Service Config Specification

Overview

Most self-hosted applications require the user to tell the app how to behave using a config file in a specific format, environment variables, command-line arguments, or some combination of these inputs. One of the coolest features of EmbassyOS is that, when packaged correctly, the app’s configuration will be available to the user as a slick GUI that always produces a valid configuration no matter how little experience or skill the user has.

With EmbassyOS, this means a service wrappers’ configuration requires a particular format and rule structure to ensure it integrates smoothly with the user interface. This format enables clean handling of improper values and dependency management.

The outcome of this step is two files:

config_spec.yaml

config_rules.yaml

These files contain a detailed mapping of configuration options with acceptable values, defaults, and relational rule-sets.

For example, if the user chooses config option A, then config option B must be between 5 and 10. This enables a simple GUI configuration experience, complete with validations and protections, for users. They do not have to worry about the consequences of a wrong value in a .conf file.

Config Spec

Overview

Bitcoin Config

This file defines the structure of configuration options your service depends on to run. It additionally can include configuration options that users might want to enable for more advanced or customized usage. Ultimately, these values influence the UI elements for a user to interact with. Specifically, they evaluate to the options available when managing a service, such as:

  • Prior to service installation when the user needs to be made aware of any necessary dependency configurations

  • When the user installs a service and the service is in the “Needs Config” state

  • Whenever a user edits a service config

  • When config pointers get updated

The neat part about this file is that each ValueSpec type gets translated into a specific front end component. For instance, boolean values display as a toggle button.

Example boolean toggle

Another advantage is the ability to define default values. These values automatically get populated if the user selects the Default option when setting up a service in Needs Config state. This is super convenient for users who want to get up and running quickly.

Types

ConfigSpec Type:

key: ValueSpec

ValueSpec Type: Boolean | Enum | List | Number | Object | String | Union | Pointer (see below for details)

Implementation Guide

The following section contains implementation specifications for the config_spec.yaml file.

  • All keys are kebab-case strings, which correspond to the service (app) id

  • All values are one the following specs (ie. ValueSpec type):

  • In the examples for each value spec type below, Option means the key is optional. Otherwise, the key is required.

  • Descriptions are optional, but recommended

  • Name corresponds to the name of the config field

  • Find a complete example here

  • Change warning text displays when the value is altered

Boolean

Config value specification denoted as a boolean value. A default value is required.

ValueSpec Type:

type: boolean
name: String
description: Option<String>
changeWarning: Option<String>
default: Boolean

Example:

fetch-blocks:
    type: boolean
    name: Fetch Blocks
    description: Fetch blocks from the network if pruned from disk
    default: true

Enum

Config value specification denoted as an enum value. Enums values must be a unique set. If no default is provided, null will be the assumed value.

ValueSpec Type:

type: enum
name: String
description: Option<String>
changeWarning: Option<String>
default: Option<Enum>
values: Set<String>
theme-mode:
    type: enum
    name: Theme Mode
    values:
            - NIGHT
            - DAY
    valueNames:
            NIGHT: Night
            DAY: Day
    default: NIGHT

List

The list type describes an array of values. The values must consist of the same subtype, which can be any of the ValueSpec types available in the EmbassyOS config specification. Lists of any type do not contain the default for each item in list. The list itself can have a default. If no default is provided, null will be the assumed value.

Range is loosely based off mathematical range syntax, with infinity replaced with *:

[ || ] = inclusive

( || ) = noninclusive

* = infinity on either end

eg:

[0,*) - all numbers to infinity including 0

ValueSpec Type:

type: list
name: String
description: Option<String>
subtype: enum || number || object || string || union
range: NumRange<unsigned integer>
spec: ValueSpec
default: ValueSpec

Example:

allowed-calls:
    type: list
    name: Allowed Calls
    description: The list of all RPC methods this user is allowed to make
    subtype: enum
    range: "[0, *)"
    spec:
        type: enum
        values:
            - item
            - item

Number

A number value within an optionally defined range. Nullable field is required. If nullable is true, the default is assumed to be null if it is not provided.

ValueSpec Type:

type: number
name: String
description: Option<String>
changeWarning: Option<String>
default: Boolean
nullable: Boolean
range: Option<NumRange<64 bit floating point>>
integral: Boolean
units: Option<String>

Example:

type: number
name: Peer Message Timeout
description: How long to wait for a response from a peer before failing
nullable: false
integral: true
units: Seconds
range: "[0, *)"
default: 30

Object Type

A nested representation of a ConfigSpec. The object type takes the same structure under the spec key as a ConfigSpec: a key indicates the field name, and the value denotes the ValueSpec type for that field.

There is no default option for the object type. Rather, the option null-by-default should be used to indicate the default as null. If null by default is true, nullable must be true. If null by default is false, nullable could be either.

unique-by indicates whether duplicates can be permitted in the list.

ValueSpec Type:

type: object
name: String
description: Option<String>
changeWarning: Option<String>
nullable: Boolean
null-by-default: Boolean
display-as: Option<String>
unique-by: UniqueBy
spec: ConfigSpec

type UniqueBy = null | string | { any: UniqueBy[] } | { all: UniqueBy[] }

Example:

type: object
name: Advanced
description: Advanced settings for Bitcoin Proxy
nullable: false
spec:
    tor-only:
        type: boolean
        name: Only Tor Peers
        description: Use Tor for all peer connections
        default: false
    peer-timeout:
        type: number
        name: Peer Message Timeout
        description: How long to wait for a response from a peer before failing
        nullable: false
        integral: true
        units: Seconds
        range: "[0, *)"
        default: 30
    max-peer-age:
        type: number
        name: Maximum Peer Age
        description: How long to wait before refreshing the peer list
        nullable: false
        integral: true
        units: Seconds
        range: "[0, *)"
        default: 300
    max-peer-concurrency:
        type: number
        name: Maximum Peer Concurrency
        description: How many peers to reach out to concurrently for block data
        nullable: true
        integral: true
        range: "[1, *)"
        default: 1

String

There are various options for string values. They can optionally be marked as copyable or masked, such as for passwords, which will reflect the UI element display. A pattern, expressed in regex, can be denoted. If it exists, this field requires both the pattern type (ie. Regex) and pattern description (ie. an explanation of the pattern requirements).

If the default type is Entropy, the charset can optionally specify an inclusive ranged character set (ie. “a-f,0-9”).

ValueSpec Type:

type: string
name: String
description: Option<String>
changeWarning: Option<String>
copyable: Option<boolean>
masked: Option<boolean>
nullable: Boolean
default: String | Entropy
pattern: Option<Regex>
pattern-description: Option<String>

Entropy Type:

charset: Option<String>
len: integer

Examples:

color:
    type: string
    name: Color
    description: Color value for the Lightning Network
    nullable: false
    pattern: "[0-9a-fA-F]{6}"
    patternDescription: |
            Must be a valid 6 digit hexadecimal RGB value. The first two digits are red, middle two are green and final two are
            blue
    default:
            charset: "a-f,0-9"
            len: 6

password:
    type: string
    name: Password
    description: The password for the RPC User
    nullable: false
    copyable: true
    masked: true
    default:
        charset: "a-z,A-Z,0-9"
        len: 22

Pointer

The pointer type points to a config value on another service installed on EmbassyOS (ie. app subtype) or to the EmbassyOS system (ie. system subtype). When pointing to another service, the index field indicates the path to the desired config variable.

ValueSpec Type:

type: pointer
name: String
description: Option<String>
changeWarning: Option<String>
subtype: app | system
app-id: String (*always* kebab case)
target: AppPointerSpecVariants | SystemPointerSpecVariants
index: Option<String> (dependent on target being AppPointerSpecVariants)

AppPointerSpecVariants = LanAddress | TorAddress | TorKey | Config
SystemPointerSpecVariants = HostIp

Example:

user:
    type: pointer
    name: RPC Username
    description: The username for the RPC user for Bitcoin Core
    subtype: app
    app-id: bitcoind
    target: config
    index: "rpc.username"

Union

This type describes a necessary dependency. Multiple variants can be expressed to enable the user the option to connect to another service (internal dependency) or outside source (external dependency).

For example, the Bitcoin Proxy service is united with an instance of Bitcoin. Three variants are defined: internal, external, and a quick connect. In this case, internal refers to the Bitcoin Core instance running on EmbassyOS, and defines the RPC credentials necessary for connecting; external refers to a Bitcoin Core node running on a different device, and defines the RPC credentials necessary for connecting; quick connect refers to yet another method of connecting to a Bitcoin Core node, optimized for convenience.

Default is required and corresponds to one of the variants.

Tag is the key that will be rendered on the UI element.

ValueSpec Type;

type: union
name: String
description: Option<String>
changeWarning: Option<String>
default: Boolean
tag: Tag
variants: Map<String, ConfigSpec>
display-as: Option<String>
unique-by: any | all | exactly | notUnique

Tag Type:

id: String
name: String
description: Option<String>
variant-names: Map<String, String>

Example:

bitcoind:
    type: union
    name: Bitcoin Core
    description: The Bitcoin Core node to connect to
    tag:
        id: type
        name: Type
        description: |
        - Internal: The Bitcoin Core service installed to your Embassy
        - External: A Bitcoin Core node running on a different device
        - Quick Connect: A Quick Connect URL for an unpruned Bitcoin Core node
        variant-names:
        internal: Internal
        external: External
        quick-connect: Quick Connect
    default: internal
    variants:
        internal:
            address:
                type: pointer
                name: Local Address
                description: The LAN IP address of your Bitcoin Core service
                subtype: app
                app-id: bitcoind
                target: lan-address
            user:
                type: pointer
                name: RPC Username
                description: The username for the RPC user for Bitcoin Core
                subtype: app
                app-id: bitcoind
                target: config
                index: "rpc.username"
            password:
                type: pointer
                name: RPC Password
                description: The password for the RPC user for Bitcoin Core
                subtype: app
                app-id: bitcoind
                target: config
                index: "rpc.password"
        external:
            addressext:
                type: string
                name: Public Address
                description: The public address of your Bitcoin Core RPC server
                nullable: false
            userext:
                type: string
                name: RPC Username
                description: The username for the RPC user on your Bitcoin Core RPC server
                nullable: false
            passwordext:
                type: string
                name: RPC Password
                description: The password for the RPC user on your Bitcoin Core RPC server
                nullable: false
        quick-connect:
            quick-connect-url:
                type: string
                name: Quick Connect URL
                description: The Quick Connect URL for your Bitcoin Core RPC server
                nullable: false
                pattern: 'btcstandup://[^:]*:[^@]*@[a-zA-Z0-9.-]+:[0-9]+(/(\?(label=.+)?)?)?'
                patternDescription: Must be a valid Quick Connect URL. For help, check out https://github.com/BlockchainCommons/Gordian/blob/master/Docs/Quick-Connect-API.md

Config Rules

This file defines the configuration rules, or the rule-set that defines dependencies between config variables. In practice, config rules are for auto-configuring self dependencies. Self dependencies are internal dependencies of a service, such as if the setting of one config variable informs the option of another setting. These “dependencies” are configured as rules.

A rule is a boolean expression that we demand to be true. It is not true if the expression fails the rule parser.

They follow the Backus–Naur meta-syntax for writing rules.

Rules are composed of two main concepts:

  • Variables - accessor into a configuration

  • Terms - either a variable or type literal (ie. a boolean term is a boolean variable, a boolean expression, or a comparison operation between numbers or strings)

Variables can be booleans, numbers, or strings, and have a different syntax depending on the type. These type annotations check your config rules against your config spec and throw an error if invalid.

  • ? - Casts to boolean value. If the value is not a boolean, this notes whether or not the value is null.

  • # - Treat the value as a number. If it is not a number, the value will be parsed as NaN. String numbers are not currently supported.

  • ' - Cast the value into a string. Applies to any value except for an object or a list.

  • ! - Equals not.

Note

Config rules are processed in order.

If application does not satisfy a rule, a set of suggestions should be provided. These suggestions are in the form of the operation to preform:

  • Set - set the value

  • Push - add to the value (such as to a list)

  • Delete - delete the value

enum SuggestionVariant = Set | Delete | Push

interface Set {
    var: String, // fully qualified path without typecast
    // one of the following three variants are required
    to: Option<String> // a string expression, use when tying another config value
    to-value: Option<String>
    to-entropy: Option<{
        charset: String (eg. 'a-z,A-Z,0-9')
        len: Number
    }>
}

interface Delete {
    src: String, // path to key - removes if in a list
}

interface Push {
    to: String,
    value: String, // string literal of value to be set
}

Set Examples:

- SET:
    # the key in config you want to set
    var: 'users.[first(item => ''item.name = "c-lightning")].password'
    # the value in config that you will set
    to-entropy:
        charset: "a-z,A-Z,0-9"
        len: 22

- SET:
    var: 'users.[first(item => ''item.name = "c-lightning")].fetch-blocks'
    to-value: true

Push Examples:

- PUSH:
    to: "users"
    value:
        name: c-lightning
        allowed-calls: []

- PUSH:
    to: 'users.[first(item => ''item.name = "c-lightning")].allowed-calls'
    value: "getnetworkinfo"

Full example from c-lightning manifest:

config:
    - rule: '''users.*.name = "c-lightning"'
    description: 'Must have an RPC user named "c-lightning"'
    suggestions:
        - PUSH:
            to: "users"
            value:
                name: c-lightning
                allowed-calls: []
        - SET:
            var: 'users.[first(item => ''item.name = "c-lightning")].password'
            to-entropy:
                charset: "a-z,A-Z,0-9"
                len: 22