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|
package ber
import (
"errors"
"fmt"
"io"
"math"
)
func readIdentifier(reader io.Reader) (Identifier, int, error) {
identifier := Identifier{}
read := 0
// identifier byte
b, err := readByte(reader)
if err != nil {
if Debug {
fmt.Printf("error reading identifier byte: %v\n", err)
}
return Identifier{}, read, err
}
read++
identifier.ClassType = Class(b) & ClassBitmask
identifier.TagType = Type(b) & TypeBitmask
if tag := Tag(b) & TagBitmask; tag != HighTag {
// short-form tag
identifier.Tag = tag
return identifier, read, nil
}
// high-tag-number tag
tagBytes := 0
for {
b, err := readByte(reader)
if err != nil {
if Debug {
fmt.Printf("error reading high-tag-number tag byte %d: %v\n", tagBytes, err)
}
return Identifier{}, read, err
}
tagBytes++
read++
// Lowest 7 bits get appended to the tag value (x.690, 8.1.2.4.2.b)
identifier.Tag <<= 7
identifier.Tag |= Tag(b) & HighTagValueBitmask
// First byte may not be all zeros (x.690, 8.1.2.4.2.c)
if tagBytes == 1 && identifier.Tag == 0 {
return Identifier{}, read, errors.New("invalid first high-tag-number tag byte")
}
// Overflow of int64
// TODO: support big int tags?
if tagBytes > 9 {
return Identifier{}, read, errors.New("high-tag-number tag overflow")
}
// Top bit of 0 means this is the last byte in the high-tag-number tag (x.690, 8.1.2.4.2.a)
if Tag(b)&HighTagContinueBitmask == 0 {
break
}
}
return identifier, read, nil
}
func encodeIdentifier(identifier Identifier) []byte {
b := []byte{0x0}
b[0] |= byte(identifier.ClassType)
b[0] |= byte(identifier.TagType)
if identifier.Tag < HighTag {
// Short-form
b[0] |= byte(identifier.Tag)
} else {
// high-tag-number
b[0] |= byte(HighTag)
tag := identifier.Tag
highBit := uint(63)
for {
if tag&(1<<highBit) != 0 {
break
}
highBit--
}
tagBytes := int(math.Ceil(float64(highBit) / 7.0))
for i := tagBytes - 1; i >= 0; i-- {
offset := uint(i) * 7
mask := Tag(0x7f) << offset
tagByte := (tag & mask) >> offset
if i != 0 {
tagByte |= 0x80
}
b = append(b, byte(tagByte))
}
}
return b
}
|
