Configure Viper using Struct

Meta-Viper is a wrapper over viper, it uses a Go tagged struct to:

1. Initialize viper's configuration.

2. Load application configuration on that same struct.

You can find examples at ./examples or in this article: https://carlosvin.github.io/posts/create-cmd-tool-golang.

Usage

Define the struct holding your application config

Meta-Viper will try to load the configuration in that struct from configuration files, environment variables or flags.

Example

package main

import (
	"fmt"
	"os"

	config "github.com/carlosvin/meta-viper"
)

type appConfig struct {
	Host      string `cfg_name:"host" cfg_desc:"Server host"`
	Port      int    `cfg_name:"port" cfg_desc:"Server port"`
	SearchAPI string `cfg_name:"apis.search" cfg_desc:"Search API endpoint"`
}

func main() {
    cfg := &appConfig{ // (1)
        Host: "localhost",
        Port: 6000,
        SearchAPI: "https://google.es",
    }

    _, err := config.New(cfg, os.Args) // (2)
	if err != nil {
        panic(err)
    }
    log.Printf("Loaded Configuration %v...", cfg)
}

1. We instantiate the declared struct. As you can see you can optionally specify default values.

2. It loads the configuration in the passed struct cfg. The os.Args are required to parse the application flags.

Let’s focus on one application configuration attribute to explain the example. Meta-Viper will allow you to load the config into Host structure attribute in 3 different ways:

Using flags

./your-program --host=my.host

Using environment variables

HOST=my.host ./your-program

Loading the data from a file in json, yaml or toml format

./your-program --config=qa (1)

1. Following the qa configuration file content

qa.json

{
    "host": "qa.host",
    "port": 8000,
    "apis": {
        "search": "https://search.api/"
    }
}

Note	You can combine flags, environment variables and configuration files.

Tags

cfg_name

Required tag to specify the configuration parameter name.

cfg_description

Optional tag to describe how to use the configuration parameter.