yaml: unmarshal errors: cannot unmarshal string into time.Duration in Golang

Question

I have struct as below:

type Connect struct {
     ClientID string `yaml:"clientid"`
     Password string `yaml:"password"`
     Timeout  time.Duration `yaml:"timeout"`
}

c1 := `
    id: 'client1'
    password: 'hhhhhhha'
    timeout: 10
    `

c2 := `
    id: 'client2'
    password: 'llllllla'
    timeout: '10'
    `

c3 := `
    id: 'client3'
    password: 'hhhhhhha'
    timeout: 10s
    `

c4 := `
    id: 'client4'
    password: 'llllllla'
    timeout: '10s'
    `

as shown above, type of Timeout is time.Duration, the default unit is Nanosecond, but I want to get the result: c1 && c2 has error, c3 && c4 is valid(the config of Timeout must have unit). How should I do to rewrite the UnmarshalYAML() Method for yaml? Thanks a lot.

Answer 1

I would create an aliased type in the UnmarshalYAML function so that all the values could be unmarshaled to some primitive types. Then I will rewrite those values that match and convert those which do not:

package main

import (
    "fmt"
    "time"

    "gopkg.in/yaml.v2"
)

type Connect struct {
    ClientID string        `yaml:"clientid"`
    Password string        `yaml:"password"`
    Timeout  time.Duration `yaml:"timeout"`
}

func (ut *Connect) UnmarshalYAML(unmarshal func(interface{}) error) error {
    type alias struct {
        ClientID string `yaml:"clientid"`
        Password string `yaml:"password"`
        Timeout  string `yaml:"timeout"`
    }

    var tmp alias
    if err := unmarshal(&tmp); err != nil {
        return err
    }

    t, err := time.ParseDuration(tmp.Timeout)
    if err != nil {
        return fmt.Errorf("failed to parse '%s' to time.Duration: %v", tmp.Timeout, err)
    }

    ut.ClientID = tmp.ClientID
    ut.Password = tmp.Password
    ut.Timeout = t

    return nil
}

func main() {
    c1 := `
id: 'client1'
password: 'hhhhhhha'
timeout: 10
`

    c2 := `
id: 'client2'
password: 'llllllla'
timeout: '10'
`

    c3 := `
id: 'client3'
password: 'hhhhhhha'
timeout: 10s
`

    c4 := `
id: 'client4'
password: 'llllllla'
timeout: '10s'
`

    cc := []string{c1, c2, c3, c4}
    for i, cstr := range cc {
        var c Connect
        err := yaml.Unmarshal([]byte(cstr), &c)
        if err != nil {
            fmt.Printf("Error for c%d: %v\n", (i + 1), err)
            continue
        }
        fmt.Printf("c%d: %+v\n", (i + 1), c)
    }
}

The output looks as follows:

$ go run main.go
Error for c1: failed to parse '10' to time.Duration: time: missing unit in duration10
Error for c2: failed to parse '10' to time.Duration: time: missing unit in duration10
c3: {ClientID: Password:hhhhhhha Timeout:10s}
c4: {ClientID: Password:llllllla Timeout:10s}