gin: Working with BindJSON and error return

Hello,

First of all, thanks for your great project, I’m using it a on daily basis and it’s just awesome.

TL;DR

I have no clue on how to properly handle response format when validation fails on BindJSON and I want to send back the errors as JSON.

Context

I’m currently having trouble working with context.BindJSON. I have two fields that are required when receiving JSON, let’s call them first and second

type params struct {
	First  string `json:"first" binding:"required"`
	Second string `json:"second" binding:"required"`
}

Now when I receive the request, I handle it like this :

func postFirstSecond(c *gin.Context) {
	var err error
	c.Header("Content-Type", "application/json; charset=utf-8")

	p := params{}
	if err = c.BindJSON(&p); err != nil {
		c.JSON(http.StatusBadRequest, gin.H{
			"error":  "json decoding : " + err.Error(),
			"status": http.StatusBadRequest,
		})
		return
	}
}

So first of all, I don’t understand why c.JSON() doesn’t return the appropriate content-type, I found that when BindJSON fails, it writes the header to be plain text. Anyway my endpoint always returns JSON so I just set the content-type on top of the handler, problem solved (I guess).

When one field is missing, this endpoint returns something like that :

{
    "error": "json decoding : Key: 'params.First' Error:Field validation for 'First' failed on the 'required' tag",
    "status": 400
}

That’s fine. I mean it’s not really what I expected but it works.

Problem

When both fields are missing, this is what I get back :

{
    "error": "json decoding : Key: 'params.First' Error:Field validation for 'First' failed on the 'required' tag\nKey: 'params.Second' Error:Field validation for 'Second' failed on the 'required' tag",
    "status": 400
}

Question

Is there a simple way to handle those errors ? I’d like to get something more user-friendly, or at least a separate field for my errors. Something like :

{
    "errors": [
        "Key: 'params.First' Error:Field validation for 'First' failed on the 'required' tag",
        "Key: 'params.Second' Error:Field validation for 'Second' failed on the 'required' tag"
     ],
    "status": 400
}

I’m aware that checking manually the fields should allow me to do that, but the fact is : I feel like the documentation and examples are pretty vague about error handling.

Could someone help me with that ? How do you handle errors generated by Bind or BindJSON ?