavaScript ArrayBuffer

var ab = new ArrayBuffer(8 + 8 + 8);
var f64ry = new Float64Array(ab);

var records_added = 1;

var i1 = records_added * 0;
var i2 = records_added * 1;
var i3 = records_added * 2;
////////////////////////////
var timestamp = 1.1;
var price = 2.2;
var amount = 3.3;

f64ry[i1] = timestamp;
f64ry[i2] = price;
f64ry[i3] = amount;

console.log(f64ry[i1], f64ry[i2],f64ry[i3]); //shows correctly

    var buffer = new Buffer(ab.byteLength);
    for (var i = 0; i < f64ry.length; ++i) {
       // console.log(i + " " +f64ry[i]);
        buffer[i] = f64ry[i];
    }
    console.log("buffer '" + buffer + "'");
    var st = buffer.toString('hex');
    console.log("ST '" + st + "'");
    //var ab = buffer.toArrayBuffer(); //doesn't work in Node v.10

    var buffer2 = new Buffer(st, 'hex');

    console.log("buffer2 '" + buffer2 + "'");
    var ab2 = new ArrayBuffer(buffer2.byteLength);
    var f64ry2 = new Float64Array(ab2);

   for (var i = 0; i < buffer2.length; ++i) {
        console.log(i + " " +buffer2[i]);
        f64ry2[i] = buffer2[i];
    }


}

timestamp2 = f64ry2[i1];
price2 = f64ry2[i2];
amount2 = f64ry2[i3];

console.log(timestamp, price, amount);
console.log(timestamp2, price2, amount2);

Similarly this alternate approach didn't work either:

OUTPUT

>1.1 2.2 3.3
>buffer ''
>ST '010203'
>buffer2 ''
>1.1 2.2 3.3
>undefined undefined undefined

CODE

var f64ry = new Float64Array(3);
var records_added = 1;


var i1 = records_added * 0;
var i2 = records_added * 1;
var i3 = records_added * 2;
////////////////////////////
var timestamp = 1.1;
var price = 2.2;
var amount = 3.3;

var ary = [timestamp,price,amount];

f64ry.set(ary,0);
console.log(f64ry[i1], f64ry[i2],f64ry[i3]);


    var buffer = new Buffer(f64ry);

    console.log("buffer '" + buffer + "'");
    var st = buffer.toString('hex');
    console.log("ST '" + st + "'");
    //var ab = buffer.toArrayBuffer();

    var buffer2 = new Buffer(st, 'hex');

    console.log("buffer2 '" + buffer2 + "'");
    var ab2 = new ArrayBuffer(buffer2);
    var f64ry2 = new Float64Array(ab2);




timestamp2 = f64ry2[i1];
price2 = f64ry2[i2];
amount2 = f64ry2[i3];

console.log(timestamp, price, amount);
console.log(timestamp2, price2, amount2);