Merge pull request #3 from FlowFuse/simple-jsonschema-generator

Add simple JSONSchema generator

Author: knolleary

lib/schema-generator/index.js

@@ -0,0 +1,107 @@
+// Get the type description of a value.
+// This only needs to handle JSON-compatible values:
+//  - object
+//  - array
+//  - string
+//  - number
+//  - boolean
+//  - null
+function getObjectType (obj) {
+    let type = typeof obj
+    if (type === 'object') {
+        if (Array.isArray(obj)) {
+            type = 'array'
+        } else if (obj === null) {
+            type = 'null'
+        }
+    }
+    return type
+}
+
+function handleArray (obj) {
+    const schema = {
+        type: 'array'
+    }
+    // Check types of array values.
+    let arrayType
+    let multipleTypes = false
+    let itemsSchema
+    for (let i = 0; i < obj.length; i++) {
+        const elementSchema = generateSchema(obj[i])
+        const elementType = elementSchema.type
+        if (i > 0 && elementType !== arrayType) {
+            // Mixed fundamental types in the array.
+            multipleTypes = true
+            // For now, we just skip trying to representing multiple types
+            break
+        } else {
+            arrayType = elementType
+            if (elementType === 'object') {
+                if (!itemsSchema) {
+                    itemsSchema = elementSchema
+                } else {
+                    // Merge the properties of multiple objects rather than
+                    // try to create oneOf type schemas
+                    const keys = Object.keys(elementSchema.properties)
+                    keys.forEach(key => {
+                        if (!Object.hasOwn(itemsSchema.properties, key)) {
+                            itemsSchema.properties[key] = elementSchema.properties[key]
+                        }
+                    })
+                }
+            } else if (elementType === 'array') {
+                if (!itemsSchema) {
+                    itemsSchema = elementSchema
+                } else {
+                    // TODO: Check if they match
+                }
+            } else {
+                itemsSchema = generateSchema(obj[i])
+            }
+        }
+    }
+    if (!multipleTypes && arrayType) {
+        schema.items = itemsSchema
+    }
+    return schema
+}
+
+function handleObject (obj) {
+    const schema = {
+        type: 'object',
+        properties: {}
+    }
+    for (const [key, value] of Object.entries(obj)) {
+        schema.properties[key] = generateSchema(value)
+    }
+
+    return schema
+}
+
+/**
+ * Generates a JSONSchema doc for the provided value.
+ * This assumes the value comes from a JSON-parsed string - so only handles the
+ * strict subset of valid JSON types.
+ * Limitations:
+ *  - Arrays of mixed types - doesn't include type information
+ *  - Arrays of Objects with different properties - returns the set of all properties seen
+ *    - If a property has different types in different objects, the first type is returned
+ * @param {*} obj The JSON-parsed value to generate a schema for
+ * @returns The JSONSchema for the provided value
+ */
+function generateSchema (obj) {
+    const type = getObjectType(obj)
+    switch (type) {
+    case 'object':
+        return handleObject(obj)
+    case 'array':
+        return handleArray(obj)
+    default:
+        return {
+            type
+        }
+    }
+}
+module.exports = {
+    generateSchema
+}

package-lock.json

@@ -12,7 +12,7 @@
     "url": "git+https://github.com/FlowFuse/mqtt-schema-agent.git"
   },
   "scripts": {
-    "test": "mocha 'test/unit/**/*_spec.js'",
+    "test": "mocha 'test/**/*_spec.js' --timeout 10000 --node-option=unhandled-rejections=strict",
     "lint": "eslint -c .eslintrc \"*.js\" \"lib/**/*.js\" \"test/**/*.js\"",
     "lint:fix": "eslint -c .eslintrc \"*.js\" \"lib/**/*.js\" \"test/**/*.js\" --fix"
   },
@@ -34,6 +34,7 @@
     "mqtt": "^5.10.3"
   },
   "devDependencies": {
+    "ajv": "8.17.1",
     "aedes": "^0.49.0",
     "eslint": "^8.48.0",
     "eslint-config-standard": "^17.0.0",

package.json

@@ -0,0 +1,108 @@
+const { generateSchema } = require('../../../lib/schema-generator/index')
+const Ajv = require('ajv')
+const validator = new Ajv()
+
+const TESTCASES = [
+    'abc',
+    123,
+    false,
+    true,
+    null,
+    {},
+    { a: 1, b: 2, c: null, d: [1, 2, 3] },
+    { a: { b: { c: 1 } } },
+    [],
+    [1, 2, 3],
+    ['a', 'b', 'c'],
+    [true, 'a', 1],
+    [{ a: 1 }, { b: 'abc' }],
+    {
+        Account: {
+            'Account Name': 'Firefly',
+            Order: [
+                {
+                    OrderID: 'order103',
+                    Product: [
+                        {
+                            'Product Name': 'Bowler Hat',
+                            ProductID: 858383,
+                            SKU: '0406654608',
+                            Description: {
+                                Colour: 'Purple',
+                                Width: 300,
+                                Height: 200,
+                                Depth: 210,
+                                Weight: 0.75
+                            },
+                            Price: 34.45,
+                            Quantity: 2
+                        },
+                        {
+                            'Product Name': 'Trilby hat',
+                            ProductID: 858236,
+                            SKU: '0406634348',
+                            Description: {
+                                Colour: 'Orange',
+                                Width: 300,
+                                Height: 200,
+                                Depth: 210,
+                                Weight: 0.6
+                            },
+                            Price: 21.67,
+                            Quantity: 1
+                        }
+                    ]
+                },
+                {
+                    OrderID: 'order104',
+                    Product: [
+                        {
+                            'Product Name': 'Bowler Hat',
+                            ProductID: 858383,
+                            SKU: '040657863',
+                            Description: {
+                                Colour: 'Purple',
+                                Width: 300,
+                                Height: 200,
+                                Depth: 210,
+                                Weight: 0.75
+                            },
+                            Price: 34.45,
+                            Quantity: 4
+                        },
+                        {
+                            ProductID: 345664,
+                            SKU: '0406654603',
+                            'Product Name': 'Cloak',
+                            Description: {
+                                Colour: 'Black',
+                                Width: 30,
+                                Height: 20,
+                                Depth: 210,
+                                Weight: 2
+                            },
+                            Price: 107.99,
+                            Quantity: 1
+                        }
+                    ]
+                }
+            ]
+        }
+    }
+]
+
+describe('Schema Generator', function () {
+    TESTCASES.forEach((value, index) => {
+        it('generates valid schema ' + index, function () {
+            const schema = generateSchema(value)
+            const validate = validator.compile(schema)
+            const valid = validate(value)
+            if (!valid) {
+                console.log(`Value: ${JSON.stringify(value)}`)
+                console.log(`Schema: ${JSON.stringify(schema)}`)
+                console.log(`Errors: ${validate.errors}`)
+                valid.should.be.true()
+            }
+        })
+    })
+})