Bandwidth Speed Test Slower Than Expected - dart

Question

Im trying to create a bandwidth test using Dart using a LibreSpeed server, but for some reason it's reporting a much slower speed than expected. When I test using the web client for LibreSpeed I get around 30mb/s download bandwidth, however with my Dart program I'm only getting around 4mb/s.
The code for the speed test is as follows:
Future<void> start() async {
var rand = Random();
var req = await client.getUrl(Uri.http(_serverAddress, '/garbage.php',
{'r': rand.nextDouble().toString(), 'ckSize': '20'}));
var resp = await req.close();
var bytesDownloaded = 0;
var start = DateTime.now();
await for (var bytes in resp) {
bytesDownloaded += bytes.length;
}
var timeTaken = DateTime.now().difference(start).inSeconds;
var mbsDownloaded = bytesDownloaded / 1000000;
print(
'$mbsDownloaded megabytes downloaded in $timeTaken seconds at a rate of ${mbsDownloaded / timeTaken} mbs per second');
}
I think I'm probably not understanding a crucial reason as to why it appears to be so slow compared to the web client. Can anyone give me any ideas as to what the bottleneck might be?

Answer 1

The problem is confusion between the use of units when measure internet speed. In general terms there are two ways we can measure the speed:
Mbps (MegaBit Per Second)
MB/s (MegaByte per second)
To understand your problem we need to notice that 1 byte = 8 bits. Also, that the unit LibreSpeed (and most internet providers) uses is Mbps.
The unit your current program are measuring in is MB/s since you are using the length of the list (each element of the list is 1 byte = 8 bit:
await for (var bytes in resp) {
bytesDownloaded += bytes.length;
}
And never multiply that number by 8 later in your code. You are then comparing this number against the number from LibreSpeed which uses Mbps (same as most internet providers) which means your number is 8 times smaller that expected.