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82 lines
2.0 KiB
82 lines
2.0 KiB
package ber
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import (
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"errors"
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"fmt"
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"io"
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)
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func readLength(reader io.Reader) (length int, read int, err error) {
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// length byte
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b, err := readByte(reader)
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if err != nil {
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if Debug {
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fmt.Printf("error reading length byte: %v\n", err)
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}
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return 0, 0, err
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}
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read++
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switch {
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case b == 0xFF:
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// Invalid 0xFF (x.600, 8.1.3.5.c)
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return 0, read, errors.New("invalid length byte 0xff")
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case b == LengthLongFormBitmask:
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// Indefinite form, we have to decode packets until we encounter an EOC packet (x.600, 8.1.3.6)
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length = LengthIndefinite
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case b&LengthLongFormBitmask == 0:
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// Short definite form, extract the length from the bottom 7 bits (x.600, 8.1.3.4)
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length = int(b) & LengthValueBitmask
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case b&LengthLongFormBitmask != 0:
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// Long definite form, extract the number of length bytes to follow from the bottom 7 bits (x.600, 8.1.3.5.b)
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lengthBytes := int(b) & LengthValueBitmask
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// Protect against overflow
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// TODO: support big int length?
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if lengthBytes > 8 {
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return 0, read, errors.New("long-form length overflow")
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}
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// Accumulate into a 64-bit variable
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var length64 int64
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for i := 0; i < lengthBytes; i++ {
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b, err = readByte(reader)
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if err != nil {
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if Debug {
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fmt.Printf("error reading long-form length byte %d: %v\n", i, err)
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}
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return 0, read, err
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}
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read++
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// x.600, 8.1.3.5
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length64 <<= 8
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length64 |= int64(b)
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}
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// Cast to a platform-specific integer
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length = int(length64)
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// Ensure we didn't overflow
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if int64(length) != length64 {
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return 0, read, errors.New("long-form length overflow")
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}
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default:
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return 0, read, errors.New("invalid length byte")
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}
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return length, read, nil
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}
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func encodeLength(length int) []byte {
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lengthBytes := encodeUnsignedInteger(uint64(length))
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if length > 127 || len(lengthBytes) > 1 {
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longFormBytes := []byte{LengthLongFormBitmask | byte(len(lengthBytes))}
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longFormBytes = append(longFormBytes, lengthBytes...)
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lengthBytes = longFormBytes
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}
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return lengthBytes
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}
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