/// <summary>
/// Decodes the data from the buffer and stores the data in this object.
/// </summary>
/// <param name="buffer">A buffer that stores a BER encoding result.</param>
/// <param name="length">The length of the encoding result of the data in the given buffer.</param>
/// <returns>The number of the bytes consumed in the buffer to decode the data.</returns>
/// <remarks>
/// For the TLV (Tag, Length, Value) triple in the encoding result,
/// this method provides the functionality of decoding Value.
/// The decoding for Tag and Length will be done in Asn1Object::BerDecode method.
/// </remarks>
protected override int ValueBerDecode(IAsn1DecodingBuffer buffer, int length)
{
int consumedLen = 0;
Asn1Tag tag = null; //The current decoded tag.
int tagLen = 0; //The consumed length of the bytes in the buffer when decoding the current tag.
bool tagUsed = true;
int curFieldIndex = 0;//The index of the field that currently is trying to decode.
Asn1Object[] tempFields = FieldsTypeInstances;
while (consumedLen < length)
{
if (curFieldIndex >= tempFields.Length)
{
throw new Asn1DecodingUnexpectedData(ExceptionMessages.DecodingUnexpectedData);
}
if (tagUsed)
{
tagLen = TagBerDecode(buffer, out tag);
//The decoded tag may be context , application or universal tag.
}
if (fieldsMetaData[curFieldIndex].Optional == false)
{
//Current field is mandatory.
if (fieldsMetaData[curFieldIndex].AttachedTag != null)
{
//Current field has a context class tag.
//The decoded tag must be the context class tag of the field.
if (tag.Equals(fieldsMetaData[curFieldIndex].AttachedTag))
{
consumedLen += tagLen;
int lengthAfterCtxTag;
consumedLen += LengthBerDecode(buffer, out lengthAfterCtxTag);
//Decodes this field by Asn1Object::BerDecode when the if-else statement for fieldOptionalFlags ends.
}
else
{
throw new Asn1DecodingUnexpectedData(ExceptionMessages.DecodingUnexpectedData + " Context Tag Decode fail.");
}
}
else
{
//Current field doesn't have a context class tag.
//The decoded tag must be the application or universal class tag of the field.
//Retreat the buffer since the decoding of application or universal class is part of Asn1Object::BerDecode.
buffer.SeekBytePosition(-tagLen);
//Decode this field by Asn1Object::BerDecode when the if-else statement for fieldOptionalFlags ends.
}
}
else
{
//Current field is optional.
if (fieldsMetaData[curFieldIndex].AttachedTag != null)
{
//Current field has a context class tag.
//Check whether it is the encoding result of this field by the context-specific class tag.
if (tag.Equals(fieldsMetaData[curFieldIndex].AttachedTag))
{
//Yes
consumedLen += tagLen;
int lengthAfterCtxTag;
consumedLen += LengthBerDecode(buffer, out lengthAfterCtxTag);
//Decode this field by Asn1Object::BerDecode when the if-else statement for OptionalFlags ends.
}
else
{
//No
tagUsed = false;
tempFields[curFieldIndex] = null;
curFieldIndex++;
//Check the next field.
continue;
}
}
else
{
//Current field doesn't have a context class tag.
//Check whether it is the encoding result of this field by the top most class tag.
if (tag.Equals(tempFields[curFieldIndex].TopTag))
{
//Yes
buffer.SeekBytePosition(-tagLen);
//Decode this field by Asn1Object::BerDecode when the if-else statement for OptionalFlags ends.
}
else
{
//No
tagUsed = false;
tempFields[curFieldIndex] = null;
curFieldIndex++;
//Check the next field.
continue;
}
}
}
consumedLen += tempFields[curFieldIndex].BerDecode(buffer);
tagUsed = true;
curFieldIndex++;
}
//Ensure consumedLen equals to length.
if (consumedLen > length)
{
throw new Asn1DecodingUnexpectedData(ExceptionMessages.DecodingUnexpectedData);
}
//Stores the decoded fields in this object.
if (tempFields.Length != fieldsMetaData.Length)
{
throw new Asn1DecodingUnexpectedData(ExceptionMessages.DecodingUnexpectedData);
}
for (int i = 0; i < curFieldIndex; i++)
{
if (fieldsMetaData[i].MemberInfo.MemberType == MemberTypes.Property)
{
(fieldsMetaData[i].MemberInfo as PropertyInfo).SetValue(this, tempFields[i], null);
}
else if (fieldsMetaData[i].MemberInfo.MemberType == MemberTypes.Field)
{
(fieldsMetaData[i].MemberInfo as FieldInfo).SetValue(this, tempFields[i]);
}
else
{
//Unreachable. Ensured by the AttributeUsage of Asn1Field.
throw new Asn1UserDefinedTypeInconsistent(ExceptionMessages.UserDefinedTypeInconsistent
+ " Asn1Field property could only be used in properties or fields.");
}
}
return(consumedLen);
}
