config

README

= Configure Viper using Struct
Carlos Martin Sanchez
v0.0.1

:viper: https://github.com/spf13/viper[viper,window=_blank]
:go: https://golang.org/[golang,window=_blank]
:go-tagged-struct: https://golang.org/ref/spec#Tag[Go tagged struct,window=_blank]

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 link:./examples[./examples].

image:https://pkg.go.dev/badge/github.com/carlosvin/meta-viper[link="https://pkg.go.dev/github.com/carlosvin/meta-viper"]


== 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
[source,go]
----
package main

import (
	"fmt"
	"os"

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

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
[source,bash]
----
./your-program --host=my.host
----

.Using environment variables
[source,bash]
----
HOST=my.host ./your-program
----

.Loading the data from a file in json, yaml or toml format
[source,bash]
----
./your-program --config=qa <1>
----
<1> Following the qa configuration file content

.qa.json
[source,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. 

Documentation

Index

• type Cfg
  • func New(cfg interface{}, args []string) (Cfg, error)

Types

type Cfg

type Cfg interface {
	// Reload the configured attributes in the structure from env, flags and/or configuration files
	Reload() error
}

Cfg Configuration loader

func New

func New(cfg interface{}, args []string) (Cfg, error)

New Instantiate a configuration loader. It loads the configuration into cfg argument.