Ulf Wiger
128 lines
3.5 KiB
Markdown
128 lines
3.5 KiB
Markdown
# Gmconfig - A JSON-SCHEMA-based configuration management support library
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## Introduction
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This library offers the basic support functions for the Gajumaru configuration
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management subsystem. It is based on JSON-Schema, and includes, among other things:
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* A reasonably complete JSON-Schema validator
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* Validating user configurations against the schema
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* In-service update of the user config
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* Caching of the user config (and schema) as persistent terms
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* Fast config lookups using key paths
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* Lookups can handle both schema defaults and user-provided defaults
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* Optional type coercion during validation
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* Optional conversion of enums to atoms
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* Optional extensions with custom validator funs
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## JSON-Schema validator
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The main thing the validator currently doesn't support is proper
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management of complex sets of schemas and subSchemas. There are
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some preparations made for supporting `"$id"` and uris, but this
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is still incomplete. `"definitions"` and `"$ref"` properties are recognized.
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As almost anything is theoretically possible with JSON-Schema,
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there are surely other things that are unsupported.
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### All standard data types
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* `"null"`
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* `"boolean"`
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* `"integer"`
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* `"number"`
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* `"boolean"`
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* `"string"`
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* `"array"`
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* `"object"`
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### Dynamic properties
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* `"if"`
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* `"not"`
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* `"oneOf"`
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* `"anyOf"`
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* `"allOf"`
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### Static Properties
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#### Array
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* `"maxItems"`
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* `"minItems"`
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* `"uniqueItems"`
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* `"prefixItems"`
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* `"contains"` (`"minContains"`, `"maxContains"`)
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#### Object
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* `"properties"` (`"minProperties"`, `"maxProperties"`)
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* `"patternProperties"`
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* `"additionalProperties"`
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* `"required"`
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#### String
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* `"pattern"`
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* `"minLength"`
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* `"maxLength"`
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#### Number, Integer
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* `"minimum"`
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* `"maximum"`
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* `"exclusiveMinimum"`
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* `"exclusiveMinimum"`
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* `"multipleOf"` (only if object is an integer)
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### `"$updateSemantics"`
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* `"replace"` (fully replaces any old data)
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* `"merge"` (for objects, keeps and/or updates existing values)
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* `"suggest"` (adds value if not already present)
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### Custom validation options
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Using `gmconfig_schema_utils:validate(Json, Schema, Opts)`, a few options are supported
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to further enhance the validation (`Opts` is of type `map()`):
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`coerce => boolean()` converts strings to integers, null and booleans when needed.
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`enums_to_atoms => boolean()` converts enum strings to atoms
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`extensions => map()` supports mapping `x-...` properties to custom validators.
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#### Validator extensions
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See the following test case:
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```erlang
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t_nested_refs() ->
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S = read("data/nested_refs_schema.json"),
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F = fun(Str, #{<<"tags">> := Tags}) ->
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true = lists:any(
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fun(T) ->
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nomatch =/= string:prefix(Str, T)
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end, Tags)
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end,
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Opts = #{extensions => #{<<"x-serialization">> => F}},
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Vs = #{<<"tx">> => #{<<"from">> => <<"ak_good">>}},
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Vf = #{<<"tx">> => #{<<"from">> => <<"ac_bad">>}},
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validate(Vs, S, Opts),
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fails(Vf, S, Opts, #{e => failing_schemas}),
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ok.
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```
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This simulates an encoding extension, where the example fun here simply checks
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if tags specified under the `x-serialization` property are prefixes of the
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given string value.
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In the test schema, we can see the following definition:
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```json
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"Pubkey": {
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"type": "string",
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"x-serialization": {
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"tags": ["ak", "ct"]
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}
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```
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Whenever the validator encounters an `x-...` property mapped to a validator fun,
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this fun is called with the value and the schema part of the property. The return
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value of the fun is ignored, and any normal return is treated as a validation success.
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