deepmerge.go

package main

import (
	"encoding/json"
	"fmt"
	"github.com/ghodss/yaml"
	"io/ioutil"
	"path/filepath"
)

/*
NOTE: adapted from https://play.golang.org/p/8jlJUbEJKf to support merging slices
*/

// merge merges the two JSON-marshalable values x1 and x2,
// preferring x1 over x2 except where x1 and x2 are
// JSON objects, in which case the keys from both objects
// are included and their values merged recursively.
//
// It returns an error if x1 or x2 cannot be JSON-marshaled.
func merge(x1, x2 interface{}) (interface{}, error) {
	data1, err := json.Marshal(x1)
	if err != nil {
		return nil, err
	}
	data2, err := json.Marshal(x2)
	if err != nil {
		return nil, err
	}
	var j1 interface{}
	err = json.Unmarshal(data1, &j1)
	if err != nil {
		return nil, err
	}
	var j2 interface{}
	err = json.Unmarshal(data2, &j2)
	if err != nil {
		return nil, err
	}
	return merge1(j1, j2), nil
}

func merge1(x1, x2 interface{}) interface{} {
	switch x1 := x1.(type) {
	case map[string]interface{}:
		x2, ok := x2.(map[string]interface{})
		if !ok {
			return x1
		}
		for k, v2 := range x2 {
			if v1, ok := x1[k]; ok {
				x1[k] = merge1(v1, v2)
			} else {
				x1[k] = v2
			}
		}
	case []interface{}:
		x2, ok := x2.([]interface{})
		if !ok {
			return x1
		}
		for i := range x2 {
			x1 = append(x1, x2[i])
		}
		return x1
	case nil:
		// merge(nil, map[string]interface{...}) -> map[string]interface{...}
		x2, ok := x2.(map[string]interface{})
		if ok {
			return x2
		}
	}
	return x1
}

func main() {
	var config interface{}

	files, _ := filepath.Glob("conf.d/*.yml")
	for i := range files {
		// Read
		raw, err := ioutil.ReadFile(files[i])
		if err != nil {
			fmt.Println(err.Error())
		}

		// Unmarshal
		var c map[string]interface{}
		err = yaml.Unmarshal(raw, &c)
		if err != nil {
			fmt.Println(err.Error())
		}

		// Merge
		config, err = merge(c, config)
		if err != nil {
			fmt.Println(err.Error())
		}
	}
	data, err := yaml.Marshal(config)
	if err != nil {
		fmt.Println(err.Error())
	}
	fmt.Printf("%s\n", data)

}