当yaml已初始化默认值时，如何在Golang中测试默认值？

Question

I'm writing a daemon's configuration handler and utilizing the yaml package to do so. Importing my file works like this:

package daemon

import (
    "ioutil"
    "log"

    "gopkg.in/yaml.v2"
)

type daemonConfig struct {
    BindAddress string `yaml:"bind_address"`
    BindPort    int    `yaml:"bind_port"`
    VerifySSL   bool   `yaml:"verify_ssl"`
}

I easily unmarshall data from my YAML files like so:

func (config *daemonConfig) getConf() *daemonConfig {
    yamlFile, err := ioutil.ReadFile("config.yaml")
    if err != nil {
        log.Fatal("Unable to open config.yaml:", err)
    }
    err = yaml.Unmarshal(yamlFile, config)
    if err != nil {
        log.Fatal("Failed to unmarshall config.yaml:", err)
    }
    config, err = setDefaults(config)

    return config
}

My question is regarding my custom setDefaults function. If a field isn't provided, like bind_port or bind_address, I'd like to just set them to defaults:

func setDefaults(config *daemonConfig) (*daemonConfig, error) {
    if len(config.BindAddress) <= 0 {
        config.BindAddress = "0.0.0.0"
    }
    if config.BindPort == 0 {
        config.BindPort = 9999
    }

    return config, nil
}

You'll note I'm not setting a default to verify_ssl; when yaml unmarshalls this and fails to find the field, it initializes the bool as false, which is precisely the opposite of what I want the default behavior to be. I'd prefer the user to explicitly set verification of SSL to be off, instead of having it off by default if not specified. If I have a totally empty config.yaml, and expect the default values to be set, it will always put verify_ssl as false (this log is from elsewhere in the application):

2019/02/19 03:56:08 Currently loaded config: {0.0.0.0 9999 false}

How would I go about, if this field is not present in the YAML fields that are being unmarshalled, to checking if the line exists? I could just read the file manually and check for that parameter first, but I was wondering if there's a more elegant way with what I have; otherwise, I'll just use ioutil and string checking to do it. Thanks!

Answer 1

Thanks to Thomas and mh-cbon I found out I can just use a pointer for this. If I change my VerifySSL field to utilize a pointer and add omitempty:

type daemonConfig struct {
    BindAddress string `yaml:"bind_address"`
    BindPort    int    `yaml:"bind_port"`
    VerifySSL   *bool  `yaml:"verify_ssl",omitempty`
}

I can simply dereference the field in the struct to get the true value of what yaml unmarshalled. Setting defaults is as easy as:

func setDefaults(config *daemonConfig) (*daemonConfig, error) {
    if len(config.BindAddress) <= 0 {
        config.BindAddress = "0.0.0.0"
    }
    if config.BindPort == 0 {
        config.BindPort = 9999
    }
    if config.VerifySSL == nil {
        ssl := true
        config.VerifySSL = &ssl
    }

    return config, nil
}

If it's loaded in the file, config.VerifySSL will contain the address of the bool, so it won't be nil, and if it's truly not in the file at all then the field is simply nil and I can set it or get it via a pointer.

EDIT: Just a note, if your VerifySSL pointer is nil, you can't assign it like this:

*config.VerifySSL = true

That's dereferencing a nil pointer. I've updated the solution to include something more manageable.