public static GitObjectId FindNode(Stream stream, ReadOnlySpan <byte> name)
{
byte[] buffer = ArrayPool <byte> .Shared.Rent((int)stream.Length);
Span <byte> contents = new Span <byte>(buffer, 0, (int)stream.Length);
stream.ReadAll(contents);
GitObjectId value = GitObjectId.Empty;
while (contents.Length > 0)
{
// Format: [mode] [file/ folder name]\0[SHA - 1 of referencing blob or tree]
// Mode is either 6-bytes long (directory) or 7-bytes long (file).
// If the entry is a file, the first byte is '1'
var fileNameEnds = contents.IndexOf((byte)0);
bool isFile = contents[0] == (byte)'1';
var modeLength = isFile ? 7 : 6;
var currentName = contents.Slice(modeLength, fileNameEnds - modeLength);
if (currentName.SequenceEqual(name))
{
value = GitObjectId.Parse(contents.Slice(fileNameEnds + 1, 20));
break;
}
else
{
contents = contents.Slice(fileNameEnds + 1 + 20);
}
}
ArrayPool <byte> .Shared.Return(buffer);
return(value);
}
public long?GetOffset(GitObjectId objectId)
{
this.Initialize();
Span <byte> buffer = stackalloc byte[4];
Span <byte> objectName = stackalloc byte[20];
objectId.CopyTo(objectName);
var packStart = this.fanoutTable[objectName[0]];
var packEnd = this.fanoutTable[objectName[0] + 1];
var objectCount = this.fanoutTable[256];
// The fanout table is followed by a table of sorted 20-byte SHA-1 object names.
// These are packed together without offset values to reduce the cache footprint of the binary search for a specific object name.
// The object names start at: 4 (header) + 4 (version) + 256 * 4 (fanout table) + 20 * (packStart)
// and end at 4 (header) + 4 (version) + 256 * 4 (fanout table) + 20 * (packEnd)
this.stream.Seek(4 + 4 + 256 * 4 + 20 * packStart, SeekOrigin.Begin);
var i = 0;
var order = 0;
var tableSize = 20 * (packEnd - packStart + 1);
byte[] table = ArrayPool <byte> .Shared.Rent(tableSize);
this.stream.Seek(4 + 4 + 256 * 4 + 20 * packStart, SeekOrigin.Begin);
this.stream.Read(table.AsSpan(0, tableSize));
Span <byte> current = stackalloc byte[20];
int originalPackStart = packStart;
packEnd -= originalPackStart;
packStart = 0;
while (packStart <= packEnd)
{
i = (packStart + packEnd) / 2;
order = table.AsSpan(20 * i, 20).SequenceCompareTo(objectName);
if (order < 0)
{
packStart = i + 1;
}
else if (order > 0)
{
packEnd = i - 1;
}
else
{
break;
}
}
ArrayPool <byte> .Shared.Return(table);
if (order != 0)
{
return(null);
}
// Get the offset value. It's located at:
// 4 (header) + 4 (version) + 256 * 4 (fanout table) + 20 * objectCount (SHA1 object name table) + 4 * objectCount (CRC32) + 4 * i (offset values)
this.stream.Seek(4 + 4 + 256 * 4 + 20 * objectCount + 4 * objectCount + 4 * (i + originalPackStart), SeekOrigin.Begin);
this.stream.ReadAll(buffer);
// If the most significant bit is not set we have a 4-byte offset
if (buffer[0] < 128)
{
var offset = BinaryPrimitives.ReadInt32BigEndian(buffer);
return(offset);
}
// 8-byte offset
buffer[0] &= 0x7f;
var offset64 = BinaryPrimitives.ReadInt32BigEndian(buffer);
Span <byte> buffer64 = stackalloc byte[8];
// 4 (header) + 4 (version) + 256 * 4 (fanout table) + 20 * objectCount (SHA1 object name table) + 4 * objectCount (CRC32) + 4 * objectCount (offset values) + 8 * offset64
this.stream.Seek(4 + 4 + 256 * 4 + 20 * objectCount + 4 * objectCount + 4 * objectCount + 8 * offset64, SeekOrigin.Begin);
this.stream.ReadAll(buffer64);
return(BinaryPrimitives.ReadInt64BigEndian(buffer64));
}
public static Stream GetObject(GitPack pack, Stream stream, long offset, string objectType, GitPackObjectType packObjectType)
{
if (pack == null)
{
throw new ArgumentNullException(nameof(pack));
}
if (stream == null)
{
throw new ArgumentNullException(nameof(stream));
}
// Read the signature
#if DEBUG
stream.Seek(0, SeekOrigin.Begin);
Span <byte> buffer = stackalloc byte[12];
stream.ReadAll(buffer);
Debug.Assert(buffer.Slice(0, 4).SequenceEqual(Signature));
var versionNumber = BinaryPrimitives.ReadInt32BigEndian(buffer.Slice(4, 4));
Debug.Assert(versionNumber == 2);
var numberOfObjects = BinaryPrimitives.ReadInt32BigEndian(buffer.Slice(8, 4));
#endif
stream.Seek(offset, SeekOrigin.Begin);
var(type, decompressedSize) = ReadObjectHeader(stream);
if (type == GitPackObjectType.OBJ_OFS_DELTA)
{
var baseObjectRelativeOffset = ReadVariableLengthInteger(stream);
var baseObjectOffset = (long)(offset - baseObjectRelativeOffset);
var deltaStream = GitObjectStream.Create(stream, decompressedSize);
int baseObjectlength = ReadMbsInt(deltaStream);
int targetLength = ReadMbsInt(deltaStream);
var baseObjectStream = pack.GetObject(baseObjectOffset, objectType);
return(new GitPackDeltafiedStream(baseObjectStream, deltaStream, targetLength));
}
else if (type == GitPackObjectType.OBJ_REF_DELTA)
{
Span <byte> baseObjectId = stackalloc byte[20];
stream.ReadAll(baseObjectId);
Stream baseObject = pack.Repository.GetObjectBySha(GitObjectId.Parse(baseObjectId), objectType, seekable: true);
var deltaStream = GitObjectStream.Create(stream, decompressedSize);
int baseObjectlength = ReadMbsInt(deltaStream);
int targetLength = ReadMbsInt(deltaStream);
return(new GitPackDeltafiedStream(baseObject, deltaStream, targetLength));
}
// Tips for handling deltas: https://github.com/choffmeister/gitnet/blob/4d907623d5ce2d79a8875aee82e718c12a8aad0b/src/GitNet/GitPack.cs
if (type != packObjectType)
{
throw new GitException();
}
return(GitObjectStream.Create(stream, decompressedSize));
}
