Tap

Website · Downloads · Device support

Read and write NFC tags, through org.freedesktop.portal.NFC.

Hold a tag against the back of the device and Tap shows its type, its protocol, its UID and any NDEF records on it. With a writable tag in the field it can store a text or a link record.

Build from source

meson setup _build
meson compile -C _build
meson test -C _build          # validates the desktop and metainfo files
meson install -C _build

Needs GTK 4.14, libadwaita 1.6 and blueprint-compiler at build time.

As a Flatpak, the manifest is build-aux/io.github.porthole_dev.Tap.json:

flatpak-builder --user --install --force-clean _flatpak build-aux/io.github.porthole_dev.Tap.json

On Nura, the package is temp/tap in porthole-dev/pmaports, built from this repository's release tarballs.

Contributing

See CONTRIBUTING.md.

Licence

GPL-3.0-or-later, see COPYING.

Project links

Device support · Packaged builds · Contribution policy

Independent project; not endorsed by Nura or GNOME. See AI.md for the assistance policy.

Portal integration and permissions

What talking to the portal costs

One function. connect_to_portal() in src/tap-nfc.c reads IsNFCPresent, calls AccessNFC, waits for the Response, calls OpenNFCRemote and wraps the file descriptor it gets back. Everything after that is ordinary neard on an ordinary GDBusObjectManager -- the same code an unsandboxed program would write against the system bus.

Three things in there are not guessable and are commented where they happen:

• the filtered connection's lifetime is tied to the session bus connection the portal calls were made on, not to the file descriptor;
• g_dbus_connection_new_for_address ("unix:fd=N") does not work, the fd has to become a real GSocketConnection;
• G_DBUS_CONNECTION_FLAGS_MESSAGE_BUS_CONNECTION is required, or every call fails with Hello() was not yet called.

What it deliberately cannot do

Turn the radio on. Properties.Set on org.neard.Adapter is refused by the portal's filter, permanently and by design -- the switch is the user's, in Settings ▸ Privacy & Security ▸ NFC. When the radio is off Tap says so and points there.

Permissions, and one caveat about the native build

As a Flatpak, Tap has its own app id, its own grant, and its own row in Settings ▸ Privacy & Security ▸ NFC ▸ Permitted Apps.

As a native package on a xdg-desktop-portal built -Dsystemd=disabled (Alpine's stock default), every unsandboxed caller collapses to the same blank app id: Tap still works and still gets a grant, but it shares that grant with every other host process and gets no row in Permitted Apps. Tap says this in its own permission screen rather than claiming a permission model it does not have there. The fix is a portal rebuild with -Dsystemd=enabled, which is a packaging change and not a design one.