Golang httpserver.NewReplacer函數代碼示例

func (l Logger) ServeHTTP(w http.ResponseWriter, r *http.Request) (int, error) {
	for _, rule := range l.Rules {
		if httpserver.Path(r.URL.Path).Matches(rule.PathScope) {
			// Record the response
			responseRecorder := httpserver.NewResponseRecorder(w)

			// Attach the Replacer we'll use so that other middlewares can
			// set their own placeholders if they want to.
			rep := httpserver.NewReplacer(r, responseRecorder, CommonLogEmptyValue)
			responseRecorder.Replacer = rep

			// Bon voyage, request!
			status, err := l.Next.ServeHTTP(responseRecorder, r)

			if status >= 400 {
				// There was an error up the chain, but no response has been written yet.
				// The error must be handled here so the log entry will record the response size.
				if l.ErrorFunc != nil {
					l.ErrorFunc(responseRecorder, r, status)
				} else {
					// Default failover error handler
					responseRecorder.WriteHeader(status)
					fmt.Fprintf(responseRecorder, "%d %s", status, http.StatusText(status))
				}
				status = 0
			}

			// Write log entry
			rule.Log.Println(rep.Replace(rule.Format))

			return status, err
		}
	}
	return l.Next.ServeHTTP(w, r)
}

// ServeHTTP implements the httpserver.Handler interface and serves requests,
// setting headers on the response according to the configured rules.
func (h Headers) ServeHTTP(w http.ResponseWriter, r *http.Request) (int, error) {
	replacer := httpserver.NewReplacer(r, nil, "")
	rww := &responseWriterWrapper{w: w}
	for _, rule := range h.Rules {
		if httpserver.Path(r.URL.Path).Matches(rule.Path) {
			for name := range rule.Headers {

				// One can either delete a header, add multiple values to a header, or simply
				// set a header.

				if strings.HasPrefix(name, "-") {
					rww.delHeader(strings.TrimLeft(name, "-"))
				} else if strings.HasPrefix(name, "+") {
					for _, value := range rule.Headers[name] {
						rww.Header().Add(strings.TrimLeft(name, "+"), replacer.Replace(value))
					}
				} else {
					for _, value := range rule.Headers[name] {
						rww.Header().Set(name, replacer.Replace(value))
					}
				}
			}
		}
	}
	return h.Next.ServeHTTP(rww, r)
}

// ServeHTTP implements the httpserver.Handler interface.
func (rd Redirect) ServeHTTP(w http.ResponseWriter, r *http.Request) (int, error) {
	for _, rule := range rd.Rules {
		if (rule.FromPath == "/" || r.URL.Path == rule.FromPath) && schemeMatches(rule, r) && rule.Match(r) {
			to := httpserver.NewReplacer(r, nil, "").Replace(rule.To)
			if rule.Meta {
				safeTo := html.EscapeString(to)
				fmt.Fprintf(w, metaRedir, safeTo, safeTo)
			} else {
				http.Redirect(w, r, to, rule.Code)
			}
			return 0, nil
		}
	}
	return rd.Next.ServeHTTP(w, r)
}

// ServeHTTP implements the httpserver.Handler interface and serves requests,
// setting headers on the response according to the configured rules.
func (h Headers) ServeHTTP(w http.ResponseWriter, r *http.Request) (int, error) {
	replacer := httpserver.NewReplacer(r, nil, "")
	for _, rule := range h.Rules {
		if httpserver.Path(r.URL.Path).Matches(rule.Path) {
			for _, header := range rule.Headers {
				if strings.HasPrefix(header.Name, "-") {
					w.Header().Del(strings.TrimLeft(header.Name, "-"))
				} else {
					w.Header().Set(header.Name, replacer.Replace(header.Value))
				}
			}
		}
	}
	return h.Next.ServeHTTP(w, r)
}

func TestReverseProxy(t *testing.T) {
	log.SetOutput(ioutil.Discard)
	defer log.SetOutput(os.Stderr)

	var requestReceived bool
	backend := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		requestReceived = true
		w.Write([]byte("Hello, client"))
	}))
	defer backend.Close()

	// set up proxy
	p := &Proxy{
		Next:      httpserver.EmptyNext, // prevents panic in some cases when test fails
		Upstreams: []Upstream{newFakeUpstream(backend.URL, false)},
	}

	// create request and response recorder
	r, err := http.NewRequest("GET", "/", nil)
	if err != nil {
		t.Fatalf("Failed to create request: %v", err)
	}
	w := httptest.NewRecorder()

	p.ServeHTTP(w, r)

	if !requestReceived {
		t.Error("Expected backend to receive request, but it didn't")
	}

	// Make sure {upstream} placeholder is set
	rr := httpserver.NewResponseRecorder(httptest.NewRecorder())
	rr.Replacer = httpserver.NewReplacer(r, rr, "-")

	p.ServeHTTP(rr, r)

	if got, want := rr.Replacer.Replace("{upstream}"), backend.URL; got != want {
		t.Errorf("Expected custom placeholder {upstream} to be set (%s), but it wasn't; got: %s", want, got)
	}
}

func newReplacer(r *http.Request) httpserver.Replacer {
	return httpserver.NewReplacer(r, nil, "")
}

// ServeHTTP satisfies the httpserver.Handler interface.
func (p Proxy) ServeHTTP(w http.ResponseWriter, r *http.Request) (int, error) {
	// start by selecting most specific matching upstream config
	upstream := p.match(r)
	if upstream == nil {
		return p.Next.ServeHTTP(w, r)
	}

	// this replacer is used to fill in header field values
	replacer := httpserver.NewReplacer(r, nil, "")

	// outreq is the request that makes a roundtrip to the backend
	outreq := createUpstreamRequest(r)

	// since Select() should give us "up" hosts, keep retrying
	// hosts until timeout (or until we get a nil host).
	start := time.Now()
	for time.Now().Sub(start) < tryDuration {
		host := upstream.Select(r)
		if host == nil {
			return http.StatusBadGateway, errUnreachable
		}
		if rr, ok := w.(*httpserver.ResponseRecorder); ok && rr.Replacer != nil {
			rr.Replacer.Set("upstream", host.Name)
		}

		proxy := host.ReverseProxy

		// a backend's name may contain more than just the host,
		// so we parse it as a URL to try to isolate the host.
		if nameURL, err := url.Parse(host.Name); err == nil {
			outreq.Host = nameURL.Host
			if proxy == nil {
				proxy = NewSingleHostReverseProxy(nameURL, host.WithoutPathPrefix, http.DefaultMaxIdleConnsPerHost)
			}

			// use upstream credentials by default
			if outreq.Header.Get("Authorization") == "" && nameURL.User != nil {
				pwd, _ := nameURL.User.Password()
				outreq.SetBasicAuth(nameURL.User.Username(), pwd)
			}
		} else {
			outreq.Host = host.Name
		}
		if proxy == nil {
			return http.StatusInternalServerError, errors.New("proxy for host '" + host.Name + "' is nil")
		}

		// set headers for request going upstream
		if host.UpstreamHeaders != nil {
			// modify headers for request that will be sent to the upstream host
			mutateHeadersByRules(outreq.Header, host.UpstreamHeaders, replacer)
			if hostHeaders, ok := outreq.Header["Host"]; ok && len(hostHeaders) > 0 {
				outreq.Host = hostHeaders[len(hostHeaders)-1]
			}
		}

		// prepare a function that will update response
		// headers coming back downstream
		var downHeaderUpdateFn respUpdateFn
		if host.DownstreamHeaders != nil {
			downHeaderUpdateFn = createRespHeaderUpdateFn(host.DownstreamHeaders, replacer)
		}

		// tell the proxy to serve the request
		atomic.AddInt64(&host.Conns, 1)
		backendErr := proxy.ServeHTTP(w, outreq, downHeaderUpdateFn)
		atomic.AddInt64(&host.Conns, -1)

		// if no errors, we're done here; otherwise failover
		if backendErr == nil {
			return 0, nil
		}
		timeout := host.FailTimeout
		if timeout == 0 {
			timeout = 10 * time.Second
		}
		atomic.AddInt32(&host.Fails, 1)
		go func(host *UpstreamHost, timeout time.Duration) {
			time.Sleep(timeout)
			atomic.AddInt32(&host.Fails, -1)
		}(host, timeout)
	}

	return http.StatusBadGateway, errUnreachable
}

// ServeHTTP satisfies the httpserver.Handler interface.
func (p Proxy) ServeHTTP(w http.ResponseWriter, r *http.Request) (int, error) {
	// start by selecting most specific matching upstream config
	upstream := p.match(r)
	if upstream == nil {
		return p.Next.ServeHTTP(w, r)
	}

	// this replacer is used to fill in header field values
	replacer := httpserver.NewReplacer(r, nil, "")

	// outreq is the request that makes a roundtrip to the backend
	outreq := createUpstreamRequest(r)

	// record and replace outreq body
	body, err := newBufferedBody(outreq.Body)
	if err != nil {
		return http.StatusBadRequest, errors.New("failed to read downstream request body")
	}
	if body != nil {
		outreq.Body = body
	}

	// The keepRetrying function will return true if we should
	// loop and try to select another host, or false if we
	// should break and stop retrying.
	start := time.Now()
	keepRetrying := func() bool {
		// if we've tried long enough, break
		if time.Since(start) >= upstream.GetTryDuration() {
			return false
		}
		// otherwise, wait and try the next available host
		time.Sleep(upstream.GetTryInterval())
		return true
	}

	var backendErr error
	for {
		// since Select() should give us "up" hosts, keep retrying
		// hosts until timeout (or until we get a nil host).
		host := upstream.Select(r)
		if host == nil {
			if backendErr == nil {
				backendErr = errors.New("no hosts available upstream")
			}
			if !keepRetrying() {
				break
			}
			continue
		}
		if rr, ok := w.(*httpserver.ResponseRecorder); ok && rr.Replacer != nil {
			rr.Replacer.Set("upstream", host.Name)
		}

		proxy := host.ReverseProxy

		// a backend's name may contain more than just the host,
		// so we parse it as a URL to try to isolate the host.
		if nameURL, err := url.Parse(host.Name); err == nil {
			outreq.Host = nameURL.Host
			if proxy == nil {
				proxy = NewSingleHostReverseProxy(nameURL, host.WithoutPathPrefix, http.DefaultMaxIdleConnsPerHost)
			}

			// use upstream credentials by default
			if outreq.Header.Get("Authorization") == "" && nameURL.User != nil {
				pwd, _ := nameURL.User.Password()
				outreq.SetBasicAuth(nameURL.User.Username(), pwd)
			}
		} else {
			outreq.Host = host.Name
		}
		if proxy == nil {
			return http.StatusInternalServerError, errors.New("proxy for host '" + host.Name + "' is nil")
		}

		// set headers for request going upstream
		if host.UpstreamHeaders != nil {
			// modify headers for request that will be sent to the upstream host
			mutateHeadersByRules(outreq.Header, host.UpstreamHeaders, replacer)
			if hostHeaders, ok := outreq.Header["Host"]; ok && len(hostHeaders) > 0 {
				outreq.Host = hostHeaders[len(hostHeaders)-1]
			}
		}

		// prepare a function that will update response
		// headers coming back downstream
		var downHeaderUpdateFn respUpdateFn
		if host.DownstreamHeaders != nil {
			downHeaderUpdateFn = createRespHeaderUpdateFn(host.DownstreamHeaders, replacer)
		}

		// rewind request body to its beginning
		if err := body.rewind(); err != nil {
			return http.StatusInternalServerError, errors.New("unable to rewind downstream request body")
		}

		// tell the proxy to serve the request
		atomic.AddInt64(&host.Conns, 1)
//.........這裏部分代碼省略.........

// buildEnv returns a set of CGI environment variables for the request.
func (h Handler) buildEnv(r *http.Request, rule Rule, fpath string) (map[string]string, error) {
	var env map[string]string

	// Get absolute path of requested resource
	absPath := filepath.Join(h.AbsRoot, fpath)

	// Separate remote IP and port; more lenient than net.SplitHostPort
	var ip, port string
	if idx := strings.LastIndex(r.RemoteAddr, ":"); idx > -1 {
		ip = r.RemoteAddr[:idx]
		port = r.RemoteAddr[idx+1:]
	} else {
		ip = r.RemoteAddr
	}

	// Remove [] from IPv6 addresses
	ip = strings.Replace(ip, "[", "", 1)
	ip = strings.Replace(ip, "]", "", 1)

	// Split path in preparation for env variables.
	// Previous rule.canSplit checks ensure this can never be -1.
	splitPos := rule.splitPos(fpath)

	// Request has the extension; path was split successfully
	docURI := fpath[:splitPos+len(rule.SplitPath)]
	pathInfo := fpath[splitPos+len(rule.SplitPath):]
	scriptName := fpath
	scriptFilename := absPath

	// Strip PATH_INFO from SCRIPT_NAME
	scriptName = strings.TrimSuffix(scriptName, pathInfo)

	// Get the request URI. The request URI might be as it came in over the wire,
	// or it might have been rewritten internally by the rewrite middleware (see issue #256).
	// If it was rewritten, there will be a header indicating the original URL,
	// which is needed to get the correct RequestURI value for PHP apps.
	reqURI := r.URL.RequestURI()
	if origURI := r.Header.Get(internalRewriteFieldName); origURI != "" {
		reqURI = origURI
	}

	// Some variables are unused but cleared explicitly to prevent
	// the parent environment from interfering.
	env = map[string]string{

		// Variables defined in CGI 1.1 spec
		"AUTH_TYPE":         "", // Not used
		"CONTENT_LENGTH":    r.Header.Get("Content-Length"),
		"CONTENT_TYPE":      r.Header.Get("Content-Type"),
		"GATEWAY_INTERFACE": "CGI/1.1",
		"PATH_INFO":         pathInfo,
		"QUERY_STRING":      r.URL.RawQuery,
		"REMOTE_ADDR":       ip,
		"REMOTE_HOST":       ip, // For speed, remote host lookups disabled
		"REMOTE_PORT":       port,
		"REMOTE_IDENT":      "", // Not used
		"REMOTE_USER":       "", // Not used
		"REQUEST_METHOD":    r.Method,
		"SERVER_NAME":       h.ServerName,
		"SERVER_PORT":       h.ServerPort,
		"SERVER_PROTOCOL":   r.Proto,
		"SERVER_SOFTWARE":   h.SoftwareName + "/" + h.SoftwareVersion,

		// Other variables
		"DOCUMENT_ROOT":   h.AbsRoot,
		"DOCUMENT_URI":    docURI,
		"HTTP_HOST":       r.Host, // added here, since not always part of headers
		"REQUEST_URI":     reqURI,
		"SCRIPT_FILENAME": scriptFilename,
		"SCRIPT_NAME":     scriptName,
	}

	// compliance with the CGI specification that PATH_TRANSLATED
	// should only exist if PATH_INFO is defined.
	// Info: https://www.ietf.org/rfc/rfc3875 Page 14
	if env["PATH_INFO"] != "" {
		env["PATH_TRANSLATED"] = filepath.Join(h.AbsRoot, pathInfo) // Info: http://www.oreilly.com/openbook/cgi/ch02_04.html
	}

	// Some web apps rely on knowing HTTPS or not
	if r.TLS != nil {
		env["HTTPS"] = "on"
	}

	replacer := httpserver.NewReplacer(r, nil, "")
	// Add env variables from config
	for _, envVar := range rule.EnvVars {
		// replace request placeholders in environment variables
		env[envVar[0]] = replacer.Replace(envVar[1])
	}

	// Add all HTTP headers (except Caddy-Rewrite-Original-URI ) to env variables
	for field, val := range r.Header {
		if strings.ToLower(field) == strings.ToLower(internalRewriteFieldName) {
			continue
		}
		header := strings.ToUpper(field)
		header = headerNameReplacer.Replace(header)
		env["HTTP_"+header] = strings.Join(val, ", ")
//.........這裏部分代碼省略.........

func TestDownstreamHeadersUpdate(t *testing.T) {
	log.SetOutput(ioutil.Discard)
	defer log.SetOutput(os.Stderr)

	backend := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		w.Header().Add("Merge-Me", "Initial")
		w.Header().Add("Remove-Me", "Remove-Value")
		w.Header().Add("Replace-Me", "Replace-Value")
		w.Write([]byte("Hello, client"))
	}))
	defer backend.Close()

	upstream := newFakeUpstream(backend.URL, false)
	upstream.host.DownstreamHeaders = http.Header{
		"+Merge-Me":  {"Merge-Value"},
		"+Add-Me":    {"Add-Value"},
		"-Remove-Me": {""},
		"Replace-Me": {"{hostname}"},
	}
	// set up proxy
	p := &Proxy{
		Next:      httpserver.EmptyNext, // prevents panic in some cases when test fails
		Upstreams: []Upstream{upstream},
	}

	// create request and response recorder
	r, err := http.NewRequest("GET", "/", nil)
	if err != nil {
		t.Fatalf("Failed to create request: %v", err)
	}
	w := httptest.NewRecorder()

	p.ServeHTTP(w, r)

	replacer := httpserver.NewReplacer(r, nil, "")
	actualHeaders := w.Header()

	headerKey := "Merge-Me"
	values, ok := actualHeaders[headerKey]
	if !ok {
		t.Errorf("Downstream response does not contain expected %v header. Expected header should be added", headerKey)
	} else if len(values) < 2 && (values[0] != "Initial" || values[1] != replacer.Replace("{hostname}")) {
		t.Errorf("Values for header `+Merge-Me` should be merged. Got %v", values)
	}

	headerKey = "Add-Me"
	if _, ok := actualHeaders[headerKey]; !ok {
		t.Errorf("Downstream response does not contain expected %v header", headerKey)
	}

	headerKey = "Remove-Me"
	if _, ok := actualHeaders[headerKey]; ok {
		t.Errorf("Downstream response should not contain %v header received from upstream", headerKey)
	}

	headerKey = "Replace-Me"
	headerValue := replacer.Replace("{hostname}")
	value, ok := actualHeaders[headerKey]
	if !ok {
		t.Errorf("Downstream response should contain %v header and not remove it", headerKey)
	} else if len(value) > 0 && headerValue != value[0] {
		t.Errorf("Downstream response should have header %v with value %v. Instead value was %v", headerKey, headerValue, value)
	}

}

func TestUpstreamHeadersUpdate(t *testing.T) {
	log.SetOutput(ioutil.Discard)
	defer log.SetOutput(os.Stderr)

	var actualHeaders http.Header
	var actualHost string
	backend := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		w.Write([]byte("Hello, client"))
		actualHeaders = r.Header
		actualHost = r.Host
	}))
	defer backend.Close()

	upstream := newFakeUpstream(backend.URL, false)
	upstream.host.UpstreamHeaders = http.Header{
		"Connection": {"{>Connection}"},
		"Upgrade":    {"{>Upgrade}"},
		"+Merge-Me":  {"Merge-Value"},
		"+Add-Me":    {"Add-Value"},
		"-Remove-Me": {""},
		"Replace-Me": {"{hostname}"},
		"Host":       {"{>Host}"},
	}
	// set up proxy
	p := &Proxy{
		Next:      httpserver.EmptyNext, // prevents panic in some cases when test fails
		Upstreams: []Upstream{upstream},
	}

	// create request and response recorder
	r, err := http.NewRequest("GET", "/", nil)
	if err != nil {
		t.Fatalf("Failed to create request: %v", err)
	}
	w := httptest.NewRecorder()

	const expectHost = "example.com"
	//add initial headers
	r.Header.Add("Merge-Me", "Initial")
	r.Header.Add("Remove-Me", "Remove-Value")
	r.Header.Add("Replace-Me", "Replace-Value")
	r.Header.Add("Host", expectHost)

	p.ServeHTTP(w, r)

	replacer := httpserver.NewReplacer(r, nil, "")

	headerKey := "Merge-Me"
	values, ok := actualHeaders[headerKey]
	if !ok {
		t.Errorf("Request sent to upstream backend does not contain expected %v header. Expected header to be added", headerKey)
	} else if len(values) < 2 && (values[0] != "Initial" || values[1] != replacer.Replace("{hostname}")) {
		t.Errorf("Values for proxy header `+Merge-Me` should be merged. Got %v", values)
	}

	headerKey = "Add-Me"
	if _, ok := actualHeaders[headerKey]; !ok {
		t.Errorf("Request sent to upstream backend does not contain expected %v header", headerKey)
	}

	headerKey = "Remove-Me"
	if _, ok := actualHeaders[headerKey]; ok {
		t.Errorf("Request sent to upstream backend should not contain %v header", headerKey)
	}

	headerKey = "Replace-Me"
	headerValue := replacer.Replace("{hostname}")
	value, ok := actualHeaders[headerKey]
	if !ok {
		t.Errorf("Request sent to upstream backend should not remove %v header", headerKey)
	} else if len(value) > 0 && headerValue != value[0] {
		t.Errorf("Request sent to upstream backend should replace value of %v header with %v. Instead value was %v", headerKey, headerValue, value)
	}

	if actualHost != expectHost {
		t.Errorf("Request sent to upstream backend should have value of Host with %s, but got %s", expectHost, actualHost)
	}

}

func TestDownstreamHeadersUpdate(t *testing.T) {
	log.SetOutput(ioutil.Discard)
	defer log.SetOutput(os.Stderr)

	backend := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		w.Header().Add("Merge-Me", "Initial")
		w.Header().Add("Remove-Me", "Remove-Value")
		w.Header().Add("Replace-Me", "Replace-Value")
		w.Header().Add("Content-Type", "text/html")
		w.Header().Add("Overwrite-Me", "Overwrite-Value")
		w.Write([]byte("Hello, client"))
	}))
	defer backend.Close()

	upstream := newFakeUpstream(backend.URL, false)
	upstream.host.DownstreamHeaders = http.Header{
		"+Merge-Me":  {"Merge-Value"},
		"+Add-Me":    {"Add-Value"},
		"-Remove-Me": {""},
		"Replace-Me": {"{hostname}"},
	}
	// set up proxy
	p := &Proxy{
		Next:      httpserver.EmptyNext, // prevents panic in some cases when test fails
		Upstreams: []Upstream{upstream},
	}

	// create request and response recorder
	r, err := http.NewRequest("GET", "/", nil)
	if err != nil {
		t.Fatalf("Failed to create request: %v", err)
	}
	w := httptest.NewRecorder()
	// set a predefined skip header
	w.Header().Set("Content-Type", "text/css")
	// set a predefined overwritten header
	w.Header().Set("Overwrite-Me", "Initial")

	p.ServeHTTP(w, r)

	replacer := httpserver.NewReplacer(r, nil, "")
	actualHeaders := w.Header()

	headerKey := "Merge-Me"
	got := actualHeaders[headerKey]
	expect := []string{"Initial", "Merge-Value"}
	if !reflect.DeepEqual(got, expect) {
		t.Errorf("Downstream response does not contain expected %s header: expect %v, but got %v",
			headerKey, expect, got)
	}

	headerKey = "Add-Me"
	got = actualHeaders[headerKey]
	expect = []string{"Add-Value"}
	if !reflect.DeepEqual(got, expect) {
		t.Errorf("Downstream response does not contain expected %s header: expect %v, but got %v",
			headerKey, expect, got)
	}

	headerKey = "Remove-Me"
	if _, ok := actualHeaders[headerKey]; ok {
		t.Errorf("Downstream response should not contain %v header received from upstream", headerKey)
	}

	headerKey = "Replace-Me"
	got = actualHeaders[headerKey]
	expect = []string{replacer.Replace("{hostname}")}
	if !reflect.DeepEqual(got, expect) {
		t.Errorf("Downstream response does not contain expected %s header: expect %v, but got %v",
			headerKey, expect, got)
	}

	headerKey = "Content-Type"
	got = actualHeaders[headerKey]
	expect = []string{"text/css"}
	if !reflect.DeepEqual(got, expect) {
		t.Errorf("Downstream response does not contain expected %s header: expect %v, but got %v",
			headerKey, expect, got)
	}

	headerKey = "Overwrite-Me"
	got = actualHeaders[headerKey]
	expect = []string{"Overwrite-Value"}
	if !reflect.DeepEqual(got, expect) {
		t.Errorf("Downstream response does not contain expected %s header: expect %v, but got %v",
			headerKey, expect, got)
	}
}

func TestUpstreamHeadersUpdate(t *testing.T) {
	log.SetOutput(ioutil.Discard)
	defer log.SetOutput(os.Stderr)

	var actualHeaders http.Header
	var actualHost string
	backend := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		w.Write([]byte("Hello, client"))
		actualHeaders = r.Header
		actualHost = r.Host
	}))
	defer backend.Close()

	upstream := newFakeUpstream(backend.URL, false)
	upstream.host.UpstreamHeaders = http.Header{
		"Connection": {"{>Connection}"},
		"Upgrade":    {"{>Upgrade}"},
		"+Merge-Me":  {"Merge-Value"},
		"+Add-Me":    {"Add-Value"},
		"-Remove-Me": {""},
		"Replace-Me": {"{hostname}"},
		"Host":       {"{>Host}"},
	}
	// set up proxy
	p := &Proxy{
		Next:      httpserver.EmptyNext, // prevents panic in some cases when test fails
		Upstreams: []Upstream{upstream},
	}

	// create request and response recorder
	r, err := http.NewRequest("GET", "/", nil)
	if err != nil {
		t.Fatalf("Failed to create request: %v", err)
	}
	w := httptest.NewRecorder()

	const expectHost = "example.com"
	//add initial headers
	r.Header.Add("Merge-Me", "Initial")
	r.Header.Add("Remove-Me", "Remove-Value")
	r.Header.Add("Replace-Me", "Replace-Value")
	r.Header.Add("Host", expectHost)

	p.ServeHTTP(w, r)

	replacer := httpserver.NewReplacer(r, nil, "")

	headerKey := "Merge-Me"
	got := actualHeaders[headerKey]
	expect := []string{"Initial", "Merge-Value"}
	if !reflect.DeepEqual(got, expect) {
		t.Errorf("Request sent to upstream backend does not contain expected %v header: expect %v, but got %v",
			headerKey, expect, got)
	}

	headerKey = "Add-Me"
	got = actualHeaders[headerKey]
	expect = []string{"Add-Value"}
	if !reflect.DeepEqual(got, expect) {
		t.Errorf("Request sent to upstream backend does not contain expected %v header: expect %v, but got %v",
			headerKey, expect, got)
	}

	headerKey = "Remove-Me"
	if _, ok := actualHeaders[headerKey]; ok {
		t.Errorf("Request sent to upstream backend should not contain %v header", headerKey)
	}

	headerKey = "Replace-Me"
	got = actualHeaders[headerKey]
	expect = []string{replacer.Replace("{hostname}")}
	if !reflect.DeepEqual(got, expect) {
		t.Errorf("Request sent to upstream backend does not contain expected %v header: expect %v, but got %v",
			headerKey, expect, got)
	}

	if actualHost != expectHost {
		t.Errorf("Request sent to upstream backend should have value of Host with %s, but got %s", expectHost, actualHost)
	}

}