216 lines
9 KiB
XML
216 lines
9 KiB
XML
<section xmlns="http://docbook.org/ns/docbook"
|
|
xmlns:xlink="http://www.w3.org/1999/xlink"
|
|
xmlns:xi="http://www.w3.org/2001/XInclude"
|
|
version="5.0"
|
|
xml:id="sec-settings-options">
|
|
<title>Options for Program Settings</title>
|
|
|
|
<para>
|
|
Many programs have configuration files where program-specific settings can be declared. File formats can be separated into two categories:
|
|
<itemizedlist>
|
|
<listitem>
|
|
<para>
|
|
Nix-representable ones: These can trivially be mapped to a subset of Nix syntax. E.g. JSON is an example, since its values like <literal>{"foo":{"bar":10}}</literal> can be mapped directly to Nix: <literal>{ foo = { bar = 10; }; }</literal>. Other examples are INI, YAML and TOML. The following section explains the convention for these settings.
|
|
</para>
|
|
</listitem>
|
|
<listitem>
|
|
<para>
|
|
Non-nix-representable ones: These can't be trivially mapped to a subset of Nix syntax. Most generic programming languages are in this group, e.g. bash, since the statement <literal>if true; then echo hi; fi</literal> doesn't have a trivial representation in Nix.
|
|
</para>
|
|
<para>
|
|
Currently there are no fixed conventions for these, but it is common to have a <literal>configFile</literal> option for setting the configuration file path directly. The default value of <literal>configFile</literal> can be an auto-generated file, with convenient options for controlling the contents. For example an option of type <literal>attrsOf str</literal> can be used for representing environment variables which generates a section like <literal>export FOO="foo"</literal>. Often it can also be useful to also include an <literal>extraConfig</literal> option of type <literal>lines</literal> to allow arbitrary text after the autogenerated part of the file.
|
|
</para>
|
|
</listitem>
|
|
</itemizedlist>
|
|
</para>
|
|
<section xml:id="sec-settings-nix-representable">
|
|
<title>Nix-representable Formats (JSON, YAML, TOML, INI, ...)</title>
|
|
<para>
|
|
By convention, formats like this are handled with a generic <literal>settings</literal> option, representing the full program configuration as a Nix value. The type of this option should represent the format. The most common formats have a predefined type and string generator already declared under <literal>pkgs.formats</literal>:
|
|
<variablelist>
|
|
<varlistentry>
|
|
<term>
|
|
<varname>pkgs.formats.json</varname> { }
|
|
</term>
|
|
<listitem>
|
|
<para>
|
|
A function taking an empty attribute set (for future extensibility) and returning a set with JSON-specific attributes <varname>type</varname> and <varname>generate</varname> as specified <link linkend='pkgs-formats-result'>below</link>.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
<varlistentry>
|
|
<term>
|
|
<varname>pkgs.formats.yaml</varname> { }
|
|
</term>
|
|
<listitem>
|
|
<para>
|
|
A function taking an empty attribute set (for future extensibility) and returning a set with YAML-specific attributes <varname>type</varname> and <varname>generate</varname> as specified <link linkend='pkgs-formats-result'>below</link>.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
<varlistentry>
|
|
<term>
|
|
<varname>pkgs.formats.ini</varname> { <replaceable>listsAsDuplicateKeys</replaceable> ? false, ... }
|
|
</term>
|
|
<listitem>
|
|
<para>
|
|
A function taking an attribute set with values
|
|
<variablelist>
|
|
<varlistentry>
|
|
<term>
|
|
<varname>listsAsDuplicateKeys</varname>
|
|
</term>
|
|
<listitem>
|
|
<para>
|
|
A boolean for controlling whether list values can be used to represent duplicate INI keys
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
</variablelist>
|
|
It returns a set with INI-specific attributes <varname>type</varname> and <varname>generate</varname> as specified <link linkend='pkgs-formats-result'>below</link>.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
<varlistentry>
|
|
<term>
|
|
<varname>pkgs.formats.toml</varname> { }
|
|
</term>
|
|
<listitem>
|
|
<para>
|
|
A function taking an empty attribute set (for future extensibility) and returning a set with TOML-specific attributes <varname>type</varname> and <varname>generate</varname> as specified <link linkend='pkgs-formats-result'>below</link>.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
</variablelist>
|
|
|
|
</para>
|
|
<para xml:id="pkgs-formats-result">
|
|
These functions all return an attribute set with these values:
|
|
<variablelist>
|
|
<varlistentry>
|
|
<term>
|
|
<varname>type</varname>
|
|
</term>
|
|
<listitem>
|
|
<para>
|
|
A module system type representing a value of the format
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
<varlistentry>
|
|
<term>
|
|
<varname>generate</varname> <replaceable>filename</replaceable> <replaceable>jsonValue</replaceable>
|
|
</term>
|
|
<listitem>
|
|
<para>
|
|
A function that can render a value of the format to a file. Returns a file path.
|
|
<note>
|
|
<para>
|
|
This function puts the value contents in the Nix store. So this should be avoided for secrets.
|
|
</para>
|
|
</note>
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
</variablelist>
|
|
</para>
|
|
<example xml:id="ex-settings-nix-representable">
|
|
<title>Module with conventional <literal>settings</literal> option</title>
|
|
<para>
|
|
The following shows a module for an example program that uses a JSON configuration file. It demonstrates how above values can be used, along with some other related best practices. See the comments for explanations.
|
|
</para>
|
|
<programlisting>
|
|
{ options, config, lib, pkgs, ... }:
|
|
let
|
|
cfg = config.services.foo;
|
|
# Define the settings format used for this program
|
|
settingsFormat = pkgs.formats.json {};
|
|
in {
|
|
|
|
options.services.foo = {
|
|
enable = lib.mkEnableOption "foo service";
|
|
|
|
settings = lib.mkOption {
|
|
# Setting this type allows for correct merging behavior
|
|
type = settingsFormat.type;
|
|
default = {};
|
|
description = ''
|
|
Configuration for foo, see
|
|
<link xlink:href="https://example.com/docs/foo"/>
|
|
for supported settings.
|
|
'';
|
|
};
|
|
};
|
|
|
|
config = lib.mkIf cfg.enable {
|
|
# We can assign some default settings here to make the service work by just
|
|
# enabling it. We use `mkDefault` for values that can be changed without
|
|
# problems
|
|
services.foo.settings = {
|
|
# Fails at runtime without any value set
|
|
log_level = lib.mkDefault "WARN";
|
|
|
|
# We assume systemd's `StateDirectory` is used, so we require this value,
|
|
# therefore no mkDefault
|
|
data_path = "/var/lib/foo";
|
|
|
|
# Since we use this to create a user we need to know the default value at
|
|
# eval time
|
|
user = lib.mkDefault "foo";
|
|
};
|
|
|
|
environment.etc."foo.json".source =
|
|
# The formats generator function takes a filename and the Nix value
|
|
# representing the format value and produces a filepath with that value
|
|
# rendered in the format
|
|
settingsFormat.generate "foo-config.json" cfg.settings;
|
|
|
|
# We know that the `user` attribute exists because we set a default value
|
|
# for it above, allowing us to use it without worries here
|
|
users.users.${cfg.settings.user} = {};
|
|
|
|
# ...
|
|
};
|
|
}
|
|
</programlisting>
|
|
</example>
|
|
<section xml:id="sec-settings-attrs-options">
|
|
<title>Option declarations for attributes</title>
|
|
<para>
|
|
Some <literal>settings</literal> attributes may deserve some extra care. They may need a different type, default or merging behavior, or they are essential options that should show their documentation in the manual. This can be done using <xref linkend='sec-freeform-modules'/>.
|
|
<example xml:id="ex-settings-typed-attrs">
|
|
<title>Declaring a type-checked <literal>settings</literal> attribute</title>
|
|
<para>
|
|
We extend above example using freeform modules to declare an option for the port, which will enforce it to be a valid integer and make it show up in the manual.
|
|
</para>
|
|
<programlisting>
|
|
settings = lib.mkOption {
|
|
type = lib.types.submodule {
|
|
|
|
freeformType = settingsFormat.type;
|
|
|
|
# Declare an option for the port such that the type is checked and this option
|
|
# is shown in the manual.
|
|
options.port = lib.mkOption {
|
|
type = lib.types.port;
|
|
default = 8080;
|
|
description = ''
|
|
Which port this service should listen on.
|
|
'';
|
|
};
|
|
|
|
};
|
|
default = {};
|
|
description = ''
|
|
Configuration for Foo, see
|
|
<link xlink:href="https://example.com/docs/foo"/>
|
|
for supported values.
|
|
'';
|
|
};
|
|
</programlisting>
|
|
</example>
|
|
</para>
|
|
</section>
|
|
</section>
|
|
|
|
</section>
|