field.go

// Copyright 2016 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package tiff

// A Field is primarily comprised of an Entry.  If the Entry's value is actually
// an offset to the data that the entry describes, then the Field will contain
// both the offset and the data that the offset points to in the file.

import (
	"encoding/binary"
	"encoding/json"
	"fmt"
	"reflect"
	"sync"
)

type FieldParser func(BReader, TagSpace, FieldTypeSpace) (Field, error)

var (
	tiffFieldPrintFullFieldValue bool
	printMu                      sync.RWMutex
)

func SetTiffFieldPrintFullFieldValue(b bool) {
	printMu.Lock()
	defer printMu.Unlock()
	tiffFieldPrintFullFieldValue = b
}

func GetTiffFieldPrintFullFieldValue() bool {
	printMu.RLock()
	defer printMu.RUnlock()
	return tiffFieldPrintFullFieldValue
}

type FieldValue interface {
	Order() binary.ByteOrder
	Bytes() []byte
}

type fieldValue struct {
	order binary.ByteOrder
	value []byte
}

func (fv *fieldValue) Order() binary.ByteOrder {
	return fv.order
}

func (fv *fieldValue) Bytes() []byte {
	return fv.value
}

func (fv *fieldValue) MarshalJSON() ([]byte, error) {
	tmp := struct {
		Bytes []byte
	}{
		Bytes: fv.value,
	}
	return json.Marshal(tmp)
}

// Field represents a field in an IFD in a TIFF file.
type Field interface {
	Tag() Tag
	Type() FieldType
	Count() uint64
	Offset() uint64
	Value() FieldValue // TODO: Change to BReader??
}

type field struct {
	entry Entry

	// If the offset from entry is actually a value, then the bytes will be
	// stored here and offset should be considered 0.  Otherwise, the offset
	// will indicate the location in the file where the values can be found.
	// Then value will be used to hold the bytes associated with those values.
	value FieldValue

	// ftsp is the FieldTypeSpace that can be used to look up the FieldType
	// that corresponds to the typeId of this entry.  If ftsp is nil, the
	// default set DefaultFieldTypeSpace is used instead.
	ftsp FieldTypeSpace

	// tsp is the TagSpace that can be used to look up the Tag that
	// corresponds to the result of entry.TagID().
	tsp TagSpace
}

func (f *field) Tag() Tag {
	if f.tsp == nil {
		return DefaultTagSpace.GetTag(f.entry.TagID())
	}
	return f.tsp.GetTag(f.entry.TagID())
}

func (f *field) Type() FieldType {
	if f.ftsp == nil {
		return DefaultFieldTypeSpace.GetFieldType(f.entry.TypeID())
	}
	return f.ftsp.GetFieldType(f.entry.TypeID())
}

func (f *field) Count() uint64 {
	return uint64(f.entry.Count())
}

func (f *field) Offset() uint64 {
	if f.Type().Size()*f.Count() <= 4 {
		return 0
	}
	offsetBytes := f.entry.ValueOffset()
	return uint64(f.value.Order().Uint32(offsetBytes[:]))
}

func (f *field) Value() FieldValue {
	return f.value
}

func (f *field) String() string {
	var (
		theTSP  = f.tsp
		theFTSP = f.ftsp
	)
	if theTSP == nil {
		theTSP = DefaultTagSpace
	}
	if theFTSP == nil {
		theFTSP = DefaultFieldTypeSpace
	}
	var valueRep string
	switch f.Type().ReflectType().Kind() {
	case reflect.String:
		if GetTiffFieldPrintFullFieldValue() {
			valueRep = fmt.Sprintf("%q", f.value.Bytes()[:f.Count()])
		} else {
			if f.Count() > 40 {
				valueRep = fmt.Sprintf("%q...", f.value.Bytes()[:41])
			} else {
				valueRep = fmt.Sprintf("%q", f.value.Bytes()[:f.Count()])
			}
		}
	default:
		// For general display purposes, don't show more than maxItems
		// amount of elements.  In this case, 10 is reasonable.  Beyond
		// 10 starts to line wrap in some cases like rationals.  If
		// we encounter that the value contains more than 10, we append
		// the ... to the end during string formatting to indicate that
		// there were more values, but they are not displayed here.
		const maxItems = 10
		buf := f.Value().Bytes()
		size := f.Type().Size()
		count := f.Count()
		if !GetTiffFieldPrintFullFieldValue() {
			if count > maxItems {
				count = maxItems
				buf = buf[:count*size]
			}
		}
		vals := make([]string, 0, count)
		for len(buf) > 0 {
			if f.Type().Repr() != nil {
				vals = append(vals, f.Type().Repr()(buf[:size], f.Value().Order()))
			} else {
				vals = append(vals, fmt.Sprintf("%v", buf[:size]))
			}
			buf = buf[size:]
		}
		if count == 1 {
			valueRep = vals[0]
		} else {
			if GetTiffFieldPrintFullFieldValue() {
				valueRep = fmt.Sprintf("%v", vals[:f.Count()])
			} else {
				// Keep a limit of 40 base characters when printing
				var totalLen, stop int
				for i := range vals {
					totalLen += len(vals[i])
					if totalLen > 40 {
						stop = i
						break
					}
					totalLen += 1 // account for space between values
				}
				if stop > 0 {
					vals = vals[:stop]
				}
				if stop > 0 || f.Count() > maxItems {
					valueRep = fmt.Sprintf("%v...", vals)
				} else {
					valueRep = fmt.Sprintf("%v", vals[:f.Count()])
				}
			}
		}
	}
	tagID := f.Tag().ID()
	return fmt.Sprintf(`<Tag: (%#04x/%05[1]d) %v	Type: (%02d) %v	Count: %d	Offset: %d	Value: %s	FieldTypeSpace: %q	TagSpaceSet: "%s.%s">`,
		tagID, f.Tag().Name(), f.Type().ID(), f.Type().Name(), f.Count(), f.Offset(), valueRep,
		theFTSP.Name(), theTSP.Name(), theTSP.GetTagSetNameFromTag(tagID))
}

func (f *field) MarshalJSON() ([]byte, error) {
	tmp := struct {
		E    Entry          `json:"Entry"`
		V    FieldValue     `json:"FieldValue"`
		FTSP FieldTypeSpace `json:"FieldTypeSpace"`
		TSP  TagSpace       `json:"TagSpace"`
	}{
		E:    f.entry,
		V:    f.value,
		FTSP: f.ftsp,
		TSP:  f.tsp,
	}
	return json.Marshal(tmp)
}

func ParseField(br BReader, tsp TagSpace, ftsp FieldTypeSpace) (out Field, err error) {
	if ftsp == nil {
		ftsp = DefaultFieldTypeSpace
	}
	if tsp == nil {
		tsp = DefaultTagSpace
	}
	f := &field{ftsp: ftsp, tsp: tsp}
	if f.entry, err = ParseEntry(br); err != nil {
		return
	}
	fv := &fieldValue{order: br.ByteOrder()}
	valSize := int64(f.Count()) * int64(f.Type().Size())
	valOffBytes := f.entry.ValueOffset()
	if valSize > 4 {
		fv.value = make([]byte, valSize)
		offset := int64(br.ByteOrder().Uint32(valOffBytes[:]))
		if err = br.BReadSection(&fv.value, offset, valSize); err != nil {
			return
		}
	} else {
		fv.value = valOffBytes[:]
	}
	f.value = fv
	return f, nil
}