filedecoders.go

// Copyright (c) 2017 Steven Roose <steven@stevenroose.org>.
// Use of this source code is governed by an MIT-style
// license that can be found in the LICENSE file.

package gonfig

import (
	"encoding/json"
	"fmt"
	"strings"

	"github.com/pelletier/go-toml"
	yaml "gopkg.in/yaml.v2"
)

// FileDecoderFn represents a method that translates the content of a config file
// to a map[string]interface{}.  It is important that in this map, all
// interface{} types are either:
// - a simple Go type (intX, uintX, bool, string, floatXX)
// - a value implementing encoding.TextUnmarshaler
// - a []byte
// - a slice of one of those
// - a map[string]interface{}
type FileDecoderFn func(content []byte) (map[string]interface{}, error)

// DecoderJSON is the JSON decoding function for config files.
var DecoderJSON FileDecoderFn = func(c []byte) (map[string]interface{}, error) {
	var m map[string]interface{}
	if err := json.Unmarshal(c, &m); err != nil {
		return nil, fmt.Errorf("error parsing JSON config file: %v", err)
	}

	return m, nil
}

// DecoderTOML is the TOML decoding function for config files.
var DecoderTOML FileDecoderFn = func(c []byte) (map[string]interface{}, error) {
	tomlTree, err := toml.LoadBytes(c)
	if err != nil {
		return nil, fmt.Errorf("error parsing TOML config file: %v", err)
	}

	return tomlTree.ToMap(), nil
}

// DecoderYAML is the YAML decoding function for config files.
var DecoderYAML FileDecoderFn = func(c []byte) (map[string]interface{}, error) {
	var m map[string]interface{}
	if err := yaml.Unmarshal(c, &m); err != nil {
		return nil, fmt.Errorf("error parsing YAML config file: %v", err)
	}
	// Cast map[interface{}]interface{} to map[string]interface{}.
	m = cleanUpYAML(m).(map[string]interface{})
	return m, nil
}

// NewMultiFileDecoder is a hybrid decoders that will try all the given decoders
// and return the result of the first one that does not produce an error.
func NewMultiFileDecoder(decoders []FileDecoderFn) FileDecoderFn {
	return func(c []byte) (map[string]interface{}, error) {
		errs := make([]string, len(decoders))
		for i, decoder := range decoders {
			m, err := decoder(c)
			if err == nil {
				return m, nil
			}
			errs[i] = err.Error()
		}

		errStr := fmt.Sprintf("[\"%v\"]", strings.Join(errs, "\", \""))
		return nil, fmt.Errorf("config file failed to decode with decoders for "+
			"YAML, TOML and JSON: %v", errStr)
	}
}

// DecoderTryAll is an encoding function that tries all other existing encoding
// functions and uses the first one that does not produce an error.
//
// The order in which they are tried is:
// 1. YAML
// 2. TOML
// 3. JSON
// To have them tried in a different order, construct a custom decoder using
// NewMultiDecoder.
var DecoderTryAll = NewMultiFileDecoder([]FileDecoderFn{
	DecoderYAML,
	DecoderTOML,
	DecoderJSON,
})