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Asn1Writer.cs
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Asn1Writer.cs
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using System;
namespace NSec.Cryptography.Formatting
{
// ITU-T X.690 5.0 DER
internal struct Asn1Writer
{
private readonly Span<byte> _buffer;
private readonly int[] _stack;
private int _depth;
private int _pos;
public Asn1Writer(
Span<byte> buffer,
int maxDepth = 8)
{
_buffer = buffer;
_depth = 0;
_pos = buffer.Length;
_stack = new int[maxDepth];
}
public ReadOnlySpan<byte> Bytes => _buffer.Slice(_pos);
public void BeginSequence()
{
_depth--;
WriteLength(_stack[_depth] - _pos);
WriteByte(0x30);
}
public void BitString(
ReadOnlySpan<byte> bits)
{
WriteBytes(bits);
WriteByte(0);
WriteLength(1 + bits.Length);
WriteByte(0x03);
}
public void Bool(
bool value)
{
unchecked
{
WriteByte((byte)(value ? -1 : 0));
}
WriteLength(1);
WriteByte(0x01);
}
public void End()
{
_stack[_depth] = _pos;
_depth++;
}
public void Integer(
int value)
{
int end = _pos;
unchecked
{
WriteByte((byte)value);
while ((value & ~0x7F) != 0 && (value & ~0x7F) != ~0x7F)
{
value >>= 8;
WriteByte((byte)value);
}
}
WriteLength(end - _pos);
WriteByte(0x02);
}
public void Integer(
long value)
{
int end = _pos;
unchecked
{
WriteByte((byte)value);
while ((value & ~0x7F) != 0 && (value & ~0x7F) != ~0x7F)
{
value >>= 8;
WriteByte((byte)value);
}
}
WriteLength(end - _pos);
WriteByte(0x02);
}
public void Null()
{
WriteLength(0);
WriteByte(0x05);
}
public void ObjectIdentifier(
ReadOnlySpan<byte> oid)
{
WriteBytes(oid);
WriteLength(oid.Length);
WriteByte(0x06);
}
public void OctetString(
ReadOnlySpan<byte> octets)
{
WriteBytes(octets);
WriteLength(octets.Length);
WriteByte(0x04);
}
private void WriteByte(
byte value)
{
if (_pos == 0)
throw new ArgumentException(); // not enough space
_pos--;
_buffer[_pos] = value;
}
private void WriteBytes(
ReadOnlySpan<byte> bytes)
{
if (bytes.Length > _pos)
throw new ArgumentException(); // not enough space
_pos -= bytes.Length;
bytes.CopyTo(_buffer.Slice(_pos));
}
private void WriteLength(
int length)
{
if (length < 0x80)
{
WriteByte((byte)length);
}
else
{
int end = _pos;
unchecked
{
WriteByte((byte)length);
while ((length & ~0xFF) != 0)
{
length >>= 8;
WriteByte((byte)length);
}
}
WriteByte((byte)(0x80 + (end - _pos)));
}
}
}
}