source: code/trunk/morty.go@ 51

package main

import (
        "bytes"
        "crypto/hmac"
        "crypto/sha256"
        "encoding/hex"
        "errors"
        "flag"
        "fmt"
        "io"
        "log"
        "net/url"
        "regexp"
        "strings"
        "time"

        "github.com/valyala/fasthttp"
        "golang.org/x/net/html"
        "golang.org/x/net/html/charset"
        "golang.org/x/text/encoding"
)

const (
        STATE_DEFAULT     int = 0
        STATE_IN_STYLE    int = 1
        STATE_IN_NOSCRIPT int = 2
)

var CLIENT *fasthttp.Client = &fasthttp.Client{
        MaxResponseBodySize: 10 * 1024 * 1024, // 10M
}

var CSS_URL_REGEXP *regexp.Regexp = regexp.MustCompile("url\\((['\"]?)[ \\t\\f]*([\u0009\u0021\u0023-\u0026\u0028\u002a-\u007E]+)(['\"]?)\\)?")

var UNSAFE_ELEMENTS [][]byte = [][]byte{
        []byte("applet"),
        []byte("canvas"),
        []byte("embed"),
        //[]byte("iframe"),
        []byte("math"),
        []byte("script"),
        []byte("svg"),
}

var SAFE_ATTRIBUTES [][]byte = [][]byte{
        []byte("abbr"),
        []byte("accesskey"),
        []byte("align"),
        []byte("alt"),
        []byte("as"),
        []byte("autocomplete"),
        []byte("charset"),
        []byte("checked"),
        []byte("class"),
        []byte("content"),
        []byte("contenteditable"),
        []byte("contextmenu"),
        []byte("dir"),
        []byte("for"),
        []byte("height"),
        []byte("hidden"),
        []byte("hreflang"),
        []byte("id"),
        []byte("lang"),
        []byte("media"),
        []byte("method"),
        []byte("name"),
        []byte("nowrap"),
        []byte("placeholder"),
        []byte("property"),
        []byte("rel"),
        []byte("spellcheck"),
        []byte("tabindex"),
        []byte("target"),
        []byte("title"),
        []byte("translate"),
        []byte("type"),
        []byte("value"),
        []byte("width"),
}

var SELF_CLOSING_ELEMENTS [][]byte = [][]byte{
        []byte("area"),
        []byte("base"),
        []byte("br"),
        []byte("col"),
        []byte("embed"),
        []byte("hr"),
        []byte("img"),
        []byte("input"),
        []byte("keygen"),
        []byte("link"),
        []byte("meta"),
        []byte("param"),
        []byte("source"),
        []byte("track"),
        []byte("wbr"),
}

var LINK_REL_SAFE_VALUES [][]byte = [][]byte{
        []byte("alternate"),
        []byte("archives"),
        []byte("author"),
        []byte("copyright"),
        []byte("first"),
        []byte("help"),
        []byte("icon"),
        []byte("index"),
        []byte("last"),
        []byte("license"),
        []byte("manifest"),
        []byte("next"),
        []byte("pingback"),
        []byte("prev"),
        []byte("publisher"),
        []byte("search"),
        []byte("shortcut icon"),
        []byte("stylesheet"),
        []byte("up"),
}

var LINK_HTTP_EQUIV_SAFE_VALUES [][]byte = [][]byte{
        // X-UA-Compatible will be added automaticaly, so it can be skipped
        []byte("date"),
        []byte("last-modified"),
        []byte("refresh"), // URL rewrite
        // []byte("location"), TODO URL rewrite
        []byte("content-language"),
}

type Proxy struct {
        Key            []byte
        RequestTimeout time.Duration
}

type RequestConfig struct {
        Key     []byte
        BaseURL *url.URL
}

var HTML_FORM_EXTENSION string = `<input type="hidden" name="mortyurl" value="%s" /><input type="hidden" name="mortyhash" value="%s" />`

var HTML_BODY_EXTENSION string = `
<div id="mortyheader">
  <input type="checkbox" id="mortytoggle" autocomplete="off" />
  <div><p>This is a proxified and sanitized view of the page,<br />visit <a href="%s" rel="noreferrer">original site</a>.</p><p><label for="mortytoggle">hide</label></p></div>
</div>
<style>
#mortyheader { position: fixed; padding: 12px 12px 12px 0; margin: 0; box-sizing: content-box; top: 15%%; left: 0; max-width: 140px; color: #444; overflow: hidden; z-index: 110000; font-size: 12px; line-height: normal; }
#mortyheader a { color: #3498db; font-weight: bold; }
#mortyheader p { padding: 0 0 0.7em 0; margin: 0; }
#mortyheader > div { padding: 8px; font-size: 12px !important; font-family: sans !important; border-width: 4px 4px 4px 0; border-style: solid; border-color: #1abc9c; background: #FFF; line-height: 1em; }
#mortyheader label { text-align: right; cursor: pointer; display: block; color: #444; padding: 0; margin: 0; }
input[type=checkbox]#mortytoggle { display: none; }
input[type=checkbox]#mortytoggle:checked ~ div { display: none; }
</style>
`

var HTML_HEAD_CONTENT_TYPE string = `<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
`

func (p *Proxy) RequestHandler(ctx *fasthttp.RequestCtx) {

        if appRequestHandler(ctx) {
                return
        }

        requestHash := popRequestParam(ctx, []byte("mortyhash"))

        requestURI := popRequestParam(ctx, []byte("mortyurl"))

        if requestURI == nil {
                p.serveMainPage(ctx, 200, nil)
                return
        }

        if p.Key != nil {
                if !verifyRequestURI(requestURI, requestHash, p.Key) {
                        // HTTP status code 403 : Forbidden
                        p.serveMainPage(ctx, 403, errors.New(`invalid "mortyhash" parameter`))
                        return
                }
        }

        parsedURI, err := url.Parse(string(requestURI))

        if strings.HasSuffix(parsedURI.Host, ".onion") {
                // HTTP status code 501 : Not Implemented
                p.serveMainPage(ctx, 501, errors.New("Tor urls are not supported yet"))
                return
        }

        if err != nil {
                // HTTP status code 500 : Internal Server Error
                p.serveMainPage(ctx, 500, err)
                return
        }

        req := fasthttp.AcquireRequest()
        defer fasthttp.ReleaseRequest(req)
        req.SetConnectionClose()

        requestURIStr := string(requestURI)

        log.Println("getting", requestURIStr)

        req.SetRequestURI(requestURIStr)
        req.Header.SetUserAgentBytes([]byte("Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/53.0.2785.143 Safari/537.36"))

        resp := fasthttp.AcquireResponse()
        defer fasthttp.ReleaseResponse(resp)

        req.Header.SetMethodBytes(ctx.Method())
        if ctx.IsPost() || ctx.IsPut() {
                req.SetBody(ctx.PostBody())
        }

        err = CLIENT.DoTimeout(req, resp, p.RequestTimeout)

        if err != nil {
                if err == fasthttp.ErrTimeout {
                        // HTTP status code 504 : Gateway Time-Out
                        p.serveMainPage(ctx, 504, err)
                } else {
                        // HTTP status code 500 : Internal Server Error
                        p.serveMainPage(ctx, 500, err)
                }
                return
        }

        if resp.StatusCode() != 200 {
                switch resp.StatusCode() {
                case 301, 302, 303, 307, 308:
                        loc := resp.Header.Peek("Location")
                        if loc != nil {
                                rc := &RequestConfig{Key: p.Key, BaseURL: parsedURI}
                                url, err := rc.ProxifyURI(string(loc))
                                if err == nil {
                                        ctx.SetStatusCode(resp.StatusCode())
                                        ctx.Response.Header.Add("Location", url)
                                        log.Println("redirect to", string(loc))
                                        return
                                }
                        }
                }
                error_message := fmt.Sprintf("invalid response: %d (%s)", resp.StatusCode(), requestURIStr)
                p.serveMainPage(ctx, resp.StatusCode(), errors.New(error_message))
                return
        }

        contentType := resp.Header.Peek("Content-Type")

        if contentType == nil {
                // HTTP status code 503 : Service Unavailable
                p.serveMainPage(ctx, 503, errors.New("invalid content type"))
                return
        }

        if bytes.Contains(bytes.ToLower(contentType), []byte("javascript")) {
                // HTTP status code 403 : Forbidden
                p.serveMainPage(ctx, 403, errors.New("forbidden content type"))
                return
        }

        contentInfo := bytes.SplitN(contentType, []byte(";"), 2)

        var responseBody []byte

        if len(contentInfo) == 2 && bytes.Contains(contentInfo[0], []byte("text")) {
                e, ename, _ := charset.DetermineEncoding(resp.Body(), string(contentType))
                if (e != encoding.Nop) && (!strings.EqualFold("utf-8", ename)) {
                        responseBody, err = e.NewDecoder().Bytes(resp.Body())
                        if err != nil {
                                // HTTP status code 503 : Service Unavailable
                                p.serveMainPage(ctx, 503, err)
                                return
                        }
                } else {
                        responseBody = resp.Body()
                }
        } else {
                responseBody = resp.Body()
        }

        ctx.SetContentType(fmt.Sprintf("%s; charset=UTF-8", contentInfo[0]))

        switch {
        case bytes.Contains(contentType, []byte("css")):
                sanitizeCSS(&RequestConfig{Key: p.Key, BaseURL: parsedURI}, ctx, responseBody)
        case bytes.Contains(contentType, []byte("html")):
                sanitizeHTML(&RequestConfig{Key: p.Key, BaseURL: parsedURI}, ctx, responseBody)
        default:
                if ctx.Request.Header.Peek("Content-Disposition") != nil {
                        ctx.Response.Header.AddBytesV("Content-Disposition", ctx.Request.Header.Peek("Content-Disposition"))
                }
                ctx.Write(responseBody)
        }
}

func appRequestHandler(ctx *fasthttp.RequestCtx) bool {
        // serve robots.txt
        if bytes.Equal(ctx.Path(), []byte("/robots.txt")) {
                ctx.SetContentType("text/plain")
                ctx.Write([]byte("User-Agent: *\nDisallow: /\n"))
                return true
        }

        return false
}

func popRequestParam(ctx *fasthttp.RequestCtx, paramName []byte) []byte {
        param := ctx.QueryArgs().PeekBytes(paramName)

        if param == nil {
                param = ctx.PostArgs().PeekBytes(paramName)
                if param != nil {
                        ctx.PostArgs().DelBytes(paramName)
                }
        } else {
                ctx.QueryArgs().DelBytes(paramName)
        }

        return param
}

func sanitizeCSS(rc *RequestConfig, out io.Writer, css []byte) {
        // TODO

        urlSlices := CSS_URL_REGEXP.FindAllSubmatchIndex(css, -1)

        if urlSlices == nil {
                out.Write(css)
                return
        }

        startIndex := 0

        for _, s := range urlSlices {
                urlStart := s[4]
                urlEnd := s[5]

                if uri, err := rc.ProxifyURI(string(css[urlStart:urlEnd])); err == nil {
                        out.Write(css[startIndex:urlStart])
                        out.Write([]byte(uri))
                        startIndex = urlEnd
                } else {
                        log.Println("cannot proxify css uri:", string(css[urlStart:urlEnd]))
                }
        }
        if startIndex < len(css) {
                out.Write(css[startIndex:len(css)])
        }
}

func sanitizeHTML(rc *RequestConfig, out io.Writer, htmlDoc []byte) {
        r := bytes.NewReader(htmlDoc)
        decoder := html.NewTokenizer(r)
        decoder.AllowCDATA(true)

        unsafeElements := make([][]byte, 0, 8)
        state := STATE_DEFAULT
        for {
                token := decoder.Next()
                if token == html.ErrorToken {
                        err := decoder.Err()
                        if err != io.EOF {
                                log.Println("failed to parse HTML:")
                        }
                        break
                }

                if len(unsafeElements) == 0 {

                        switch token {
                        case html.StartTagToken, html.SelfClosingTagToken:
                                tag, hasAttrs := decoder.TagName()
                                safe := !inArray(tag, UNSAFE_ELEMENTS)
                                if !safe {
                                        if !inArray(tag, SELF_CLOSING_ELEMENTS) {
                                                var unsafeTag []byte = make([]byte, len(tag))
                                                copy(unsafeTag, tag)
                                                unsafeElements = append(unsafeElements, unsafeTag)
                                        }
                                        break
                                }
                                if bytes.Equal(tag, []byte("base")) {
                                        for {
                                                attrName, attrValue, moreAttr := decoder.TagAttr()
                                                if bytes.Equal(attrName, []byte("href")) {
                                                        parsedURI, err := url.Parse(string(attrValue))
                                                        if err == nil {
                                                                rc.BaseURL = parsedURI
                                                        }
                                                }
                                                if !moreAttr {
                                                        break
                                                }
                                        }
                                        break
                                }
                                if bytes.Equal(tag, []byte("noscript")) {
                                        state = STATE_IN_NOSCRIPT
                                        break
                                }
                                var attrs [][][]byte
                                if hasAttrs {
                                        for {
                                                attrName, attrValue, moreAttr := decoder.TagAttr()
                                                attrs = append(attrs, [][]byte{
                                                        attrName,
                                                        attrValue,
                                                        []byte(html.EscapeString(string(attrValue))),
                                                })
                                                if !moreAttr {
                                                        break
                                                }
                                        }
                                }
                                if bytes.Equal(tag, []byte("link")) {
                                        sanitizeLinkTag(rc, out, attrs)
                                        break
                                }

                                if bytes.Equal(tag, []byte("meta")) {
                                        sanitizeMetaTag(rc, out, attrs)
                                        break
                                }

                                fmt.Fprintf(out, "<%s", tag)

                                if hasAttrs {
                                        sanitizeAttrs(rc, out, attrs)
                                }

                                if token == html.SelfClosingTagToken {
                                        fmt.Fprintf(out, " />")
                                } else {
                                        fmt.Fprintf(out, ">")
                                        if bytes.Equal(tag, []byte("style")) {
                                                state = STATE_IN_STYLE
                                        }
                                }

                                if bytes.Equal(tag, []byte("head")) {
                                        fmt.Fprintf(out, HTML_HEAD_CONTENT_TYPE)
                                }

                                if bytes.Equal(tag, []byte("form")) {
                                        var formURL *url.URL
                                        for _, attr := range attrs {
                                                if bytes.Equal(attr[0], []byte("action")) {
                                                        formURL, _ = url.Parse(string(attr[1]))
                                                        formURL = mergeURIs(rc.BaseURL, formURL)
                                                        break
                                                }
                                        }
                                        if formURL == nil {
                                                formURL = rc.BaseURL
                                        }
                                        urlStr := formURL.String()
                                        var key string
                                        if rc.Key != nil {
                                                key = hash(urlStr, rc.Key)
                                        }
                                        fmt.Fprintf(out, HTML_FORM_EXTENSION, urlStr, key)

                                }

                        case html.EndTagToken:
                                tag, _ := decoder.TagName()
                                writeEndTag := true
                                switch string(tag) {
                                case "body":
                                        fmt.Fprintf(out, HTML_BODY_EXTENSION, rc.BaseURL.String())
                                case "style":
                                        state = STATE_DEFAULT
                                case "noscript":
                                        state = STATE_DEFAULT
                                        writeEndTag = false
                                }
                                // skip noscript tags - only the tag, not the content, because javascript is sanitized
                                if writeEndTag {
                                        fmt.Fprintf(out, "</%s>", tag)
                                }

                        case html.TextToken:
                                switch state {
                                case STATE_DEFAULT:
                                        fmt.Fprintf(out, "%s", decoder.Raw())
                                case STATE_IN_STYLE:
                                        sanitizeCSS(rc, out, decoder.Raw())
                                case STATE_IN_NOSCRIPT:
                                        sanitizeHTML(rc, out, decoder.Raw())
                                }

                        case html.DoctypeToken, html.CommentToken:
                                out.Write(decoder.Raw())
                        }
                } else {
                        switch token {
                        case html.StartTagToken:
                                tag, _ := decoder.TagName()
                                if inArray(tag, UNSAFE_ELEMENTS) {
                                        unsafeElements = append(unsafeElements, tag)
                                }

                        case html.EndTagToken:
                                tag, _ := decoder.TagName()
                                if bytes.Equal(unsafeElements[len(unsafeElements)-1], tag) {
                                        unsafeElements = unsafeElements[:len(unsafeElements)-1]
                                }
                        }
                }
        }
}

func sanitizeLinkTag(rc *RequestConfig, out io.Writer, attrs [][][]byte) {
        exclude := false
        for _, attr := range attrs {
                attrName := attr[0]
                attrValue := attr[1]
                if bytes.Equal(attrName, []byte("rel")) {
                        if !inArray(attrValue, LINK_REL_SAFE_VALUES) {
                                exclude = true
                                break
                        }
                }
                if bytes.Equal(attrName, []byte("as")) {
                        if bytes.Equal(attrValue, []byte("script")) {
                                exclude = true
                                break
                        }
                }
        }

        if !exclude {
                out.Write([]byte("<link"))
                for _, attr := range attrs {
                        sanitizeAttr(rc, out, attr[0], attr[1], attr[2])
                }
                out.Write([]byte(">"))
        }
}

func sanitizeMetaTag(rc *RequestConfig, out io.Writer, attrs [][][]byte) {
        var http_equiv []byte
        var content []byte

        for _, attr := range attrs {
                attrName := attr[0]
                attrValue := attr[1]
                if bytes.Equal(attrName, []byte("http-equiv")) {
                        http_equiv = bytes.ToLower(attrValue)
                        // exclude some <meta http-equiv="..." ..>
                        if !inArray(http_equiv, LINK_HTTP_EQUIV_SAFE_VALUES) {
                                return
                        }
                }
                if bytes.Equal(attrName, []byte("content")) {
                        content = attrValue
                }
                if bytes.Equal(attrName, []byte("charset")) {
                        // exclude <meta charset="...">
                        return
                }
        }

        out.Write([]byte("<meta"))
        urlIndex := bytes.Index(bytes.ToLower(content), []byte("url="))
        if bytes.Equal(http_equiv, []byte("refresh")) && urlIndex != -1 {
                contentUrl := content[urlIndex+4:]
                // special case of <meta http-equiv="refresh" content="0; url='example.com/url.with.quote.outside'">
                if len(contentUrl) >= 2 && (contentUrl[0] == byte('\'') || contentUrl[0] == byte('"')) {
                        if contentUrl[0] == contentUrl[len(contentUrl)-1] {
                                contentUrl = contentUrl[1 : len(contentUrl)-1]
                        }
                }
                // output proxify result
                if uri, err := rc.ProxifyURI(string(contentUrl)); err == nil {
                        fmt.Fprintf(out, ` http-equiv="refresh" content="%surl=%s"`, content[:urlIndex], uri)
                }
        } else {
                if len(http_equiv) > 0 {
                        fmt.Fprintf(out, ` http-equiv="%s"`, http_equiv)
                }
                sanitizeAttrs(rc, out, attrs)
        }
        out.Write([]byte(">"))
}

func sanitizeAttrs(rc *RequestConfig, out io.Writer, attrs [][][]byte) {
        for _, attr := range attrs {
                sanitizeAttr(rc, out, attr[0], attr[1], attr[2])
        }
}

func sanitizeAttr(rc *RequestConfig, out io.Writer, attrName, attrValue, escapedAttrValue []byte) {
        if inArray(attrName, SAFE_ATTRIBUTES) {
                fmt.Fprintf(out, " %s=\"%s\"", attrName, escapedAttrValue)
                return
        }
        switch string(attrName) {
        case "src", "href", "action":
                if uri, err := rc.ProxifyURI(string(attrValue)); err == nil {
                        fmt.Fprintf(out, " %s=\"%s\"", attrName, uri)
                } else {
                        log.Println("cannot proxify uri:", string(attrValue))
                }
        case "style":
                cssAttr := bytes.NewBuffer(nil)
                sanitizeCSS(rc, cssAttr, attrValue)
                fmt.Fprintf(out, " %s=\"%s\"", attrName, html.EscapeString(string(cssAttr.Bytes())))
        }
}

func mergeURIs(u1, u2 *url.URL) *url.URL {
        return u1.ResolveReference(u2)
}

func (rc *RequestConfig) ProxifyURI(uri string) (string, error) {
        // remove javascript protocol
        if strings.HasPrefix(uri, "javascript:") {
                return "", nil
        }

        // TODO check malicious data: - e.g. data:script
        if strings.HasPrefix(uri, "data:") {
                return uri, nil
        }

        // parse the uri
        u, err := url.Parse(uri)
        if err != nil {
                return "", err
        }

        // get the fragment (with the prefix "#")
        fragment := ""
        if len(u.Fragment) > 0 {
                fragment = "#" + u.Fragment
        }

        // reset the fragment: it is not included in the mortyurl
        u.Fragment = ""

        // merge the URI with the document URI
        u = mergeURIs(rc.BaseURL, u)

        // simple internal link ?
        // some web pages describe the whole link https://same:auth@same.host/same.path?same.query#new.fragment
        if u.Scheme == rc.BaseURL.Scheme &&
                ((u.User == nil && rc.BaseURL.User == nil) || (u.User.String() == rc.BaseURL.User.String())) &&
                u.Host == rc.BaseURL.Host &&
                u.Path == rc.BaseURL.Path &&
                u.RawQuery == rc.BaseURL.RawQuery {
                // the fragment is the only difference between the document URI and the uri parameter
                return fragment, nil
        }

        // return full URI and fragment (if not empty)
        uri = u.String()

        if rc.Key == nil {
                return fmt.Sprintf("./?mortyurl=%s%s", url.QueryEscape(uri), fragment), nil
        }
        return fmt.Sprintf("./?mortyhash=%s&mortyurl=%s%s", hash(uri, rc.Key), url.QueryEscape(uri), fragment), nil
}

func inArray(b []byte, a [][]byte) bool {
        for _, b2 := range a {
                if bytes.Equal(b, b2) {
                        return true
                }
        }
        return false
}

func hash(msg string, key []byte) string {
        mac := hmac.New(sha256.New, key)
        mac.Write([]byte(msg))
        return hex.EncodeToString(mac.Sum(nil))
}

func verifyRequestURI(uri, hashMsg, key []byte) bool {
        h := make([]byte, hex.DecodedLen(len(hashMsg)))
        _, err := hex.Decode(h, hashMsg)
        if err != nil {
                log.Println("hmac error:", err)
                return false
        }
        mac := hmac.New(sha256.New, key)
        mac.Write(uri)
        return hmac.Equal(h, mac.Sum(nil))
}

func (p *Proxy) serveMainPage(ctx *fasthttp.RequestCtx, statusCode int, err error) {
        ctx.SetContentType("text/html")
        ctx.SetStatusCode(statusCode)
        ctx.Write([]byte(`<!doctype html>
<head>
<title>MortyProxy</title>
<meta name="viewport" content="width=device-width, initial-scale=1 , maximum-scale=1.0, user-scalable=1" />
<style>
html { height: 100%; }
body { min-height : 100%; display: flex; flex-direction:column; font-family: 'Garamond', 'Georgia', serif; text-align: center; color: #444; background: #FAFAFA; margin: 0; padding: 0; font-size: 1.1em; }
input { border: 1px solid #888; padding: 0.3em; color: #444; background: #FFF; font-size: 1.1em; }
input[placeholder] { width:80%; }
a { text-decoration: none; #2980b9; }
h1, h2 { font-weight: 200; margin-bottom: 2rem; }
h1 { font-size: 3em; }
.container { flex:1; min-height: 100%; margin-bottom: 1em; }
.footer { margin: 1em; }
.footer p { font-size: 0.8em; }
</style>
</head>
<body>
        <div class="container">
                <h1>MortyProxy</h1>
`))
        if err != nil {
                log.Println("error:", err)
                ctx.Write([]byte("<h2>Error: "))
                ctx.Write([]byte(html.EscapeString(err.Error())))
                ctx.Write([]byte("</h2>"))
        }
        if p.Key == nil {
                ctx.Write([]byte(`
                <form action="post">
                Visit url: <input placeholder="https://url.." name="mortyurl" autofocus />
                <input type="submit" value="go" />
                </form>`))
        } else {
                ctx.Write([]byte(`<h3>Warning! This instance does not support direct URL opening.</h3>`))
        }
        ctx.Write([]byte(`
        </div>
        <div class="footer">
                <p>Morty rewrites web pages to exclude malicious HTML tags and CSS/HTML attributes. It also replaces external resource references to prevent third-party information leaks.<br />
                <a href="https://github.com/asciimoo/morty">view on github</a>
                </p>
        </div>
</body>
</html>`))
}

func main() {

        listen := flag.String("listen", "127.0.0.1:3000", "Listen address")
        key := flag.String("key", "", "HMAC url validation key (hexadecimal encoded) - leave blank to disable")
        ipv6 := flag.Bool("ipv6", false, "Allow IPv6 HTTP requests")
        requestTimeout := flag.Uint("timeout", 2, "Request timeout")
        flag.Parse()

        if *ipv6 {
                CLIENT.Dial = fasthttp.DialDualStack
        }

        p := &Proxy{RequestTimeout: time.Duration(*requestTimeout) * time.Second}

        if *key != "" {
                p.Key = []byte(*key)
        }

        log.Println("listening on", *listen)

        if err := fasthttp.ListenAndServe(*listen, p.RequestHandler); err != nil {
                log.Fatal("Error in ListenAndServe:", err)
        }
}