DRPC

A lightweight, bi-directional RPC library with support for method routing, middleware chains, and error handling.

Features

• Bi-directional RPC communication
• Method routing with middleware support
• Handler chains with parameter modification
• Automatic reconnection
• Error handling and propagation
• Comprehensive type support
• Connection state management

Installation

fibjs --install @instun/drpc

Basic Usage

const { open } = require('@instun/drpc');

// Server-side handler
const server = open(connection, {
    routing: {
        add: (a, b) => a + b,
        echo: msg => msg
    }
});

// Client-side connection
const client = open(connection);

// Make RPC calls
const result = await client.add(1, 2);  // Returns 3
const echo = await client.echo('test'); // Returns 'test'

Method Routing

Basic Routing

Methods can be organized in a nested structure:

const server = open(connection, {
    routing: {
        math: {
            add: (a, b) => a + b,
            multiply: (a, b) => a * b
        },
        user: {
            profile: {
                get: id => ({ id, name: 'Test' }),
                update: (id, data) => ({ ...data, id })
            }
        }
    }
});

// Client usage
await client.math.add(1, 2);
await client.user.profile.get(123);

Handler Chains

Handler chains allow you to process requests through multiple handlers, with each handler modifying the parameters before passing them to the next handler:

const server = open(connection, {
    routing: {
        transform: [
            // First handler: convert to uppercase
            async function(text) {
                this.params[0] = text.toUpperCase();
            },
            // Second handler: add exclamation mark
            async function(text) {
                this.params[0] = text + '!';
            },
            // Last handler: return final result
            async function(text) {
                return `[${text}]`;
            }
        ],
        
        processNumbers: [
            // First handler: double the number
            async function(num) {
                this.params[0] = num * 2;
            },
            // Second handler: add 5
            async function(num) {
                this.params[0] = num + 5;
            },
            // Last handler: format result
            async function(num) {
                return `Result: ${num}`;
            }
        ]
    }
});

// Usage:
const result1 = await client.transform('hello');
console.log(result1); // '[HELLO!]'

const result2 = await client.processNumbers(10);
console.log(result2); // 'Result: 25' (10 * 2 + 5)

Handler Chain Rules

1. Only the last handler in a chain can return a value
2. Intermediate handlers must modify parameters using this.params
3. Each handler has access to:
   • this.method: Current method path
   • this.params: Array of method parameters
   • this.invoke: For making nested RPC calls

const server = open(connection, {
    routing: [
        // Middleware for logging
        async function() {
            console.log(`Called: ${this.method}`);
            console.log(`Params:`, this.params);
        },
        
        // Middleware for parameter validation
        async function() {
            if (!this.params[0]) {
                throw new Error('Missing required parameter');
            }
            // Modify parameters for next handler
            this.params[0] = { validated: true, ...this.params[0] };
        },
        
        // Final handler
        {
            process: async function(data) {
                return { result: 'success', data };
            }
        }
    ]
});

Cross-Method Context Sharing

Using WeakMap with this.invoke enables sharing context between method calls. This is particularly useful for implementing authentication, session management, and complex workflows:

// Server-side authentication example
const sessions = new WeakMap();

const server = open(connection, {
    routing: {
        auth: {
            // Login and initialize session
            login: [
                async function validateCredentials(credentials) {
                    if (!credentials?.username || !credentials?.password) {
                        throw new Error('Invalid credentials');
                    }
                    
                    // Store session using this.invoke as key
                    sessions.set(this.invoke, {
                        username: credentials.username,
                        roles: ['user'],
                        loginTime: Date.now()
                    });
                    return { success: true };
                }
            ],

            // Check session and return user info
            getSession: async function() {
                const session = sessions.get(this.invoke);
                if (!session) {
                    throw new Error('Not authenticated');
                }
                return session;
            },

            // Protected methods that require authentication
            admin: {
                action: [
                    // Middleware to check admin role
                    async function checkAdminRole() {
                        const session = sessions.get(this.invoke);
                        if (!session) {
                            throw new Error('Not authenticated');
                        }
                        if (!session.roles.includes('admin')) {
                            throw new Error('Insufficient privileges');
                        }
                        this.params[0] = {
                            ...this.params[0],
                            actor: session.username
                        };
                    },
                    async function performAction(data) {
                        return {
                            success: true,
                            action: data.action,
                            actor: data.actor,
                            timestamp: Date.now()
                        };
                    }
                ]
            },

            // Logout and clean up session
            logout: async function() {
                const hadSession = sessions.delete(this.invoke);
                return { success: true, hadSession };
            }
        }
    }
});

// Client usage example:
await client.auth.login({ 
    username: 'admin', 
    password: 'secret' 
});

const session = await client.auth.getSession();
// { username: 'admin', roles: ['user'], loginTime: ... }

const actionResult = await client.auth.admin.action({ 
    action: 'delete_user' 
});
// { success: true, action: 'delete_user', actor: 'admin', ... }

await client.auth.logout();

The WeakMap-based session management provides several benefits:

• Automatic cleanup when the connection is closed
• No memory leaks from abandoned sessions
• Secure context isolation between connections
• Natural integration with middleware chains

Fuzzy Matching in Handler Chains

The library supports flexible method routing with fuzzy matching, where a handler can process multiple method paths using a common prefix:

const server = open(connection, {
    routing: [
        function() {
            console.log(`Processing: ${this.method}`);
            this.params[0] = { ...this.params[0], processed: true };
        },
        {
            // Handle all methods under "user.*"
            "user": async function() {
                // If client calls "user.profile.get",
                // this.method will be "profile.get"
                console.log(`Processing: ${this.method}`);
                this.params[0] = { ...this.params[0], processed: true };
            },
            
            // Specific handlers still take precedence
            "user.special": async function(data) {
                return { special: true, data };
            },
            // Handle all methods under "admin.*"
            "admin": [
                function() {
                    // If client calls "admin.add_user",
                    // this.method will be "add_user"
                    console.log(`Processing: ${this.method}`);
                    this.params[0] = { ...this.params[0], processed: true };
                },
                {
                    "add_user": async function(data) {
                        return { success: true, data };
                    }   ,
                    "remove_user": async function(data) {
                        return { success: true, data };
                    }
                }
            ]
        }
    ]
});

// Example flows:
// 1. client.user.profile.get({ name: 'test' })
//    - Matches "user" handler
//    - this.method is "profile.get"
//    - Modifies params[0] to { name: 'test', processed: true }

// 2. client.user.special({ type: 'test' })
//    - Matches "user.special" handler directly
//    - Returns { special: true, data: { type: 'test' } }

// 3. client.admin.add_user({ id: 123 })
//    - Matches "admin" handler
//    - this.method is "add_user"
//    - Modifies params[0] to { id: 123, processed: true }

// 4. client.admin.remove_user({ id: 123 })
//    - Matches "admin" handler
//    - this.method is "remove_user"
//    - Modifies params[0] to { id: 123, processed: true }

The router will find the longest matching prefix handler, which allows for flexible routing patterns like:

• user.* - Handle all methods under user
• user.profile.* - Handle all profile-related methods
• admin.* - Handle all admin methods

This is particularly useful for:

• Implementing middleware for groups of methods
• API versioning
• Dynamic method handling
• Request preprocessing
• Access control by path patterns

Bidirectional Communication

The library supports full-duplex RPC communication, allowing both server and client to initiate calls:

// Server-side
const server = open(connection, {
    routing: {
        // Server method that calls client
        processWithCallback: async function(data) {
            // Call client's transformData method
            const result = await this.invoke.transformData(data);
            return `Processed: ${result}`;
        }
    }
});

// Client-side
const client = open(connection, {
    // Client exposes methods for server to call
    routing: {
        transformData: async function(data) {
            return data.toUpperCase();
        }
    }
});

// Example flow:
// 1. Client initiates call
const result = await client.processWithCallback('hello');
console.log(result); 
// Output: "Processed: HELLO"

// 2. Server can also initiate calls to client's exposed methods
// This happens automatically when server uses this.invoke

This enables:

• Server push notifications
• Real-time updates
• Client-side API exposure
• Callback-based workflows
• Event-driven architectures

Connection Management

Auto Reconnection

const client = open(connection, {
    timeout: 5000,      // Request timeout
    maxRetries: 3,      // Max reconnection attempts
    retryDelay: 1000    // Delay between attempts
});

Connection State

// Get current connection state
const state = client[Symbol.for('drpc.state')]();

// Listen for state changes
const client = open(connection, {
    onStateChange: (oldState, newState) => {
        console.log(`Connection state changed: ${oldState} -> ${newState}`);
    }
});

License

This project is licensed under the MIT License - see the LICENSE file for details.