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+-- Copyright (C) 2021 Kim Alvefur
+--
+-- This project is MIT/X11 licensed. Please see the
+-- COPYING file in the source package for more information.
+--
+-- Based on
+-- https://json-schema.org/draft/2020-12/json-schema-core.html
+-- https://json-schema.org/draft/2020-12/json-schema-validation.html
+--
+
+local json = require"util.json"
+local null = json.null;
+
+local type json_type_name = json.json_type_name
+
+-- json_type_name here is non-standard
+local type schema_t = boolean | json_type_name | json_schema_object
+
+local record json_schema_object
+ type json_type_name = json.json_type_name
+ type schema_object = json_schema_object
+
+ type : json_type_name
+ enum : { any }
+ const : any
+
+ allOf : { schema_t }
+ anyOf : { schema_t }
+ oneOf : { schema_t }
+
+ ["not"] : schema_t
+ ["if"] : schema_t
+ ["then"] : schema_t
+ ["else"] : schema_t
+
+ -- numbers
+ multipleOf : number
+ maximum : number
+ exclusiveMaximum : number
+ minimum : number
+ exclusiveMinimum : number
+
+ -- strings
+ maxLength : integer
+ minLength : integer
+ pattern : string
+ format : string
+
+ -- arrays
+ prefixItems : { schema_t }
+ items : schema_t
+ contains : schema_t
+ maxItems : integer
+ minItems : integer
+ uniqueItems : boolean
+ maxContains : integer
+ minContains : integer
+
+ -- objects
+ properties : { string : schema_t }
+ maxProperties : integer
+ minProperties : integer
+ required : { string }
+ dependentRequired : { string : { string } }
+ additionalProperties: schema_t
+ patternProperties: schema_t
+ propertyNames : schema_t
+
+ -- xml
+ record xml_t
+ name : string
+ namespace : string
+ prefix : string
+ attribute : boolean
+ wrapped : boolean
+
+ -- nonstantard, maybe in the future
+ text : boolean
+ x_name_is_value : boolean
+ x_single_attribute : string
+ end
+
+ xml : xml_t
+
+ -- descriptive
+ title : string
+ description : string
+ deprecated : boolean
+ readOnly : boolean
+ writeOnly : boolean
+
+ -- methods
+ validate : function ( schema_t, any) : boolean
+end
+
+-- TODO validator function per schema property
+
+local type_validators : { json_type_name : function (schema_t, any) : boolean } = {}
+
+local function simple_validate(schema : json_type_name, data : any) : boolean
+ if schema == "object" and data is table then
+ return type(data) == "table" and (next(data)==nil or type((next(data, nil))) == "string")
+ elseif schema == "array" and data is table then
+ return type(data) == "table" and (next(data)==nil or type((next(data, nil))) == "number")
+ elseif schema == "integer" then
+ return math.type(data) == schema
+ elseif schema == "null" then
+ return data == null
+ else
+ return type(data) == schema
+ end
+end
+
+type_validators.string = function (schema : json_schema_object, data : any) : boolean
+ -- XXX this is measured in byte, while JSON measures in ... bork
+ -- TODO use utf8.len?
+ if data is string then
+ if schema.maxLength and #data > schema.maxLength then
+ return false
+ end
+ if schema.minLength and #data < schema.minLength then
+ return false
+ end
+ return true
+ end
+ return false
+end
+
+type_validators.number = function (schema : json_schema_object, data : number) : boolean
+ if schema.multipleOf and data % schema.multipleOf ~= 0 then
+ return false
+ end
+
+ if schema.maximum and not ( data <= schema.maximum ) then
+ return false
+ end
+
+ if schema.exclusiveMaximum and not ( data < schema.exclusiveMaximum ) then
+ return false
+ end
+
+ if schema.minimum and not ( data >= schema.minimum ) then
+ return false
+ end
+
+ if schema.exclusiveMinimum and not ( data > schema.exclusiveMinimum ) then
+ return false
+ end
+
+ return true
+end
+
+type_validators.integer = type_validators.number
+
+local function validate(schema : schema_t, data : any) : boolean
+ if schema is boolean then
+ return schema
+ end
+ if schema is json_type_name then
+ return simple_validate(schema, data)
+ end
+ if schema is json_schema_object then
+ if schema.allOf then
+ for _, sub in ipairs(schema.allOf) do
+ if not validate(sub, data) then
+ return false
+ end
+ end
+ return true
+ end
+
+ if schema.oneOf then
+ local valid = 0
+ for _, sub in ipairs(schema.oneOf) do
+ if validate(sub, data) then
+ valid = valid + 1
+ end
+ end
+ return valid == 1
+ end
+
+ if schema.anyOf then
+ for _, sub in ipairs(schema.anyOf) do
+ if validate(sub, data) then
+ return true
+ end
+ end
+ return false
+ end
+
+ if schema["not"] then
+ if validate(schema["not"], data) then
+ return false
+ end
+ end
+
+ if schema["if"] then
+ if validate(schema["if"], data) then
+ if schema["then"] then
+ return validate(schema["then"], data)
+ end
+ else
+ if schema["else"] then
+ return validate(schema["else"], data)
+ end
+ end
+ end
+
+ if schema.const ~= nil and schema.const ~= data then
+ return false
+ end
+
+ if schema["enum"] ~= nil then
+ for _, v in ipairs(schema["enum"]) do
+ if v == data then
+ return true
+ end
+ end
+ return false
+ end
+
+ if schema.type then
+ if not simple_validate(schema.type, data) then
+ return false
+ end
+
+ local validator = type_validators[schema.type]
+ if validator then
+ return validator(schema, data)
+ end
+ end
+ return true
+ end
+end
+
+type_validators.table = function (schema : json_schema_object, data : any) : boolean
+ if data is table then
+
+ if schema.maxItems and #data > schema.maxItems then
+ return false
+ end
+
+ if schema.minItems and #data < schema.minItems then
+ return false
+ end
+
+ if schema.required then
+ for _, k in ipairs(schema.required) do
+ if data[k] == nil then
+ return false
+ end
+ end
+ end
+
+ if schema.properties then
+ local additional : schema_t = schema.additionalProperties or true
+ for k, v in pairs(data) do
+ if schema.propertyNames and not validate(schema.propertyNames, k) then
+ return false
+ end
+ local s = schema.properties[k as string] or additional
+ if not validate(s, v) then
+ return false
+ end
+ end
+ elseif schema.additionalProperties then
+ for k, v in pairs(data) do
+ if schema.propertyNames and not validate(schema.propertyNames, k) then
+ return false
+ end
+ if not validate(schema.additionalProperties, v) then
+ return false
+ end
+ end
+ end
+
+ if schema.uniqueItems then
+ -- only works for scalars, would need to deep-compare for objects/arrays/tables
+ local values : { any : boolean } = {}
+ for _, v in pairs(data) do
+ if values[v] then
+ return false
+ end
+ values[v] = true
+ end
+ end
+
+ local p = 0
+ if schema.prefixItems then
+ for i, s in ipairs(schema.prefixItems) do
+ if validate(s, data[i]) then
+ p = i
+ else
+ return false
+ end
+ end
+ end
+
+ if schema.items then
+ for i = p+1, #data do
+ if not validate(schema.items, data[i]) then
+ return false
+ end
+ end
+ end
+
+ if schema.contains then
+ local found = false
+ for i = 1, #data do
+ if validate(schema.contains, data[i]) then
+ found = true
+ break
+ end
+ end
+ if not found then
+ return false
+ end
+ end
+
+ return true
+ end
+ return false
+end
+
+type_validators.object = function (schema : schema_t, data : any) : boolean
+ if data is table then
+ for k in pairs(data) do
+ if not k is string then
+ return false
+ end
+ end
+
+ return type_validators.table(schema, data)
+ end
+ return false
+end
+
+type_validators.array = function (schema : schema_t, data : any) : boolean
+ if data is table then
+
+ -- just check that there the keys are all numbers
+ for i in pairs(data) do
+ if not i is number then
+ return false
+ end
+ end
+
+ return type_validators.table(schema, data)
+ end
+ return false
+end
+
+json_schema_object.validate = validate;
+
+return json_schema_object;