cli-plugins/hooks: fix max-message off-by-one

Author: fallintoplace

cli-plugins/hooks/template.go

@@ -40,7 +40,7 @@ func ParseTemplate(hookTemplate string, cmd *cobra.Command) ([]string, error) {
 		}
 		out = b.String()
 	}
-	if n := strings.Count(out, "\n"); n > maxMessages {
+	if n := strings.Count(out, "\n") + 1; n > maxMessages {
 		return nil, fmt.Errorf("hook template contains too many messages (%d): maximum is %d", n, maxMessages)
 	}
 	return strings.SplitN(out, "\n", maxMessages), nil

cli-plugins/hooks/template_test.go

@@ -1,6 +1,7 @@
 package hooks_test
 
 import (
+	"strings"
 	"testing"
 
 	"github.com/docker/cli/cli-plugins/hooks"
@@ -123,3 +124,10 @@ func TestParseTemplate(t *testing.T) {
 		})
 	}
 }
+
+func TestParseTemplateTooManyMessages(t *testing.T) {
+	testCmd := &cobra.Command{Use: "pull"}
+
+	_, err := hooks.ParseTemplate(strings.Repeat("line\n", 10)+"line", testCmd)
+	assert.Error(t, err, "hook template contains too many messages (11): maximum is 10")
+}