/// <summary>
/// Locates the contents range for the encoded value at the beginning of the
/// <paramref name="source"/> buffer using the specified encoding rules.
/// </summary>
/// <param name="source">The buffer containing encoded data.</param>
/// <param name="ruleSet">The encoding constraints to use when interpreting the data.</param>
/// <param name="contentOffset">
/// When this method returns, the offset of the content payload relative to the start of
/// <paramref name="source"/>.
/// This parameter is treated as uninitialized.
/// </param>
/// <param name="contentLength">
/// When this method returns, the number of bytes in the content payload (which may be 0).
/// This parameter is treated as uninitialized.
/// </param>
/// <param name="bytesConsumed">
/// When this method returns, the total number of bytes for the encoded value.
/// This parameter is treated as uninitialized.
/// </param>
/// <returns>
/// The tag identifying the content.
/// </returns>
/// <remarks>
/// <para>
/// This method performs very little validation on the contents.
/// If the encoded value uses a definite length, the contents are not inspected at all.
/// If the encoded value uses an indefinite length, the contents are only inspected
/// as necessary to determine the location of the relevant end-of-contents marker.
/// </para>
/// <para>
/// When the encoded value uses an indefinite length, the <paramref name="bytesConsumed"/>
/// value will be larger than the sum of <paramref name="contentOffset"/> and
/// <paramref name="contentLength"/> to account for the end-of-contents marker.
/// </para>
/// </remarks>
/// <exception cref="ArgumentOutOfRangeException">
/// <paramref name="ruleSet"/> is not defined.
/// </exception>
/// <exception cref="AsnContentException">
/// <paramref name="source"/> does not represent a value encoded under the specified
/// encoding rules.
/// </exception>
public static Asn1Tag ReadEncodedValue(
ReadOnlySpan <byte> source,
AsnEncodingRules ruleSet,
out int contentOffset,
out int contentLength,
out int bytesConsumed)
{
CheckEncodingRules(ruleSet);
Asn1Tag tag = Asn1Tag.Decode(source, out int tagLength);
int? encodedLength = ReadLength(source.Slice(tagLength), ruleSet, out int lengthLength);
int headerLength = tagLength + lengthLength;
LengthValidity validity = ValidateLength(
source.Slice(headerLength),
ruleSet,
tag,
encodedLength,
out int len,
out int consumed);
if (validity == LengthValidity.Valid)
{
contentOffset = headerLength;
contentLength = len;
bytesConsumed = headerLength + consumed;
return(tag);
}
throw GetValidityException(validity);
}
private static AsnContentException GetValidityException(LengthValidity validity)
{
Debug.Assert(validity != LengthValidity.Valid);
switch (validity)
{
case LengthValidity.CerRequiresIndefinite:
return(new AsnContentException(SR.ContentException_CerRequiresIndefiniteLength));
case LengthValidity.LengthExceedsInput:
return(new AsnContentException(SR.ContentException_LengthExceedsPayload));
case LengthValidity.PrimitiveEncodingRequiresDefinite:
return(new AsnContentException());
default:
Debug.Fail($"No handler for validity {validity}.");
goto case LengthValidity.PrimitiveEncodingRequiresDefinite;
}
}
/// <summary>
/// Attempts locate the contents range for the encoded value at the beginning of the
/// <paramref name="source"/> buffer using the specified encoding rules.
/// </summary>
/// <param name="source">The buffer containing encoded data.</param>
/// <param name="ruleSet">The encoding constraints to use when interpreting the data.</param>
/// <param name="tag">
/// When this method returns, the tag identifying the content.
/// This parameter is treated as uninitialized.
/// </param>
/// <param name="contentOffset">
/// When this method returns, the offset of the content payload relative to the start of
/// <paramref name="source"/>.
/// This parameter is treated as uninitialized.
/// </param>
/// <param name="contentLength">
/// When this method returns, the number of bytes in the content payload (which may be 0).
/// This parameter is treated as uninitialized.
/// </param>
/// <param name="bytesConsumed">
/// When this method returns, the total number of bytes for the encoded value.
/// This parameter is treated as uninitialized.
/// </param>
/// <returns>
/// <see langword="true" /> if <paramref name="source"/> represents a valid structural
/// encoding for the specified encoding rules; otherwise, <see langword="false"/>.
/// </returns>
/// <remarks>
/// <para>
/// This method performs very little validation on the contents.
/// If the encoded value uses a definite length, the contents are not inspected at all.
/// If the encoded value uses an indefinite length, the contents are only inspected
/// as necessary to determine the location of the relevant end-of-contents marker.
/// </para>
/// <para>
/// When the encoded value uses an indefinite length, the <paramref name="bytesConsumed"/>
/// value will be larger than the sum of <paramref name="contentOffset"/> and
/// <paramref name="contentLength"/> to account for the end-of-contents marker.
/// </para>
/// </remarks>
/// <exception cref="ArgumentOutOfRangeException">
/// <paramref name="ruleSet"/> is not defined.
/// </exception>
public static bool TryReadEncodedValue(
ReadOnlySpan <byte> source,
AsnEncodingRules ruleSet,
out Asn1Tag tag,
out int contentOffset,
out int contentLength,
out int bytesConsumed)
{
CheckEncodingRules(ruleSet);
if (Asn1Tag.TryDecode(source, out Asn1Tag localTag, out int tagLength) &&
TryReadLength(source.Slice(tagLength), ruleSet, out int?encodedLength, out int lengthLength))
{
int headerLength = tagLength + lengthLength;
LengthValidity validity = ValidateLength(
source.Slice(headerLength),
ruleSet,
localTag,
encodedLength,
out int len,
out int consumed);
if (validity == LengthValidity.Valid)
{
tag = localTag;
contentOffset = headerLength;
contentLength = len;
bytesConsumed = headerLength + consumed;
return(true);
}
}
tag = default;
contentOffset = contentLength = bytesConsumed = 0;
return(false);
}