Gin context.BindJSON does not respond with error message

Description

Based on the docs https://github.com/gin-gonic/gin#model-binding-and-validation I tried to use context.BindJSON instead of c.ShouldBindJSON. Unfortunately only c.ShouldBindJSON responds with the error message.

How to reproduce

package main

import (
  "net/http"

  "github.com/gin-gonic/gin"
)

type MyStruct struct {
    AField string `json:"aField" binding:"required"`
}

func main() {
  r := gin.Default()

  // This one only responds with a 400
  r.POST("/foo", func(c *gin.Context) {
    var ms MyStruct

    err := c.BindJSON(&ms)

    if err != nil {
        return
    }

    c.JSON(http.StatusOK, "passes")
  })

  // This one responds with the error message
  r.POST("/bar", func(c *gin.Context) {
    var ms MyStruct

    err := c.ShouldBindJSON(&ms)

    if err != nil {
        c.JSON(http.StatusBadRequest, err.Error())

        return
    }

    c.JSON(http.StatusOK, "passes")
  })

  r.Run()
}

Expectations

Using Postman I would expect the following result from the endpoint /bar

Actual result

Instead I get a 400 but no error message

Environment

• go version: 1.18
• gin version (or commit ref): 1.8.1
• operating system: Linux

Comment From: Gasoid

Looks like it is somehow connected to issue #622 https://github.com/gin-gonic/gin/issues/662 BindJSON returns "EOF"

Comment From: tiredsosha

Yeah, I have the same problem

Comment From: Heliner

Description

Based on the docs https://github.com/gin-gonic/gin#model-binding-and-validation I tried to use context.BindJSON instead of c.ShouldBindJSON. Unfortunately only c.ShouldBindJSON responds with the error message.

How to reproduce

```go package main

import ( "net/http"

"github.com/gin-gonic/gin" )

type MyStruct struct { AField string json:"aField" binding:"required" }

func main() { r := gin.Default()

// This one only responds with a 400 r.POST("/foo", func(c *gin.Context) { var ms MyStruct

err := c.BindJSON(&ms)

if err != nil {
    return
}

c.JSON(http.StatusOK, "passes") })

// This one responds with the error message r.POST("/bar", func(c *gin.Context) { var ms MyStruct

err := c.ShouldBindJSON(&ms)

if err != nil {
    c.JSON(http.StatusBadRequest, err.Error())

    return
}

c.JSON(http.StatusOK, "passes") })

r.Run() } ```

Expectations

Using Postman I would expect the following result from the endpoint /bar

Actual result

Instead I get a 400 but no error message

Environment

* go version: 1.18

* gin version (or commit ref): 1.8.1

* operating system: Linux

try this

    r.POST("/bar", func(c *gin.Context) {
        var ms MyStruct

        err := c.ShouldBindJSON(&ms)

        if err != nil {
            c.JSON(http.StatusBadRequest, gin.H{"error": err.Error()})
                        // gin.H{}
            //c.JSON(http.StatusBadRequest, err.Error())

            return
        }

        c.JSON(http.StatusOK, "passes")
    })

same with the doc : https://github.com/gin-gonic/gin#model-binding-and-validation