MM-13185: Fix Message Export config special case. (#9898)

It should only apply when setting through the System Console, to avoid
messing up externally managed config files.

api4/system.go

@@ -130,6 +130,20 @@ func updateConfig(c *Context, w http.ResponseWriter, r *http.Request) {
 	// Do not allow plugin uploads to be toggled through the API
 	cfg.PluginSettings.EnableUploads = c.App.GetConfig().PluginSettings.EnableUploads
 
+	// If the Message Export feature has been toggled in the System Console, rewrite the ExportFromTimestamp field to an
+	// appropriate value. The rewriting occurs here to ensure it doesn't affect values written to the config file
+	// directly and not through the System Console UI.
+	if *cfg.MessageExportSettings.EnableExport != *c.App.GetConfig().MessageExportSettings.EnableExport {
+		if *cfg.MessageExportSettings.EnableExport && *cfg.MessageExportSettings.ExportFromTimestamp == int64(0) {
+			// When the feature is toggled on, use the current timestamp as the start time for future exports.
+			cfg.MessageExportSettings.ExportFromTimestamp = model.NewInt64(model.GetMillis())
+		} else if !*cfg.MessageExportSettings.EnableExport {
+			// When the feature is disabled, reset the timestamp so that the timestamp will be set if
+			// the feature is re-enabled from the System Console in future.
+			cfg.MessageExportSettings.ExportFromTimestamp = model.NewInt64(0)
+		}
+	}
+
 	err := c.App.SaveConfig(cfg, true)
 	if err != nil {
 		c.Err = err

api4/system_test.go

@@ -147,6 +147,74 @@ func TestUpdateConfig(t *testing.T) {
 	})
 }
 
+func TestUpdateConfigMessageExportSpecialHandling(t *testing.T) {
+	th := Setup().InitBasic()
+	defer th.TearDown()
+
+	messageExportEnabled := *th.App.Config().MessageExportSettings.EnableExport
+	messageExportTimestamp := *th.App.Config().MessageExportSettings.ExportFromTimestamp
+
+	defer th.App.UpdateConfig(func(cfg *model.Config) {
+		*cfg.MessageExportSettings.EnableExport = messageExportEnabled
+		*cfg.MessageExportSettings.ExportFromTimestamp = messageExportTimestamp
+	})
+
+	th.App.UpdateConfig(func(cfg *model.Config) {
+		*cfg.MessageExportSettings.EnableExport = false
+		*cfg.MessageExportSettings.ExportFromTimestamp = int64(0)
+	})
+
+	// Turn it on, timestamp should be updated.
+	cfg, resp := th.SystemAdminClient.GetConfig()
+	CheckNoError(t, resp)
+
+	*cfg.MessageExportSettings.EnableExport = true
+	cfg, resp = th.SystemAdminClient.UpdateConfig(cfg)
+	CheckNoError(t, resp)
+
+	assert.True(t, *th.App.Config().MessageExportSettings.EnableExport)
+	assert.NotEqual(t, int64(0), *th.App.Config().MessageExportSettings.ExportFromTimestamp)
+
+	// Turn it off, timestamp should be cleared.
+	cfg, resp = th.SystemAdminClient.GetConfig()
+	CheckNoError(t, resp)
+
+	*cfg.MessageExportSettings.EnableExport = false
+	cfg, resp = th.SystemAdminClient.UpdateConfig(cfg)
+	CheckNoError(t, resp)
+
+	assert.False(t, *th.App.Config().MessageExportSettings.EnableExport)
+	assert.Equal(t, int64(0), *th.App.Config().MessageExportSettings.ExportFromTimestamp)
+
+	// Set a value from the config file.
+	th.App.UpdateConfig(func(cfg *model.Config) {
+		*cfg.MessageExportSettings.EnableExport = false
+		*cfg.MessageExportSettings.ExportFromTimestamp = int64(12345)
+	})
+
+	// Turn it on, timestamp should *not* be updated.
+	cfg, resp = th.SystemAdminClient.GetConfig()
+	CheckNoError(t, resp)
+
+	*cfg.MessageExportSettings.EnableExport = true
+	cfg, resp = th.SystemAdminClient.UpdateConfig(cfg)
+	CheckNoError(t, resp)
+
+	assert.True(t, *th.App.Config().MessageExportSettings.EnableExport)
+	assert.Equal(t, int64(12345), *th.App.Config().MessageExportSettings.ExportFromTimestamp)
+
+	// Turn it off, timestamp should be cleared.
+	cfg, resp = th.SystemAdminClient.GetConfig()
+	CheckNoError(t, resp)
+
+	*cfg.MessageExportSettings.EnableExport = false
+	cfg, resp = th.SystemAdminClient.UpdateConfig(cfg)
+	CheckNoError(t, resp)
+
+	assert.False(t, *th.App.Config().MessageExportSettings.EnableExport)
+	assert.Equal(t, int64(0), *th.App.Config().MessageExportSettings.ExportFromTimestamp)
+}
+
 func TestGetEnvironmentConfig(t *testing.T) {
 	os.Setenv("MM_SERVICESETTINGS_SITEURL", "http://example.mattermost.com")
 	os.Setenv("MM_SERVICESETTINGS_ENABLECUSTOMEMOJI", "true")