Description

I have a simple web server with a search api that accepts three string query parameters: a, b, and c. I can use ShouldBindQuery to bind these parameters to a struct, but if I call the endpoint without any query in the path the handler panics (and recovers).

How to reproduce

package main

import (
    "net/http"

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

type Params struct {
    A string `form:"a"`
    B string `form:"b"`
    C string `form:"c"`
}

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

    g.GET("/search", func(c *gin.Context) {
        var params *Params
        if err := c.ShouldBindQuery(&params); err != nil {
            c.JSON(http.StatusBadRequest, gin.H{
                "error": err.Error(),
            })
            return
        }

        c.JSON(200, params)
    })

    g.Run(":9000")
}

Expectations

$ curl http://localhost:9000/search?a=a&b=b&c=c
{"A":"a","B":"b","C":"c"}

$ curl http://localhost:9000/search
{"A":"","B":"","C":""}

Actual result

$ curl http://localhost:9000/search?a=a&b=b&c=c
{"A":"a","B":"b","C":"c"}

$ curl http://localhost:9000/search
(handler panics and recovers)

2023/09/21 10:13:53 [Recovery] 2023/09/21 - 10:13:53 panic recovered:
GET /search HTTP/1.1
Host: localhost:9000
Accept: */*
User-Agent: curl/8.1.2


reflect: call of reflect.Value.Interface on zero Value
/usr/local/go/src/reflect/value.go:1495 (0x102812f3b)
    valueInterface: panic(&ValueError{"reflect.Value.Interface", Invalid})
/usr/local/go/src/reflect/value.go:1490 (0x102a4b357)
    Value.Interface: return valueInterface(v, true)
/Users/dfarr/go/pkg/mod/github.com/gin-gonic/gin@v1.9.1/binding/default_validator.go:57 (0x102a4b340)
    (*defaultValidator).ValidateStruct: return v.ValidateStruct(value.Elem().Interface())
/Users/dfarr/go/pkg/mod/github.com/gin-gonic/gin@v1.9.1/binding/default_validator.go:57 (0x102a4b367)
    (*defaultValidator).ValidateStruct: return v.ValidateStruct(value.Elem().Interface())
/Users/dfarr/go/pkg/mod/github.com/gin-gonic/gin@v1.9.1/binding/binding.go:120 (0x102a4dd97)
    validate: return Validator.ValidateStruct(obj)
/Users/dfarr/go/pkg/mod/github.com/gin-gonic/gin@v1.9.1/binding/query.go:20 (0x102a4dd7c)
    queryBinding.Bind: return validate(obj)
/Users/dfarr/go/pkg/mod/github.com/gin-gonic/gin@v1.9.1/context.go:741 (0x102a7f9ff)
    (*Context).ShouldBindWith: return b.Bind(c.Request, obj)
/Users/dfarr/go/pkg/mod/github.com/gin-gonic/gin@v1.9.1/context.go:711 (0x102a7f9e4)
    (*Context).ShouldBindQuery: return c.ShouldBindWith(obj, binding.Query)
/Users/dfarr/Desktop/gin-bug/main.go:20 (0x102a7fa00)
    main.func1: if err := c.ShouldBindQuery(&params); err != nil {
/Users/dfarr/go/pkg/mod/github.com/gin-gonic/gin@v1.9.1/context.go:174 (0x102a7a6ef)
    (*Context).Next: c.handlers[c.index](c)
/Users/dfarr/go/pkg/mod/github.com/gin-gonic/gin@v1.9.1/recovery.go:102 (0x102a7a6d4)
    CustomRecoveryWithWriter.func1: c.Next()
/Users/dfarr/go/pkg/mod/github.com/gin-gonic/gin@v1.9.1/context.go:174 (0x102a79a8f)
    (*Context).Next: c.handlers[c.index](c)
/Users/dfarr/go/pkg/mod/github.com/gin-gonic/gin@v1.9.1/logger.go:240 (0x102a79a60)
    LoggerWithConfig.func1: c.Next()
/Users/dfarr/go/pkg/mod/github.com/gin-gonic/gin@v1.9.1/context.go:174 (0x102a78bc3)
    (*Context).Next: c.handlers[c.index](c)
/Users/dfarr/go/pkg/mod/github.com/gin-gonic/gin@v1.9.1/gin.go:620 (0x102a788ec)
    (*Engine).handleHTTPRequest: c.Next()
/Users/dfarr/go/pkg/mod/github.com/gin-gonic/gin@v1.9.1/gin.go:576 (0x102a7863f)
    (*Engine).ServeHTTP: engine.handleHTTPRequest(c)
/usr/local/go/src/net/http/server.go:2938 (0x10294a40b)
    serverHandler.ServeHTTP: handler.ServeHTTP(rw, req)
/usr/local/go/src/net/http/server.go:2009 (0x102947587)
    (*conn).serve: serverHandler{c.server}.ServeHTTP(w, w.req)
/usr/local/go/src/runtime/asm_arm64.s:1197 (0x1027cc953)
    goexit: MOVD    R0, R0  // NOP

Environment

  • go version: go version go1.21.0 darwin/arm64
  • gin version (or commit ref): v1.9.1
  • operating system: mac m2

Comment From: dfarr

I can work around this by instantiating params, or by passing in a struct instead of a pointer to a struct.

// works
params := &Params{}
c.ShouldBindQuery(&params)

// works
var params Params
c.ShouldBindQuery(params)

// does not work
var params *Params
c.ShouldBindQuery(&params)

I primarily use ShouldBindJSON for my other endpoints and calls to this function work fine when passing a pointer to struct, even if the underlying struct is nil.

Comment From: VarusHsu

It's a error about improper use of pointers. Modify var params *Params to var params Params. In your previous code, the type of params is *Param, then you pass &params, so ShouldBindQuery accept a varaible type of **Param. So there is a null pointer exception.

Comment From: VarusHsu

Make sure your ShouldBindQuery accepted type is *Param, So if you define params like this 

var params *Params

Then you call should like this:

if err := c.ShouldBindQuery(params); err != nil {

It will work fine :)

Comment From: dfarr

Thanks @VarusHsu, that works!

I think the confusion stems from the discrepancy between ShouldBindJSON and ShouldBindQuery, my bad.

// valid
var params *Params
c.ShouldBindJSON(&params)

// invalid
var params *Params
c.ShouldBindQuery(&params)

Comment From: dfarr

Make sure your ShouldBindQuery accepted type is *Param, So if you define params like this

var params *Params

Then you call should like this:

if err := c.ShouldBindQuery(params); err != nil {

It will work fine :)

Actually this results in a panic as well