Charonless is a simple, lightweight, and easy-to-use library for creating HTTP proxy server in serverless environments. It use basic Fetch API to proxy requests and responses.

Charonless provides a single function charon to create a fetch handler. It is a high-level function that takes a default configuration object for handling invalid requests, and a list of testers for proxying requests. The tester is a function that takes a request and returns a proxy configuration object.

Example (serverless env with Bun.js):

import {charon} from 'charonless';

Bun.serve({
    fetch(req) {
        return charon(
            {
                host: '192.168.1.1',
                port: 2000,
            },
            (req) => {
                if (req.location.host === 'a.example.com') {
                    return {
                        host: '192.168.1.2',
                        port: 2001,
                    }
                }
            },
            () => {
                if (req.location.host === 'b.example.com') {
                    return {
                        host: '192.168.1.3',
                        port: 2002,
                    }
                }
            }
        )(req);
    }
})

The proxy behavior is defined through the BackendConfig interface, which allows fine-grained control over request forwarding and response handling. Below are the configuration options available:

type BackendConfig = {
    host: string;
    port?: number;
    ssl?: boolean;
    followRedirects?: boolean;
    request?: {
        path?: (p: string[]) => string[];
        headers?: (o: Record<string, string>) => Record<string, string>;
        query?: (o: Array<[string, string]>) => Array<[string, string]>;
        json?: (o: any) => Object | undefined;
    };
    response?: {
        headers?: (o: Record<string, string>) => Record<string, string>;
        status?: number;
        body?: (b?: ReadableStream<Uint8Array>) => ReadableStream<Uint8Array> | string;
        map?: (r?: Response) => Response;
    };
};

Key Features Explanation:

1. Core Configuration

host and port define the target backend server location

ssl if true then use https or else use http (default: false)

2. Request Manipulation

Use request object methods to:

• Rewrite URL paths
• Modify headers
• Adjust query parameters

3. Response Customization

The response object allows:

• Header transformations
• Status code overrides
• Body modification (supports stream processing)

This structure provides both basic routing and advanced middleware capabilities for proxy operations.