Files
firezone/rust/headless-client
Thomas Eizinger 1914ea7076 refactor(rust): remove forced callback indirection (#9362)
As relict from very early designs of `connlib`, the `Callbacks` trait is
still present and defines how the host app receives events from a
running `Session`. Callbacks are not a great design pattern however
because they force the running code, i.e. `connlib`s event-loop to
execute unknown code. For example, if that code panics, all of `connlib`
is taken down. Additionally, not all consumers may want to receive
events via callbacks. The GUI and headless client for example already
have their own event-loop in which they process all kinds of things.
Having to deal with the `Callbacks` interface introduces an odd
indirection here.

To fix this, we instead return an `EventStream` when constructing a
`Session`. This essentially aligns the API of `Session` with that of a
channel. You receive two handles, one for sending in commands and one
for receiving events. A `Session` will automatically spawn itself onto
the given runtime so progress is made even if one does not poll on these
channel handles.

This greatly simplifies the code:

- We get to delete the `Callbacks` interface.
- We can delete the threaded callback adapter. This was only necessary
because we didn't want to block `connlib` with the handling of the
event. By using a channel for events, this is automatically guaranteed.
- The GUI and headless client can directly integrate the event handling
in their event-loop, without having to create an indirection with a
channel.
- It is now clear that only the Apple and Android FFI layers actually
use callbacks to communicate these events.
- We net-delete 100 LoC
2025-06-02 11:28:04 +00:00
..

headless-client

This crate acts as the CLI / headless Client, and the privileged tunnel service for the GUI Client, for both Linux and Windows.

It is built as:

  • headless-client to act as the Linux / Windows headless Client
  • firezone-headless-client to act as the Linux tunnel service, Windows headless Client, or Windows tunnel service

In general, the brand name should be part of the file name, but the OS name should not be.

Running

To run the headless Client:

  1. Generate a new Service account token from the "Actors -> Service Accounts" section of the admin portal and save it in your secrets manager. The Firezone Linux client requires a service account at this time.
  2. Ensure /etc/dev.firezone.client/token is only readable by root (i.e. chmod 400)
  3. Ensure /etc/dev.firezone.client/token contains the Service account token. The Client needs this before it can start
  4. Set FIREZONE_ID to a unique string to identify this client in the portal, e.g. export FIREZONE_ID=$(uuidgen). The client requires this variable at startup.
  5. Set LOG_DIR to a suitable directory for writing logs
    export LOG_DIR=/tmp/firezone-logs
    mkdir $LOG_DIR
    
  6. Now, you can start the client with:
./firezone-headless-client standalone

If you're running as an unprivileged user, you'll need the CAP_NET_ADMIN capability to open /dev/net/tun. You can add this to the client binary with:

sudo setcap 'cap_net_admin+eip' /path/to/firezone-headless-client

Building

Assuming you have Rust installed, you can build the headless Client with:

cargo build --release -p firezone-headless-client

The binary will be in target/release/firezone-headless-client

The release on Github are built with musl. To build this way, use:

rustup target add x86_64-unknown-linux-musl
sudo apt-get install musl-tools
cargo build --release -p headless-client --target x86_64-unknown-linux-musl

Files

  • /etc/dev.firezone.client/token - The service account token, provided by the human administrator. Must be owned by root and have 600 permissions (r/w by owner, nobody else can read) If present, the tunnel will ignore any GUI Client and run as a headless Client. If absent, the tunnel will wait for commands from a GUI Client
  • /usr/bin/firezone-headless-client - The tunnel binary. This must run as root so it can modify the system's DNS settings. If DNS is not needed, it only needs CAP_NET_ADMIN.
  • /usr/lib/systemd/system/firezone-headless-client.service - A systemd service unit, installed by the deb package.
  • /var/lib/dev.firezone.client/config/firezone-id - The device ID, unique across an organization. The tunnel will generate this if it's not present.