public static bool TryRead(Stream logStream, out LogEntry entry)
{
long position = logStream.Position;
byte[] sectorBuffer = new byte[LogSectorSize];
Utilities.ReadFully(logStream, sectorBuffer, 0, sectorBuffer.Length);
uint sig = Utilities.ToUInt32LittleEndian(sectorBuffer, 0);
if (sig != LogEntryHeader.LogEntrySignature)
{
entry = null;
return false;
}
LogEntryHeader header = new LogEntryHeader();
header.ReadFrom(sectorBuffer, 0);
if (!header.IsValid || header.EntryLength > logStream.Length)
{
entry = null;
return false;
}
byte[] logEntryBuffer = new byte[header.EntryLength];
Array.Copy(sectorBuffer, logEntryBuffer, LogSectorSize);
Utilities.ReadFully(logStream, logEntryBuffer, LogSectorSize, logEntryBuffer.Length - LogSectorSize);
Utilities.WriteBytesLittleEndian((int)0, logEntryBuffer, 4);
if (header.Checksum != Crc32LittleEndian.Compute(Crc32Algorithm.Castagnoli, logEntryBuffer, 0, (int)header.EntryLength))
{
entry = null;
return false;
}
int dataPos = Utilities.RoundUp(((int)header.DescriptorCount * 32) + 64, LogSectorSize);
List<Descriptor> descriptors = new List<Descriptor>();
for (int i = 0; i < header.DescriptorCount; ++i)
{
int offset = (i * 32) + 64;
Descriptor descriptor;
uint descriptorSig = Utilities.ToUInt32LittleEndian(logEntryBuffer, offset);
switch (descriptorSig)
{
case Descriptor.ZeroDescriptorSignature:
descriptor = new ZeroDescriptor();
break;
case Descriptor.DataDescriptorSignature:
descriptor = new DataDescriptor(logEntryBuffer, dataPos);
dataPos += LogSectorSize;
break;
default:
entry = null;
return false;
}
descriptor.ReadFrom(logEntryBuffer, offset);
if (!descriptor.IsValid(header.SequenceNumber))
{
entry = null;
return false;
}
descriptors.Add(descriptor);
}
entry = new LogEntry(position, header, descriptors);
return true;
}
internal LogEntryInfo(LogEntry entry)
{
_entry = entry;
}