本章示例为通过【边缘函数】实现站点代理。
代码说明：支持反向代理某个站点（以某网站为例）。其中，【边缘函数】中涉及到了多种改写操作，包括：请求URL、请求头、响应头、响应包体等。

详细代码

const UPSTREAM = "www.douban.com"
const PATH_PREFIX = "/douban-proxy"
const RW_START = "/--rw--"
const RW_STOP = "--wr--"
let g_origin_url
let g_path_pfrefix

async function handleRequest(request) {
    g_origin_url = new URL(request.url)

    if (request.method == "POST") {
        let body = await request.text()
        console.log("post body", request.url, "body", body)
    }
    
    const {urlString, pathPrefix} = restoreURL(request.url)
    g_path_pfrefix = pathPrefix

    const url = new URL(urlString)
    console.log("request.url", request.url)
    console.log("restore url", urlString)
    // return new Response("xx1:" + request.url + "\nxx2:" + urlString)

    const newRequest = new Request(urlString, request)
    const headers = newRequest.headers
    headers.set("Host", url.host)
    headers.delete("Accept-Encoding")
    const referer = headers.get("Referer")
    if (referer) {
        const {urlString} = restoreURL(referer)
        // console.log('referer', urlString)
        headers.set("Referer", urlString)
    }
    const origin = headers.get("Origin")
    if (origin) {
        const {urlString} = restoreURL(origin)
        // console.log('origin', urlString)
        headers.set("Origin", urlString)
    }

    const response = await fetch(newRequest, {cdnProxy: false, redirect: "manual"})
    const responseHeaders = response.headers
    let cookie = responseHeaders.get("Set-Cookie")
    if (cookie) {
        cookie = cookie.replace(/(domain=)([^;]+);/gi, '$1'+g_origin_url.host+';')
        responseHeaders.set("Set-Cookie", cookie)
    }

    const contentType = responseHeaders.get("Content-Type")
    
    if (contentType.includes("text/html")) {
        return new HTMLRewriter()
                    .on("a", new URLHandler(["href"]))
                    .on("link", new URLHandler(["href"]))
                    .on("script", new URLHandler(["src"]))
                    .on("iframe", new URLHandler(["src"]))
                    .on("div", new URLHandler(["style"]))
                    .on("img", new URLHandler(["src", "data-origin"]))
                    .transform(response)
    } else if (contentType.includes("text/css")) {
        let text = await response.text()
        text = rewriteText(text, /url\((.*?)\)/g)
        return new Response(text, response)
    } else if (contentType.includes("application/x-javascript")) {
        let text = await response.text()
        text = rewriteText(text, /"https?:(\/\/.*?)"/gi)
        return new Response(text, response)
    } else if (url.pathname.endsWith("login/qrlogin_code")) {
        let json = await response.json()
        json["payload"]["img"] = rewriteURL(json["payload"]["img"])
        return new Response(JSON.stringify(json, null, 2), response)
    } else {
        return response
    }
}

function rewriteText(text, reg) {
    let result = text.replace(reg,  function(match, str){
        let result = match.replace(str, rewriteURL(str));
        result = result.replace("https", "http")
        return result
    });
    // if (text != result) {
    //     console.log("text", text, result)
    // }
    return result
}

class URLHandler {
    constructor(attrs) {
        this.attrs = attrs
    }
    text(text) {
        let result = rewriteText(text.text, /':?(\/\/.*?)'/g)
        result = rewriteText(result, /'https?:(\/\/.*?)'/gi)
        if (result != text.text) {
            text.replace(result)
        }
        
    }
	element(element) {
        for (let attr of this.attrs) {
            const href1 = element.getAttribute(attr)
            if (!href1) return
            let href2
            if (attr == "style") {
                href2 = rewriteText(href1,  /url\((.*?)\)/g)
            } else {
                href2 = rewriteURL(href1)
            }
            // console.log('rewrite', href1, href2)
            element.setAttribute(attr, href2)
        }
	}
}

function rewriteURL(originURL) {
    if (!originURL.startsWith("/") && !originURL.startsWith("http")) {
        return originURL
    }
    if (originURL.startsWith("https://")) {
        originURL = originURL.replace("https://", "http://")
    }
    originURL = originURL.replace(///g, "/")
    let fullURL = originURL
    if (originURL.startsWith("//")) {
        fullURL = "http:" + originURL
    } else if (originURL.startsWith("/")) {
        return g_path_pfrefix + originURL
    }
    try {
        const url = new URL(fullURL)
        let host = ''
        if (url.host != UPSTREAM) {
            host = `${RW_START}${url.host.replace(/\./g, "---")}${RW_STOP}`
        }
        const rw = `${g_origin_url.host}${PATH_PREFIX}${host}`
        return originURL.replace(url.host, rw)
    } catch (e) {
        console.error("rewriter error", e, originURL)
        return originURL
    }
}

function restoreURL(rewritedURL) {
    if (rewritedURL.endsWith(PATH_PREFIX) || rewritedURL.endsWith(RW_STOP)) {
        rewritedURL += "/"
    }

    const url = new URL(rewritedURL)
    let pathname = url.pathname
    let pathPrefix, host

    if (pathname.startsWith(PATH_PREFIX)) {
        pathname = pathname.substring(PATH_PREFIX.length)
    }
    
    if (pathname.startsWith(RW_START) && pathname.includes(RW_STOP)) {
        const stop = pathname.indexOf(RW_STOP)
        pathPrefix = PATH_PREFIX + pathname.substring(0, stop + RW_STOP.length)
        host = pathname.substring(RW_START.length, stop).replace(/---/g, ".")
    } else {
        host = UPSTREAM
        pathPrefix = PATH_PREFIX
    }

    return {urlString: rewritedURL.replace(url.protocol, "https:").replace(url.host, host).replace(pathPrefix, ''), 
            pathPrefix: pathPrefix}
}
                    
addEventListener("fetch", event => {
    return event.respondWith(handleRequest(event.request))
})

注：该案例，提供了多维度的改写代码逻辑，并展示了流式和非流式改写方式的结合。