// This function reads all the EOCD stuff it needs to find the offset to the start of the central directory
// This offset gets put in _centralDirectoryStart and the number of this disk gets put in _numberOfThisDisk
// Also does some verification that this isn't a split/spanned archive
// Also checks that offset to CD isn't out of bounds
private void ReadEndOfCentralDirectory()
{
try
{
// this seeks to the start of the end of central directory record
ArchiveStream.Seek(-ZipEndOfCentralDirectoryBlock.SizeOfBlockWithoutSignature, SeekOrigin.End);
if (!ZipHelper.SeekBackwardsToSignature(ArchiveStream, ZipEndOfCentralDirectoryBlock.SignatureConstant))
{
throw new InvalidDataException(SR.EOCDNotFound);
}
long eocdStart = ArchiveStream.Position;
// read the EOCD
ZipEndOfCentralDirectoryBlock eocd;
bool eocdProper = ZipEndOfCentralDirectoryBlock.TryReadBlock(ArchiveReader, out eocd);
Debug.Assert(eocdProper); // we just found this using the signature finder, so it should be okay
if (eocd.NumberOfThisDisk != eocd.NumberOfTheDiskWithTheStartOfTheCentralDirectory)
{
throw new InvalidDataException(SR.SplitSpanned);
}
NumberOfThisDisk = eocd.NumberOfThisDisk;
_centralDirectoryStart = eocd.OffsetOfStartOfCentralDirectoryWithRespectToTheStartingDiskNumber;
if (eocd.NumberOfEntriesInTheCentralDirectory != eocd.NumberOfEntriesInTheCentralDirectoryOnThisDisk)
{
throw new InvalidDataException(SR.SplitSpanned);
}
_expectedNumberOfEntries = eocd.NumberOfEntriesInTheCentralDirectory;
// only bother looking for zip64 EOCD stuff if we suspect it is needed because some value is FFFFFFFFF
// because these are the only two values we need, we only worry about these
// if we don't find the zip64 EOCD, we just give up and try to use the original values
if (eocd.NumberOfThisDisk == ZipHelper.Mask16Bit ||
eocd.OffsetOfStartOfCentralDirectoryWithRespectToTheStartingDiskNumber == ZipHelper.Mask32Bit ||
eocd.NumberOfEntriesInTheCentralDirectory == ZipHelper.Mask16Bit)
{
// we need to look for zip 64 EOCD stuff
// seek to the zip 64 EOCD locator
ArchiveStream.Seek(eocdStart - Zip64EndOfCentralDirectoryLocator.SizeOfBlockWithoutSignature, SeekOrigin.Begin);
// if we don't find it, assume it doesn't exist and use data from normal eocd
if (ZipHelper.SeekBackwardsToSignature(ArchiveStream, Zip64EndOfCentralDirectoryLocator.SignatureConstant))
{
// use locator to get to Zip64EOCD
Zip64EndOfCentralDirectoryLocator locator;
bool zip64EOCDLocatorProper = Zip64EndOfCentralDirectoryLocator.TryReadBlock(ArchiveReader, out locator);
Debug.Assert(zip64EOCDLocatorProper); // we just found this using the signature finder, so it should be okay
if (locator.OffsetOfZip64EOCD > long.MaxValue)
{
throw new InvalidDataException(SR.FieldTooBigOffsetToZip64EOCD);
}
long zip64EOCDOffset = (long)locator.OffsetOfZip64EOCD;
ArchiveStream.Seek(zip64EOCDOffset, SeekOrigin.Begin);
// read Zip64EOCD
Zip64EndOfCentralDirectoryRecord record;
if (!Zip64EndOfCentralDirectoryRecord.TryReadBlock(ArchiveReader, out record))
{
throw new InvalidDataException(SR.Zip64EOCDNotWhereExpected);
}
NumberOfThisDisk = record.NumberOfThisDisk;
if (record.NumberOfEntriesTotal > long.MaxValue)
{
throw new InvalidDataException(SR.FieldTooBigNumEntries);
}
if (record.OffsetOfCentralDirectory > long.MaxValue)
{
throw new InvalidDataException(SR.FieldTooBigOffsetToCD);
}
if (record.NumberOfEntriesTotal != record.NumberOfEntriesOnThisDisk)
{
throw new InvalidDataException(SR.SplitSpanned);
}
_expectedNumberOfEntries = (long)record.NumberOfEntriesTotal;
_centralDirectoryStart = (long)record.OffsetOfCentralDirectory;
}
}
if (_centralDirectoryStart > ArchiveStream.Length)
{
throw new InvalidDataException(SR.FieldTooBigOffsetToCD);
}
}
catch (EndOfStreamException ex)
{
throw new InvalidDataException(SR.CDCorrupt, ex);
}
catch (IOException ex)
{
throw new InvalidDataException(SR.CDCorrupt, ex);
}
}