Inconsistent DateTime UTC conversion between Response and Parameters

[deanmccrae]

I am using NSwag to generate a controller.

I have a DateTime field in my response, which is generated as follows:

/// <summary>The UTC timestamp.</summary> [Newtonsoft.Json.JsonProperty("timestamp", Required = Newtonsoft.Json.Required.DisallowNull, NullValueHandling = Newtonsoft.Json.NullValueHandling.Ignore)] [System.ComponentModel.DataAnnotations.Required(AllowEmptyStrings = true)] public System.DateTime Timestamp { get; set; }

The yaml definition is:

timestamp: description: The UTC timestamp. type: string format: date-time

The DateTime value in my c# is always DateTimeKind.Utc and in the response it undergoes no conversion to local time, and has a value such as: "timestamp": "2020-04-03T09:33:52.784818Z" in the json.

However I have now added a DateTime query parameter, defined as follows in the yaml file:

name: fromdate in: query type: string format: date-time required: false

The parameter in my c# code generated method is as follows:

[Microsoft.AspNetCore.Mvc.FromQuery] System.DateTime? fromdate = null

I now pass in a value for this parameter in the API call, e.g. the one returned above as follows, via Postman:

requests?fromDate=2020-04-03T09:33:52.784818Z

The problem here is that the value in my fromDate DateTime parameter in the method call has undergone a utc/local time conversion (in my case it is 11:33 not 09:33), which does not occur when a DateTime value is returned in the response.

I would expect the value to have had no conversion and be the exact same value as that passed in.

I tried setting the configuration parameter as follows "parameterDateTimeFormat": "u" in the hope that specifying the UTC format instead of the default "s" format would influence this, but it had no effect.

I have attached my nswag configuration file.

Can anyone explain the behavior - do I need to configure something, is it a bug, etc.?

Thank you!

api.txt

[deanmccrae]

It seems this is a bug in ASP.Net Core, which NSwag has no influence over. More details can be found here: dotnet/aspnetcore#11584.

[augustoproiete]

I can confirm there is a bug within NSwag from the point of view of the request - not related to the ASP .NET Core bug dotnet/aspnetcore#11584 referenced above (which causes issues on the response).

Reproduced with the latest version of NSwag.CodeGeneration.CSharp as of this writing (v13.8.2).

Given a Controller/Action that looks like this:

[HttpGet("test/{value:datetime}")]
[ProducesResponseType(typeof(DateTime), StatusCodes.Status200OK)]
public IActionResult GetDateAndReturnDate(DateTime value)
{
    return Ok(value);
}

Generating a client with NSwag results in the following client code being generated:

// ...
var urlBuilder_ = new System.Text.StringBuilder();
urlBuilder_.Append("test/{value}");
urlBuilder_.Replace("{value}", System.Uri.EscapeDataString(value.ToString("s",
    System.Globalization.CultureInfo.InvariantCulture)));
// ...

As can be seen, the generated code is assuming a Sortable format rather than expected ISO 8601-1:2019 format that you would get with the JSON serializer, and results in this request:

GET https://augustoproiete.net/test/2020-11-02T17%3A00%3A02

Expected:

GET https://augustoproiete.net/test/2020-11-02T17%3A00%3A02.1097278Z

---

Swagger definition from the Controller above

{
   "/test/{value}": {
      "get": {
         "tags": [
            "Test"
         ],
         "operationId": "Test_GetDateAndReturnDate",
         "produces": [
            "text/plain",
            "application/json",
            "text/json"
         ],
         "parameters": [
            {
               "type": "string",
               "name": "value",
               "in": "path",
               "required": true,
               "format": "date-time",
               "x-nullable": false
            }
         ],
         "responses": {
            "200": {
               "x-nullable": false,
               "description": "",
               "schema": {
                  "type": "string",
                  "format": "date-time"
               }
            }
         }
      }
   }
}

[augustoproiete]

A workaround for now is to set the CSharpClientGeneratorSettings.ParameterDateTimeFormat to a format that you want across all APIs. e.g. yyyy'-'MM'-'dd'T'HH':'mm':'ss'.'FFFFFFFZ.

This should work for most cases when all APIs handle DateTime the same way.

Of course, this is not ideal given that each API client can have a different JsonSerializerSettings.DateTimeZoneHandling (by implementing UpdateJsonSerializerSettings) and the serialization of DateTime should honor the JsonSerializerSettings.DateTimeZoneHandling of each individual API.

This is what I ended up with:

var clientSettings = new CSharpClientGeneratorSettings
{
    ClientBaseClass = "ApiClientBase",
    ClientClassAccessModifier = "internal",
    GenerateUpdateJsonSerializerSettingsMethod = false,

    // Inconsistent DateTime UTC conversion between Response and Parameters #2770
    // https://github.com/RicoSuter/NSwag/issues/2770
    ParameterDateTimeFormat = "yyyy'-'MM'-'dd'T'HH':'mm':'ss'.'FFFFFFFZ",

    CSharpGeneratorSettings =
    {
        DateType = "System.DateTime",
        DateTimeType = "System.DateTime",

        // ...
    },

    // ...
};

---

internal abstract class ApiClientBase
{
    protected void UpdateJsonSerializerSettings(JsonSerializerSettings settings)
    {
        // Json.NET interprets and modifies ISO dates when deserializing to JObject #862
        // https://github.com/JamesNK/Newtonsoft.Json/issues/862
        settings.DateParseHandling = DateParseHandling.None;
        
        // Inconsistent DateTime UTC conversion between Response and Parameters #2770
        // https://github.com/RicoSuter/NSwag/issues/2770
        settings.DateTimeZoneHandling = DateTimeZoneHandling.Utc;
    }
}