Readme

README.md

@@ -0,0 +1,250 @@
+# Dynamic Schema Records API
+
+A lightweight, high-performance JSON records service built with **Rust**, **Axum**, and **SQLite**. 
+
+The service validates incoming JSON payloads against a dynamic schema specification defined in a JSON configuration file. Schemas support validation modes (`strict` vs. `loose`), data type constraints, and exact forced values (e.g., pinning API payload versions). Schemas can be reloaded at runtime without restarting the server.
+
+---
+
+## Features
+
+- **Dynamic Schema Validation**:
+  - Enforce required types: `string`, `integer`, `number`, `boolean`, `object`, `array`, `null`.
+  - Force exact values on any field (e.g., pin `"version": 2`).
+  - Validation modes:
+    - **`strict`**: All defined fields are required, and unknown fields are rejected.
+    - **`loose`**: All defined fields are required, but additional unknown fields are accepted.
+- **Hot-Reloadable Configuration**: Reload `config.json` via an HTTP admin endpoint with atomic swap and rollback on error.
+- **Persistent Storage**: Validated records are stored with a generated UUID and ISO-8601 UTC timestamp in an SQLite database (`messages.db`).
+- **Structured Logging**: Built with `tracing` outputting to standard output.
+
+---
+
+## Prerequisites
+
+- [Rust toolchain](https://rustup.rs/) (1.75+ recommended)
+- SQLite development libraries (if linking dynamically)
+
+---
+
+## Configuration
+
+The service looks for a configuration file at the path specified by the `APP_CONFIG` environment variable, defaulting to `config.json` in the current working directory.
+
+### Example: `config.json`
+
+```json
+{
+  "mode": "strict",
+  "fields": {
+    "version": {
+      "type": "integer",
+      "value": 2
+    },
+    "message": {
+      "type": "string"
+    },
+    "enabled": {
+      "type": "boolean"
+    }
+  }
+}
+```
+
+### Schema Specification
+
+| Property | Type | Description |
+| :--- | :--- | :--- |
+| `mode` | `string` | `"strict"` or `"loose"`. |
+| `fields` | `object` | Map of field names to validation specifications. Must contain at least one field. |
+| `fields.<name>.type` | `string` | Expected JSON type: `string`, `integer`, `number`, `boolean`, `object`, `array`, `null`. |
+| `fields.<name>.value` | *any* *(optional)* | Expected exact value. Rejects any request where the value does not strictly match. |
+
+---
+
+## Getting Started
+
+### 1. Build and Run
+
+```bash
+# Clone the repository and enter the directory
+cd your-project-name
+
+# Create your config file
+cat <<EOF > config.json
+{
+  "mode": "strict",
+  "fields": {
+    "version": {
+      "type": "integer",
+      "value": 1
+    },
+    "message": {
+      "type": "string"
+    }
+  }
+}
+EOF
+
+# Run the server (default: 127.0.0.1:3000)
+cargo run
+```
+
+To specify a custom configuration file path:
+
+```bash
+APP_CONFIG=custom_config.json cargo run
+```
+
+---
+
+## API Reference
+
+### Health / Service Info
+- **Endpoint:** `GET /` or `GET /api/now`
+- **Description:** Returns server timestamp and status payload.
+- **Example Response:**
+  ```json
+  {
+    "uuid": "4fc736f8-45e0-47da-8da9-6c30fef6a72e",
+    "date": "2026-10-25T10:19:00Z",
+    "data": {
+      "version": 1,
+      "message": "Hello from Rust!"
+    }
+  }
+  ```
+
+---
+
+### Create Record
+- **Endpoint:** `POST /api/records`
+- **Headers:** `Content-Type: application/json`
+- **Request Body:**
+  ```json
+  {
+    "data": {
+      "version": 1,
+      "message": "Hello, world!"
+    }
+  }
+  ```
+- **Response (`201 Created`):**
+  ```json
+  {
+    "uuid": "f3b392b9-dc81-42cb-b9ef-dc7e90aa7ce5",
+    "date": "2026-10-25T10:20:15Z",
+    "data": {
+      "version": 1,
+      "message": "Hello, world!"
+    }
+  }
+  ```
+- **Error Responses (`400 Bad Request`):**
+  - Missing field: `Missing required field: message`
+  - Wrong type: `Field 'version' must be of type integer`
+  - Value mismatch: `Field 'version' must equal 1`
+  - Unknown field (in strict mode): `Unknown field: extra_field`
+
+---
+
+### List Records
+- **Endpoint:** `GET /api/records`
+- **Description:** Returns up to 100 most recent records ordered by `date DESC`.
+- **Response (`200 OK`):**
+  ```json
+  [
+    {
+      "uuid": "f3b392b9-dc81-42cb-b9ef-dc7e90aa7ce5",
+      "date": "2026-10-25T10:20:15Z",
+      "data": {
+        "version": 1,
+        "message": "Hello, world!"
+      }
+    }
+  ]
+  ```
+
+---
+
+### Get Active Configuration
+- **Endpoint:** `GET /api/admin/config`
+- **Description:** Inspect the currently running schema and mode.
+- **Response (`200 OK`):**
+  ```json
+  {
+    "mode": "strict",
+    "fields": {
+      "version": {
+        "type": "integer",
+        "value": 1
+      },
+      "message": {
+        "type": "string"
+      }
+    }
+  }
+  ```
+
+---
+
+### Hot-Reload Configuration
+- **Endpoint:** `POST /api/admin/reload-config`
+- **Description:** Reads and validates the file at `APP_CONFIG`. If valid, atomically updates the active schema in memory.
+- **Response (`200 OK`):**
+  ```json
+  {
+    "status": "ok",
+    "mode": "strict",
+    "fields": 2
+  }
+  ```
+- **Error Response (`422 Unprocessable Entity`):** Returned if the configuration file is unreadable, invalid JSON, or contains no fields. The active schema remains untouched.
+
+---
+
+## Example Usage Workflow
+
+```bash
+# 1. Create a valid record
+curl -i -X POST http://127.0.0.1:3000/api/records \
+  -H "Content-Type: application/json" \
+  -d '{"data": {"version": 1, "message": "First record"}}'
+
+# 2. Modify config.json (e.g. bump required version to 2)
+# Update "value": 2 in config.json...
+
+# 3. Reload config without downtime
+curl -i -X POST http://127.0.0.1:3000/api/admin/reload-config
+
+# 4. Old version requests are now rejected
+curl -i -X POST http://127.0.0.1:3000/api/records \
+  -H "Content-Type: application/json" \
+  -d '{"data": {"version": 1, "message": "Rejected"}}'
+# -> HTTP 400: Field 'version' must equal 2
+
+# 5. New version requests succeed
+curl -i -X POST http://127.0.0.1:3000/api/records \
+  -H "Content-Type: application/json" \
+  -d '{"data": {"version": 2, "message": "Accepted"}}'
+```
+
+---
+
+## Database Architecture
+
+On startup, the application creates a local SQLite database named `messages.db` with the following schema:
+
+```sql
+CREATE TABLE IF NOT EXISTS records (
+    uuid TEXT PRIMARY KEY,
+    date TEXT NOT NULL,
+    data TEXT NOT NULL
+);
+```
+This project is licensed under the [MIT License](LICENSE) (or choose your preferred license).
+
+
+## License
+
+This project is licensed under the MIT License.

src/main.rs

@@ -1,4 +1,3 @@
-
 use axum::{
     extract::{rejection::JsonRejection, State},
     http::StatusCode,
@@ -34,6 +33,9 @@ enum ValidationMode {
 struct FieldSpec {
     #[serde(rename = "type")]
     data_type: DataType,
+
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    value: Option<Value>,
 }
 
 #[derive(Debug, Clone, Serialize, Deserialize)]
@@ -122,6 +124,15 @@ fn validate_data(data: &Value, schema: &SchemaConfig) -> Result<(), String> {
                 type_name(&spec.data_type)
             ));
         }
+
+        if let Some(expected) = &spec.value {
+            if value != expected {
+                return Err(format!(
+                    "Field '{key}' must equal {}",
+                    expected
+                ));
+            }
+        }
     }
 
     if matches!(schema.mode, ValidationMode::Strict) {
@@ -405,4 +416,4 @@ async fn main() {
     axum::serve(listener, app)
         .await
         .expect("HTTP server failed");
-}
+}