source: code/trunk/vendor/gopkg.in/yaml.v2/yaml.go@ 67

// 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"
        "io"
        "reflect"
        "strings"
        "sync"
)

// MapSlice encodes and decodes as a YAML map.
// The order of keys is preserved when encoding and decoding.
type MapSlice []MapItem

// MapItem is an item in a MapSlice.
type MapItem struct {
        Key, Value interface{}
}

// The Unmarshaler interface may be implemented by types to customize their
// behavior when being unmarshaled from a YAML document. The UnmarshalYAML
// method receives a function that may be called to unmarshal the original
// YAML value into a field or variable. It is safe to call the unmarshal
// function parameter more than once if necessary.
type Unmarshaler interface {
        UnmarshalYAML(unmarshal func(interface{}) error) error
}

// The Marshaler interface may be implemented by types to customize their
// behavior when being marshaled into a YAML document. The returned value
// is marshaled in place of the original value implementing Marshaler.
//
// If an error is returned by MarshalYAML, the marshaling procedure stops
// and returns with the provided error.
type Marshaler interface {
        MarshalYAML() (interface{}, error)
}

// 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 should be compatible with the respective
// values in out. If one or more values cannot be decoded due to a type
// mismatches, decoding continues partially until the end of the YAML
// content, and a *yaml.TypeError is returned with details for all
// missed values.
//
// 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) {
        return unmarshal(in, out, false)
}

// UnmarshalStrict is like Unmarshal except that any fields that are found
// in the data that do not have corresponding struct members, or mapping
// keys that are duplicates, will result in
// an error.
func UnmarshalStrict(in []byte, out interface{}) (err error) {
        return unmarshal(in, out, true)
}

// A Decoder reads and decodes YAML values from an input stream.
type Decoder struct {
        strict bool
        parser *parser
}

// NewDecoder returns a new decoder that reads from r.
//
// The decoder introduces its own buffering and may read
// data from r beyond the YAML values requested.
func NewDecoder(r io.Reader) *Decoder {
        return &Decoder{
                parser: newParserFromReader(r),
        }
}

// SetStrict sets whether strict decoding behaviour is enabled when
// decoding items in the data (see UnmarshalStrict). By default, decoding is not strict.
func (dec *Decoder) SetStrict(strict bool) {
        dec.strict = strict
}

// Decode reads the next YAML-encoded value from its input
// and stores it in the value pointed to by v.
//
// See the documentation for Unmarshal for details about the
// conversion of YAML into a Go value.
func (dec *Decoder) Decode(v interface{}) (err error) {
        d := newDecoder(dec.strict)
        defer handleErr(&err)
        node := dec.parser.parse()
        if node == nil {
                return io.EOF
        }
        out := reflect.ValueOf(v)
        if out.Kind() == reflect.Ptr && !out.IsNil() {
                out = out.Elem()
        }
        d.unmarshal(node, out)
        if len(d.terrors) > 0 {
                return &TypeError{d.terrors}
        }
        return nil
}

func unmarshal(in []byte, out interface{}, strict bool) (err error) {
        defer handleErr(&err)
        d := newDecoder(strict)
        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)
        }
        if len(d.terrors) > 0 {
                return &TypeError{d.terrors}
        }
        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 marshalled if they are exported (have an upper case
// first letter), and are marshalled 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.
//                  Zero valued structs will be omitted if all their public
//                  fields are zero, unless they implement an IsZero
//                  method (see the IsZeroer interface type), in which
//                  case the field will be excluded if IsZero returns true.
//
//     flow         Marshal using a flow style (useful for structs,
//                  sequences and maps).
//
//     inline       Inline the field, which must be a struct or a map,
//                  causing all of its fields or keys to be processed as if
//                  they were part of the outer struct. For maps, keys must
//                  not conflict with the yaml keys of other struct fields.
//
// In addition, if the key is "-", the field is ignored.
//
// For example:
//
//     type T struct {
//         F int `yaml:"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.marshalDoc("", reflect.ValueOf(in))
        e.finish()
        out = e.out
        return
}

// An Encoder writes YAML values to an output stream.
type Encoder struct {
        encoder *encoder
}

// NewEncoder returns a new encoder that writes to w.
// The Encoder should be closed after use to flush all data
// to w.
func NewEncoder(w io.Writer) *Encoder {
        return &Encoder{
                encoder: newEncoderWithWriter(w),
        }
}

// Encode writes the YAML encoding of v to the stream.
// If multiple items are encoded to the stream, the
// second and subsequent document will be preceded
// with a "---" document separator, but the first will not.
//
// See the documentation for Marshal for details about the conversion of Go
// values to YAML.
func (e *Encoder) Encode(v interface{}) (err error) {
        defer handleErr(&err)
        e.encoder.marshalDoc("", reflect.ValueOf(v))
        return nil
}

// Close closes the encoder by writing any remaining data.
// It does not write a stream terminating string "...".
func (e *Encoder) Close() (err error) {
        defer handleErr(&err)
        e.encoder.finish()
        return nil
}

func handleErr(err *error) {
        if v := recover(); v != nil {
                if e, ok := v.(yamlError); ok {
                        *err = e.err
                } else {
                        panic(v)
                }
        }
}

type yamlError struct {
        err error
}

func fail(err error) {
        panic(yamlError{err})
}

func failf(format string, args ...interface{}) {
        panic(yamlError{fmt.Errorf("yaml: "+format, args...)})
}

// A TypeError is returned by Unmarshal when one or more fields in
// the YAML document cannot be properly decoded into the requested
// types. When this error is returned, the value is still
// unmarshaled partially.
type TypeError struct {
        Errors []string
}

func (e *TypeError) Error() string {
        return fmt.Sprintf("yaml: unmarshal errors:\n  %s", strings.Join(e.Errors, "\n  "))
}

// --------------------------------------------------------------------------
// 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
        // Id holds the unique field identifier, so we can cheaply
        // check for field duplicates without maintaining an extra map.
        Id int

        // 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 != "" && !field.Anonymous {
                        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() {
                        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...)
                                        }
                                        finfo.Id = len(fieldsList)
                                        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)
                }

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

        sinfo = &structInfo{
                FieldsMap:  fieldsMap,
                FieldsList: fieldsList,
                InlineMap:  inlineMap,
        }

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

// IsZeroer is used to check whether an object is zero to
// determine whether it should be omitted when marshaling
// with the omitempty flag. One notable implementation
// is time.Time.
type IsZeroer interface {
        IsZero() bool
}

func isZero(v reflect.Value) bool {
        kind := v.Kind()
        if z, ok := v.Interface().(IsZeroer); ok {
                if (kind == reflect.Ptr || kind == reflect.Interface) && v.IsNil() {
                        return true
                }
                return z.IsZero()
        }
        switch 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.Float32, reflect.Float64:
                return v.Float() == 0
        case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
                return v.Uint() == 0
        case reflect.Bool:
                return !v.Bool()
        case reflect.Struct:
                vt := v.Type()
                for i := v.NumField() - 1; i >= 0; i-- {
                        if vt.Field(i).PkgPath != "" {
                                continue // Private field
                        }
                        if !isZero(v.Field(i)) {
                                return false
                        }
                }
                return true
        }
        return false
}

// FutureLineWrap globally disables line wrapping when encoding long strings.
// This is a temporary and thus deprecated method introduced to faciliate
// migration towards v3, which offers more control of line lengths on
// individual encodings, and has a default matching the behavior introduced
// by this function.
//
// The default formatting of v2 was erroneously changed in v2.3.0 and reverted
// in v2.4.0, at which point this function was introduced to help migration.
func FutureLineWrap() {
        disableLineWrapping = true
}