Add repeat option support

Add an option to repeat the same request multiple times, reusing the
same HTTP connection.

To have accurate measurement of TLS and support skipped steps (DNS, TCP
and TLS reuse), the timing code has been refactored to use Go 1.8
support for TLS tracing as well as a more descriptive variable namings
for steps time.

This commit removes support for Go versions lower than 1.8.

main.go

@@ -52,6 +52,7 @@ var (
 	// Command line flags.
 	httpMethod      string
 	postBody        string
+	repeat          int
 	followRedirects bool
 	onlyHeader      bool
 	insecure        bool
@@ -72,6 +73,7 @@ const maxRedirects = 10
 func init() {
 	flag.StringVar(&httpMethod, "X", "GET", "HTTP method to use")
 	flag.StringVar(&postBody, "d", "", "the body of a POST or PUT request; from file use @filename")
+	flag.IntVar(&repeat, "r", 0, "Repeat the same request N times on the same connection")
 	flag.BoolVar(&followRedirects, "L", false, "follow 30x redirects")
 	flag.BoolVar(&onlyHeader, "I", false, "don't read body of request")
 	flag.BoolVar(&insecure, "k", false, "allow insecure SSL connections")
@@ -127,8 +129,11 @@ func main() {
 	}
 
 	url := parseURL(args[0])
+	tr := newTransport(url)
 
-	visit(url)
+	for i := repeat + 1; i > 0; i-- {
+		visit(tr, url)
+	}
 }
 
 // readClientCert - helper function to read client certificate
@@ -197,9 +202,42 @@ func headerKeyValue(h string) (string, string) {
 	return strings.TrimRight(h[:i], " "), strings.TrimLeft(h[i:], " :")
 }
 
+func newTransport(url *url.URL) *http.Transport {
+	tr := &http.Transport{
+		Proxy:                 http.ProxyFromEnvironment,
+		MaxIdleConns:          100,
+		IdleConnTimeout:       90 * time.Second,
+		TLSHandshakeTimeout:   10 * time.Second,
+		ExpectContinueTimeout: 1 * time.Second,
+	}
+
+	switch url.Scheme {
+	case "https":
+		host, _, err := net.SplitHostPort(url.Host)
+		if err != nil {
+			host = url.Host
+		}
+
+		tr.TLSClientConfig = &tls.Config{
+			ServerName:         host,
+			InsecureSkipVerify: insecure,
+			Certificates:       readClientCert(clientCertFile),
+		}
+
+		// Because we create a custom TLSClientConfig, we have to opt-in to HTTP/2.
+		// See https://github.com/golang/go/issues/14275
+		err = http2.ConfigureTransport(tr)
+		if err != nil {
+			log.Fatalf("failed to prepare transport for HTTP/2: %v", err)
+		}
+	}
+
+	return tr
+}
+
 // visit visits a url and times the interaction.
 // If the response is a 30x, visit follows the redirect.
-func visit(url *url.URL) {
+func visit(tr *http.Transport, url *url.URL) {
 	req := newRequest(httpMethod, url, postBody)
 
 	var tStart, tDNSStart, tDNSEnd, tConnectStart, tConnectEnd, tTLSStart, tTLSEnd, tConnected, tTTBF, tDone time.Time
@@ -229,35 +267,6 @@ func visit(url *url.URL) {
 	}
 	req = req.WithContext(httptrace.WithClientTrace(context.Background(), trace))
 
-	tr := &http.Transport{
-		Proxy:                 http.ProxyFromEnvironment,
-		MaxIdleConns:          100,
-		IdleConnTimeout:       90 * time.Second,
-		TLSHandshakeTimeout:   10 * time.Second,
-		ExpectContinueTimeout: 1 * time.Second,
-	}
-
-	switch url.Scheme {
-	case "https":
-		host, _, err := net.SplitHostPort(req.Host)
-		if err != nil {
-			host = req.Host
-		}
-
-		tr.TLSClientConfig = &tls.Config{
-			ServerName:         host,
-			InsecureSkipVerify: insecure,
-			Certificates:       readClientCert(clientCertFile),
-		}
-
-		// Because we create a custom TLSClientConfig, we have to opt-in to HTTP/2.
-		// See https://github.com/golang/go/issues/14275
-		err = http2.ConfigureTransport(tr)
-		if err != nil {
-			log.Fatalf("failed to prepare transport for HTTP/2: %v", err)
-		}
-	}
-
 	client := &http.Client{
 		Transport: tr,
 		CheckRedirect: func(req *http.Request, via []*http.Request) error {
@@ -363,7 +372,7 @@ func visit(url *url.URL) {
 			log.Fatalf("maximum number of redirects (%d) followed", maxRedirects)
 		}
 
-		visit(loc)
+		visit(tr, loc)
 	}
 }