Json Patch model binding weirdness

[Jetski5822]

Environment

• Nuget Package: JsonPatch.Net
• Nuget Version: 1.0.5
• OS: Windows
• .Net Target: core 3.1

How can I help you today?
I have some patch JSON:

[
   {
      ""value"":true,
      ""OperationType"":""Replace"",
      ""path"":""/IsManualEditIndicator"",
      ""op"":""replace""
   },
   {
      ""value"":""2021-04-02T00:34:11Z"",
      ""OperationType"":""Replace"",
      ""path"":""/ClockingDateTime"",
      ""op"":""replace""
   }
]

When I call and MVC endpoint like so; it works.

        public async Task<IActionResult> Patch(
            int id,
            [FromHeader(Name = "traceId")] string traceId)
        {
            var json = "";

            using (StreamReader reader
                      = new StreamReader(Request.Body, Encoding.UTF8, true, 1024, true))
            {
                json = await reader.ReadToEndAsync();
            }

            var patch = JsonSerializer.Deserialize<Json.Patch.JsonPatch>(json);

Patch is populated, world is good.
If I change it over to this;

        public async Task<IActionResult> Patch(
            int id,
            [FromHeader(Name = "traceId")] string traceId,
            [FromBody] JsonPatch clockingPatch)
        {

I get the following;

{
   "type":"https://tools.ietf.org/html/rfc7231#section-6.5.1",
   "title":"One or more validation errors occurred.",
   "status":400,
   "traceId":"00-d4ceda59a9448c4bbfa0826d24ab93e2-03d71d05696cb54f-00",
   "errors":{
      "Operations[0].From.Segments":[
         "The Segments field is required."
      ],
      "Operations[1].From.Segments":[
         "The Segments field is required."
      ]
   }
}

Any thoughts on how I can fix this? as im a little confused :D

[gregsdennis]

Interesting scenario you've found. From the docs I'd expect that ASP.Net would just do the same deserialization that you're doing in the manual one.

Would you work up a minimal solution that replicates this, please? I want to make sure that what I debug is the same as what you're seeing.

Thanks for the report.

[gregsdennis]

The MS docs for how to do JSON Patch suggest using Newtonsoft and System.Text.Json 🤦

I wonder if this is what's happening: ASP.Net reads that it's a PATCH call and tries to deserialize into whatever Newtonsoft has provided.

[Jetski5822]

Here you go https://github.com/Jetski5822/JsonPatchBug146

Something weird for you, it works under IISExpress... but NOT Kestrel.

If you clone, build, and then flip it to be Kestrel

using Postman do... PATCH to http://localhost:5000/patchme

[
   {
      "value":true,
      "OperationType":"Replace",
      "path":"/IsManualEditIndicator",
      "op":"replace"
   },
   {
      "value":"2021-04-02T00:34:11Z",
      "OperationType":"Replace",
      "path":"/ClockingDateTime",
      "op":"replace"
   }
]

So weird.!!!

[Jetski5822]

Hmm, In here https://github.com/gregsdennis/json-everything/blob/master/JsonPatch/PatchOperation.cs#L20

Shouldnt Op and Path be the only non nullable objects? with Value and From being nullable objects? based on here http://json.schemastore.org/json-patch

[gregsdennis]

Having those non-null resolved some processing issues I had while enabling nullable reference types in the lib. I do have it nullable in a DTO in the converter defined in the same file, toward the bottom.

[gregsdennis]

Well, it's definitely deserializing the patch properly. I removed the nuget package and just imported the projects. This is just before returning from

json-everything/JsonPatch/JsonPatch.cs

Line 90 in 62bc62d

return new JsonPatch(operations);

Something's happening between the deserialization and entering the controller. Maybe ASP.Net is doing some validation, though I'm not sure what would be instructing it to do so.

[gregsdennis]

Okay. Found what might be causing it and a workaround for you.

Update Startup.cs:

// This method gets called by the runtime. Use this method to add services to the container.
public void ConfigureServices(IServiceCollection services)
{
    services.AddRazorPages()
        .AddMvcOptions(options => options.SuppressImplicitRequiredAttributeForNonNullableReferenceTypes = true);
}

What's odd is that the app doesn't have <Nullable>enable</Nullable>, but this is still enforced.

[gregsdennis]

Looked at this a bit today. I'm still not sure where that error message is being generated, so I don't know how to fix it other than the above.

[Jetski5822]

Nice one Greg, I'll give it a go - I'll also pull your code to my sln and see if I can get it to work.

It's weird that it works fine in IIS express though :/

[gregsdennis]

The validation engine is saying that JsonPointer.Segments is not nullable and so requires a value. But because your patches don't declare a from value, it gets a default pointer, and .Segments is null for that. If I make that property nullable, the problem goes away. But that doesn't feel right because it should always have a value. (I supply a static Empty pointer to be used instead of default).

Interestingly, I'm using default to fill the from value in the PatchOperationConverter. If I use JsonPointer.Empty instead, the problem also goes away. I think this is the fix.

... I still have no clue where that error message is coming from.

[gregsdennis]

Okay. Try v1.0.6.

[Jetski5822]

It works!!! Nice one - thanks for the fast turn around.