Sharing over Local Wi-Fi

Let nearby phones, laptops and tablets use the library.

A Wi-Fi network is a connection between nearby devices. It doesn’t need the internet: when a phone opens the library’s address, the host device answers directly.

Two ways to connect

1. The host’s hotspot — on Android, turn on the hotspot and let people join it. Best for the field: no router needed, and some routers block devices from seeing each other. (A Mac is easiest to use on an existing network.)
2. An existing Wi-Fi network — the host and readers join the same router.

rtw start prints the address to share, for example:

Open on this device:   http://127.0.0.1:8080
Open on other devices: http://192.168.43.1:8080   (GPS on map: https://192.168.43.1:8443)

The address changes

The address depends on the network. It changes when the host joins a different Wi-Fi, and on Android the hotspot gets a new address every time it’s turned on. Check the current one at any time:

rtw address

The library’s home page also shows it, under Share this library.

On the readers’ devices

Nothing to install. Any reasonably modern browser works, so older phones make good readers.

• Books, Wikipedia, notes, sites — open and read.
• Apps — tap an .apk in Downloads; Android asks once to allow installs from the browser.
• Location on the map — browsers only share location with HTTPS pages. The map page links to the https://…:8443 address; accept the certificate warning once.
• Chat without internet — install Bitchat from Downloads → Bitchat. It messages nearby phones over Bluetooth mesh, with no network at all.
• Turn-by-turn navigation — install OsmAnd from Downloads → OsmAnd, download the .obf map files there and open them with OsmAnd. The phone then navigates offline with its own GPS, even away from the host.

Security notes

• Anyone on the same network can read the library. Only uploads and changes need the password.
• Log in to /admin/ over the https://…:8443 address so the password isn’t sent as plain text.
• The certificate is self-signed, so browsers warn about it. That’s expected on a private network.