Add Go 1.8 TLS tracing support & refactor timing code

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

@@ -221,29 +221,30 @@ func dialContext(network string) func(ctx context.Context, network, addr string)
 func visit(url *url.URL) {
 	req := newRequest(httpMethod, url, postBody)
 
-	var t0, t1, t2, t3, t4, t5, t6 time.Time
+	var tStart, tDNSStart, tDNSEnd, tConnectStart, tConnectEnd, tTLSStart, tTLSEnd, tConnected, tTTBF, tDone time.Time
 
 	trace := &httptrace.ClientTrace{
-		DNSStart: func(_ httptrace.DNSStartInfo) { t0 = time.Now() },
-		DNSDone:  func(_ httptrace.DNSDoneInfo) { t1 = time.Now() },
+		GetConn:  func(_ string) { tStart = time.Now() },
+		DNSStart: func(_ httptrace.DNSStartInfo) { tDNSStart = time.Now() },
+		DNSDone:  func(_ httptrace.DNSDoneInfo) { tDNSEnd = time.Now() },
 		ConnectStart: func(_, _ string) {
-			if t1.IsZero() {
+			if tConnectStart.IsZero() {
 				// connecting to IP
-				t1 = time.Now()
+				tConnectStart = time.Now()
 			}
 		},
 		ConnectDone: func(net, addr string, err error) {
 			if err != nil {
 				log.Fatalf("unable to connect to host %v: %v", addr, err)
 			}
-			t2 = time.Now()
+			tConnectEnd = time.Now()
 
 			printf("\n%s%s\n", color.GreenString("Connected to "), color.CyanString(addr))
 		},
-		GotConn:              func(_ httptrace.GotConnInfo) { t3 = time.Now() },
-		GotFirstResponseByte: func() { t4 = time.Now() },
-		TLSHandshakeStart:    func() { t5 = time.Now() },
-		TLSHandshakeDone:     func(_ tls.ConnectionState, _ error) { t6 = time.Now() },
+		TLSHandshakeStart:    func() { tTLSStart = time.Now() },
+		TLSHandshakeDone:     func(_ tls.ConnectionState, _ error) { tTLSEnd = time.Now() },
+		GotConn:              func(_ httptrace.GotConnInfo) { tConnected = time.Now() },
+		GotFirstResponseByte: func() { tTTBF = time.Now() },
 	}
 	req = req.WithContext(httptrace.WithClientTrace(context.Background(), trace))
 
@@ -300,10 +301,18 @@ func visit(url *url.URL) {
 	bodyMsg := readResponseBody(req, resp)
 	resp.Body.Close()
 
-	t7 := time.Now() // after read body
-	if t0.IsZero() {
-		// we skipped DNS
-		t0 = t1
+	tDone = time.Now() // after read body
+	if tDNSStart.IsZero() {
+		tDNSStart = tStart
+		tDNSEnd = tStart
+	}
+	if tConnectStart.IsZero() {
+		tConnectStart = tStart
+		tConnectEnd = tStart
+	}
+	if tTLSStart.IsZero() {
+		tTLSStart = tStart
+		tTLSEnd = tStart
 	}
 
 	// print status line and headers
@@ -341,27 +350,27 @@ func visit(url *url.URL) {
 	switch url.Scheme {
 	case "https":
 		printf(colorize(HTTPSTemplate),
-			fmta(t1.Sub(t0)), // dns lookup
-			fmta(t2.Sub(t1)), // tcp connection
-			fmta(t6.Sub(t5)), // tls handshake
-			fmta(t4.Sub(t3)), // server processing
-			fmta(t7.Sub(t4)), // content transfer
-			fmtb(t1.Sub(t0)), // namelookup
-			fmtb(t2.Sub(t0)), // connect
-			fmtb(t3.Sub(t0)), // pretransfer
-			fmtb(t4.Sub(t0)), // starttransfer
-			fmtb(t7.Sub(t0)), // total
+			fmta(tDNSEnd.Sub(tDNSStart)),         // dns lookup
+			fmta(tConnectEnd.Sub(tConnectStart)), // tcp connection
+			fmta(tTLSEnd.Sub(tTLSStart)),         // tls handshake
+			fmta(tTTBF.Sub(tConnected)),          // server processing
+			fmta(tDone.Sub(tTTBF)),               // content transfer
+			fmtb(tDNSEnd.Sub(tStart)),            // namelookup
+			fmtb(tConnectEnd.Sub(tStart)),        // connect
+			fmtb(tConnected.Sub(tStart)),         // pretransfer
+			fmtb(tTTBF.Sub(tStart)),              // starttransfer
+			fmtb(tDone.Sub(tStart)),              // total
 		)
 	case "http":
 		printf(colorize(HTTPTemplate),
-			fmta(t1.Sub(t0)), // dns lookup
-			fmta(t3.Sub(t1)), // tcp connection
-			fmta(t4.Sub(t3)), // server processing
-			fmta(t7.Sub(t4)), // content transfer
-			fmtb(t1.Sub(t0)), // namelookup
-			fmtb(t3.Sub(t0)), // connect
-			fmtb(t4.Sub(t0)), // starttransfer
-			fmtb(t7.Sub(t0)), // total
+			fmta(tDNSEnd.Sub(tDNSStart)),         // dns lookup
+			fmta(tConnectEnd.Sub(tConnectStart)), // tcp connection
+			fmta(tTTBF.Sub(tConnected)),          // server processing
+			fmta(tDone.Sub(tTTBF)),               // content transfer
+			fmtb(tDNSEnd.Sub(tStart)),            // namelookup
+			fmtb(tConnectEnd.Sub(tStart)),        // connect
+			fmtb(tTTBF.Sub(tStart)),              // starttransfer
+			fmtb(tDone.Sub(tStart)),              // total
 		)
 	}