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Update some of the protocol details
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r n s h  Shell over Reticulum

CI  Release  PyPI version   PyPI - Downloads

rnsh is a utility written in Python that facilitates shell sessions over Reticulum networks. It is based on the rnx utility that ships with Reticulum and aims to provide a similar experience to SSH.

Contents

Reminder: Alpha Software

These early versions will be buggy. There will sometimes be major breaking changes to the command line parameters between releases. There will sometimes be breaking changes in the protocol between releases. Use at your own peril!

Recent Changes

v0.0.12

  • Remove service name from RNS destination aspects. Service name now selects a suffix for the identity file and should only be supplied on the listener. The initiator only needs the destination hash of the listener to connect.
  • Show a spinner during link establishment on tty sessions
  • Attempt to catch and beautify exceptions on initiator

v0.0.11

  • Event loop bursting improves throughput and CPU utilization on both listener and initiator.
  • Packet retries use RNS resend feature to prevent duplicate packets.

v0.0.10

  • Rate limit window change events to prevent saturation of transport
  • Tweaked some loop timers to improve CPU utilization

v0.0.9

  • Switch to a new packet-based protocol
  • Bug fixes and dependency updates

Quickstart

Tested (thus far) on Python 3.11 macOS 13.1 ARM64. Should run on Python 3.6+ on Linux or Unix. WSL probably works. Cygwin might work, too.

  • Activate a virtualenv
  • pip3 install rnsh
    • Or from a whl release, pip3 install /path/to/rnsh-0.0.1-py3-none-any.whl
  • Configure Reticulum interfaces, check with rnstatus
  • Ready to run rnsh. The options are shown below.

Example: Shell server

Setup

Before running the listener or initiator, you'll need to get the listener destination hash and the initiator identity hash.

# On listener
rnsh -l -p

# On initiator
rnsh -p

Note: service name no longer is supplied on initiator. The destination hash encapsulates this information.

Listener

  • Listening for default service name ("default").
  • Using user's default Reticulum config dir (~/.reticulum).
  • Using default identity ($RNSCONFIGDIR/storage/identities/rnsh).
  • Allowing remote identity 6d47805065fa470852cf1b1ef417a1ac to connect.
  • Launching /bin/zsh on authorized connect.
rnsh -l -a 6d47805065fa470852cf1b1ef417a1ac -- /bin/zsh

Initiator

  • Connecting to default service name ("default").
  • Using user's default Reticulum config dir (~/.reticulum).
  • Using default identity ($RNSCONFIGDIR/storage/identities/rnsh).
  • Connecting to destination a5f72aefc2cb3cdba648f73f77c4e887
rnsh a5f72aefc2cb3cdba648f73f77c4e887

Options

Usage:
    rnsh -l [-c <configdir>] [-i <identityfile> | -s <service_name>] [-v... | -q...] -p
    rnsh -l [-c <configdir>] [-i <identityfile> | -s <service_name>] [-v... | -q...] 
            [-b <period>] (-n | -a <identity_hash> [-a <identity_hash>] ...) [-A | -C] 
            [[--] <program> [<arg> ...]]
    rnsh [-c <configdir>] [-i <identityfile>] [-v... | -q...] -p
    rnsh [-c <configdir>] [-i <identityfile>] [-v... | -q...] [-N] [-m] [-w <timeout>] 
         <destination_hash> [[--] <program> [<arg> ...]]
    rnsh -h
    rnsh --version

Options:
    -c DIR --config DIR          Alternate Reticulum config directory to use
    -i FILE --identity FILE      Specific identity file to use
    -s NAME --service NAME       Service name for identity file if not default
    -p --print-identity          Print identity information and exit
    -l --listen                  Listen (server) mode. If supplied, <program> <arg>...will 
                                   be used as the command line when the initiator does not
                                   provide one or when remote command is disabled. If
                                   <program> is not supplied, the default shell of the 
                                   user rnsh is running under will be used.
    -b --announce PERIOD         Announce on startup and every PERIOD seconds
                                 Specify 0 for PERIOD to announce on startup only.
    -a HASH --allowed HASH       Specify identities allowed to connect
    -n --no-auth                 Disable authentication
    -N --no-id                   Disable identify on connect
    -A --remote-command-as-args  Concatenate remote command to argument list of <program>/shell
    -C --no-remote-command       Disable executing command line from remote
    -m --mirror                  Client returns with code of remote process
    -w TIME --timeout TIME       Specify client connect and request timeout in seconds
    -q --quiet                   Increase quietness (move level up), multiple increases effect
                                          DEFAULT LOGGING LEVEL
                                                  CRITICAL (silent)
                                    Initiator ->  ERROR
                                                  WARNING
                                     Listener ->  INFO
                                                  DEBUG    (insane)
    -v --verbose                 Increase verbosity (move level down), multiple increases effect
    --version                    Show version
    -h --help                    Show this help

How it works

Listeners

Listener instances are the servers. Each listener is configured with an RNS identity, and a service name. Together, RNS makes these into a destination hash that can be used to connect to your listener.

Each listener must use a unique identity. The -s parameter can be used to specify a service name, which creates a unique identity file.

Listeners can be configured with a command line to run on connect. Initiators can supply a command line as well. There are several different options for the way the command line is handled:

  • -C no initiator command line is allowed; the connection will be terminated if one is supplied.
  • -A initiator-supplied command line is appended to listener- configured command line
  • With neither of these options, the listener will use the first valid command line from this list:
    1. Initiator-supplied command line
    2. Listener command line argument
    3. Default shell of user listener is running under

If the -n option is not set on the listener, the initiator is required to identify before starting a command. The program will be started with the initiator's identity hash string is set in the environment variable RNS_REMOTE_IDENTITY.

Listeners are set up using the -l flag.

Initiators

Initiators are the clients. Each initiator has an identity hash which is used as an authentication mechanism on Reticulum. You'll need this value to configure the listener to allow your connection. It is possible to run the server without authentication, but hopefully it's obvious that this is an advanced use case.

To get the identity hash, use the -p flag.

With the initiator identity set up in the listener command line, and with the listener identity copied (you'll need to do -p on the listener side, too), you can run the initiator.

I recommend staying pretty vanilla to start with and trying /bin/zsh or whatever your favorite shell is these days. The shell should start in login mode. Ideally it works just like an ssh shell session.

Protocol

The protocol is build on top of the Reticulum Packet API. Application software sends and receives Message objects, which are encapsulated by Packet objects. Messages are (currently) sent one per packet, and only one packet is sent at a time (per link). The next packet is not sent until the receiver proves the outstanding packet.

A future update will work to allow a sliding window of outstanding packets to improve channel utilization.

Session Establishment

  1. Initiator establishes link. Listener session enters state LSSTATE_WAIT_IDENT, or LSSTATE_WAIT_VERS if running with --no-auth option.

  2. Initiator identifies on link if not using --no-id.

    • If using --allowed-hash, listener validates identity against configuration and if no match, sends a protocol error message and tears down link after prune timer.

  3. Initiator transmits a VersionInformationMessage, which is evaluated by the server for compatibility. If incompatible, a protocol error is sent.

  4. Listener responds with a VersionInfoMessage and enters state LSSTATE_WAIT_CMD

  5. Initiator evaluates the listener's version information for compatibility and if incompatible, tears down link.

  6. Initiator sends an ExecuteCommandMessage (which could be an empty command) and enters the session event loop.

  7. Listener evaluates the command message against the configured options such as -A or -C and responds with a protocol error if not allowed.

  8. Listener starts the program. If success, the listener enters the session event loop. If failure, responds with a CommandExitedMessage.

Session Event Loop

Listener state LSSTATE_RUNNING

Process messages received from initiator.

  • WindowSizeMessage: set window size on child tty if appropriate
  • StreamDataMessage: binary data stream for child process; streams ids 0, 1, 2 = stdin, stdout, stderr
  • NoopMessage: no operation - listener replies with NoopMessage
  • When link is torn down, child process is terminated if running and session destroyed
  • If command terminates, a CommandExitedMessage is sent and session is pruned after an idle timeout.
Initiator state ISSTATE_RUNNING

Process messages received from listener.

  • ErrorMessage: print error, terminate link, and exit
  • StreamDataMessage: binary stream information; streams ids 0, 1, 2 = stdin, stdout, stderr
  • CommandExitedMessage: remote command exited
  • If link is torn down unexpectedly, print message and exit

Roadmap

  1. Plan a better roadmap
  2. ?
  3. Keep my day job

TODO

  • Initial version
  • Pip package with command-line utility support
  • Publish to PyPI
  • Improve signal handling
  • Make it scriptable (currently requires a tty)
  • Protocol improvements (throughput!)
  • Documentation improvements
  • Fix issues with running rnsh in a binary pipeline, i.e. piping the output of tar over rsh.
  • Test on several platforms
  • Fix issues that come up with testing
  • v0.1.0 beta
  • Test and fix more issues
  • More betas
  • Enhancement Ideas
    • authorized_keys mode similar to SSH to allow one listener process to serve multiple users
    • Git over rnsh (git remote helper)
    • Sliding window acknowledgements for improved throughput
  • v1.0 someday probably maybe

Miscellaneous

By piping into/out of rnsh, it is possible to transfer files using the same method discussed in this article. It's not terribly fast currently, due to the round-trip rule enforced by the protocol. Sliding window acknowledgements will speed this up significantly.