lt-auth-proxy/src/ltProxyHandler.ts

import { Handler } from 'http-kernel/Types/mod.ts';
import { Env } from './env.ts';

/**
 * Forwards the incoming request to the actual LanguageTool server.
 * Dynamically passes through path and query string.
 * Removes `username` and `apiKey` from the FormData body if present.
 */
export const handler: Handler = async (ctx) => {
    const originalUrl = new URL(ctx.req.url);
    const proxyUrl = new URL(
        `${originalUrl.pathname}${originalUrl.search}`,
        `http://${Env.ltServerHost}:${Env.ltServerPort}`,
    );

    const contentType = ctx.req.headers.get('content-type') ?? '';
    let body: BodyInit | null = null;

    if (
        contentType.includes('application/x-www-form-urlencoded') &&
        ctx.state.body
    ) {
        const text = new TextDecoder().decode(ctx.state.body as Uint8Array);
        const params = new URLSearchParams(text);

        // Remove `apiKey` and `username` from the params
        // LanguageTool will react with a error if they are present
        params.delete('apiKey');
        params.delete('username');

        body = params.toString();
    } else {
        console.debug('Unsupported content type:', contentType);
        body = ctx.state.body as BodyInit | null;
    }

    const headers = new Headers(ctx.req.headers);
    headers.delete('content-length');

    console.debug('Forwarding request to:', proxyUrl.toString());

    const forwarded = await fetch(proxyUrl.toString(), {
        method: ctx.req.method,
        headers,
        body,
    });

    console.debug('Received response from LT server:', forwarded.status);

    const respHeaders = new Headers(forwarded.headers);
    return new Response(forwarded.body, {
        status: forwarded.status,
        headers: respHeaders,
    });
};

export { handler as ltProxyHandler };