[{offset, length}] of chunks `size` assuming `delimiter` for a file with `total` size.
function getOffsets(size, total, delimiter) {
    if (total === 0) {
        return [];
    }
    if (total < size) {
        return [{ length: total, offset: 0 }];
    }
    const fullChunks = Math.floor(total / size);
    const delta = delimiter.length;
    const length = size + delta;
    const chunks = [];
    for (let chunk = 1; chunk < fullChunks; chunk += 1) {
        chunks.push({ length, offset: (chunk * size) - delta });
    }
    // First chunk doesn't need +/- delta.
    chunks.unshift({ offset: 0, length: size });
    // When last chunk is not full chunk size.
    const lastChunk = total % size;
    if (lastChunk > 0) {
        chunks.push({ offset: (fullChunks * size) - delta, length: lastChunk + delta });
    }
    return chunks;
}