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// Copyright The Notary Project Authors.
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package ber
import "io"
// writer is the interface that wraps the basic Write and WriteByte methods.
type writer interface {
io.Writer
io.ByteWriter
}
// encodeLength encodes length octets in DER.
// Reference:
// - ISO/IEC 8825-1: 10.1
// - https://learn.microsoft.com/windows/win32/seccertenroll/about-encoded-length-and-value-bytes
func encodeLength(w io.ByteWriter, length int) error {
// DER restriction: short form must be used for length less than 128
if length < 0x80 {
return w.WriteByte(byte(length))
}
// DER restriction: long form must be encoded in the minimum number of octets
lengthSize := encodedLengthSize(length)
err := w.WriteByte(0x80 | byte(lengthSize-1))
if err != nil {
return err
}
for i := lengthSize - 1; i > 0; i-- {
if err = w.WriteByte(byte(length >> (8 * (i - 1)))); err != nil {
return err
}
}
return nil
}
// encodedLengthSize gives the number of octets used for encoding the length
// in DER.
// Reference:
// - ISO/IEC 8825-1: 10.1
// - https://learn.microsoft.com/windows/win32/seccertenroll/about-encoded-length-and-value-bytes
func encodedLengthSize(length int) int {
if length < 0x80 {
return 1
}
lengthSize := 1
for length > 0 {
length >>= 8
lengthSize++
}
return lengthSize
}
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