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How to validate request in Gin with Golang

Golang is an amazing language, and gin is a great backend framework to use. Conceptually, it has no differences than the any backend framework we used in other languages. But its documentation does cause some problems for a accomplish a simple thing like request validation. Here, I will share my findings in terms of how to grab the value and validation in gin.

There are 2 models here for request validation here.

  1. You get the value first using ctx.Param("userId"), then validate by yourself.
  2. You bind the request to struct, and do retrieve/validation in one go using ctx.Bind() or ctx.ShouldBind().

I won’t cover the 1st part, since you would rarely want to do that, but if you prefer code style validation to string like struct-binding, then combine with ozzo-validation might not be that bad.

The 2nd way is idiomatic-gin, and leads to less code. I suggest you look into it.

2nd way, use struct-binding to grab and validate in one go.

Gin is using a package called validator to do the struct-binding.

For the path param

Let’s say you want to grab the userId and action from /user/:userId/*action, and making sure they always there, you also want to make sure that the userId is a valid uuid. You can do something like this.

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type RequestParam struct {
UserId string `uri:"userId", binding:"required,uuid"`
Action string `uri:"action", binding:"required"`
}

func handler(ctx *gin.Context) {
var param RequestParam

if err := c.BindUri(&param); err != nil {
c.AbortWithStatusJSON(400, gin.H{
"message": "bad request",
"detail": err.Error()
})
return
}
}

It’s easy to digest, for example, the UserId field, has a meta data attached to it: uri:"userId", binding:"required,uuid"

  • uri:"userId" means grab the value from uri which means a path parameter.
  • binding:"required,uuid" means we will bind this value to the struct’s property UserId, and it is a required field, and we expect its type to be uuid.

Then in the handler, you use c.BindUri() to do the getting and validation in one go.

If you want to use some other types other than uuid, check the validator‘s documentation.

For the query strings

For example, to get the userId from /user?userId=aaa-bbb-ccc-ddd

You just use this struct.

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type getUserByIdUri struct {
ID string `form:"userId" binding:"required,uuid"`
}

And both ctx.Bind() or ctx.BindQuery() would do the trick for you.

For the json body

For example, to get the {"name":"albert", "birthday": "06/30"} of the request body, you would use:

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type RequestBody struct {
Name: string `json:"name", binding:"required"`
Birthday: string `json:"birthday", binding:"required,datetime=01/02"`
}

For getting/validation, ctx.Bind() and ctx.BindJson() are your friends.

What about using one struct for combining the path param/query string/body part?

No, you can not, just call the Bind methods for multiple times.

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var reqBody RequestBody
var reqPathParam RequestPathParam
var reqQueryStr RequestQueryString

if err := c.BindJSON(&reqBody); err != nil {
// handle error
return
}

if err := c.BindUri(&reqPathParam); err != nil {
// handle error
return
}

if err := c.BindQuery(&reqQueryStr); err != nil {
// handle error
return
}

This is a lot of code, but actually the validation logic is declarative, unless you are dealing with a custom validation which validator package is different.

For validating the different type

Just swap the uuid to something else in the documentation.

For example:

  • an email: binding:"required,email"
  • an timezone: binding:"required,timezone"
  • an datetime: binding:"required,datetime=2006/01/02"

If you want to use some other types other than uuid, check the validator‘s documentation.

End

Hope it helps, thanks.