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 environment 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 environment variables (e.g. ER_DB_TEST) 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 via environment variables. The primary configuration parameters include:

• ER_PORT:
  The port on which the server listens (default: 8080).

• ER_CHECK_SCOPE:
  Enables or disables scope checking. When set to "1", the server verifies that the JWT token has the proper scopes (e.g., users-read for GET and users-write for modifications). If unset or any other value, scope checking is disabled (default: enabled).

• ER_TOKEN_SECRET:
  The secret used to sign/verify JWT tokens.

• ER_TOKEN_USER_SEARCH:
  The claim key used to extract the user ID from the JWT token (default: "sub").

• ER_NO_PLUGIN_LOG:
  Controls plugin logging. When set to "1", plugin logging is enabled; otherwise, it is disabled.

• ER_DEFAULT_TIMEZONE:
  The default timezone to use if none is provided via the Prefer header (e.g., "GMT" or "America/New_York").

• ER_DB_:
  For each database connection, you set an environment variable in the form ER_DB_TEST, ER_DB_PROD, etc. The value should be in the format:

  sqlite://path/to/database.db
  

  or for other plugins, a URI scheme that the plugin understands.

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)

Set environment variables:

export ER_DB_TEST="sqlite://./test.db"
export ER_DB_ORDERS="sqlite://./orders.db"
export ER_TOKEN_SECRET="your-secret"
export ER_TOKEN_USER_SEARCH="sub"
export ER_DEFAULT_TIMEZONE="GMT"

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

To create an external plugin (e.g., a MySQL plugin):

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

2. Import Required Modules:
   In your plugin's go.mod, add:

   require (
       github.com/onegreyonewhite/easyrest v0.1.0
       github.com/hashicorp/go-plugin v1.6.3
   )
   

   Then, import the required packages:

   import (
       easyrest "github.com/onegreyonewhite/easyrest/plugin"
       hplugin "github.com/hashicorp/go-plugin"
   )
   

3. Implement the Interface:
   Implement the DBPlugin interface defined in easyrest/plugin. Use the same handshake configuration (accessible as easyrest.Handshake).

4. Structure Your Repository:

   • Have a main package (e.g., main.go) that registers your plugin using:

     func main() {
         impl := &mysqlPlugin{}
         hplugin.Serve(&hplugin.ServeConfig{
             HandshakeConfig: easyrest.Handshake,
             Plugins: map[string]hplugin.Plugin{
                 "db": &easyrest.DBPluginPlugin{Impl: impl},
             },
         })
     }
     

   • Organize your code so that the core logic is in packages that can be independently tested.

5. Build and Deploy:
   Build the plugin binary with go build and ensure it is discoverable by EasyREST (via naming conventions and PATH configuration).

Changes in EasyREST Repository

In the EasyREST core, nothing changes except that you now reference plugins by their binary names (e.g., easyrest-plugin-mysql) using exec.LookPath. Document the expected naming convention so that external plugins can be built and integrated independently.

License

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

Copyright 2025 Sergei Kliuikov