After an intensive round of cpu profiling for bottlenecks, the GigaPush client (dart_rtc_client (Yea, messy code)) can now push data a bit faster again. On Local network I managed to get it peak at 2.5MB/s. Somewhat steady at 2.3MB/s.

This totally depends on your cpu though, the process of splitting the file to 500ish byte chunks, adding udp headers and converting to string takes some extreme cycles at the moment.

The latest speed up was due to finding an alternative way to convert ByteBuffer to String.
Original code looked like this:


new String.fromCharCodes(new Uint8List.view(buffer));

This worked somewhat well in Dartium, but the dart2js compiled javascript suffered a lot. There was almost an 1MB/s speed difference between Dartium and Chrome.
The new version uses a lookup table for characters, Since all content is Uint8 i just created an static List containing all characters that fit Uint8 and use that.
This change brought Chrome to same speed with Dartium.

Dart team (Emily Fortuna) has been looking at getting WebRTC working on Firefox, big thanks to her, hoping to see results soon. At this very moment at least RTCDataChannel is still not working.

Whats next? The current way of storing the file as Object url is not very cool. So, looking at FileSystem API and perhaps IndexedDB.

Ok ok.. Not quite Giga.. yet =)
But since Kim Dotcom owns Mega, i decided to go for Giga.

Reached 1.40MB/s transfer rate with the gigapush.com site on local network.
This with dart2js compiled javascript version of the app. Pure Dart version is a bit faster.

Some nasty bottlenecks so far are:

Chrome doesn’t support sending binary data, so bytebuffers have to be converted to string and then back at the opposite end. This takes a bit of time.

Can not send large packets, so, at the moment i have to split the files to 500ish byte chunks and add udp headers for each packet.
Using sublist for the splitting didn’t quite amaze me with the speed and since sublist returns List<int>, it’s not going to work on the javascript side of the fence, which meant that i ended up with this

new Uint8List.fromList(new Uint8List.view(buffer).sublist(read, read+toRead));

Which was very slow.
I replaced that with a simplified home built version which gave me a speed boost of 100 KB/s.
There’s a bug for the sublist problem here https://code.google.com/p/dart/issues/detail?id=10354

Downloading the file after transfer is an issue also. At the moment i’m generating an object url for the finished download and use the html5 download attribute to set a filename and force download of the file. This sort of works, but consumes huge amounts of memory from the browser. Chromes filesystem api would be best solution but that works only on Chrome then.

Android issues. The object url download. This part does not work on Android version of Chrome. You can send files with the Chrome on Android, but receiving files will be a problem.

Firefox issues. dart2js is still not able to generate javascript which would work on Firefox, which is a shame and limits the site only to Chrome users.
Bug for this here https://code.google.com/p/dart/issues/detail?id=8361

Signaling issues, Sometimes when both participants on same signaling channel quit at the same time, an exception is thrown and i haven’t managed to trace that yet.

ACK issues. I’m no Udp expert so i just went with the solution i thought would be cool. Currently i’m waiting that either 50 packets arrive or time since last arrived packet is 5 ms, then build a ACK packet containing the sequence numbers from the received packets and send that back to the sender. The sender will retransmit the packets if no ACK is received within some time which i can’t remember at the moment =). Not sure if there’s a better way.

Connectivity issues are also quite nasty. If both participants are behind a router which has symmetric NAT, the peer connection will fail.
From Norwegian operators at least Nextgentel and Get both offer a wireless router by default which has symmetric NAT. I’m using Get at home and had to replace the router with shop bought D-Link router.

Managed to push the gigapush.com speed up to 700KB/s on local network.
The udp library is still horribly inefficient but it’s getting there.. slowly =)

The site is good for sending pics of cats and such now =)

New experimental file transfer website I’ve made.
Located at gigapush.com.
It’s an early alpha version and the transfer speeds are not really Giga so far =).