Application descriptors

The install command goes from an application name (scala, ammonite, scalafmt, etc.) to actual dependencies via "channels", which contain one application descriptor per application.

For example, the application descriptor of mdoc in the default channel contains:

{
  "repositories": [
    "central"
  ],
  "dependencies": [
    "org.scalameta::mdoc:latest.stable"
  ]
}

"repositories": ["central"] says that mdoc should be pulled from Maven Central, that "central" is an alias for.

"dependencies": ["org.scalameta::mdoc:latest.stable"] gives the Maven coordinates of mdoc. Note the use of ::, as mdoc is a Scala dependency, and of latest.stable to automatically select the latest version, excluding versions corresponding to nightlies.

Creating your own applications

Publish your application

In order for your application to be install-able via install, it should be published to Maven / Ivy repositories.

Once published, you should be able to pull its class path via the fetch command:

$ cs fetch my-app-org::my-app-name:latest.release
…

Replace my-app-org and my-app-name by the Maven group id and artifact id of your application. Note the use of :: to separate them if your application corresponds to a Scala module. Use a simple : for Java modules. ::: is also accepted for fully cross-versioned Scala modules.

Pass any missing Maven / Ivy repository via the -r / --repository option.

Run your application via `bootstrap`

You should then check that your application runs fine via the bootstrap command:

$ cs bootstrap my-app-org::my-app-name:latest.release -o my-app
$ ./my-app # should run your application
…

Adjust the dependency string as above, and pass any required repository.

Pass -M my.main.class to bootstrap if the main class of your application isn't detected automatically, or if the wrong main class is detected.

Create an application descriptor

You should then put the details passed to the bootstrap command in an application descriptor. Examples of such application descriptors live in the default channel GitHub repository.

At the minimum, your application descriptor should have repositories and dependencies sections, like

{
  "repositories": [
    "central"
  ],
  "dependencies": [
    "my-app-org::my-app-name:latest.release"
  ]
}

Add a "mainClass": "my.main.class" field if you passed an explicit main class to the bootstrap command.

If your application should be run via my-app once installed, its application descriptor should be written in a file named my-app.json.

Check that your application runs fine via its application descriptor by installing it to a temporary directory with

$ cs install \
    --install-dir tmp-install \
    --default-channels=false \
    --channel directory/of/app/descriptor \
    my-app
$ tmp-install/my-app # should run your application
…

Replace directory/of/app/descriptor by the directory where you wrote your application descriptor (my-app.json in the example here). Replace my-app by your application name.

Publish your application descriptor

You should then make your application descriptor available to your users. You can either:

add it to an existing channel, such as the contrib channel, or
create your own channel.

Use the contrib channel

Send a pull requests adding your application channel under the resources directory of the contrib channel. Once the maintainers of this repository merge your pull request and cut a release, your users should be able to install and run your appplication like

$ cs install --contrib my-app
$ my-app
…

Create your own channel

If you wish to create your own channel, You can either create a JAR-based channel or a URL-based channel.

For the sake of simplicity, we'll only describe URL-based channels here.

Create a JSON file, containing a JSON object with your application name as key, and your application descriptor as value, like

{
  "my-app": {
    "repositories": [
      "central"
    ],
    "dependencies": [
      "my-app-org::my-app-name:latest.release"
    ]
  }
}

Put that file on at a URL where your users can consume it. It can be a file in a GitHub repository, or a GitHub gist, but any service allowing to download that file via HTTP should work. Don't forget to give your users the link to the "raw" content of your channel.

Once that file is available at some URL, like https://git.io/Jv8um, your users should be able to install your application with

$ cs install --channel https://git.io/Jv8um my-app
$ my-app
…

Channel types

Channels consist either of

a single JSON file, available at some URL, or
a collection of JSON files in a JAR, published on a Maven repository, or
a local directory, containing JSON files.

For example, the default channel, io.get-coursier:apps is JAR-based. It lives in this GitHub repository. It is published as io.get-coursier:apps on Maven Central.

Its JAR contains a number of JSON files at its root:

$ unzip -l "$(cs fetch io.get-coursier:apps:0.0.8)" | grep json
      188  02-09-2020 17:48   ammonite.json
      175  02-09-2020 17:48   coursier.json
      332  02-09-2020 17:48   cs.json
      241  02-09-2020 17:48   dotty-repl.json
      150  02-09-2020 17:48   echo-graalvm.json
      108  02-09-2020 17:48   echo-java.json
      172  02-09-2020 17:48   echo-native.json
      335  02-09-2020 17:48   giter8.json
      135  02-09-2020 17:48   mdoc.json
      323  02-09-2020 17:48   mill-interactive.json
      321  02-09-2020 17:48   mill.json
      524  02-09-2020 17:48   sbt-launcher.json
      222  02-09-2020 17:48   scala.json
      209  02-09-2020 17:48   scalac.json
      213  02-09-2020 17:48   scaladoc.json
      180  02-09-2020 17:48   scalafix.json
      184  02-09-2020 17:48   scalafmt.json
      204  02-09-2020 17:48   scalap.json

JAR-based channels

These channels can be created by publishing a JAR to a Maven or Ivy repository. The default channel, io.get-coursier:apps, living in this GitHub repository, is published this way.

The JAR it publishes contains JSON files at its root (scala.json, ammonite.json, etc.) Each of these JSON files gives the Maven coordinates of the corresponding application, plus other parameters, like Java properties that need to be set for the application to start fine, an explicit main class if the manifest of the application JAR doesn't contain one or if this JAR has several main classes to choose from, etc. See this section for more details.

JAR-based channels can be passed to the --channel option of install command, via their Maven coordinates, with no version, like io.get-coursier:apps. The latest version of the channel module is automatically pulled.

The following command explicitly adds the default channel via its coordinates:

$ cs install --default-channels=false \
    --channel io.get-coursier:apps \
    mdoc

JAR-based channels should be the most reliable kind of channels for end-users (if published on Central, the channel JARs can't a priori be deleted, and previous versions can be manually inspected if needed), but are the less straightforward to setup.

This giter8 template facilitates and describes how to create your own JAR-based channel.

URL-based channels

These channels consist in a single JSON file, containing a JSON object. This object's keys correspond to application names, and its values are application descriptors.

Such a file must be made available at a public URL. This URL can then be passed to the --channel option of the install command.

For example, the following URL contains two application descriptors, for "my-scala" and "my-scalac", that can be installed via

$ cs install --channel https://gist.githubusercontent.com/alexarchambault/5f6c8c25997063a07ea769d7a2b61466/raw/3aadef1c006777bba024f492a28da8d6698ee6a0/demo-channel.json my-scala
$ my-scala --help
…

These channels are the easiest to setup, yet don't provide the ability to inspect former versions out-of-the-box.

Directory-based channels

These channels consist in a single local directory, containing JSON files at its root. Each of these JSON files correspond to an application descriptor. For example, JSON file foo.json contains the application descriptor for application foo.

You get an example of such a directory if you clone the default channel GitHub repository:

$ git clone https://github.com/coursier/apps.git
$ cs install --default-channels=false \
    --channel ./apps/apps/resources \
    mdoc

These channels are intended for local usage and debugging mostly.

Application metadata

When installing an application with cs install, the install command puts a self-executable JAR for that application in the application directory. It puts some metadata of its own in this JAR too, under META-INF/coursier/.

These metadata keep track of:

the channel used to go from the application name to an application descriptor, and the repositories used to fetch this channel JAR if it is JAR-based,
the application descriptor itself, that gives the application dependencies, and other parameters to start the application (see below too),
the list of JARs used by this application, along with their checksums.

Updates:

check the channel for updates of the application descriptor, and
check that the resolved artifacts of the application descriptor didn't change.

If any of these two changed, the launcher of the application is generated again, from the newest data.

Application descriptor reference

Application descriptors are parsed from RawAppDescriptor.scala, that contains the full up-to-date list of supported fields.

Unrecognized fields in an application descriptor are simply ignored.

`repositories`

Specifies repositories this application should be pulled from. Accepts the same inputs as the -r / --repository option of the coursier CLI.

Example:

"repositories": [
  "central",
  "typesafe:ivy-releases",
  "https://some.custom.maven/repository"
]

`dependencies`

The dependency list of this application. Can contain Java dependencies (org:name:version), binary or fully cross-versioned Scala dependencies (org::name:version, org:::name:version), and Scala platform specific dependencies (for Scala Native typically, like org::name::version).

Example

"dependencies": [
  "org.scalameta::mdoc:latest.stable"
]

`launcherType`

Specifies the type of launcher that should be built for this application. Can be one of

bootstrap: builds a bootstrap as built by the bootstrap command by default
assembly: builds an assembly (corresponds to the --assembly option of the bootstrap command)
standalone: builds a bootstrap embedding its JAR dependencies as resources (corresponds to the --standalone option of the bootstrap command - these JARs are similar to the ones one-jar builds)
scala-native: builds a Scala Native application (requires the right environment setup, and requires coursier to be started via its JAR-based launcher for now)
graalvm-native-image: builds a GraalVM native image
prebuilt: points to an existing prebuilt executable (requires the prebuilt field to be set as well)

`mainClass`

Specifies an explicit main class to start. Add a ? suffix to use the specified main class only if none is found in the application JAR manifest.

Examples

"mainClass": "scala.tools.nsc.MainGenericRunner"

"mainClass": "ammonite.Main?"

`name`

Specifies the name under which this application should be installed. The default name is the same as the JSON file (foo.json gets installed as foo). The name field allows to override that.

Example

"name": "amm"

`prebuilt`

Specifies a URL at which prebuilt versions of the application are available.

This field is only used if launcherType is scala-native or graalvm-native-image.

That URL can contain expressions like ${version} and ${platform}, that are replaced by the selected version of the application, and the platform it is installed in. Currently ${platform} can be replaced by one of

x86_64-pc-linux
x86_64-apple-darwin
x86_64-pc-win32
aarch64-pc-linux
aarch64-apple-darwin

Example

"prebuilt": "https://github.com/coursier/coursier/releases/download/v${version}/cs-${platform}"

For version 2.0.0-RC6-6 on macOS, this gets transformed as this URL.

`prebuiltBinaries`

Like prebuilt, specifies the URLs at which prebuilt versions of the application are available, but URLs are specific to platforms.

Example

"prebuiltBinaries": {
  "x86_64-apple-darwin": "gz+https://github.com/coursier/coursier/releases/download/v${version}/cs-x86_64-apple-darwin.gz",
  "x86_64-pc-win32": "zip+https://github.com/coursier/coursier/releases/download/v${version}/cs-x86_64-pc-win32.zip"
}

For version 2.1.0 on Windows, this gets transformed as this URL.

The possible values for platforms are listed in the previous section.

Coursier

2.1.8

Application descriptors

Creating your own applications

Publish your application

Run your application via `bootstrap`

Create an application descriptor

Publish your application descriptor

Use the contrib channel

Create your own channel

Channel types

JAR-based channels

URL-based channels

Directory-based channels

Application metadata

Application descriptor reference

`repositories`

`dependencies`

`launcherType`

`mainClass`

`name`

`prebuilt`

`prebuiltBinaries`

Creating your own applications

Publish your application

Run your application via bootstrap

Create an application descriptor

Publish your application descriptor

Use the contrib channel

Create your own channel

Channel types

JAR-based channels

URL-based channels

Directory-based channels

Application metadata

Application descriptor reference

repositories

dependencies

launcherType

mainClass

name

prebuilt

prebuiltBinaries

Run your application via `bootstrap`

`repositories`

`dependencies`

`launcherType`

`mainClass`

`name`

`prebuilt`

`prebuiltBinaries`