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authorFilip Navara <filip.navara@gmail.com>2019-05-07 10:49:39 +0200
committerFilip Navara <filip.navara@gmail.com>2019-05-07 10:49:39 +0200
commit7d2695741f4d1f572a36f7225b6bbb2f569d59d7 (patch)
treee794d037e57d13a816a162fe1c31ab6ce45d58c0
parent940460f5422b02f01351396af703e9b63e8596ae (diff)
downloadgo-git-7d2695741f4d1f572a36f7225b6bbb2f569d59d7.tar.gz
Add doc.go for commitgraph packages
Signed-off-by: Filip Navara <filip.navara@gmail.com>
-rw-r--r--plumbing/format/commitgraph/doc.go103
-rw-r--r--plumbing/format/commitgraph/encoder.go1
-rw-r--r--plumbing/format/commitgraph/memory.go2
-rw-r--r--plumbing/object/commitgraph/doc.go7
4 files changed, 113 insertions, 0 deletions
diff --git a/plumbing/format/commitgraph/doc.go b/plumbing/format/commitgraph/doc.go
new file mode 100644
index 0000000..41cd8b1
--- /dev/null
+++ b/plumbing/format/commitgraph/doc.go
@@ -0,0 +1,103 @@
+// Package commitgraph implements encoding and decoding of commit-graph files.
+//
+// Git commit graph format
+// =======================
+//
+// The Git commit graph stores a list of commit OIDs and some associated
+// metadata, including:
+//
+// - The generation number of the commit. Commits with no parents have
+// generation number 1; commits with parents have generation number
+// one more than the maximum generation number of its parents. We
+// reserve zero as special, and can be used to mark a generation
+// number invalid or as "not computed".
+//
+// - The root tree OID.
+//
+// - The commit date.
+//
+// - The parents of the commit, stored using positional references within
+// the graph file.
+//
+// These positional references are stored as unsigned 32-bit integers
+// corresponding to the array position within the list of commit OIDs. Due
+// to some special constants we use to track parents, we can store at most
+// (1 << 30) + (1 << 29) + (1 << 28) - 1 (around 1.8 billion) commits.
+//
+// == Commit graph files have the following format:
+//
+// In order to allow extensions that add extra data to the graph, we organize
+// the body into "chunks" and provide a binary lookup table at the beginning
+// of the body. The header includes certain values, such as number of chunks
+// and hash type.
+//
+// All 4-byte numbers are in network order.
+//
+// HEADER:
+//
+// 4-byte signature:
+// The signature is: {'C', 'G', 'P', 'H'}
+//
+// 1-byte version number:
+// Currently, the only valid version is 1.
+//
+// 1-byte Hash Version (1 = SHA-1)
+// We infer the hash length (H) from this value.
+//
+// 1-byte number (C) of "chunks"
+//
+// 1-byte (reserved for later use)
+// Current clients should ignore this value.
+//
+// CHUNK LOOKUP:
+//
+// (C + 1) * 12 bytes listing the table of contents for the chunks:
+// First 4 bytes describe the chunk id. Value 0 is a terminating label.
+// Other 8 bytes provide the byte-offset in current file for chunk to
+// start. (Chunks are ordered contiguously in the file, so you can infer
+// the length using the next chunk position if necessary.) Each chunk
+// ID appears at most once.
+//
+// The remaining data in the body is described one chunk at a time, and
+// these chunks may be given in any order. Chunks are required unless
+// otherwise specified.
+//
+// CHUNK DATA:
+//
+// OID Fanout (ID: {'O', 'I', 'D', 'F'}) (256 * 4 bytes)
+// The ith entry, F[i], stores the number of OIDs with first
+// byte at most i. Thus F[255] stores the total
+// number of commits (N).
+//
+// OID Lookup (ID: {'O', 'I', 'D', 'L'}) (N * H bytes)
+// The OIDs for all commits in the graph, sorted in ascending order.
+//
+// Commit Data (ID: {'C', 'D', 'A', 'T' }) (N * (H + 16) bytes)
+// * The first H bytes are for the OID of the root tree.
+// * The next 8 bytes are for the positions of the first two parents
+// of the ith commit. Stores value 0x7000000 if no parent in that
+// position. If there are more than two parents, the second value
+// has its most-significant bit on and the other bits store an array
+// position into the Extra Edge List chunk.
+// * The next 8 bytes store the generation number of the commit and
+// the commit time in seconds since EPOCH. The generation number
+// uses the higher 30 bits of the first 4 bytes, while the commit
+// time uses the 32 bits of the second 4 bytes, along with the lowest
+// 2 bits of the lowest byte, storing the 33rd and 34th bit of the
+// commit time.
+//
+// Extra Edge List (ID: {'E', 'D', 'G', 'E'}) [Optional]
+// This list of 4-byte values store the second through nth parents for
+// all octopus merges. The second parent value in the commit data stores
+// an array position within this list along with the most-significant bit
+// on. Starting at that array position, iterate through this list of commit
+// positions for the parents until reaching a value with the most-significant
+// bit on. The other bits correspond to the position of the last parent.
+//
+// TRAILER:
+//
+// H-byte HASH-checksum of all of the above.
+//
+// Source:
+// https://raw.githubusercontent.com/git/git/master/Documentation/technical/commit-graph-format.txt
+package commitgraph
diff --git a/plumbing/format/commitgraph/encoder.go b/plumbing/format/commitgraph/encoder.go
index 648153f..a06871c 100644
--- a/plumbing/format/commitgraph/encoder.go
+++ b/plumbing/format/commitgraph/encoder.go
@@ -22,6 +22,7 @@ func NewEncoder(w io.Writer) *Encoder {
return &Encoder{mw, h}
}
+// Encode writes an index into the commit-graph file
func (e *Encoder) Encode(idx Index) error {
var err error
diff --git a/plumbing/format/commitgraph/memory.go b/plumbing/format/commitgraph/memory.go
index f084b85..a4a96e9 100644
--- a/plumbing/format/commitgraph/memory.go
+++ b/plumbing/format/commitgraph/memory.go
@@ -4,6 +4,8 @@ import (
"gopkg.in/src-d/go-git.v4/plumbing"
)
+// MemoryIndex provides a way to build the commit-graph in memory
+// for later encoding to file.
type MemoryIndex struct {
commitData []*CommitData
indexMap map[plumbing.Hash]int
diff --git a/plumbing/object/commitgraph/doc.go b/plumbing/object/commitgraph/doc.go
new file mode 100644
index 0000000..0a55ad5
--- /dev/null
+++ b/plumbing/object/commitgraph/doc.go
@@ -0,0 +1,7 @@
+// Package commitgraph provides an interface for efficient traversal over Git
+// commit graph either through the regular object storage, or optionally with
+// the index stored in commit-graph file (Git 2.18+).
+//
+// The API and functionality of this package are considered EXPERIMENTAL and is
+// not considered stable nor production ready.
+package commitgraph