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package ber
import (
"errors"
"fmt"
"io"
)
func readLength(reader io.Reader) (length int, read int, err error) {
// length byte
b, err := readByte(reader)
if err != nil {
if Debug {
fmt.Printf("error reading length byte: %v\n", err)
}
return 0, 0, err
}
read++
switch {
case b == 0xFF:
// Invalid 0xFF (x.600, 8.1.3.5.c)
return 0, read, errors.New("invalid length byte 0xff")
case b == LengthLongFormBitmask:
// Indefinite form, we have to decode packets until we encounter an EOC packet (x.600, 8.1.3.6)
length = LengthIndefinite
case b&LengthLongFormBitmask == 0:
// Short definite form, extract the length from the bottom 7 bits (x.600, 8.1.3.4)
length = int(b) & LengthValueBitmask
case b&LengthLongFormBitmask != 0:
// Long definite form, extract the number of length bytes to follow from the bottom 7 bits (x.600, 8.1.3.5.b)
lengthBytes := int(b) & LengthValueBitmask
// Protect against overflow
// TODO: support big int length?
if lengthBytes > 8 {
return 0, read, errors.New("long-form length overflow")
}
for i := 0; i < lengthBytes; i++ {
b, err = readByte(reader)
if err != nil {
if Debug {
fmt.Printf("error reading long-form length byte %d: %v\n", i, err)
}
return 0, read, err
}
read++
// x.600, 8.1.3.5
length <<= 8
length |= int(b)
}
default:
return 0, read, errors.New("invalid length byte")
}
return length, read, nil
}
func encodeLength(length int) []byte {
length_bytes := encodeUnsignedInteger(uint64(length))
if length > 127 || len(length_bytes) > 1 {
longFormBytes := []byte{(LengthLongFormBitmask | byte(len(length_bytes)))}
longFormBytes = append(longFormBytes, length_bytes...)
length_bytes = longFormBytes
}
return length_bytes
}
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