private List <Zip64LocalFileDataField> ReadZip64DataFields(LocalFileHeader entry)
{
// The Zip64 data field in the local file header is a subset of the information in the central directory
// header, so use the central directory flow and map the input/output.
var centralDirectoryHeader = new CentralDirectoryHeader
{
DataFields = entry.DataFields,
UncompressedSize = entry.UncompressedSize,
CompressedSize = entry.CompressedSize,
};
var fields = ReadZip64DataFields(centralDirectoryHeader, ZipConstants.MaximumZip64LocalFileDataFieldSize);
return(fields
.Select(x => new Zip64LocalFileDataField
{
CompressedSize = x.CompressedSize,
UncompressedSize = x.UncompressedSize,
})
.ToList());
}
private async Task <DataDescriptor> ReadDataDescriptor(
ZipDirectory directory,
List <CentralDirectoryHeader> entries,
CentralDirectoryHeader entry,
Zip64DataField zip64,
LocalFileHeader localEntry)
{
var compressedSize = zip64?.CompressedSize ?? entry.CompressedSize;
var uncompressedSize = zip64?.UncompressedSize ?? entry.UncompressedSize;
var dataDescriptorPosition = entry.LocalHeaderOffset
+ ZipConstants.LocalFileHeaderSize
+ localEntry.NameSize
+ localEntry.ExtraFieldSize
+ compressedSize;
_stream.Position = (long)dataDescriptorPosition;
var dataDescriptor = new DataDescriptor();
using (var buffer = await LoadBinaryReaderAsync(_buffer, ZipConstants.DataDescriptorSize))
{
var fieldA = buffer.ReadUInt32();
var fieldB = buffer.ReadUInt32();
var fieldC = buffer.ReadUInt32();
var fieldD = buffer.ReadUInt32();
// Check the first field to see if is the signature. This is the most reliable check but can yield
// false negatives. This is because it's possible for the CRC-32 to be the same as the optional
// data descriptor signature. There is no possibility for false positive. That is, if the first
// byte does not match signature, then the first byte is definitely the CRC-32.
var firstFieldImpliesNoSignature = fieldA != ZipConstants.DataDescriptorSignature;
// 1. Use the known field values from the central directory, given the first field matches the signature.
var valuesImplySignature = !firstFieldImpliesNoSignature &&
fieldB == entry.Crc32 &&
fieldC == compressedSize &&
fieldD == uncompressedSize;
if (valuesImplySignature)
{
return(CreateDataDescriptor(fieldB, fieldC, fieldD, hasSignature: true));
}
// 2. Use the known field values from the central directory.
var valuesImplyNoSignature = fieldA == entry.Crc32 &&
fieldB == compressedSize &&
fieldC == uncompressedSize;
if (valuesImplyNoSignature)
{
return(CreateDataDescriptor(fieldA, fieldB, fieldC, hasSignature: false));
}
// 3. Use just the signature.
if (!firstFieldImpliesNoSignature)
{
return(CreateDataDescriptor(fieldB, fieldC, fieldD, hasSignature: true));
}
return(CreateDataDescriptor(fieldA, fieldB, fieldC, hasSignature: false));
}
}
/// <summary>
/// Reads a specific local file header given a central directory header for a file.
/// </summary>
/// <param name="directory">The ZIP directory instance containing the provided <paramref name="entry"/>.</param>
/// <param name="entry">The central directory header to read the local file header for.</param>
/// <param name="readDataDescriptor">Whether or not to read the data descriptor, if present.</param>
/// <returns>The local file header.</returns>
public async Task <LocalFileHeader> ReadLocalFileHeaderAsync(ZipDirectory directory, CentralDirectoryHeader entry, bool readDataDescriptor)
{
if (directory == null)
{
throw new ArgumentNullException(nameof(directory));
}
if (entry == null)
{
throw new ArgumentNullException(nameof(entry));
}
var entries = directory.Entries ?? new List <CentralDirectoryHeader>();
if (!entries.Contains(entry))
{
throw new ArgumentException(Strings.HeaderDoesNotMatchDirectory, nameof(entry));
}
if ((entry.Flags & (ushort)ZipEntryFlags.Encrypted) != 0)
{
throw new MiniZipException(Strings.EncryptedFilesNotSupported);
}
var zip64 = entry.Zip64DataFields.FirstOrDefault();
var localHeaderOffset = zip64?.LocalHeaderOffset ?? entry.LocalHeaderOffset;
_stream.Position = (long)localHeaderOffset;
if (await ReadUInt32Async() != ZipConstants.LocalFileHeaderSignature)
{
throw new MiniZipException(Strings.InvalidLocalFileHeaderSignature);
}
var localEntry = new LocalFileHeader();
using (var buffer = await LoadBinaryReaderAsync(_buffer, ZipConstants.LocalFileHeaderSizeWithoutSignature))
{
localEntry.VersionToExtract = buffer.ReadUInt16();
localEntry.Flags = buffer.ReadUInt16();
localEntry.CompressionMethod = buffer.ReadUInt16();
localEntry.LastModifiedTime = buffer.ReadUInt16();
localEntry.LastModifiedDate = buffer.ReadUInt16();
localEntry.Crc32 = buffer.ReadUInt32();
localEntry.CompressedSize = buffer.ReadUInt32();
localEntry.UncompressedSize = buffer.ReadUInt32();
localEntry.NameSize = buffer.ReadUInt16();
localEntry.ExtraFieldSize = buffer.ReadUInt16();
}
localEntry.Name = new byte[localEntry.NameSize];
await ReadFullyAsync(localEntry.Name);
localEntry.ExtraField = new byte[localEntry.ExtraFieldSize];
await ReadFullyAsync(localEntry.ExtraField);
localEntry.DataFields = ReadDataFields(localEntry.ExtraField);
localEntry.Zip64DataFields = ReadZip64DataFields(localEntry);
// Try to read the data descriptor.
if (readDataDescriptor && (localEntry.Flags & (ushort)ZipEntryFlags.DataDescriptor) != 0)
{
localEntry.DataDescriptor = await ReadDataDescriptor(directory, entries, entry, zip64, localEntry);
}
return(localEntry);
}
