Asp.net core 2.0 POST endpoint works without json payload, but fails (400 Bad request) with a json payload

Question

I have the following endpoint in my asp.net core 2.0 app:

[HttpPost("postself")]
public IActionResult post([FromBody]JObject email)
{
    try
    {
        var service = new EmailService();
        var emailHtml = service.GenerateEmail(email.ToString(), false);
        return Json(new { Email = emailHtml });
    }
    catch
    {
        return Json(new { Email = "error" });
    }
}

When calling the API like so:

curl -X POST \
  http://myapp/api/v1/emails/postself \
  -H 'cache-control: no-cache' \
  -H 'content-type: application/json' \
  -H 'postman-token: 85c9bbe7-2112-0746-5f41-8dc01b52ab59'

The endpoint gets hit and returns at return Jason(new { Email = "error" }); so that works. It returns error because the JObject is null but still this is expected behavior.

However, when calling the API like so (with JSON payload):

curl -X POST \
  http://myapp/api/v1/emails/postself \
  -H 'cache-control: no-cache' \
  -H 'content-type: application/json' \
  -H 'postman-token: a80c85de-8939-01d8-4a5d-c2108bf1491d' \
  -d '{
  "body": [
    {
      "image": {
        "url": "mailing_logo_slice.png",
        "alt": "This is my logo"
      }
    }
  ]
}'

...my app returns 400 Bad request.

Also, the requests work in development, but only returns 400 in production.

Any ideas?

=========

Updated code:

[HttpPost("postself")]
public IActionResult PostSameDomain([FromBody]string email)
{
    try
    {
        var service = new EmailGenerationService();
        var emailHtml = service.GenerateEmailFromJson(email, false);
        return Json(new { Email = emailHtml });
    }
    catch
    {
        return Json(new { Email = "error" });
    }
}

[HttpPost("test")]
        public IActionResult PostSameDomain([FromBody]EmailViewModel email)
        {
            try
            {
                var service = new EmailGenerationService();
                var emailHtml = service.GenerateEmailFromJson(email.Raw, false);
                return Json(new { Email = emailHtml });
            }
            catch
            {
                return Json(new { Email = "error" });
            }
        }

Have you debugged and looked at `ModelState.IsValid` + its various other properties? — Peter B, Apr 09 '18 at 15:20
Also, you might want to do things 'the proper way' and use an actual Model class. See e.g. https://app.quicktype.io/ to generate example code based on your input JSON. — Peter B, Apr 09 '18 at 15:26
For your CURL data property, does -d '{"username":"abc","password":"abc"}' work? If you don't get a 400 then I think it has to do with the structure of your current JSON object in the request. — Ben Krueger, Apr 09 '18 at 15:41
Make sure your `FromBody` parameter can be deserialized https://stackoverflow.com/a/46196415/804385 Also use catch (Exception ex) to see what is the error details - `ex.Message` Also check in production that `Newtonsoft.Json.dll` is not missed — Dmitry Pavlov, Apr 09 '18 at 16:50
@PeterB I checked out ModelState in development. All seems fine. Regarding your suggestion to do things the "proper way", as the format/model of the posted json differs every time I cant define a POCO. I just need the raw string or JObject. I switch from a JObject parameter to a plain string. In Development this works like before but still returns 400 in production... Any additional thoughts? — Corstiaan, Apr 10 '18 at 09:30
@BenKrueger When I post the request with your json example I still get a 400 response unfortunately. — Corstiaan, Apr 10 '18 at 09:31
@Corstiaan An API implements an interface between a client and a server, with a clear definition of what is accepted, and a model+code to support that. A catch-all interface is almsot never a good idea. If your JSON is actually a way to describe HTML tags, then why not post and accept a HTML string? — Peter B, Apr 10 '18 at 09:39
@PeterB Yes, you are right of course. But for this particular use case it would make sense. However, I wrapped the request in a simple model (see edited code). Again, this works in Development but still returns 400 in Production... Any more wisdom? :-) — Corstiaan, Apr 10 '18 at 10:18
@PeterB I should also add that regular form posts (so from an actual html form) also fail with 400 in production but work in development. — Corstiaan, Apr 10 '18 at 10:28
If all POSTs produce 400 then you'd better look at logfiles (if you have those) or the Windows Event Log. The problem is then most likely not with this code. — Peter B, Apr 10 '18 at 10:55
@PeterB Im on Docker/Linux. The logs are output to the console but nothing shows up regarding the 400 responses. I have set the LogLevel to Trace... — Corstiaan, Apr 10 '18 at 11:40

score 2 · Answer 1 · answered Apr 09 '18 at 16:11

2

JObject is specific to Newtonsoft.Json and will not work. Please specify a POCO class that contains url and alt properties.

answered Apr 09 '18 at 16:11

Ricardo Peres

13,724
5
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Marc LaFleur · Answer 2 · 2018-04-09T19:10:49.373

I believe your problem here is that you're passing in an JSON Array and attempting to deserialize it into a singular JObject.

Possible fixes:

Pass in a single JSON object:

curl -X POST \
  http://myapp/api/v1/emails/postself \
  -H 'cache-control: no-cache' \
  -H 'content-type: application/json' \
  -H 'postman-token: a80c85de-8939-01d8-4a5d-c2108bf1491d' \
  -d '{
  "body": {
      "image": {
        "url": "mailing_logo_slice.png",
        "alt": "This is my logo"
      }
    }
}'

Switch to JArray instead of JObject:

[HttpPost("postself")]
public IActionResult post([FromBody]JArray email)
{
    try
    {
        var service = new EmailService();
        var emailHtml = service.GenerateEmail(email.ToString(), false);
        return Json(new { Email = emailHtml });
    }
    catch
    {
        return Json(new { Email = "error" });
    }
}

Take in the data as a string and deserialize it within. This would allow you to test if you've received an array or a single object and then deserialize to a JObject or JArray as needed (this would be my personal recommendation for what its worth).

I tried option 3. This works in Development but in Production it still returns 400. See updated question. — Corstiaan, Apr 10 '18 at 09:33
I should also add that regular form posts (so from an actual html form) also fail with 400. — Corstiaan, Apr 10 '18 at 10:27
An HTML form will `POST` using `application/x-www-form-urlencoded`, not `application/json`. You cannot using a JSON deserializer against `form-urlencoded` data. — Marc LaFleur, Apr 10 '18 at 17:14

score 0 · Answer 3 · answered Apr 12 '18 at 08:29

0

For anyone else stumbling onto this issue, this was the root of the problem.

Thanks to everybody for thinking along with my issue.

answered Apr 12 '18 at 08:29

Corstiaan

1,114
15
34

Asp.net core 2.0 POST endpoint works without json payload, but fails (400 Bad request) with a json payload

3 Answers3