yaml/yaml.go

// Package yaml implements YAML support for the Go language.
//
// Source code and other details for the project are available at GitHub:
//
//   https://github.com/go-yaml/yaml
//
package yaml

import (
	"errors"
	"fmt"
	"reflect"
	"strings"
	"sync"
)

type yamlError string

func fail(msg string) {
	panic(yamlError(msg))
}

func handleErr(err *error) {
	if r := recover(); r != nil {
		if e, ok := r.(yamlError); ok {
			*err = errors.New("YAML error: " + string(e))
		} else {
			panic(r)
		}
	}
}

// The Setter interface may be implemented by types to do their own custom
// unmarshalling of YAML values, rather than being implicitly assigned by
// the yaml package machinery. If setting the value works, the method should
// return true.  If it returns false, the value is considered unsupported
// and is omitted from maps and slices.
type Setter interface {
	SetYAML(tag string, value interface{}) bool
}

// The Getter interface is implemented by types to do their own custom
// marshalling into a YAML tag and value.
type Getter interface {
	GetYAML() (tag string, value interface{})
}

// Unmarshal decodes the first document found within the in byte slice
// and assigns decoded values into the out value.
//
// Maps and pointers (to a struct, string, int, etc) are accepted as out
// values.  If an internal pointer within a struct is not initialized,
// the yaml package will initialize it if necessary for unmarshalling
// the provided data. The out parameter must not be nil.
//
// The type of the decoded values and the type of out will be considered,
// and Unmarshal will do the best possible job to unmarshal values
// appropriately.  It is NOT considered an error, though, to skip values
// because they are not available in the decoded YAML, or if they are not
// compatible with the out value. To ensure something was properly
// unmarshaled use a map or compare against the previous value for the
// field (usually the zero value).
//
// Struct fields are only unmarshalled if they are exported (have an
// upper case first letter), and are unmarshalled using the field name
// lowercased as the default key. Custom keys may be defined via the
// "yaml" name in the field tag: the content preceding the first comma
// is used as the key, and the following comma-separated options are
// used to tweak the marshalling process (see Marshal).
// Conflicting names result in a runtime error.
//
// For example:
//
//     type T struct {
//         F int `yaml:"a,omitempty"`
//         B int
//     }
//     var T t
//     yaml.Unmarshal([]byte("a: 1\nb: 2"), &t)
//
// See the documentation of Marshal for the format of tags and a list of
// supported tag options.
//
func Unmarshal(in []byte, out interface{}) (err error) {
	defer handleErr(&err)
	d := newDecoder()
	p := newParser(in)
	defer p.destroy()
	node := p.parse()
	if node != nil {
		v := reflect.ValueOf(out)
		if v.Kind() == reflect.Ptr && !v.IsNil() {
			v = v.Elem()
		}
		d.unmarshal(node, v)
	}
	return nil
}

// Marshal serializes the value provided into a YAML document. The structure
// of the generated document will reflect the structure of the value itself.
// Maps and pointers (to struct, string, int, etc) are accepted as the in value.
//
// Struct fields are only unmarshalled if they are exported (have an upper case
// first letter), and are unmarshalled using the field name lowercased as the
// default key. Custom keys may be defined via the "yaml" name in the field
// tag: the content preceding the first comma is used as the key, and the
// following comma-separated options are used to tweak the marshalling process.
// Conflicting names result in a runtime error.
//
// The field tag format accepted is:
//
//     `(...) yaml:"[<key>][,<flag1>[,<flag2>]]" (...)`
//
// The following flags are currently supported:
//
//     omitempty    Only include the field if it's not set to the zero
//                  value for the type or to empty slices or maps.
//                  Does not apply to zero valued structs.
//
//     flow         Marshal using a flow style (useful for structs,
//                  sequences and maps.
//
//     inline       Inline the struct it's applied to, so its fields
//                  are processed as if they were part of the outer
//                  struct.
//
// In addition, if the key is "-", the field is ignored.
//
// For example:
//
//     type T struct {
//         F int "a,omitempty"
//         B int
//     }
//     yaml.Marshal(&T{B: 2}) // Returns "b: 2\n"
//     yaml.Marshal(&T{F: 1}} // Returns "a: 1\nb: 0\n"
//
func Marshal(in interface{}) (out []byte, err error) {
	defer handleErr(&err)
	e := newEncoder()
	defer e.destroy()
	e.marshal("", reflect.ValueOf(in))
	e.finish()
	out = e.out
	return
}

// --------------------------------------------------------------------------
// Maintain a mapping of keys to structure field indexes

// The code in this section was copied from mgo/bson.

// structInfo holds details for the serialization of fields of
// a given struct.
type structInfo struct {
	FieldsMap  map[string]fieldInfo
	FieldsList []fieldInfo

	// InlineMap is the number of the field in the struct that
	// contains an ,inline map, or -1 if there's none.
	InlineMap int
}

type fieldInfo struct {
	Key       string
	Num       int
	OmitEmpty bool
	Flow      bool

	// Inline holds the field index if the field is part of an inlined struct.
	Inline []int
}

var structMap = make(map[reflect.Type]*structInfo)
var fieldMapMutex sync.RWMutex

func getStructInfo(st reflect.Type) (*structInfo, error) {
	fieldMapMutex.RLock()
	sinfo, found := structMap[st]
	fieldMapMutex.RUnlock()
	if found {
		return sinfo, nil
	}

	n := st.NumField()
	fieldsMap := make(map[string]fieldInfo)
	fieldsList := make([]fieldInfo, 0, n)
	inlineMap := -1
	for i := 0; i != n; i++ {
		field := st.Field(i)
		if field.PkgPath != "" {
			continue // Private field
		}

		info := fieldInfo{Num: i}

		tag := field.Tag.Get("yaml")
		if tag == "" && strings.Index(string(field.Tag), ":") < 0 {
			tag = string(field.Tag)
		}
		if tag == "-" {
			continue
		}

		inline := false
		fields := strings.Split(tag, ",")
		if len(fields) > 1 {
			for _, flag := range fields[1:] {
				switch flag {
				case "omitempty":
					info.OmitEmpty = true
				case "flow":
					info.Flow = true
				case "inline":
					inline = true
				default:
					return nil, errors.New(fmt.Sprintf("Unsupported flag %q in tag %q of type %s", flag, tag, st))
				}
			}
			tag = fields[0]
		}

		if inline {
			switch field.Type.Kind() {
			// TODO: Implement support for inline maps.
			//case reflect.Map:
			//	if inlineMap >= 0 {
			//		return nil, errors.New("Multiple ,inline maps in struct " + st.String())
			//	}
			//	if field.Type.Key() != reflect.TypeOf("") {
			//		return nil, errors.New("Option ,inline needs a map with string keys in struct " + st.String())
			//	}
			//	inlineMap = info.Num
			case reflect.Struct:
				sinfo, err := getStructInfo(field.Type)
				if err != nil {
					return nil, err
				}
				for _, finfo := range sinfo.FieldsList {
					if _, found := fieldsMap[finfo.Key]; found {
						msg := "Duplicated key '" + finfo.Key + "' in struct " + st.String()
						return nil, errors.New(msg)
					}
					if finfo.Inline == nil {
						finfo.Inline = []int{i, finfo.Num}
					} else {
						finfo.Inline = append([]int{i}, finfo.Inline...)
					}
					fieldsMap[finfo.Key] = finfo
					fieldsList = append(fieldsList, finfo)
				}
			default:
				//return nil, errors.New("Option ,inline needs a struct value or map field")
				return nil, errors.New("Option ,inline needs a struct value field")
			}
			continue
		}

		if tag != "" {
			info.Key = tag
		} else {
			info.Key = strings.ToLower(field.Name)
		}

		if _, found = fieldsMap[info.Key]; found {
			msg := "Duplicated key '" + info.Key + "' in struct " + st.String()
			return nil, errors.New(msg)
		}

		fieldsList = append(fieldsList, info)
		fieldsMap[info.Key] = info
	}

	sinfo = &structInfo{fieldsMap, fieldsList, inlineMap}

	fieldMapMutex.Lock()
	structMap[st] = sinfo
	fieldMapMutex.Unlock()
	return sinfo, nil
}

func isZero(v reflect.Value) bool {
	switch v.Kind() {
	case reflect.String:
		return len(v.String()) == 0
	case reflect.Interface, reflect.Ptr:
		return v.IsNil()
	case reflect.Slice:
		return v.Len() == 0
	case reflect.Map:
		return v.Len() == 0
	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
		return v.Int() == 0
	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
		return v.Uint() == 0
	case reflect.Bool:
		return !v.Bool()
	}
	return false
}