assert

Dead simple 0 dependency "typed" golang validator

Motivation

Most go validators use either struct tags or a string based representation of the validation rules, and while there's nothing wrong with that, sometimes you just want to quickly validate an input and perhaps cast it to a different type from which you received it.

With assert you may also rest assured you did not typo any of the validation rules as all rules are functions, hence a bit more "typed" than something like validate:"required,min=4,max=5"

Installing

go get github.com/sindreslungaard/assert

Examples

Simple example of validating the character length of an interface and returning it as a string

package main

import "github.com/sindreslungaard/assert"

func main() {
    // This can be any value, any type.
    src := "some-value"

    str, err := assert.Is(src).MinLen(5).MaxLen(10).String()

    if err != nil {
        // handle error
    }

    // str == "some-value"
}

Every assertion formats the input to a type it prefers to test on before executing, so you can do number assertions on string values and so on

num, err := assert.Is("55").MinNum(50).Int()
num, err := assert.Is(55).MinNum(50).Int()
// Both of these are OK

Example validation for a http form POST request

func mySignupHandler(c *gin.Context) {

    username, err := assert.Is(c.PostForm("username")).MinLen(3).MaxLen(20).AlphaNumeric().String()

    if err != nil {
        // let the user know
    }

    password, err := assert.Is(c.PostForm("password")).MinLen(8)

    if err != nil {
        // let the user know
    }

}

We can recude the number of error checks with assert.First

func mySignupHandler(c *gin.Context) {

    username, err1 := assert.Is(c.PostForm("username")).MinLen(3).MaxLen(20).AlphaNumeric().String()
    email,    err2 := assert.Is(c.PostForm("email")).Email().String()
    password, err3 := assert.Is(c.PostForm("password")).MinLen(8).String()

    err := assert.First(err1, err2, err3)

    if err != nil {
        // let the user know
    }

}

Available validations

Validation	Argument type	Description
NotEmpty		Checks if the input (formatted to string) is equal to ""
MinLen	int	Checks if the length of input (formatted to string) is greater than or equal to the argument
MaxLen	int	Checks if the length of input (formatted to string) is less than or equal to the argument
MinNum	int	Checks if the value of input (formatted to int) is greater than or equal to the argument
MaxNum	int	Checks if the value of input (formatted to int) is less than or equal to the argument
Regex	string	Checks if the input (formatted to string) matches the provided regex pattern
Email		Checks if the input (formatted to string) is a valid email
Alpha		Checks if the input (formatted to string) only contains a-z and A-Z
AlphaNumeric		Checks if the input (formatted to string) only contains a-z, A-Z and 0-9

Available type cast assertions

Type casts should always be last in your assertion chain, they are what executes all assertions in the chain and returns any errors or the input converted to the new type.

Type	Description
String	Formats the input as a string using fmt.Sprintf
Int	Formats the input as an int using fmt.Sprintf -> strconv.Atoi
Float64	Formats the input as a float64 using fmt.Sprintf -> strconv.ParseFloat with 64 bit precision