Calculate HTTP Range Header for download a file in chunks in JavaScript

Question

I'm trying to download a file in chunks with HTTP Range header but I got inconsistent results:

function generateRange(originalSize, split) {
    let resultSize = 0;
    let arr = [];
    var chunkSize = Math.ceil(originalSize / split)
    for (i = 0; i < split; i++) {
        var min = i * chunkSize;
        var max = min + chunkSize - 1;
        resultSize += max - min + 1
        arr.push(`${min}-${max}`)
    }
    console.log(JSON.stringify(arr))
    console.log(`split: ${split} | originalSize: ${originalSize} bytes | resultSize: ${resultSize} bytes\n\n`)
}
generateRange(200, 4) // work
generateRange(200, 7)
generateRange(469, 4)

.as-console-wrapper { max-height: 100% !important; }

Answer 1

You have to add the following code:

if(i == split - 1)
    max = originalSize - 1;

function generateRange(originalSize, split) {
    let resultSize = 0;
    let arr = [];
    var chunkSize = Math. floor(originalSize / split)
    for (i = 0; i < split; i++) {
        var min = i * chunkSize;
        var max = min + chunkSize - 1;
        if(i == split - 1)
            max = originalSize - 1;
   
        resultSize += max - min + 1
        arr.push(`${min}-${max}`)
    }
    console.log(JSON.stringify(arr))
    console.log(`split: ${split} | originalSize: ${originalSize} bytes | resultSize: ${resultSize} bytes\n\n`)
}
generateRange(200, 4) // work
generateRange(200, 7)
generateRange(469, 4)

.as-console-wrapper { max-height: 100% !important; }