easyrest

EasyREST

EasyREST is a lightweight, extensible REST service that provides a unified API for performing CRUD and aggregating queries on relational databases. Its key innovation is the use of a plugin system that allows you to connect to virtually any database (or data source) simply by writing a plugin that conforms to the EasyREST interface. Out of the box, an SQLite plugin is provided, but you can easily add plugins for MySQL, PostgreSQL, Oracle, or any other database.

EasyREST handles authentication via JWT, validates and sanitizes request parameters at the controller level, and then passes 100% safe SQL expressions to the plugins. The service supports complex queries including aggregations, aliasing, advanced WHERE conditions, and even the use of context variables that allow you to influence query behavior dynamically.

Table of Contents

• Architecture
  • Overall Architecture Diagram
  • Plugin Communication
  • Authentication and Authorization
• Query Capabilities
  • Selecting Fields and Aliasing
  • Aggregating Queries
  • WHERE Conditions
  • Context Variables
  • Data Insertion, Updates, and Deletion
• Configuration Parameters
• Examples
  • Multiple SQLite Databases with Different Structures
• Building and Running
  • Building the Server
  • Building a Plugin (SQLite)
  • Running Tests and Benchmarks
• License

Architecture

EasyREST's design emphasizes simplicity, extensibility, and security. It follows a modular architecture where the core server is responsible for:

• Authentication & Authorization: Validates JWT tokens and verifies scopes.
• Parameter Validation: Ensures that all parameters (select, where, ordering, etc.) are safe before forwarding to the plugins.
• Plugin Orchestration: Loads and manages DB plugins based on YAML configuration.
• Context Propagation: Extracts contextual information (e.g., timezone, HTTP headers, JWT claims) from each request and passes them to plugins.

Overall Architecture Diagram

flowchart TD
    A[HTTP Request] -->|REST API| B[EasyREST Server]
    B --> C{Authentication & Validation}
    C -- Valid --> D[Process Request]
    C -- Invalid --> E[401/400 Response]
    E --> N[HTTP Response]
    D --> X{Apply Context?}
    X -- Yes --> Y[Replace request.* and erctx.* values]
    X -- No --> Z[Send as is]
    Y --> J[Plugin Client RPC Call]
    Z --> J[Plugin Client RPC Call]
    J --> K["DB Plugin (e.g., SQLite)"]
    K --> F[Build SQL Query]
    F --> L[Database]
    L --> M[Return Results to DB Plugin]
    M --> J2[Return Results to Plugin Client RPC Call]
    J2 --> B2[Return to EasyREST Server]
    B2 --> N[HTTP Response]

Plugin Communication

• RPC Communication: EasyREST uses Hashicorp's go-plugin system to load and communicate with plugins. The server launches plugin processes based on the plugins section in the YAML configuration file and establishes an RPC connection.
• Data Exchange: The server sends validated and sanitized SQL expressions and additional context data to the plugin. Context variables are directly substituted into the query.
• Type Registration: For secure and reliable encoding/decoding over RPC, custom types (e.g., time.Time and flattened JWT claims) are registered with the gob package.

Authentication and Authorization

• JWT Authentication: Requests must include a Bearer token. The server verifies the token signature (using a secret from configuration) and extracts claims.
• Scope-based Authorization: The service verifies that the token's claims include the required scope (e.g., users-read for GET operations, users-write for modifications or wide read and write for all table names).
• Token Claims: The claims are flattened and passed to plugins (under the key claims in the context map) so that plugins can leverage user-specific information if needed.

Query Capabilities

EasyREST supports a wide range of SQL query features by converting URL query parameters into SQL expressions after performing strict validation.

Selecting Fields and Aliasing

• Basic Selection:
  Use the select parameter to specify one or more columns. For example:

  /api/test/users/?select=id,name
  

• Field Aliasing:
  To alias a column, use the syntax alias:field.
  For example,

  /api/test/users/?select=username:name
  

  becomes

  SELECT name AS username FROM users
  

• SQL Functions:
  Aggregation functions are supported. For instance,

  /api/test/users/?select=count()
  

  results in:

  SELECT COUNT(*) AS count FROM users
  

  You can also use functions with aliasing:

  /api/test/orders/?select=total:amount.sum(),order_date
  

  which translates to:

  SELECT SUM(amount) AS total, order_date FROM orders GROUP BY order_date
  

Aggregating Queries

• EasyREST supports common SQL aggregate functions such as COUNT(), SUM(), AVG(), MIN(), and MAX().
• Aggregated fields are automatically excluded from the GROUP BY clause.
• Non-aggregated fields that appear in the select parameter are added to a GROUP BY clause automatically.

WHERE Conditions

• Syntax:
  Conditions are specified using parameters prefixed with where.. For example:

  /api/test/users/?where.eq.name=Alice
  

  This generates:

  WHERE name = 'Alice'
  

• Operators:
  Supported operators include:
  • eq (equals)
  • neq (not equals)
  • lt (less than)
  • lte (less than or equals)
  • gt (greater than)
  • gte (greater than or equals)
  • like (LIKE)
  • ilike (ILIKE)
  • is (IS)
  • in (IN)

Context Variables

EasyREST provides two ways to access context variables in queries:

1. erctx Format: Uses underscore notation to access context variables:

   /api/test/users/?where.eq.name=erctx.claims_sub
   

2. request Format: Uses JSON path notation with dots:

   /api/test/users/?where.eq.name=request.claims.sub
   

Available context variables:

• timezone: Current timezone from Prefer header or default
• headers: All HTTP request headers (lowercase keys)
• claims: JWT token claims (lowercase keys)
• method: HTTP request method
• path: Request URL path
• query: Raw query string
• prefer: Key-value pairs from Prefer header

The Prefer header can be used to pass plugin-specific context parameters:

Prefer: timezone=UTC param1=value1 param2=value2

Data Insertion, Updates, and Deletion

• Insertion (POST):
  Data is passed as JSON in the request body. The server builds an INSERT INTO statement after validating the column names. Context variables can be used in values using either erctx. or request. notation.
• Update (PATCH):
  The update request requires a JSON object in the request body (with columns to update) and optional where conditions in the query string. Context variables can be used in both the update data and where conditions.
• Deletion (DELETE):
  Deletion is based solely on the where parameters. Context variables can be used in where conditions.

Configuration Parameters

EasyREST is configured primarily using a YAML file or environment variables. You can specify a different path using the -config command-line flag:

./easyrest-server -config /path/to/your/custom-config.yaml

Alternatively, the path can be set using the ER_CONFIG_FILE environment variable. Environment variables (ER_*) can also be used to override specific settings, but the YAML file is the recommended approach.

YAML Configuration Structure:

# Server settings
port: 8080 # Default: 8080
default_timezone: "GMT" # Default: "GMT" or system timezone
access_log: false # Enable access logging (default: false)

# Authentication & Authorization
check_scope: true # Enable JWT scope checking (default: true)
token_secret: "your-jwt-secret" # REQUIRED: Secret for JWT verification
token_user_search: "sub" # JWT claim for user ID (default: "sub")
token_url: "" # Optional: URL for external token validation/retrieval
auth_flow: "password" # Optional: OAuth flow type (default: "password")

# CORS settings (optional)
cors:
  enabled: true # Enable CORS headers (default: false)
  origins: ["*"] # List of allowed origins
  methods: ["GET", "POST", "PUT", "DELETE", "OPTIONS"] # Allowed HTTP methods
  headers: ["Content-Type", "Authorization", "X-Requested-With"] # Allowed headers
  max_age: 86400 # Cache duration for preflight requests

# TLS settings (optional)
tls_enabled: false
tls_cert_file: "/path/to/cert.pem"
tls_key_file: "/path/to/key.pem"

# Plugin settings
plugin_log: true # Enable logging from plugins (default: false). Set to false to disable.

# --- Plugin Definitions ---

# Option 1: Include external YAML files containing plugin definitions
plugin_configs:
  - ./plugins/database1.yaml
  - /etc/easyrest/shared_plugins.yaml

# Option 2: Define plugins directly in the main config file
plugins:
  # The key ('test', 'orders', 'inventory') becomes the API path segment (/api/test/, /api/orders/, /api/inventory)
  test:
    # URI format: <plugin_type>://<connection_details>
    # The plugin_type (e.g., 'sqlite') determines the executable name (easyrest-plugin-sqlite)
    uri: "sqlite://./test.db"
    enable_cache: true # Enable ETag caching for this connection
    cache_name: test
    cache_invalidation_map:
      process_order:
        - orders
        - order_items
  orders:
    uri: "sqlite:///data/orders.db"
    enable_cache: true
    cache_name: orders
    # Example: Invalidate 'orders' and 'order_items' ETags when 'process_order' RPC is called
    cache_invalidation_map:
      process_order:
        - orders
        - order_items
  inventory:
    uri: "sqlite:///data/inventory.db"
    # enable_cache defaults to false if not specified

  # Example for a postgres plugin:
  # postgres_db:
  #   uri: "postgres://user:password@host:port/database?sslmode=disable"
  #   enable_cache: true

# --- Example External Plugin File (e.g., ./plugins/database1.yaml) --- Structure:
# - name: plugin_name # Name used in API path
#   uri: "plugin_type://connection_string"
#   path: "/path/to/plugin/binary" # Optional: Explicit path to plugin binary
#   enable_cache: true # Optional: Enable ETag caching (default: false)
#   cache_invalidation_map: # Optional: Map RPC function names to tables whose ETags should be invalidated
#     rpc_function_name:
#       - table1_to_invalidate
#       - table2_to_invalidate

Key Configuration Sections:

• Server Settings: Basic server parameters like port, default_timezone.

• Authentication & Authorization: JWT settings (token_secret is mandatory), scope checking.

• CORS: Cross-Origin Resource Sharing settings.

• TLS: Enable HTTPS by providing certificate and key files.

• Plugin Settings:

  • plugin_log: Controls whether plugin logs are captured by the server.
  • plugin_configs: A list of paths to external YAML files. Each file can define one or more plugins using the structure shown in the example.
  • plugins: A map for defining plugins directly. The map key (e.g., test) is used as the database identifier in API requests (/api/test/).
  • Plugin Definition Attributes:
    • name: (Required in external files, derived from map key in inline definitions) The identifier used in the API path (/api/<name>/).
    • uri: (Required) Specifies the plugin type and connection details. The type (e.g., sqlite) maps to the executable name (easyrest-plugin-sqlite).
    • path: (Optional) Explicit path to the plugin executable. If omitted, EasyREST searches standard locations.
    • enable_cache: (Optional, defaults to false) If true, enables ETag generation and checking (If-Match, If-None-Match) for requests to this DB plugin's tables. Requires at least one Cache plugin to be configured and loaded. This setting itself does not affect Cache plugins directly but enables the caching mechanism for operations related to this specific DB plugin.
    • cache_name: (Optional) Specifies the name (key from plugins map or name from an external file) of the Cache plugin that should be used for ETag caching for this DB plugin. If omitted, EasyREST first looks for a Cache plugin with the same name as this DB plugin (e.g., if the DB plugin name is test, it looks for Cache plugin test). If not found, it falls back to the first available Cache plugin. This setting allows flexible linking between DB and Cache plugins.
    • cache_invalidation_map: (Optional) A map where keys are RPC function names (used via /api/<name>/rpc/<function_name>) and values are lists of table names. When a listed RPC function is successfully executed for this DB plugin (<name>), the ETags for the specified tables associated with this same DB plugin are invalidated in the corresponding Cache plugin. This is useful if an RPC call modifies data in related tables.

• The server merges plugin definitions from plugin_configs files and the inline plugins map. Definitions in the inline map take precedence if names conflict.

Examples

Multiple SQLite Databases with Different Structures

Imagine you have two SQLite databases:

1. Test Database (ER_DB_TEST):

   • Path: ./test.db
   • Table: users
     Structure: id (auto-increment), name (text), update_field (text)

2. Orders Database (ER_DB_ORDERS):

   • Path: ./orders.db
   • Table: orders
     Structure: id (auto-increment), items (integer), order_date (date), amount (real)

Create a config.yaml file (or specify a different one with -config):

port: 8080
token_secret: "your-secret"
token_user_search: "sub"
default_timezone: "America/Los_Angeles"
plugins:
  test:
    uri: "sqlite://./test.db"
  orders:
    uri: "sqlite://./orders.db"

Query Examples:

• Using Context Variables:

  GET /api/test/users/?select=id,name&where.eq.name=request.claims.sub
  

  or

  GET /api/test/users/?select=id,name&where.eq.name=erctx.claims_sub
  

• Aggregating Queries:

  GET /api/orders/?select=total:amount.sum(),order_date
  

  →

  SELECT SUM(amount) AS total, order_date FROM orders GROUP BY order_date;
  

• Data Insertion with Context:

  POST /api/test/users/
  Body: [{"name": "request.claims.sub", "update_field": "new"}]
  

API Documentation

Each plugin endpoint (/api/<plugin-name>/) provides a Swagger 2.0 JSON schema describing available tables and their structure. This documentation can be used to understand the database schema and build client applications.

For example:

GET /api/test/

Returns a Swagger 2.0 JSON schema for all tables in the test database.

Developing External Plugins

External plugins allow you to extend EasyREST with support for different database backends or caching systems. A single plugin binary can provide implementations for either the DBPlugin interface, the CachePlugin interface, or both.

To create an external plugin (e.g., for MySQL DB and Redis Cache):

1. Create a New Repository: For instance, create a repository named easyrest-plugin-mysql-redis.

2. Import Required Modules: In your plugin's go.mod, add the necessary EasyREST and go-plugin dependencies:

   require (
       github.com/onegreyonewhite/easyrest v0.x.x // Use the appropriate version
       github.com/hashicorp/go-plugin v1.x.x   // Use the appropriate version
   )
   

   Then, import the required packages in your Go files:

   import (
       "context" // Often needed for context handling in implementations
       "time"    // Often needed for cache TTLs
   
       easyrest "github.com/onegreyonewhite/easyrest/plugin"
       hplugin "github.com/hashicorp/go-plugin"
   
       // Your specific DB/Cache driver imports, e.g.:
       // _ "github.com/go-sql-driver/mysql"
       // "github.com/redis/go-redis/v9"
   )
   

3. Implement the Interface(s): Create a struct (or structs) that implements the methods defined in the easyrest.DBPlugin and/or easyrest.CachePlugin interfaces from github.com/onegreyonewhite/easyrest/plugin.

   // Example structure implementing both interfaces
   type MyPlugin struct {
       // Add fields for DB connections, cache clients, etc.
       // e.g., db *sql.DB
       // e.g., redisClient *redis.Client
   }
   
   // --- DBPlugin Implementation ---
   
   func (p *MyPlugin) InitConnection(uri string) error {
       // Parse URI, establish DB connection (e.g., MySQL)
       // Store connection in p.db
       return nil
   }
   
   func (p *MyPlugin) TableGet(userID, table string, selectFields []string, where map[string]any, ordering []string, groupBy []string, limit, offset int, ctx map[string]any) ([]map[string]any, error) {
       // Implement logic to SELECT data from the database
       return nil, nil
   }
   
   func (p *MyPlugin) TableCreate(userID, table string, data []map[string]any, ctx map[string]any) ([]map[string]any, error) {
       // Implement logic to INSERT data into the database
       return nil, nil
   }
   
   func (p *MyPlugin) TableUpdate(userID, table string, data map[string]any, where map[string]any, ctx map[string]any) (int, error) {
       // Implement logic to UPDATE data in the database
       return 0, nil
   }
   
   func (p *MyPlugin) TableDelete(userID, table string, where map[string]any, ctx map[string]any) (int, error) {
       // Implement logic to DELETE data from the database
       return 0, nil
   }
   
   func (p *MyPlugin) CallFunction(userID, funcName string, data map[string]any, ctx map[string]any) (any, error) {
       // Implement logic for custom RPC functions (stored procedures, etc.)
       return nil, nil
   }
   
   func (p *MyPlugin) GetSchema(ctx map[string]any) (any, error) {
       // Implement logic to return the database schema in the expected format
       return nil, nil
   }
   
   // --- CachePlugin Implementation ---
   
   func (p *MyPlugin) InitConnection(uri string) error { // Can reuse or have separate logic from DB init
        // Parse URI, establish Cache connection (e.g., Redis)
        // Store connection in p.redisClient
        return nil
   }
   
   func (p *MyPlugin) Get(key string) (string, error) {
       // Implement logic to GET value from cache
       return "", nil
   }
   
   func (p *MyPlugin) Set(key string, value string, ttl time.Duration) error {
       // Implement logic to SET value in cache with TTL
       return nil
   }
   
   func (p *MyPlugin) Delete(keys []string) error {
       // Implement logic to DELETE keys from cache
       return nil
   }
   
   // Note: A plugin doesn't *have* to implement both interfaces.
   // If it only implements DBPlugin, only register "db".
   // If it only implements CachePlugin, only register "cache".
   

4. Register and Serve the Plugin: In your plugin's main package (main.go), register your implementation(s) and start the plugin server. Use the easyrest.Handshake configuration.

   func main() {
       // Create an instance of your plugin implementation
       impl := &MyPlugin{}
   
       // Define the plugins provided by this binary
       pluginMap := map[string]hplugin.Plugin{}
   
       // Register DBPlugin implementation if provided
       // Make sure 'impl' actually implements easyrest.DBPlugin
       pluginMap["db"] = &easyrest.DBPluginPlugin{Impl: impl}
   
       // Register CachePlugin implementation if provided
       // Make sure 'impl' actually implements easyrest.CachePlugin
       pluginMap["cache"] = &easyrest.CachePluginPlugin{Impl: impl}
   
       // Serve the plugin(s)
       hplugin.Serve(&hplugin.ServeConfig{
           HandshakeConfig: easyrest.Handshake,
           Plugins:         pluginMap,
   
       })
   }
   

   Important: Ensure your struct impl actually implements the methods for the interfaces you are registering (DBPlugin for "db", CachePlugin for "cache").

5. Build and Deploy: Build the plugin binary (e.g., go build -o easyrest-plugin-mysql-redis). The binary name should ideally follow the convention easyrest-plugin-<type> (e.g., easyrest-plugin-mysql, easyrest-plugin-redis). EasyREST will look for these binaries:

   • In the directories listed in your system's PATH environment variable.
   • In the current working directory where EasyREST is run.
   • In the same directory as the EasyREST executable itself.
   • It also checks for OS/Arch specific names like easyrest-plugin-mysql-linux-amd64.

   Alternatively, you can specify the exact path to the plugin binary in the EasyREST configuration file (ER_DB_<NAME>_PATH or ER_CACHE_<NAME>_PATH).

6. Configure EasyREST: Update your EasyREST configuration (environment variables or config file) to use your new plugin, referencing the connection name you used in main.go (e.g., mysql if the binary is easyrest-plugin-mysql).

   export ER_DB_PRIMARY="mysql://user:password@tcp(host:port)/database"
   # If the binary name doesn't match the type hint in the URI, or isn't in PATH:
   # export ER_DB_PRIMARY_PATH="/path/to/your/easyrest-plugin-mysql-redis"
   
   export ER_CACHE_PRIMARY="redis://host:port/0"
   # export ER_CACHE_PRIMARY_PATH="/path/to/your/easyrest-plugin-mysql-redis"
   

License

EasyREST is licensed under the terms of the Apache License 2.0. See the file "LICENSE" for more information.

Copyright 2025 Sergei Kliuikov