Merge pull request #330 from thaJeztah/17.09-backport-cli-version

[17.09] Fix version comparison when negotiating the the API version

components/engine/client/client.go

@@ -266,8 +266,8 @@ func (cli *Client) NegotiateAPIVersionPing(p types.Ping) {
 		cli.version = api.DefaultVersion
 	}
 
-	// if server version is lower than the maximum version supported by the Client, downgrade
-	if versions.LessThan(p.APIVersion, api.DefaultVersion) {
+	// if server version is lower than the client version, downgrade
+	if versions.LessThan(p.APIVersion, cli.version) {
 		cli.version = p.APIVersion
 	}
 }

components/engine/client/client_test.go

@@ -245,6 +245,14 @@ func TestNegotiateAPIVersion(t *testing.T) {
 	// test downgrade
 	client.NegotiateAPIVersionPing(ping)
 	assert.Equal(t, expected, client.version)
+
+	// set the client version to something older, and verify that we keep the
+	// original setting.
+	expected = "1.20"
+	client.version = expected
+	client.NegotiateAPIVersionPing(ping)
+	assert.Equal(t, expected, client.version)
+
 }
 
 // TestNegotiateAPIVersionOverride asserts that we honor