Seeding fails on files >32KiB on Safari Desktop and Mobile

[now-raymond]

What version of WebTorrent?
WebTorrent 0.98.24

What operating system and Node.js version?
macOS High Sierra 10.13.3
iOS 11.2.6

What browser and version? (if using WebTorrent in the browser)
Safari (desktop) 11.0.3 on macOS
Safari Mobile on iOS 11.2.6
Chrome Mobile on iOS 11.2.6

What did you expect to happen?
Expected a WebTorrent client in Safari on MacOS and Safari Mobile/Chrome Mobile on iOS to correctly download and upload files since they now have WebRTC support. WebTorrent docs does list Safari as a compatible web browser now.

What actually happened?
WebTorrent browser client on abovementioned platforms can download files of arbitrary size, but is unable to upload files >32KiB to peers.

When directly testing with two peers using simple-peer and torrent.addPeer, the seeder seems to stop uploading after two chunks. The peer connection is automatically closed shortly after this.

Files that are <= 32 KiB are uploaded fine.

I used the following commands to create two randomly-filled files of sizes 32768 and 32769 each:
dd if=/dev/random of=upload_rand_32768 bs=32768 count=1
dd if=/dev/random of=upload_rand_32769 bs=32769 count=1

The former uploads fine, while the latter stalls while uploading.

Interestingly, a zero-filled file uploads fine even though it is >32KiB:
dd if=/dev/zero of=upload_zeroes bs=84000 count=1

Steps to reproduce:

1. Using Safari on macOS or iOS, try to share upload_rand_32768.zip and upload_rand_32769.zip via https://instant.io/ with any other compatible web client.
2. The former can be shared as expected but the latter fails to be fully uploaded.

[feross]

I'm using Safari 11.1 on macOS and I just tested with a 100 MB file and it works. But I have to select "Enable the Legacy WebRTC API" under the "Develop" menu.