Allow HTTP tracing in push/pull via --trace flag

Signed-off-by: Phil Estes <estesp@amazon.com>

cmd/ctr/commands/images/images.go

@@ -17,7 +17,9 @@
 package images
 
 import (
+	"context"
 	"fmt"
+	"net/http/httptrace"
 	"os"
 	"sort"
 	"strings"
@@ -332,3 +334,23 @@ var removeCommand = cli.Command{
 		return exitErr
 	},
 }
+
+// NewDebugClientTrace returns a Go http trace client predefined to write DNS and connection
+// information to the log. This is used via the --trace flag on push and pull operations in ctr.
+func NewDebugClientTrace(ctx context.Context) *httptrace.ClientTrace {
+	return &httptrace.ClientTrace{
+		DNSStart: func(dnsInfo httptrace.DNSStartInfo) {
+			log.G(ctx).WithField("host", dnsInfo.Host).Debugf("DNS lookup")
+		},
+		DNSDone: func(dnsInfo httptrace.DNSDoneInfo) {
+			if dnsInfo.Err != nil {
+				log.G(ctx).WithField("lookup_err", dnsInfo.Err).Debugf("DNS lookup error")
+			} else {
+				log.G(ctx).WithField("result", dnsInfo.Addrs[0].String()).WithField("coalesced", dnsInfo.Coalesced).Debugf("DNS lookup complete")
+			}
+		},
+		GotConn: func(connInfo httptrace.GotConnInfo) {
+			log.G(ctx).WithField("reused", connInfo.Reused).WithField("remote_addr", connInfo.Conn.RemoteAddr().String()).Debugf("Connection successful")
+		},
+	}
+}