CalDavSynchronizer.DataAccess.CardDavDataAccess.TryUpdateEntity C# (CSharp) Method

    public async Task<EntityVersion<WebResourceName, string>> TryUpdateEntity (WebResourceName url, string etag, string contents)
    {
      s_logger.DebugFormat ("Updating entity '{0}'", url);

      var absoluteContactUrl = new Uri (_serverUrl, url.OriginalAbsolutePath);

      s_logger.DebugFormat ("Absolute entity location: '{0}'", absoluteContactUrl);

      IHttpHeaders responseHeaders;
      try
      {
        responseHeaders = await _webDavClient.ExecuteWebDavRequestAndReturnResponseHeaders (
            absoluteContactUrl,
            "PUT",
            null,
            etag,
            null,
            "text/vcard",
            contents);
      }
      catch (WebDavClientException x) when (x.StatusCode == HttpStatusCode.NotFound || x.StatusCode == HttpStatusCode.PreconditionFailed)
      {
        return null;
      }

      if (s_logger.IsDebugEnabled)
        s_logger.DebugFormat ("Updated entity. Server response header: '{0}'", responseHeaders.ToString().Replace ("\r\n", " <CR> "));

      Uri effectiveContactUrl;
      if (responseHeaders.Location != null)
      {
        s_logger.DebugFormat ("Server sent new location: '{0}'", responseHeaders.Location);
        effectiveContactUrl = responseHeaders.Location.IsAbsoluteUri ? responseHeaders.Location : new Uri (_serverUrl, responseHeaders.Location);
        s_logger.DebugFormat ("New entity location: '{0}'", effectiveContactUrl);
      }
      else
      {
        effectiveContactUrl = absoluteContactUrl;
      }

      var newEtag = responseHeaders.ETag;
      string version;
      if (newEtag != null)
      {
        version = newEtag;
      }
      else
      {
        version = await GetEtag (effectiveContactUrl);
      }

      return new EntityVersion<WebResourceName, string> (new WebResourceName(effectiveContactUrl), version);
    }