I am working on a Golang project which needs to dump system configuration to a designated path. Are there any libraries that can generate .cfg file from inside a golang program?

I tried to search for Viper but could not find a suitable example which reads/writes to a .cfg file. It supports JSON, toml and other formats.

CodePudding user response：

It doesn't support the .cfg file format out of the box, but it's possible to create a custom configuration file type by implementing the Marshaler and Unmarshaler interfaces, like:

package main

import (
    "fmt"
    "io"
    "os"

    "github.com/spf13/viper"
)

type cfgFile struct {
    Config map[string]string
}

func (c *cfgFile) Marshal(w io.Writer) error {
    for k, v := range c.Config {
        if _, err := fmt.Fprintf(w, "%s = %s\n", k, v); err != nil {
            return err
        }
    }
    return nil
}

func (c *cfgFile) Unmarshal(r io.Reader) error {
    c.Config = make(map[string]string)
    var key, value string
    for {
        _, err := fmt.Fscanf(r, "%s = %s\n", &key, &value)
        if err != nil {
            if err == io.EOF {
                break
            }
            return err
        }
        c.Config[key] = value
    }
    return nil
}

func main() {
    // Create a new Viper instance.
    v := viper.New()

    // Set the configuration file type to use the custom cfgFile type.
    v.SetConfigType("cfg")

    // Set the configuration file path.
    v.SetConfigFile("config.cfg")

    // Set the configuration file type marshaler and unmarshaler.
    v.SetConfigMarshaler(&cfgFile{}, viper.MarshalFunc(func(v interface{}, w io.Writer) error {
        return v.(*cfgFile).Marshal(w)
    }))
    v.SetConfigTypeUnmarshaler("cfg", viper.UnmarshalFunc(func(r io.Reader, v interface{}) error {
        return v.(*cfgFile).Unmarshal(r)
    }))

    // Read the configuration file.
    if err := v.ReadInConfig(); err != nil {
        fmt.Printf("Error reading config file: %s\n", err)
        return
    }

    // Get a value from the configuration.
    value := v.GetString("key")
    fmt.Println(value)

    // Set a value in the configuration.
    v.Set("key", "value")

    // Write the configuration to the file.
    if err := v.WriteConfig(); err != nil {
        fmt.Printf("Error writing config file: %s\n", err)
        return
    }
}