plumbing: format/index: support for EOIE extension

plumbing/format/index/decoder.go

@@ -261,6 +261,17 @@ func (d *Decoder) readExtension(idx *Index, header []byte) error {
 		if err := d.Decode(idx.ResolveUndo); err != nil {
 			return err
 		}
+	case bytes.Equal(header, endOfIndexEntryExtSignature):
+		r, err := d.getExtensionReader()
+		if err != nil {
+			return err
+		}
+
+		idx.EndOfIndexEntry = &EndOfIndexEntry{}
+		d := &endOfIndexEntryDecoder{r}
+		if err := d.Decode(idx.EndOfIndexEntry); err != nil {
+			return err
+		}
 	default:
 		return errUnknownExtension
 	}
@@ -449,3 +460,17 @@ func (d *resolveUndoDecoder) readStage(e *ResolveUndoEntry, s Stage) error {
 
 	return nil
 }
+
+type endOfIndexEntryDecoder struct {
+	r io.Reader
+}
+
+func (d *endOfIndexEntryDecoder) Decode(e *EndOfIndexEntry) error {
+	var err error
+	e.Offset, err = binary.ReadUint32(d.r)
+	if err != nil {
+		return err
+	}
+
+	return binary.Read(d.r, &e.Hash)
+}

plumbing/format/index/decoder_test.go

@@ -202,3 +202,19 @@ func (s *IndexSuite) TestDecodeV4(c *C) {
 	c.Assert(idx.Entries[6].IntentToAdd, Equals, true)
 	c.Assert(idx.Entries[6].SkipWorktree, Equals, false)
 }
+
+func (s *IndexSuite) TestDecodeEndOfIndexEntry(c *C) {
+	f, err := fixtures.Basic().ByTag("end-of-index-entry").One().DotGit().Open("index")
+	c.Assert(err, IsNil)
+	defer func() { c.Assert(f.Close(), IsNil) }()
+
+	idx := &Index{}
+	d := NewDecoder(f)
+	err = d.Decode(idx)
+	c.Assert(err, IsNil)
+
+	c.Assert(idx.Version, Equals, uint32(2))
+	c.Assert(idx.EndOfIndexEntry, NotNil)
+	c.Assert(idx.EndOfIndexEntry.Offset, Equals, uint32(716))
+	c.Assert(idx.EndOfIndexEntry.Hash.String(), Equals, "922e89d9ffd7cefce93a211615b2053c0f42bd78")
+}

plumbing/format/index/doc.go

@@ -297,5 +297,64 @@
 //        in the previous ewah bitmap.
 //
 //      - One NUL.
-// Source https://www.kernel.org/pub/software/scm/git/docs/technical/index-format.txt
+//
+//   == File System Monitor cache
+//
+//     The file system monitor cache tracks files for which the core.fsmonitor
+//     hook has told us about changes.  The signature for this extension is
+//     { 'F', 'S', 'M', 'N' }.
+//
+//     The extension starts with
+//
+//     - 32-bit version number: the current supported version is 1.
+//
+//     - 64-bit time: the extension data reflects all changes through the given
+//       time which is stored as the nanoseconds elapsed since midnight,
+//       January 1, 1970.
+//
+//    - 32-bit bitmap size: the size of the CE_FSMONITOR_VALID bitmap.
+//
+//    - An ewah bitmap, the n-th bit indicates whether the n-th index entry
+//      is not CE_FSMONITOR_VALID.
+//
+//  == End of Index Entry
+//
+//    The End of Index Entry (EOIE) is used to locate the end of the variable
+//    length index entries and the begining of the extensions. Code can take
+//    advantage of this to quickly locate the index extensions without having
+//    to parse through all of the index entries.
+//
+//    Because it must be able to be loaded before the variable length cache
+//    entries and other index extensions, this extension must be written last.
+//    The signature for this extension is { 'E', 'O', 'I', 'E' }.
+//
+//    The extension consists of:
+//
+//    - 32-bit offset to the end of the index entries
+//
+//    - 160-bit SHA-1 over the extension types and their sizes (but not
+//      their contents).  E.g. if we have "TREE" extension that is N-bytes
+//      long, "REUC" extension that is M-bytes long, followed by "EOIE",
+//      then the hash would be:
+//
+//      SHA-1("TREE" + <binary representation of N> +
+//        "REUC" + <binary representation of M>)
+//
+//  == Index Entry Offset Table
+//
+//    The Index Entry Offset Table (IEOT) is used to help address the CPU
+//    cost of loading the index by enabling multi-threading the process of
+//    converting cache entries from the on-disk format to the in-memory format.
+//    The signature for this extension is { 'I', 'E', 'O', 'T' }.
+//
+//    The extension consists of:
+//
+//    - 32-bit version (currently 1)
+//
+//    - A number of index offset entries each consisting of:
+//
+//    - 32-bit offset from the begining of the file to the first cache entry
+//      in this block of entries.
+//
+//    - 32-bit count of cache entries in this blockpackage index
 package index

plumbing/format/index/index.go

@@ -18,9 +18,10 @@ var (
 	// ErrEntryNotFound is returned by Index.Entry, if an entry is not found.
 	ErrEntryNotFound = errors.New("entry not found")
 
-	indexSignature          = []byte{'D', 'I', 'R', 'C'}
-	treeExtSignature        = []byte{'T', 'R', 'E', 'E'}
-	resolveUndoExtSignature = []byte{'R', 'E', 'U', 'C'}
+	indexSignature              = []byte{'D', 'I', 'R', 'C'}
+	treeExtSignature            = []byte{'T', 'R', 'E', 'E'}
+	resolveUndoExtSignature     = []byte{'R', 'E', 'U', 'C'}
+	endOfIndexEntryExtSignature = []byte{'E', 'O', 'I', 'E'}
 )
 
 // Stage during merge
@@ -50,6 +51,8 @@ type Index struct {
 	Cache *Tree
 	// ResolveUndo represents the 'Resolve undo' extension
 	ResolveUndo *ResolveUndo
+	// EndOfIndexEntry represents the 'End of Index Entry' extension
+	EndOfIndexEntry *EndOfIndexEntry
 }
 
 // Add creates a new Entry and returns it. The caller should first check that
@@ -193,3 +196,18 @@ type ResolveUndoEntry struct {
 	Path   string
 	Stages map[Stage]plumbing.Hash
 }
+
+// EndOfIndexEntry is the End of Index Entry (EOIE) is used to locate the end of
+// the variable length index entries and the begining of the extensions. Code
+// can take advantage of this to quickly locate the index extensions without
+// having to parse through all of the index entries.
+//
+//  Because it must be able to be loaded before the variable length cache
+//  entries and other index extensions, this extension must be written last.
+type EndOfIndexEntry struct {
+	// Offset to the end of the index entries
+	Offset uint32
+	// Hash is a SHA-1 over the extension types and their sizes (but not
+	//	their contents).
+	Hash plumbing.Hash
+}