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An implementation of a Signal K server in Node.js. Intended to run on embedded devices (e.g. Raspberry Pi, Beaglebone or UDOO).

The server multiplexes data from NMEA0183, NMEA 2000, Signal K and sensor inputs (eg. I2C connected sensors) and provides the data in Signal K format over HTTP, WebSocket and TCP. It also functions as a NMEA0183 server over TCP.

The server's capabilities can be expanded with the help of plugins that provide additional features such as

• conversion to NMEA2000
• conversion to NMEA0183
• read and write interfacing with cloud services such as MarineTraffic
• logging to database such as InfluxDb

Installation

Detailed instructions for installation on Raspberry Pi

Prerequisites

• Node.js version 16 with latest npm installed (the server works for the time being on Node version >=10, but we are moving to the latest LTS version that is v16 in 9/2021)

Use: Install from npm

$ sudo npm install -g signalk-server

Now you can start the server with sample data:

• NMEA0183 sample data: signalk-server --sample-nmea0183-data
• NMEA2000 sample data: signalk-server --sample-n2k-data

To generate your own vessel settings file and configure your Pi to start the server automatically run

$ sudo signalk-server-setup

Develop: Install from git

git clone https://github.com/SignalK/signalk-server.git
cd signalk-server
npm install
npm run build:all

Start the server with sample data:

• NMEA0183 sample data: bin/nmea-from-file
• NMEA2000 sample data: bin/n2k-from-file

This will start the server with a sample configuration file and the server will start playing back data from a sample file under samples/. The data is available immediately via the REST interface at https://localhost:3000/signalk/v1/api/.

A simple way to connect to the WebSocket interface from the command line is to install wscat2 and use that:

npm install -g wscat2
wscat 'ws://localhost:3000/signalk/v1/stream?subscribe=all'

Provision: Ansible on a Raspberry Pi

Marinepi-provisioning has useful roles and examples for provisioning Signal K and auxiliary services on a headless Raspberry Pi.

Docker

You can start a local server on port 3000 with demo data with

docker run --init -it --rm --name signalk-server --publish 3000:3000 --entrypoint /home/node/signalk/bin/signalk-server signalk/signalk-server --sample-nmea0183-data

For real use you need to persist /home/node/.signalk where the server's configuration is stored, with for example

docker run -d --init  --name signalk-server -p 3000:3000 -v $(pwd):/home/node/.signalk signalk/signalk-server

This will run the server as background process and current directory as the settings directory. You will be prompted to create admin credentials the first time you you access the configuration admin web UI.

More docker information can found from docker -folder

Now what?

Once you have the data streams in place you probably want to use the data or at least see it in a nice format. Some sample plugins and apps are installed during the installation process.

• Apps or Webapps are mainly web pages for accessing the Signal K output such as dashboards, configurable gauges or web maps. See Webapps doc for more information.
• If you have internet connectivity for your server App Store in the admin user interfaces shows all the Signal K Plugins and Apps that have been published via npm with the right keywords. It also shows their current status on your server and allows you to install and update these.
• Plugins are web forms to tailor your server to your needs, change parameters or get information from various sources. See Server Plugins

Configuration

Please take a look at the different settings files in the settings directory and read the brief intro.

You can specify the settings file via command line with bin/signalk-server -s <path-to-your-settings-file>.

You can also configure the path to the settings file with environment variable SIGNALK_NODE_SETTINGS.

The http port can be configured separately with environment variable PORT. You can also run on port 80 with systemd. Environment variable NMEA0183PORT sets the NMEA 0183 tcp port.

Storing Configuration Outside The Server Install Directory

You can store configuration like the settings file, plugin cofiguration and defaults.js in a directory outside of the server install using the -c option (or the SIGNALK_NODE_CONFIG_DIR env variable).

By default, the server will look for a settings.json and a defaults.json file in the given directory.

For example, ./bin/signalk-server -c /usr/local/etc/node_server_config

In this case, the server would look for the settings file at /usr/local/etc/node_server_config/settings.json

You can overwrite the default settings file name by specifying the -s argument.

For example, ./bin/signalk-server -c /usr/local/etc/node_server_config -s test_settings.json`

In this case, the server would look for the settings file at /usr/local/etc/node_server_config/test_settings.json

Environment variables

• SIGNALK_NODE_SETTINGS override the path to the settings file.
• SIGNALK_NODE_CONFIG_DIR override the path to find server configuration files.
• PORT override the port for http/ws service (default is 3000).
• SSLPORT override the port for https/wss service. If defined activates ssl as forced, default protocol (default is 3443).
• EXTERNALPORT the port used in /signalk response and Bonjour advertisement. Has precedence over configuration file.
• EXTERNALHOST the host used in /signalk response and Bonjour advertisement. Has precedence over configuration file.
• FILEUPLOADSIZELIMIT override the file upload size limit (default is '10mb').
• NMEA0183PORT override the port for the NMEA 0183 over tcp service (default is 10110).
• TCPSTREAMPORT override the port for the Signal K Streaming (deltas) over TCP.
• TCPSTREAMADDRESS override the address the Signal K Stream (deltas) over TCP is listening on.
• DISABLEPLUGINS disable all plugins so that they can not be enabled (default is false).
• DEFAULTENABLEDPLUGINS a comma separated list of plugin ids that are overridden to be enabled by default if no setttings exist. lower preference than DISABLEPLUGINS.
• PLUGINS_WITH_UPDATE_DISABLED a comma separated list of plugin that will not be updated.
• SECURITYSTRATEGY override the security strategy module name.
• WSCOMPRESSION compress websocket messages (default is false).
• MAXSENDBUFFERSIZE the maximum number of bytes allowed in the server's send buffer of a WebSocket connection. The connection will be terminated if this is exceeded. Guards against slow or dysfunctional clients that can not cope with the message volume (default is 512 * 1024 bytes).
• SIGNALK_SERVER_IS_UPDATABLE allows the server to be updated through the GUI even if it is not installed in the standard paths (default is false). if set to true, the server must have been installed with npm install -g signalk-server.
• SIGNALK_DISABLE_SERVER_UPDATES disables server updates in the GUI (default is false).
• DEBUG a comma-separated list of tags for debugging the specified module (For example: signalk-server*,signalk-provider-tcp). Can now be defined directly in the graphical interface. More help on how to use the debug here: https://www.npmjs.com/package/debug#wildcards
• IS_IN_DOCKER used to tell the server it is in Docker and not normally updateable (default is false).
• NPMREGISTRYTIMEOUT how long to wait for the registry when retrieving the App Store listing (default is 20s).
• SECRETKEY a secret string used to generate an authentication token (the internal default autogenerated is a string of 512 hex chars like 'ef8307a4c7a4bd7...309d947bca3')
• ALLOW_DEVICE_ACCESS_REQUESTS used when a device needs to gain access to a secured Signal K server (default is true) (https://signalk.org/specification/1.4.0/doc/access_requests.html).
• ALLOW_NEW_USER_REGISTRATION (default is true).
• ADMINUSER force a account for admin user (username:password format).
• PRESERIALCOMMAND command to run before opening a serial port.

Real Inputs

To hook the server up to your real inputs you need to create a configuration file that connects to your input source and applies the relevant parsers / converters in the provider pipeline.

Inputs are configured as an array of pipedProviders, each with an id and an array of pipeElements. You need to create a pipedProviders entry for each of your inputs. The pipedProvider must include 'id' (name of the interface, e.g. NMEA0183 from AIS could be called "AIS"). The first pipeElement is the source of the data ("providers/serialport" for a serial interface such as USB, "providers/filestream" if the data comes from a file, "providers/tcp" if the source is a TCP port etc.). You will see in the example settings that the second pipeElement is often "providers/liner". This is a pipeElement that splits the input into separate lines and passes one line at a time to the next pipeElement. The final pipeElement or group of pipeElements is where the translation or passing to the server occurs. For NMEA0183, this is "providers/nmea0183-signalk", for N2K (NMEA2000) it is "providers/n2kAnalyzer" and then "providers/n2k-signalk".

There are also special pipeElements such as "providers/log" (see below), and "providers/throttle" which changes the playback from files to the bytes per second rate set in the options. The "providers/execute" pipeElement lets you pass a command to the server, as set in the options.

Each PipeElement is configured with options. Different PipeElements use different configuration parameters, like for serialport you can configure baud rate and for udp connection the port.

A PipeElement may require some options entry that is available already in the configuration file (nmea0183-signalk needs the self id). This can be accomplished with optionMappings property.

You can also use optionMappings property to optionally override options entries with command line parameters. For example you can specify the data file for file playback from the command line as bin/signalk-server -s settings/volare-file-settings.json --nmeafilename=samples/nais400-merrimac.log with this configuration.

Look through the examples in the settings folder and copy pipedProviders that suit your setup. You can combine as many as you want. See multiple sources example

Make sure that the settings file you are using is valid JSON. This can be done in an online validator like JSONLint

NMEA0183

There is an example settings file for using NMEA 0183 input from a serial device that you can use to start up the server: bin/signalk-settings -s settings/volare-serial-settings.json. You can change the port and baudrate in the settings file.

NMEA 2000 (via NGT-1 & Canboat)

There is an example settings file for N2K from N2K/CANBus. Make sure to change the command option to match the NGT-1 port like in this example

Signal K

A provider that handles Signal K deltas can be set up with the following elements:

• a source pipeElement (providers/filestream, providers/serialport, providers/tcp, providers/udp)
• providers/liner
• providers/from_json

Furthermore you can use data from a Signal K server with the providers/mdns-ws source. Without any configuration it will use the Signal K discovery process to discover any Signal K servers in the local network, such as iKommunicate, and connect to it. No other pipeElements are needed. See the example configuration file. You can also configure mdns-ws with host and port, which will disable the discovery process and make it connect directly to the specified server.

File

An input from a file uses the providers/filestream. The options to change are filename and fromAppProperty ,see NMEA0183 and N2K examples.

Serial

An input from a serial port uses the providers/serialport pipeElement. It takes the options device and baudrate and optionally "toStdout"(see example). serialport has an internal line splitter, so a pipedProvider with serialport as the source does not need liner and will not work with one.

TCP

providers/tcp is a TCP client that can connect to a server and receive input from a TCP socket. It takes the options host and port (see example).

UDP

settings/volare-udp-settings provides an example of NMEA0183 input over UDP port 7777. If you have trouble getting this to work try setting up DEBUG environment variable with export DEBUG=signalk-server:udp-provider and sending manually input with netcat echo '$IIDBT,034.25,f,010.44,M,005.64,F*27' | nc -4u -w1 localhost 7777. This should result in the server logging the NMEA sentence it receives. UDP source takes port option.

GPSD

Please see example settings files.

Bonjour support

Bonjour support will be enabled by default if your system supports it and has the required software installed. See also https://github.com/agnat/node_mdns#installation for more information.

When Bonjour is enabled the server advertises itself via Bonjour. This means that Bonjour-aware software running in the same network can discover the Signal K server and access it. For example the server shows up in Safari at Bookmarks => Bonjour => Webpages.

You can disable Bonjour/mDNS by adding the entry "mdns": false to the config file. See settings/volare-gpsd-settings.json for example.

The server can also automatically discover other Signal K devices and connect to them. See settings/signalk-ws-settings.json for an example. If the incoming data should be treated as data about self the identity in the settings file and in the incoming data need to match or the incoming data should not include context, as the default is self.

HTTPS

Https is not enabled by default. To enable it, set "ssl":true in the settings file. If no ssl-key.pem & ssl-cert.pem files are found under settings they will be created. If you need to configure a certificate chain add it in ssl-chain.pem under settings.

By default the server listens to both http and https in the same port.

Logging

You can log all the input data in pre-Signal K format by adding the log element to your pipeElement pipeline. It creates hourly files with the data from all the configured providers, interleaved/multiplexed with one message per line. The multiplexed log files can be played back with multiplexedlog pipeElement element. Please beware the standard discriminators in multiplexedlog. For extensive use of logging, please see Cassiopeia

Server Plugins

Plugin configuration interface is at /plugins/configure. See Server Plugins for more information.

Charts

Signal K chart support is provided by the @signalk/charts-plugin plugin.

After installing and configuring the plugin from the admin console, use a client app such as Freeboard SK or Tuktuk Plotter to retrieve a list of charts and present them.

Custom logo

You can change the admin application's top left logo by placing a SVG file named logo.svg in the settings directory (default: $HOME/.signalk/).

Source Priority

You can specify relative precedence between sources for a single Signal K path.

The idea is that for a specific path you list sources in decreasing precedence with source specific timeouts.

Incoming data from a source is dropped (not handled at all) by the server if the previous value for the path is from a source with higher precedence and it is not older than the timeout.

The source priority algorithm compares the latest value that was passed through against a new value:

• is the latest value from a source that has a lower or equal priority than the incoming value's source? if true pass the value
• else: is the latest value older than the timeout for incoming source's timeout? if yes pass the value
• else: ignore the value

Note that the filtering takes place on path level, not on delta level: if a delta contains multiple path-value pairs some may be filtered out and others handled.

There is no timeout for the highest priority source, it is handled always.

Timeout for data from unlisted sources is 10 seconds.

FAQ

Further Reading

• http://signalk.org/index.html
• http://signalk.org/dev/messageFormat.html
• NMEA0183 support: nmea0183-signalk
• NMEA 2000 support: n2k-signalk via canboat

License

Copyright [2015] [Fabian Tollenaar, Teppo Kurki and Signal K committers]

Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at

http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.