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Fix bugs with > 2 GB pack files #634

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merged 2 commits into from Jul 28, 2021
Merged

Fix bugs with > 2 GB pack files #634

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357099c
Fix bugs with > 2 GB pack files
filipnavara Jul 28, 2021
a7eaba9
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filipnavara Jul 28, 2021
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2 changes: 1 addition & 1 deletion src/NerdBank.GitVersioning/ManagedGit/GitPackIndexMappedReader.cs
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Expand Up @@ -128,7 +128,7 @@ public override (long?, GitObjectId?) GetOffset(Span<byte> objectName, bool ends
{
// If the first bit of the offset address is set, the offset is stored as a 64-bit value in the table of 8-byte offset entries,
// which follows the table of 4-byte offset entries: "large offsets are encoded as an index into the next table with the msbit set."
offset = offset & 0x7FF;
offset = offset & 0x7FFFFFFF;
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Ref: https://github.com/go-git/go-git/blob/master/plumbing/format/idxfile/idxfile.go#L146
Ref: https://git-scm.com/docs/pack-format

If the large offset chunk exists and the 31st bit is on, then removing that bit reveals the row in the large offsets containing the 8-byte offset of this object.


offsetBuffer = this.Value.Slice(offsetTableStart + 4 * objectCount + 8 * (int)offset, 8);
var offset64 = BinaryPrimitives.ReadInt64BigEndian(offsetBuffer);
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6 changes: 3 additions & 3 deletions src/NerdBank.GitVersioning/ManagedGit/GitPackReader.cs
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Expand Up @@ -44,7 +44,7 @@ public static Stream GetObject(GitPack pack, Stream stream, long offset, string
if (type == GitPackObjectType.OBJ_OFS_DELTA)
{
var baseObjectRelativeOffset = ReadVariableLengthInteger(stream);
var baseObjectOffset = (int)(offset - baseObjectRelativeOffset);
var baseObjectOffset = offset - baseObjectRelativeOffset;
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var deltaStream = new ZLibStream(stream, decompressedSize);
var baseObjectStream = pack.GetObject(baseObjectOffset, objectType);
Expand Down Expand Up @@ -98,9 +98,9 @@ private static (GitPackObjectType, long) ReadObjectHeader(Stream stream)
return (type, length);
}

private static int ReadVariableLengthInteger(Stream stream)
private static long ReadVariableLengthInteger(Stream stream)
{
int offset = -1;
long offset = -1;
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Ref: https://git-scm.com/docs/pack-format

Observation: length of each object is encoded in a variable length format and is not constrained to 32-bit or anything.

Example: Base offset is 4 000 000 000, delta relative offset would be 3 000 000 000. The computed delta offset would thus be 1 000 000 000. The number 3 000 000 000 must fit in the data type returned here.

int b;

do
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