Quick Share/Nearby Share Plugin for KoReader

[unrealJune]

Hi everyone! I got really tired of the Tailscale dance I had to do to get documents from my phone onto my Kindle, especially when the two weren't on a common LAN. So I implemented Google's Quick Share (Nearby Share) protocol for KoReader and my kindle.

https://github.com/unrealJune/kindshare

You share a file from your Android phone exactly the way you'd share it to any other device — the Kindle shows up in the Quick Share sheet. Nothing to install on the phone, no cloud, no cable, and no Bluetooth (the Voyage doesn't have any).

Features

1. Quick Share receiving. Files land in /mnt/us/documents, so an epub sent this way just appears in your library.
2. SoftAP mode. The Kindle can run as a Wi-Fi access point that your phone joins directly (default SSID kindrop, WPA2), so this works with no router at all — cafes, trains, work networks that block device-to-device traffic. Quick Share keeps working over it automatically.
3. KOReader plugin for all of it — turn receiving on/off, enable it at boot, start the access point, view diagnostics. No shell needed after install.

How it works
It's a from-scratch Go implementation of the protocol: mDNS discovery, the UKEY2 handshake, the encrypted D2D layer, and the frame state machine through to chunked file payloads. It cross-compiles to a single static ARM binary, so it doesn't care what libc the device has. (Go, not Rust, because Rust's minimum kernel is above the 3.0.35 these devices run.)

For SoftAP I did not patch or replace any driver — the Voyage already runs the upstream ath6kl driver, which supports AP mode; Kindle firmware just doesn't ship hostapd. So it's a cross-compiled hostapd plus busybox udhcpd. Nothing is flashed and nothing touches the kernel.

Requirements
Jailbroken Kindle with KUAL and KOReader. Tested end to end on a Voyage, FW 5.13.6 (kernel 3.0.35-lab126, AR6003 / ath6kl_sdio).

Will it work on my device?
The two halves have very different requirements, and this is the bit worth reading:

• The Quick Share receiver needs no AP support and no Bluetooth — just a network and the ability to run a static binary. It should port to most jailbroken readers with little more than path changes.
• SoftAP needs a driver that advertises AP mode. Check with:
  

  iw phy phy0 info | sed -n '/Supported interface modes/,/^\t[A-Z]/p'

  If you don't see "* AP" in that list, SoftAP won't work — but the receiver still will, over your normal wifi or your phone's hotspot. Note that some Kindles ship Amazon's proprietary ar6000 driver instead, which doesn't expose AP this way.

There are porting and compatibility notes in the repo, plus a troubleshooting doc covering the failure modes I hit (several of which look identical to everything working correctly).

Caveats

• Receive only — you can't send from the Kindle.
• Transfers are auto-accepted. There's no good way to prompt mid-transfer on e-ink, so anything sent to the device gets written. Bear that in mind on shared networks.
• The Kindle can't receive while it's asleep. It re-registers when it wakes.
• The device shows as "unknown" on the phone since it holds no Nearby Share certificates. Transfers work fine.

Built on the reverse engineering in https://github.com/grishka/NearDrop and https://github.com/Martichou/rquickshare — the protocol documentation and the collected .proto files came from those projects, and rquickshare's docs are where I found the crucial detail that Bluetooth is only needed for the other direction. Thanks also to NiLuJe, whose usbnetwork hack and fbink are load-bearing here as usual.

Please give it a try! Issues and contributions welcome.