commitgraph: Add basic commit-graph implementation

1 files changed, 558 insertions, 0 deletions

diff --git a/commitgraph_read_test.go b/commitgraph_read_test.go
new file mode 100644
index 00000000..9a8ea49e
--- /dev/null
+++ b/commitgraph_read_test.go
@@ -0,0 +1,558 @@
+package furgit
+
+import (
+	"bytes"
+	"encoding/binary"
+	"fmt"
+	"os"
+	"path/filepath"
+	"sort"
+	"strconv"
+	"strings"
+	"testing"
+
+	"codeberg.org/lindenii/furgit/internal/bloom"
+)
+
+func TestCommitGraphReadBasic(t *testing.T) {
+	repoPath, cleanup := setupTestRepo(t)
+	defer cleanup()
+
+	workDir, cleanupWork := setupWorkDir(t)
+	defer cleanupWork()
+
+	files := []string{"a.txt", "b.txt", "c.txt"}
+	for i, name := range files {
+		path := filepath.Join(workDir, name)
+		content := fmt.Sprintf("content-%d\n", i)
+		if err := os.WriteFile(path, []byte(content), 0o644); err != nil {
+			t.Fatalf("write %s: %v", name, err)
+		}
+		gitCmd(t, repoPath, "--work-tree="+workDir, "add", ".")
+		gitCmd(t, repoPath, "--work-tree="+workDir, "commit", "-m", fmt.Sprintf("commit %d", i))
+	}
+
+	gitCmd(t, repoPath, "repack", "-a", "-d")
+	gitCmd(t, repoPath, "commit-graph", "write", "--reachable", "--changed-paths")
+
+	repo, err := OpenRepository(repoPath)
+	if err != nil {
+		t.Fatalf("OpenRepository failed: %v", err)
+	}
+	defer func() { _ = repo.Close() }()
+
+	cg, err := repo.CommitGraph()
+	if err != nil {
+		t.Fatalf("CommitGraph failed: %v", err)
+	}
+
+	revList := gitCmd(t, repoPath, "rev-list", "--all")
+	commits := strings.Fields(revList)
+	if len(commits) == 0 {
+		t.Fatal("no commits found")
+	}
+
+	falsePositives := 0
+	for _, oidStr := range commits {
+		id, err := repo.ParseHash(oidStr)
+		if err != nil {
+			t.Fatalf("ParseHash failed: %v", err)
+		}
+		pos, ok := cg.CommitPosition(id)
+		if !ok {
+			t.Fatalf("commit %s not found in commit-graph", oidStr)
+		}
+		cc, err := cg.CommitAt(pos)
+		if err != nil {
+			t.Fatalf("CommitAt failed: %v", err)
+		}
+
+		treeStr := string(gitCmd(t, repoPath, "show", "-s", "--format=%T", oidStr))
+		tree, err := repo.ParseHash(treeStr)
+		if err != nil {
+			t.Fatalf("ParseHash tree failed: %v", err)
+		}
+		if cc.Tree != tree {
+			t.Fatalf("tree mismatch for %s: got %s want %s", oidStr, cc.Tree.String(), tree.String())
+		}
+
+		parentStr := string(gitCmd(t, repoPath, "show", "-s", "--format=%P", oidStr))
+		parents := strings.Fields(parentStr)
+		if len(parents) != len(cc.Parents) {
+			t.Fatalf("parent count mismatch for %s: got %d want %d", oidStr, len(cc.Parents), len(parents))
+		}
+		for i, p := range parents {
+			pid, err := repo.ParseHash(p)
+			if err != nil {
+				t.Fatalf("ParseHash parent failed: %v", err)
+			}
+			got, err := cg.OIDAt(cc.Parents[i])
+			if err != nil {
+				t.Fatalf("OIDAt parent failed: %v", err)
+			}
+			if got != pid {
+				t.Fatalf("parent mismatch for %s: got %s want %s", oidStr, got.String(), pid.String())
+			}
+		}
+
+		ctStr := gitCmd(t, repoPath, "show", "-s", "--format=%ct", oidStr)
+		ct, err := strconv.ParseInt(ctStr, 10, 64)
+		if err != nil {
+			t.Fatalf("parse commit time: %v", err)
+		}
+		if cc.CommitTime != uint64(ct) {
+			t.Fatalf("commit time mismatch for %s: got %d want %d", oidStr, cc.CommitTime, ct)
+		}
+
+		changed := gitCmd(t, repoPath, "diff-tree", "--no-commit-id", "--name-only", "-r", "--root", oidStr)
+		for _, path := range strings.Fields(changed) {
+			if path == "" {
+				continue
+			}
+			if !cc.ChangedPathMightContain([]byte(path)) {
+				t.Fatalf("bloom filter missing changed path %q in %s", path, oidStr)
+			}
+		}
+		if cc.ChangedPathMightContain([]byte("this-path-should-not-exist-abcdefg")) {
+			falsePositives++
+		}
+	}
+	if falsePositives > 1 {
+		t.Fatalf("unexpected bloom false positive rate: %d", falsePositives)
+	}
+}
+
+func TestCommitGraphReadExtraEdges(t *testing.T) {
+	workDir, cleanupWork := setupWorkDir(t)
+	defer cleanupWork()
+
+	gitCmd(t, workDir, "init")
+
+	if err := os.WriteFile(filepath.Join(workDir, "base.txt"), []byte("base\n"), 0o644); err != nil {
+		t.Fatalf("write base: %v", err)
+	}
+	gitCmd(t, workDir, "add", ".")
+	gitCmd(t, workDir, "commit", "-m", "base")
+
+	gitCmd(t, workDir, "checkout", "-b", "branch1")
+	if err := os.WriteFile(filepath.Join(workDir, "b1.txt"), []byte("b1\n"), 0o644); err != nil {
+		t.Fatalf("write b1: %v", err)
+	}
+	gitCmd(t, workDir, "add", ".")
+	gitCmd(t, workDir, "commit", "-m", "b1")
+
+	gitCmd(t, workDir, "checkout", "master")
+	gitCmd(t, workDir, "checkout", "-b", "branch2")
+	if err := os.WriteFile(filepath.Join(workDir, "b2.txt"), []byte("b2\n"), 0o644); err != nil {
+		t.Fatalf("write b2: %v", err)
+	}
+	gitCmd(t, workDir, "add", ".")
+	gitCmd(t, workDir, "commit", "-m", "b2")
+
+	gitCmd(t, workDir, "checkout", "master")
+	gitCmd(t, workDir, "checkout", "-b", "branch3")
+	if err := os.WriteFile(filepath.Join(workDir, "b3.txt"), []byte("b3\n"), 0o644); err != nil {
+		t.Fatalf("write b3: %v", err)
+	}
+	gitCmd(t, workDir, "add", ".")
+	gitCmd(t, workDir, "commit", "-m", "b3")
+
+	gitCmd(t, workDir, "checkout", "master")
+	gitCmd(t, workDir, "merge", "--no-ff", "-m", "octopus", "branch1", "branch2", "branch3")
+
+	gitCmd(t, workDir, "repack", "-a", "-d")
+	gitCmd(t, workDir, "commit-graph", "write", "--reachable")
+
+	repo, err := OpenRepository(filepath.Join(workDir, ".git"))
+	if err != nil {
+		t.Fatalf("OpenRepository failed: %v", err)
+	}
+	defer func() { _ = repo.Close() }()
+
+	cg, err := repo.CommitGraph()
+	if err != nil {
+		t.Fatalf("CommitGraph failed: %v", err)
+	}
+
+	mergeHash := gitCmd(t, workDir, "rev-parse", "HEAD")
+	id, _ := repo.ParseHash(mergeHash)
+	pos, ok := cg.CommitPosition(id)
+	if !ok {
+		t.Fatalf("merge commit not found")
+	}
+	cc, err := cg.CommitAt(pos)
+	if err != nil {
+		t.Fatalf("CommitAt failed: %v", err)
+	}
+	parentStr := gitCmd(t, workDir, "show", "-s", "--format=%P", mergeHash)
+	parents := strings.Fields(parentStr)
+	if len(cc.Parents) != len(parents) {
+		t.Fatalf("octopus parent mismatch: got %d want %d", len(cc.Parents), len(parents))
+	}
+}
+
+func TestCommitGraphReadSplitChain(t *testing.T) {
+	repoPath, cleanup := setupTestRepo(t)
+	defer cleanup()
+
+	workDir, cleanupWork := setupWorkDir(t)
+	defer cleanupWork()
+
+	for i := 0; i < 5; i++ {
+		path := filepath.Join(workDir, fmt.Sprintf("file%d.txt", i))
+		if err := os.WriteFile(path, []byte(fmt.Sprintf("v%d\n", i)), 0o644); err != nil {
+			t.Fatalf("write %s: %v", path, err)
+		}
+		gitCmd(t, repoPath, "--work-tree="+workDir, "add", ".")
+		gitCmd(t, repoPath, "--work-tree="+workDir, "commit", "-m", fmt.Sprintf("commit %d", i))
+	}
+
+	gitCmd(t, repoPath, "repack", "-a", "-d")
+	gitCmd(t, repoPath, "commit-graph", "write", "--reachable", "--changed-paths", "--split=no-merge")
+
+	// more commits needed to get a split chain with base layer
+	for i := 5; i < 8; i++ {
+		path := filepath.Join(workDir, fmt.Sprintf("file%d.txt", i))
+		if err := os.WriteFile(path, []byte(fmt.Sprintf("v%d\n", i)), 0o644); err != nil {
+			t.Fatalf("write %s: %v", path, err)
+		}
+		gitCmd(t, repoPath, "--work-tree="+workDir, "add", ".")
+		gitCmd(t, repoPath, "--work-tree="+workDir, "commit", "-m", fmt.Sprintf("commit %d", i))
+	}
+	gitCmd(t, repoPath, "repack", "-a", "-d")
+	gitCmd(t, repoPath, "commit-graph", "write", "--reachable", "--changed-paths", "--split=no-merge", "--append")
+
+	repo, err := OpenRepository(repoPath)
+	if err != nil {
+		t.Fatalf("OpenRepository failed: %v", err)
+	}
+	defer func() { _ = repo.Close() }()
+
+	cg, err := repo.CommitGraph()
+	if err != nil {
+		t.Fatalf("CommitGraph failed: %v", err)
+	}
+	chainPath := filepath.Join(repoPath, "objects", "info", "commit-graphs", "commit-graph-chain")
+	if _, err := os.Stat(chainPath); err != nil {
+		t.Fatalf("commit-graph chain not created by git: %v", err)
+	}
+	if cg.base == nil {
+		t.Fatalf("expected split commit-graph chain")
+	}
+	if cg.numCommitsInBase == 0 {
+		t.Fatalf("expected non-zero base commit count")
+	}
+	revList := gitCmd(t, repoPath, "rev-list", "--max-parents=0", "HEAD")
+	id, _ := repo.ParseHash(revList)
+	if _, ok := cg.CommitPosition(id); !ok {
+		t.Fatalf("base commit not found in commit-graph chain")
+	}
+}
+
+func TestCommitGraphTrailerChecksum(t *testing.T) {
+	repoPath, cleanup := setupTestRepo(t)
+	defer cleanup()
+	repo, err := OpenRepository(repoPath)
+	if err != nil {
+		t.Fatalf("OpenRepository failed: %v", err)
+	}
+	defer func() { _ = repo.Close() }()
+
+	data := buildCommitGraphBytes(t, repo, 1, nil, nil, nil)
+	data[len(data)-1] ^= 0xff
+	if _, err := parseCommitGraph(repo, "corrupt.graph", data); err == nil {
+		t.Fatalf("expected checksum error")
+	}
+}
+
+func TestCommitGraphFanoutMonotonicity(t *testing.T) {
+	repoPath, cleanup := setupTestRepo(t)
+	defer cleanup()
+	repo, err := OpenRepository(repoPath)
+	if err != nil {
+		t.Fatalf("OpenRepository failed: %v", err)
+	}
+	defer func() { _ = repo.Close() }()
+
+	oids := [][]byte{
+		bytes.Repeat([]byte{0x10}, repo.hashAlgo.Size()),
+		bytes.Repeat([]byte{0x20}, repo.hashAlgo.Size()),
+	}
+	data := buildCommitGraphBytes(t, repo, 2, oids, nil, nil)
+	start, end, ok := chunkRange(t, repo, data, commitGraphChunkOIDF)
+	if !ok {
+		t.Fatalf("OIDF chunk not found")
+	}
+	fanout := make([]byte, end-start)
+	copy(fanout, data[start:end])
+	binary.BigEndian.PutUint32(fanout[0:4], 2)
+	binary.BigEndian.PutUint32(fanout[4:8], 1)
+	data = replaceChunk(t, repo, data, commitGraphChunkOIDF, fanout)
+	if _, err := parseCommitGraph(repo, "bad-fanout.graph", data); err == nil {
+		t.Fatalf("expected fanout monotonicity error")
+	}
+}
+
+func TestCommitGraphBIDXMonotonicity(t *testing.T) {
+	repoPath, cleanup := setupTestRepo(t)
+	defer cleanup()
+	repo, err := OpenRepository(repoPath)
+	if err != nil {
+		t.Fatalf("OpenRepository failed: %v", err)
+	}
+	defer func() { _ = repo.Close() }()
+
+	oids := [][]byte{
+		bytes.Repeat([]byte{0x10}, repo.hashAlgo.Size()),
+		bytes.Repeat([]byte{0x20}, repo.hashAlgo.Size()),
+	}
+	bidx := []uint32{8, 4}
+	data := buildCommitGraphBytes(t, repo, 2, oids, bidx, []byte{0, 0, 0, 0, 0, 0, 0, 0})
+	if _, err := parseCommitGraph(repo, "bad-bidx.graph", data); err == nil {
+		t.Fatalf("expected bidx monotonicity error")
+	}
+}
+
+func TestCommitGraphExtraEdgesBounds(t *testing.T) {
+	repoPath, cleanup := setupTestRepo(t)
+	defer cleanup()
+	repo, err := OpenRepository(repoPath)
+	if err != nil {
+		t.Fatalf("OpenRepository failed: %v", err)
+	}
+	defer func() { _ = repo.Close() }()
+
+	oids := [][]byte{
+		bytes.Repeat([]byte{0x10}, repo.hashAlgo.Size()),
+		bytes.Repeat([]byte{0x20}, repo.hashAlgo.Size()),
+		bytes.Repeat([]byte{0x30}, repo.hashAlgo.Size()),
+	}
+	extraEdges := []uint32{0x80000000 | 100}
+	data := buildCommitGraphBytes(t, repo, 3, oids, nil, nil)
+
+	// inject EDGE chunk with an out-of-range index
+	data = injectChunk(t, repo, data, commitGraphChunkEDGE, u32SliceToBytes(extraEdges))
+
+	// force the first commit to use the extra edges list
+	start, end, ok := chunkRange(t, repo, data, commitGraphChunkCDAT)
+	if !ok {
+		t.Fatalf("CDAT chunk not found")
+	}
+	cdat := make([]byte, end-start)
+	copy(cdat, data[start:end])
+	hashSize := repo.hashAlgo.Size()
+	binary.BigEndian.PutUint32(cdat[hashSize+4:hashSize+8], 0x80000000|100)
+	data = replaceChunk(t, repo, data, commitGraphChunkCDAT, cdat)
+
+	cg, err := parseCommitGraph(repo, "edge.graph", data)
+	if err != nil {
+		t.Fatalf("parseCommitGraph failed: %v", err)
+	}
+	pos, ok := cg.CommitPosition(hashFromBytes(repo, oids[0]))
+	if !ok {
+		t.Fatalf("commit not found")
+	}
+	if _, err := cg.CommitAt(pos); err == nil {
+		t.Fatalf("expected extra-edges bounds error")
+	}
+}
+
+func buildCommitGraphBytes(t *testing.T, repo *Repository, n int, oids [][]byte, bidx []uint32, bdat []byte) []byte {
+	t.Helper()
+	if n <= 0 {
+		t.Fatalf("invalid num commits")
+	}
+	hashSize := repo.hashAlgo.Size()
+	if len(oids) == 0 {
+		for i := 0; i < n; i++ {
+			b := bytes.Repeat([]byte{byte(0x10 + i)}, hashSize)
+			oids = append(oids, b)
+		}
+	}
+	sort.Slice(oids, func(i, j int) bool {
+		return bytes.Compare(oids[i], oids[j]) < 0
+	})
+
+	var chunks []chunkSpec
+	oidf := make([]byte, commitGraphFanoutSize)
+	for _, oid := range oids {
+		idx := int(oid[0])
+		for i := idx; i < 256; i++ {
+			v := binary.BigEndian.Uint32(oidf[i*4 : i*4+4])
+			binary.BigEndian.PutUint32(oidf[i*4:i*4+4], v+1)
+		}
+	}
+	chunks = append(chunks, chunkSpec{commitGraphChunkOIDF, oidf})
+
+	oidl := make([]byte, 0, n*hashSize)
+	for _, oid := range oids {
+		oidl = append(oidl, oid...)
+	}
+	chunks = append(chunks, chunkSpec{commitGraphChunkOIDL, oidl})
+
+	cdat := make([]byte, n*commitGraphCommitDataSize(repo.hashAlgo))
+	for i := 0; i < n; i++ {
+		base := i * commitGraphCommitDataSize(repo.hashAlgo)
+		copy(cdat[base:base+hashSize], bytes.Repeat([]byte{0xaa}, hashSize))
+		binary.BigEndian.PutUint32(cdat[base+hashSize:], commitGraphParentNone)
+		binary.BigEndian.PutUint32(cdat[base+hashSize+4:], commitGraphParentNone)
+		binary.BigEndian.PutUint32(cdat[base+hashSize+8:], 4)
+		binary.BigEndian.PutUint32(cdat[base+hashSize+12:], 0)
+	}
+	chunks = append(chunks, chunkSpec{commitGraphChunkCDAT, cdat})
+
+	if bidx != nil && bdat != nil {
+		bidxBytes := u32SliceToBytes(bidx)
+		bdatHeader := make([]byte, bloom.DataHeaderSize)
+		binary.BigEndian.PutUint32(bdatHeader[0:4], 2)
+		binary.BigEndian.PutUint32(bdatHeader[4:8], 7)
+		binary.BigEndian.PutUint32(bdatHeader[8:12], 10)
+		bdatFull := append(bdatHeader, bdat...)
+		chunks = append(chunks, chunkSpec{commitGraphChunkBIDX, bidxBytes})
+		chunks = append(chunks, chunkSpec{commitGraphChunkBDAT, bdatFull})
+	}
+
+	return assembleCommitGraphBytes(t, repo, chunks)
+}
+
+type chunkSpec struct {
+	id   uint32
+	data []byte
+}
+
+func assembleCommitGraphBytes(t *testing.T, repo *Repository, chunks []chunkSpec) []byte {
+	t.Helper()
+	var buf bytes.Buffer
+	buf.Grow(1024)
+	var header [commitGraphHeaderSize]byte
+	binary.BigEndian.PutUint32(header[0:4], commitGraphSignature)
+	header[4] = commitGraphVersion
+	header[5] = hashAlgoVersion(repo.hashAlgo)
+	header[6] = byte(len(chunks))
+	header[7] = 0
+	buf.Write(header[:])
+
+	tocStart := buf.Len()
+	tocLen := (len(chunks) + 1) * commitGraphChunkEntrySize
+	buf.Grow(tocLen)
+	buf.Write(make([]byte, tocLen))
+
+	offset := tocStart + tocLen
+	for i, ch := range chunks {
+		pos := tocStart + i*commitGraphChunkEntrySize
+		binary.BigEndian.PutUint32(buf.Bytes()[pos:pos+4], ch.id)
+		binary.BigEndian.PutUint64(buf.Bytes()[pos+4:pos+12], uint64(offset))
+		offset += len(ch.data)
+	}
+	pos := tocStart + len(chunks)*commitGraphChunkEntrySize
+	binary.BigEndian.PutUint32(buf.Bytes()[pos:pos+4], 0)
+	binary.BigEndian.PutUint64(buf.Bytes()[pos+4:pos+12], uint64(offset))
+
+	for _, ch := range chunks {
+		buf.Write(ch.data)
+	}
+
+	h, err := repo.hashAlgo.New()
+	if err != nil {
+		t.Fatalf("hash.New failed: %v", err)
+	}
+	_, _ = h.Write(buf.Bytes())
+	buf.Write(h.Sum(nil))
+	return buf.Bytes()
+}
+
+func chunkRange(t *testing.T, repo *Repository, data []byte, id uint32) (int, int, bool) {
+	t.Helper()
+	hashSize := repo.hashAlgo.Size()
+	numChunks := int(data[6])
+	tocStart := commitGraphHeaderSize
+	trailerStart := len(data) - hashSize
+
+	for i := 0; i < numChunks; i++ {
+		pos := tocStart + i*commitGraphChunkEntrySize
+		chID := binary.BigEndian.Uint32(data[pos : pos+4])
+		if chID == 0 {
+			break
+		}
+		start := int(binary.BigEndian.Uint64(data[pos+4 : pos+12]))
+		end := trailerStart
+		if i+1 < numChunks {
+			end = int(binary.BigEndian.Uint64(data[pos+commitGraphChunkEntrySize+4 : pos+commitGraphChunkEntrySize+12]))
+		}
+		if chID == id {
+			return start, end, true
+		}
+	}
+	return 0, 0, false
+}
+
+func replaceChunk(t *testing.T, repo *Repository, data []byte, id uint32, payload []byte) []byte {
+	t.Helper()
+	hashSize := repo.hashAlgo.Size()
+	numChunks := int(data[6])
+	tocStart := commitGraphHeaderSize
+	trailerStart := len(data) - hashSize
+
+	chunks := make([]chunkSpec, 0, numChunks)
+	for i := 0; i < numChunks; i++ {
+		pos := tocStart + i*commitGraphChunkEntrySize
+		chID := binary.BigEndian.Uint32(data[pos : pos+4])
+		if chID == 0 {
+			break
+		}
+		start := int(binary.BigEndian.Uint64(data[pos+4 : pos+12]))
+		end := trailerStart
+		if i+1 < numChunks {
+			end = int(binary.BigEndian.Uint64(data[pos+commitGraphChunkEntrySize+4 : pos+commitGraphChunkEntrySize+12]))
+		}
+		if chID == id {
+			chunks = append(chunks, chunkSpec{chID, payload})
+		} else {
+			chunks = append(chunks, chunkSpec{chID, data[start:end]})
+		}
+	}
+	if len(chunks) == 0 {
+		t.Fatalf("no chunks found")
+	}
+	return assembleCommitGraphBytes(t, repo, chunks)
+}
+
+func injectChunk(t *testing.T, repo *Repository, data []byte, id uint32, payload []byte) []byte {
+	t.Helper()
+	hashSize := repo.hashAlgo.Size()
+	numChunks := int(data[6])
+	tocStart := commitGraphHeaderSize
+	trailerStart := len(data) - hashSize
+
+	chunks := make([]chunkSpec, 0, numChunks+1)
+	for i := 0; i < numChunks; i++ {
+		pos := tocStart + i*commitGraphChunkEntrySize
+		chID := binary.BigEndian.Uint32(data[pos : pos+4])
+		if chID == 0 {
+			break
+		}
+		start := int(binary.BigEndian.Uint64(data[pos+4 : pos+12]))
+		end := trailerStart
+		if i+1 < numChunks {
+			end = int(binary.BigEndian.Uint64(data[pos+commitGraphChunkEntrySize+4 : pos+commitGraphChunkEntrySize+12]))
+		}
+		chunks = append(chunks, chunkSpec{chID, data[start:end]})
+	}
+	chunks = append(chunks, chunkSpec{id, payload})
+	return assembleCommitGraphBytes(t, repo, chunks)
+}
+
+func u32SliceToBytes(vals []uint32) []byte {
+	out := make([]byte, len(vals)*4)
+	for i, v := range vals {
+		binary.BigEndian.PutUint32(out[i*4:i*4+4], v)
+	}
+	return out
+}
+
+func hashFromBytes(repo *Repository, b []byte) Hash {
+	var h Hash
+	copy(h.data[:], b)
+	h.algo = repo.hashAlgo
+	return h
+}