koron / go-valid

Experimental flag with validation

validate flag constraints

Package "valid" provides constraints validatable values for "flag" package.

package main

import (
    "flag"
    "fmt"

    valid "github.com/koron/go-valid"
)

func ExampleInt() {
    fs := flag.NewFlagSet("example", flag.ContinueOnError)
    // "-user" must be set.
    var user int
    fs.Var(valid.Int(&user, 0).MustSet(), "user",
        "target user ID (required)")
    // "-mode" should be chosen from 1, 2, 3, 4 or 5.
    var mode int
    fs.Var(valid.Int(&mode, 1).Min(1).Max(5), "mode",
        "choose between 1 and 5 (default 1)")
    // parse option with validation
    if err := valid.Parse(fs, os.Args); err != nil {
        panic(err)
    }
    // run your procedure with "user" and "mode".
}

Description

Package "valid" provides flag.Value compatible values with validation for some constraints. flag.Value can be used with flag.Var() or flag.FlagSet#Var().

Functions {Type}(p *type, defaultValue type) returns a new *{Type}Value. This value have methods which declare some constraints like MustSet(), Min() or so. For example "int" value which is between 1 and 5 with default 1:

var mode int
mv := valid.IntValue(&mode, 1).Min(1).Max(5)

Another example, "int" value which must be set:

var user int
uv := valid.IntValue(&user, 0).MustSet()

Then you should combine those values with the "flag" package.

flag.Var(mv, "mode", "between 1 and 5")
flag.Var(uv, "user", "user ID (mandatory)")
if err := valid.Parse(flag.CommandLine, os.Args); err != nil {
    panic(err)
}