[[packages]]
= Cockpit Packages

Cockpit is separated into various packages, each of which brings
specific features and/or code.

[WARNING]
====
In addition, any APIs or behavior not explicitly documented here is an
internal API and can be changed at any time.
====

[[package-layout]]
== Layout of Package Files

A package consists of one or more files placed in a directory or its
subdirectories. It must have a `+manifest.json+` file and follow certain
naming conventions.

The name of a package is the name of the directory.

The name of the package must be ASCII alphanumeric, and may contain an
underscore. Names of directories and files in the package must consist
of ASCII alphanumeric along with dash, underscore, dot, and comma. No
spaces are allowed.

Cockpit uses the data directories from the
https://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html[XDG
Base Directory Specification] to locate packages. The `+$XDG_DATA_DIRS+`
represents a colon separate list of system data directories, and
`+$XDG_DATA_HOME+` is a user specific data directory. If the environment
variables are not set, defaults are used, according to the spec. If
cockpit has been built with an alternate `+--prefix=/path+` then the
`+$prefix/share/cockpit+` is used by default.

A `+cockpit/+` subdirectories in any of these data directories is the
location where packages are loaded by Cockpit. If Cockpit finds a
package with the same name, in multiple data directories, then the first
one wins. According to the spec the first data directory is
`+$XDG_DATA_HOME+` and then `+$XDG_DATA_DIRS+` in order.

This means that, by default the following directories are searched for
cockpit packages, and in this order:

* `+~/.local/share/cockpit/+`
* `+/usr/local/share/cockpit/+`
* `+/usr/share/cockpit/+`

Packages placed in `+$XDG_DATA_HOME+` are not cached by Cockpit or the
web browser. Other packages are cached aggressively, and are accessed
using a checksum of the files in the packages and their names.

You can use the following command to list the packages installed on a
server. You'll note that it's output may change when you run the command
as different users, if there are packages installed in the user's home
directory.

....
$ cockpit-bridge --packages
...
....

To further clarify things, here is an example package called
"my-package" and its file layout:

....
/usr/share/cockpit/
    my-package/
        manifest.json
        file.html
        some.js
....

Place or symlink packages in your `+~/.local/share/cockpit+` directory
(or appropriate `+$XDG_DATA_HOME+` location) that you would like to
modify and develop. System installed packages should not change while
Cockpit is running.

== Package Manifest

Each package has a `+manifest.json+` file. It is a JSON object. The
following fields may be present in the manifest:

content-security-policy::
  By default Cockpit serves packages using a strict
  https://en.wikipedia.org/wiki/Content_Security_Policy[Content Security
  Policy], which among other things does not allow inline styles or
  scripts. This can be overridden on a per-package basis, with this
  setting.
  +
  If the overridden content security policy does not contain a
  `+default-src+`, `+connect-src+`, `+base-uri+`, `+form-action+`,
  `+object-src+`, or `+block-all-mixed-content+` then these will be
  added to the policy from the manifest.
name::
  An optional string that changes the name of the package. Normally
  packages derive their name from the directory that they are located
  in. This field overrides that name.
priority::
  An optional number that specifies which package is preferred in cases
  where there are conflicts. For example given two packages with the
  same `+name+` a package is chosen based on its priority.
conditions::
  An optional list of `+{"predicate": "value"}+` objects. Cockpit will
  only consider the package if _all_ conditions are met. This is
  preferable to using `+priority+`. +
   +
  Currently supported predicates are `+path-exists+` and `+path-not-exists+`
  (since Cockpit 286) and `+any+` (since Cockpit 348). `+any+` accepts a
  list of conditions and evaluates to true if _at least one_ of the nested
  conditions is met. Unknown predicates are ignored.

requires::
  An optional JSON object that contains a `+"cockpit"+` string version
  number. The package will only be usable if the Cockpit bridge and
  javascript base are equal or newer than the given version number.
version::
  An informational version number for the package.
preload::
  A list of identifiers of the components that should be preloaded.
  Normally, the files of a component are loaded when the user navigates
  to it for the first time. The files of a preloaded component are
  loaded immediately after the user logs in, and the initialization code
  of the component is invoked.
  +
  The value of this field is an array of strings, where each string is
  one of the keys used in the `+dashboard+`, `+menu+`, or `+tool+`
  fields that are explained below.
parent::
  This option is used when module does not have its own menu item but is
  a part of a different module. This is described by JSON object with
  properties `+component+` which takes name of the superordinate
  component and `+docs+` with list of documentation URLs for the given
  page. See below for structure of `+docs+` property.

In addition, the following keys contain information about where
components of the package should appear in Cockpit's user interface.
Each of these keys is optional and contains an object mapping unique
identifiers to menu items, which are described below. (The naming of
these fields doesn't perfectly match the current user interface for
historical reasons.)

dashboard::
  Dashboard items appear in the menu under the section _Apps_.
menu::
  These items appear in the menu under the section _System_. This
  section is roughly ordered into these categories (with their _order_
  in parentheses):
  +
  * System Information (10)
  * Logs (20)
  * Configuring major subsystems (30-40)
  * Things running on the machine (VMs, Containers - 50-60)
  * Implementation Details (Accounts, Services - 70-100)
tools::
  These items appear in the menu under the section _Tools_.

Menu items and tools are registered using JSON objects that have the
following properties:

label::
  The label for the menu item or tool.
order::
  An optional order number to place this menu item or tool. Lower
  numbers are listed first.
path::
  The relative path to the HTML file within the package that implements
  the menu item or tool.
docs::
  List of documentation URLs for the given page. Each item is an object
  containing `+label+` and `+url+`.
keywords::
  Keywords that describe the page and which are used for searching.
  These keywords should be lowercase. Keywords is a list containing
  keyword items as described below. Page label is prepended as first
  keyword in the first keyword item.

Keyword items are registered using JSON objects that have the following
properties:

matches::
  List of keywords to be matched.
goto::
  Optional path that is used for all keywords in this item. When this
  argument starts with slash, then it is used as pathname, otherwise it
  is used as hash. Defining `+goto:"page_hash"+` in page with
  `+path:"/page_path"+` would redirect to `+/page_path#page_hash+`,
  while `+goto:"/page_path"+` would redirect to `+/page_path+` ignoring
  default page path.
weight::
  How much keywords are prioritized over others. Default is 3.
translate::
  `+false+` when keywords should not be localized. Default is `+true+`.

An example manifest.json with some optional properties set:

....
{
  "version": 0,
  "require": {
      "cockpit": "120"
  },
  "tools": {
     "mytool": {
        "label": "My Tool",
        "path": "tool.html"
     }
  }
}
....

....
{
  "version": 0,
  "require": {
    "cockpit": "120"
  },
  "conditions": [
    {"path-exists": "/usr/bin/mytool"},
    {"path-exists": "/etc/mytool.conf"},
    {"path-not-exist": "/etc/incompatible-tool"}
  ],
  "tools": {
     "mytool": {
        "label": "My Tool",
        "path": "tool.html"
     }
  }
}
....

The following example shows how to use disjunctive conditions with `+any+`
to specify alternative requirements (available since Cockpit 348). This
package will be available if either `+/usr/bin/alt1+` or `+/usr/bin/alt2+`
exists. In any case, `+/etc/incompatible-tool+` must not exist.

....
"conditions": [
  {"any": [{"path-exists": "/usr/bin/alt1"}, {"path-exists": "/usr/bin/alt2"}]},
  {"path-not-exists": "/etc/incompatible-tool"}
]
....

[[package-manifest-override]]
== Manifest overrides

To change a manifest system-wide, a file
`+<package-directory-name>.override.json+` may be placed into
`+/etc/cockpit/+`, or below `+$XDG_CONFIG_DIRS+` if set (see
link:./cockpit.conf.5.html[cockpit.conf]). To change it for a particular
user only, put the override into `+~/.config/cockpit+`.

These override the information in the manifest in the simple
https://tools.ietf.org/html/rfc7386[JSON Merge Patch] format.

This can be used to hide or modify menu items of an existing package.
For example `+/etc/cockpit/systemd.override.json+` or
`+~/.config/cockpit/systemd.override.json+` could hide the _Logs_ menu
item and move the _Services_ menu item to the top of the menu.

....
{
  "menu": {
    "logs": null,
    "services": {
      "order": -1
    }
  }
}
....

[[package-links]]
== Package Links and Paths

When referring to files in your package, such as in a hyperlink or a
`+<style>+` tag or `+<script>+` tag, simply use a relative path, and
refer to the files in the same directory. When you need to refer to
files in another package use a relative link.

For example here's how to include the base `+cockpit.js+` script in your
HTML from the `+latest+` package:

....
<script src="../base1/cockpit.js"></script>
....

Do not assume you can link to any file in any other package. Refer to
the link:#development[list of API packages] for those that are available
for use.

[[package-minified]]
== Content Negotiation

In order to support gzipped and/or minified data, the files in a package
are loaded using content negotiation logic. A HTTP request for the file
`+test.js+` in the package named `+mypackage+` will return
`+mypackage/test.js+` or `+mypackage/test.js.gz+` (in undefined
preference). If neither exists, then it returns
`+mypackage/test.js.min+` or `+mypackage/test.js.min.gz+` (again in
undefined preference).

When packages are loaded from a system directory, Cockpit optimizes the
file system lookups above, by pre-listing the files. This is one of the
reasons that you should never change packages installed to a system
directory while Cockpit is running.

[[package-api]]
== Using Cockpit API

Cockpit has API available for writing packages. There is no API
available for external callers to invoke via HTTP, REST or otherwise.

API from various packages can be used to implement Cockpit packages.
Each package listed here has some API available for use. Only the API
explicitly documented should be used.

* link:#development[API Listing]

To include javascript from the API, simply load it into your HTML using
a script tag. Alternatively you can use an javascript loader.

[[package-bridges]]
== Bridges for specific tasks

On the server side the link:#cockpit-bridge.1[`+cockpit-bridge+`]
connects to various system APIs that the front end UI requests it to.
There are additional bridges for specific tasks that the main
`+cockpit-bridge+` cannot handle, such as using the PCP C library API.

These additional bridges can be registered in a `+"bridges"+` section of
a package's `+manifest.json+` file. Building such a bridge is a complex
tasks, and we will skip over that here. However it is useful to adjust
how these additional bridges are called, and so we'll look at how they
are registered.

An example `+manifest.json+` with a bridges section:

....
{
    "bridges": [
        {
            "match": { "payload": "metrics1" },
            "spawn": [ "/usr/libexec/cockpit-pcp" ]
        }
    ]
}
....

The bridges are considered in the order they are listed in the array.
Use the `+manifest.json+``+"priority"+` field to control order between
packages. The bridges are registered using JSON objects that have the
following properties:

environ::
  Optional, additional environment variables to pass to the bridge
  command.
match::
  The `+"match"+` object describes which channel open command options
  need to match for a given channel to be handed over to this bridge.
privileged::
  If set to `+true+`, this marks the bridge as a superuser bridge.
  Cockpit will start one of these explicitly when trying to escalate the
  privileges of a session. A privileged bridge can not have a
  `+"match"+` property.
label::
  Setting this enables selection of privileged bridges in the UI. When
  no privileged bridge has a `+label+`, then Cockpit will start the
  bridge that runs `+sudo+`. This is the case in a default Cockpit
  installation. When at least one privileged bridge has a `+label+` then
  the user can select one of them when escalating privileges. As a
  special case, if only one bridge has a `+label+`, then the step of
  selecting a bridge is omitted in the UI and that one bridge is always
  started.
  +
  Thus, if you add a privileged bridge with a `+label+` in a new
  manifest, Cockpit will use that bridge the next time a user opens the
  "Administrative access" dialog. If you want the user to choose between
  the `+sudo+` method and your new one, you need to duplicate the
  `+sudo+` bridge definition in your manifest and give it a label.
problem::
  If a problem is specified, and this bridge fails to start up then
  channels will be closed with this problem code. Otherwise later
  bridges or internal handlers for the channel will be invoked.
spawn::
  The command and arguments to invoke.

The `+spawn+` and `+environ+` values can be dynamically taken from a
matching open command values. When a value in either the `+spawn+` or
`+environ+` array contains a named variable wrapped in `+${}+`, the
variable will be replaced with the value contained in the matching open
command. Only named variables are supported and name can only contain
letters, numbers and the following symbols: `+._-+`

For example a bridges section like:

....
{
  "bridges": [
    {
      "match": { "payload": "example" },
      "environ": [ "TAG=${tag}" ],
      "spawn: [ "/example-bridge", "--tag", "${tag}" ],
      "problem": "access-denied"
    }
  ]
}
....

when a open command is received with a payload of `+example+` with
`+tag+` value of `+tag1+`. The following command will be spawned

....
TAG=tag1 /example-bridge --tag tag1
....

Processes that are reused so if another open command with a "tag" of
`+tag1+` is received. The open command will be passed to existing
process, rather than spawning a new one. However a open command with an
tag of `+tag2+` will spawn a new command:

....
TAG=tag2 /example-bridge --tag tag2
....

If you need to include `+${}+`, as an actual value in your arguments you
can escape it by prefixing it with a `+\+`

[[package-replace]]
== Replacing an existing package

If the functionality in a package replaces that of another package then
it can replace that package by claiming the same `+name+` and a higher
`+priority+`.

For example, a package in the `+/usr/share/cockpit/disks+` directory
could replace Cockpit's _storage_ package with a `+manifest.json+` like
this:

....
{
  "version": 0,
  "name": "storage",
  "priority": 10,
  "menu": {
     "index": {
        "label": "Disk Storage",
        "order": 15
     }
  }
}
....
