ParseRestartPolicy: validate for missing policy-names

Also make it slightly more clearer we're returning a default (empty)
policy if the input is empty.

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

cli/command/container/opts_test.go

@@ -714,6 +714,10 @@ func TestParseRestartPolicy(t *testing.T) {
 				Name: "no",
 			},
 		},
+		{
+			input:       ":1",
+			expectedErr: "invalid restart policy format: no policy provided before colon",
+		},
 		{
 			input: "always",
 			expected: container.RestartPolicy{
@@ -758,11 +762,11 @@ func TestParseRestartPolicy(t *testing.T) {
 		t.Run(tc.input, func(t *testing.T) {
 			_, hostConfig, _, err := parseRun([]string{"--restart=" + tc.input, "img", "cmd"})
 			if tc.expectedErr != "" {
-				assert.Check(t, is.Nil(hostConfig))
 				assert.Check(t, is.Error(err, tc.expectedErr))
+				assert.Check(t, is.Nil(hostConfig))
 			} else {
+				assert.NilError(t, err)
 				assert.Check(t, is.DeepEqual(hostConfig.RestartPolicy, tc.expected))
-				assert.Check(t, err)
 			}
 		})
 	}

opts/parse.go

@@ -71,17 +71,22 @@ func ConvertKVStringsToMapWithNil(values []string) map[string]*string {
 
 // ParseRestartPolicy returns the parsed policy or an error indicating what is incorrect
 func ParseRestartPolicy(policy string) (container.RestartPolicy, error) {
-	p := container.RestartPolicy{}
-
 	if policy == "" {
-		return p, nil
+		// for backward-compatibility, we don't set the default ("no")
+		// policy here, because older versions of the engine may not
+		// support it.
+		return container.RestartPolicy{}, nil
 	}
 
-	k, v, _ := strings.Cut(policy, ":")
+	p := container.RestartPolicy{}
+	k, v, ok := strings.Cut(policy, ":")
+	if ok && k == "" {
+		return container.RestartPolicy{}, fmt.Errorf("invalid restart policy format: no policy provided before colon")
+	}
 	if v != "" {
 		count, err := strconv.Atoi(v)
 		if err != nil {
-			return p, fmt.Errorf("invalid restart policy format: maximum retry count must be an integer")
+			return container.RestartPolicy{}, fmt.Errorf("invalid restart policy format: maximum retry count must be an integer")
 		}
 		p.MaximumRetryCount = count
 	}