Reverse Proxy in Cloudflare Wokers

workers.js

addEventListener('fetch', event => {
    event.respondWith(handleRequest(event.request));
});

async function handleRequest(request) {
    try {
        const url = new URL(request.url);

        // リダイレクト処理
        if (url.pathname.startsWith('/redirect/')) {
            return handleRedirect(url);
        }

        // ヘルプページの表示
        if (url.pathname === '/') {
            return showUsage(url);
        }

        // CORSプリフライトリクエストの処理
        if (request.method === 'OPTIONS') {
            return handlePreflight();
        }

        // APIリクエストの処理
        return handleApiRequest(request, url);
    } catch (e) {
        return new Response(e.stack || e, { status: 500 });
    }
}

function handleRedirect(url) {
    let targetUrl = url.pathname.slice(10);
    if (url.search) {
        targetUrl += url.search;
    }
    return Response.redirect(targetUrl, 302);
}

function showUsage(url) {
    return new Response(`
        Usage:\n
          ${url.origin}/<url>
      `, {
        headers: {
            'Content-Type': 'text/plain'
        }
    });
}

function handlePreflight() {
    return new Response(null, {
        status: 200,
        headers: {
            'Access-Control-Allow-Origin': '*',
            'Access-Control-Allow-Methods': 'GET, HEAD, POST, OPTIONS',
            'Access-Control-Allow-Headers': 'Authorization, Content-Type, Notion-Version',
        },
    });
}

async function handleApiRequest(request, url) {
    const headers = new Headers(request.headers);

    // Notion API の特別なヘッダー処理
    if ('api.notion.com' === new URL(request.url.slice(url.origin.length + 1)).hostname && !headers.has('Notion-Version')) {
        headers.set('Notion-Version', '2022-06-28');
    }

    let response = await fetch(request.url.slice(url.origin.length + 1), {
        method: request.method,
        headers: headers,
        redirect: 'follow',
        body: request.body,
    });

    response = new Response(response.body, response);
    response.headers.set('Access-Control-Allow-Origin', '*');

    return response;
}