scout hint: tell user logging in is required (#2262)

The `docker scout quickview` hint, displayed
after a user pulls or builds an image, only
works if the user is logged in to Hub.

Check if user isn't logged in, and make hint
more explicit in this case.

Signed-off-by: Laura Brehm <laurabrehm@hey.com>

cli/mobycli/scout_suggest.go

@@ -20,8 +20,11 @@ import (
 	"fmt"
 	"os"
 	"strings"
+	"time"
 
+	"github.com/docker/cli/cli/config"
 	"github.com/docker/compose/v2/pkg/utils"
+	"github.com/docker/docker/registry"
 
 	"github.com/fatih/color"
 )
@@ -53,10 +56,14 @@ func displayScoutQuickViewSuggestMsg(image string) {
 	}
 	out := os.Stderr
 	b := color.New(color.Bold)
-	_, _ = fmt.Fprintln(out)
-	_, _ = b.Fprintln(out, "What's Next?")
-	_, _ = fmt.Fprintf(out, "  View summary of image vulnerabilities and recommendations → %s", color.CyanString("docker scout quickview%s", image))
-	_, _ = fmt.Fprintln(out)
+
+	_, _ = b.Fprintln(out, "\nWhat's Next?")
+	if !hubLoggedIn() {
+		_, _ = fmt.Fprintln(out, "  1. Sign in to your Docker account → "+color.CyanString("docker login"))
+		_, _ = fmt.Fprintln(out, "  2. View a summary of image vulnerabilities and recommendations → "+color.CyanString("docker scout quickview"+image))
+	} else {
+		_, _ = fmt.Fprintln(out, "  View a summary of image vulnerabilities and recommendations → "+color.CyanString("docker scout quickview"+image))
+	}
 }
 
 func pulledImageFromArgs(args []string) string {
@@ -74,3 +81,27 @@ func pulledImageFromArgs(args []string) string {
 	}
 	return image
 }
+
+// hubLoggedIn checks whether the user has credentials configured
+// for Docker Hub. If it fails to get a result within 100ms, it
+// short-circuits and returns `true`.
+// This can be an expensive operation, so use it mindfully.
+func hubLoggedIn() bool {
+	result := make(chan bool)
+	go func() {
+		creds, err := config.LoadDefaultConfigFile(nil).GetAllCredentials()
+		if err != nil {
+			// preserve original behaviour if we fail to fetch creds
+			result <- true
+		}
+		_, ok := creds[registry.IndexServer]
+		result <- ok
+	}()
+	select {
+	case loggedIn := <-result:
+		return loggedIn
+	case <-time.After(100 * time.Millisecond):
+		// preserve original behaviour if we time out
+		return true
+	}
+}