130 lines
9.0 KiB
Markdown
130 lines
9.0 KiB
Markdown
# JSPG: JSON Schema Postgres
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**JSPG** is a high-performance PostgreSQL extension for in-memory JSON Schema validation, specifically targeting **Draft 2020-12**.
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It is designed to serve as the validation engine for the "Punc" architecture, where the database is the single source of truth for all data models and API contracts.
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## 🎯 Goals
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1. **Draft 2020-12 Compliance**: Attempt to adhere to the official JSON Schema Draft 2020-12 specification.
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2. **Ultra-Fast Validation**: Compile schemas into an optimized in-memory representation for near-instant validation during high-throughput workloads.
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3. **Connection-Bound Caching**: Leverage the PostgreSQL session lifecycle to maintain a per-connection schema cache, eliminating the need for repetitive parsing.
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4. **Structural Inheritance**: Support object-oriented schema design via Implicit Keyword Shadowing and virtual `.family` schemas.
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5. **Punc Integration**: validation is aware of the "Punc" context (request/response) and can validate `cue` objects efficiently.
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## 🔌 API Reference
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The extension exposes the following functions to PostgreSQL:
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### `cache_json_schemas(enums jsonb, types jsonb, puncs jsonb) -> jsonb`
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Loads and compiles the entire schema registry into the session's memory, atomically replacing the previous validator.
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* **Inputs**:
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* `enums`: Array of enum definitions.
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* `types`: Array of type definitions (core entities).
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* `puncs`: Array of punc (function) definitions with request/response schemas.
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* **Behavior**:
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* Parses all inputs into an internal schema graph.
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* Resolves all internal references (`$ref`).
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* Generates virtual `.family` schemas for type hierarchies.
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* Compiles schemas into validators.
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* **Returns**: `{"response": "success"}` or an error object.
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### `mask_json_schema(schema_id text, instance jsonb) -> jsonb`
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Validates a JSON instance and returns a new JSON object with unknown properties removed (pruned) based on the schema.
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* **Inputs**:
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* `schema_id`: The `$id` of the schema to mask against.
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* `instance`: The JSON data to mask.
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* **Returns**:
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* On success: A `Drop` containing the **masked data**.
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* On failure: A `Drop` containing validation errors.
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### `validate_json_schema(schema_id text, instance jsonb) -> jsonb`
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Validates a JSON instance against a pre-compiled schema.
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* **Inputs**:
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* `schema_id`: The `$id` of the schema to validate against (e.g., `person`, `save_person.request`).
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* `instance`: The JSON data to validate.
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* **Returns**:
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* On success: `{"response": "success"}`
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* On failure: A JSON object containing structured errors (e.g., `{"errors": [...]}`).
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### `json_schema_cached(schema_id text) -> bool`
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Checks if a specific schema ID is currently present in the cache.
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### `clear_json_schemas() -> jsonb`
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Clears the current session's schema cache, freeing memory.
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### `show_json_schemas() -> jsonb`
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Returns a debug dump of the currently cached schemas (for development/debugging).
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## ✨ Custom Features & Deviations
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JSPG implements specific extensions to the Draft 2020-12 standard to support the Punc architecture's object-oriented needs.
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### 1. Implicit Keyword Shadowing
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Standard JSON Schema composition (`allOf`) is additive (Intersection), meaning constraints can only be tightened, not replaced. However, JSPG treats `$ref` differently when it appears alongside other properties to support object-oriented inheritance.
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* **Inheritance (`$ref` + `properties`)**: When a schema uses `$ref` *and* defines its own properties, JSPG implements **Smart Merge** (or Shadowing). If a property is defined in the current schema, its constraints take precedence over the inherited constraints for that specific keyword.
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* *Example*: If `Entity` defines `type: { const: "entity" }` and `Person` (which refs Entity) defines `type: { const: "person" }`, validation passes for "person". The local `const` shadows the inherited `const`.
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* *Granularity*: Shadowing is per-keyword. If `Entity` defined `type: { const: "entity", minLength: 5 }`, `Person` would shadow `const` but still inherit `minLength: 5`.
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* **Composition (`allOf`)**: When using `allOf`, standard intersection rules apply. No shadowing occurs; all constraints from all branches must pass. This is used for mixins or interfaces.
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### 2. Virtual Family Schemas (`.family`)
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To support polymorphic fields (e.g., a field that accepts any "User" type), JSPG generates virtual schemas representing type hierarchies.
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* **Mechanism**: When caching types, if a type defines a `hierarchy` (e.g., `["entity", "organization", "person"]`), JSPG generates a schema like `organization.family` which is a `oneOf` containing refs to all valid descendants.
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### 3. Strict by Default & Extensibility
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JSPG enforces a "Secure by Default" philosophy. All schemas are treated as if `unevaluatedProperties: false` (and `unevaluatedItems: false`) is set, unless explicitly overridden.
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* **Strictness**: By default, any property or array item in the instance data that is not explicitly defined in the schema causes a validation error. This prevents clients from sending undeclared fields or extra array elements.
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* **Extensibility (`extensible: true`)**: To allow a free-for-all of additional, undefined properties or extra array items, you must add `"extensible": true` to the schema. This globally disables the strictness check for that object or array, useful for types designed to be completely open.
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* **Structured Additional Properties (`additionalProperties: {...}`)**: Instead of a boolean free-for-all, you can define `additionalProperties` as a schema object (e.g., `{"type": "string"}`). This maintains strictness (no arbitrary keys) but allows any extra keys as long as their values match the defined structure.
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* **Ref Boundaries**: Strictness is reset when crossing `$ref` boundaries. The referenced schema's strictness is determined by its own definition (strict by default unless `extensible: true`), ignoring the caller's state.
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* **Inheritance**: Strictness is inherited. A schema extending a strict parent will also be strict unless it declares itself `extensible: true`. Conversely, a schema extending a loose parent will also be loose unless it declares itself `extensible: false`.
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### 4. Format Leniency for Empty Strings
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To simplify frontend form logic, the format validators for `uuid`, `date-time`, and `email` explicitly allow empty strings (`""`). This treats an empty string as "present but unset" rather than "invalid format".
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### 5. Masking (Constructive Validation)
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JSPG supports a "Constructive Validation" mode via `mask_json_schema`. This is designed for high-performance API responses where the schema dictates the exact shape of the returned data.
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* **Mechanism**: The validator traverses the instance against the schema.
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* **Valid Fields**: Kept in the output.
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* **Unknown/Extra Fields**: Silently removed (pruned) if `extensible: false` (default).
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* **Invalid Fields**: Still trigger standard validation errors.
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This allows the database to return "raw" joined rows (e.g. `SELECT * FROM person JOIN organization ...`) and have JSPG automatically shape the result into the expected API response, removing any internal or unrelated columns not defined in the schema.
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## 🏗️ Architecture
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The extension is written in Rust using `pgrx` and structures its schema parser to mirror the Punc Generator's design:
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* **Single `Schema` Struct**: A unified struct representing the exact layout of a JSON Schema object, including standard keywords and custom vocabularies (`form`, `display`, etc.).
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* **Compiler Phase**: schema JSONs are parsed into this struct, linked (references resolved), and then compiled into an efficient validation tree.
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* **Validation Phase**: The compiled validators traverse the JSON instance using `serde_json::Value`.
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### Concurrency & Threading ("Atomic Swap")
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To support high-throughput validation while allowing for runtime schema updates (e.g., during development or hot-reloading), JSPG uses an **Atomic Swap** pattern.
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1. **Immutable Validator**: The `Validator` struct immutably owns the `Registry`. Once created, a validator instance (and its registry) never changes.
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2. **Global Pointer**: A global `RwLock<Option<Arc<Validator>>>` holds the current active validator.
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3. **Lock-Free Reads**: Validation requests acquire a read lock just long enough to clone the `Arc` (incrementing a reference count), then release the lock immediately. Validation proceeds on the snapshot, ensuring no blocking during schema updates.
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4. **Atomic Updates**: When schemas are reloaded (`cache_json_schemas`), a new `Registry` and `Validator` are built entirely on the stack. The global pointer is then atomically swapped to the new instance under a write lock.
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## 🧪 Testing
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Testing is driven by standard Rust unit tests that load JSON fixtures.
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* **Isolation**: Each test file runs with its own isolated `Registry` and `Validator` instance, created on the stack. This eliminates global state interference and allows tests to run in parallel.
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* **Fixtures**: The tests are located in `tests/fixtures/*.json` and are executed via `cargo test`. |