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// Package packed provides packfile reading and associated indexes.
package packed
import (
"errors"
"fmt"
"os"
"sync"
"codeberg.org/lindenii/furgit/objectid"
"codeberg.org/lindenii/furgit/objectstore"
)
// Store reads Git objects from pack/index files under an objects/pack root.
//
// Store owns root and closes it in Close.
type Store struct {
// root is the objects/pack capability used for all file access.
root *os.Root
// algo is the expected object ID algorithm for lookups.
algo objectid.Algorithm
// discoverOnce guards one-time pack candidate discovery.
discoverOnce sync.Once
// discoverErr stores candidate discovery failures.
discoverErr error
// candidateHead is the first candidate in lookup priority order.
candidateHead *packCandidateNode
// candidateTail is the last candidate in lookup priority order.
candidateTail *packCandidateNode
// candidateByPack maps pack basename to discovered candidate.
candidateByPack map[string]packCandidate
// candidateNodeByPack maps pack basename to linked-list node.
candidateNodeByPack map[string]*packCandidateNode
// idxByPack caches opened and parsed indexes by pack basename.
idxByPack map[string]*idxFile
// stateMu guards pack cache and close state.
stateMu sync.RWMutex
// candidatesMu guards discovered candidates and MRU order.
candidatesMu sync.RWMutex
// idxMu guards parsed index cache.
idxMu sync.RWMutex
// cacheMu guards delta cache operations.
cacheMu sync.RWMutex
// packs caches opened .pack handles by basename.
packs map[string]*packFile
// deltaCache caches resolved base objects by pack location.
deltaCache *deltaCache
// closed reports whether Close has been called.
closed bool
}
const defaultDeltaCacheMaxBytes = 32 << 20
var _ objectstore.Store = (*Store)(nil)
// New creates a packed-object store rooted at an objects/pack directory.
func New(root *os.Root, algo objectid.Algorithm) (*Store, error) {
if algo.Size() == 0 {
return nil, objectid.ErrInvalidAlgorithm
}
return &Store{
root: root,
algo: algo,
candidateByPack: make(map[string]packCandidate),
candidateNodeByPack: make(map[string]*packCandidateNode),
idxByPack: make(map[string]*idxFile),
packs: make(map[string]*packFile),
deltaCache: newDeltaCache(defaultDeltaCacheMaxBytes),
}, nil
}
// Close releases mapped pack/index resources associated with the store.
func (store *Store) Close() error {
store.stateMu.Lock()
if store.closed {
store.stateMu.Unlock()
return nil
}
store.closed = true
root := store.root
packs := store.packs
store.stateMu.Unlock()
store.idxMu.RLock()
indexes := store.idxByPack
store.idxMu.RUnlock()
var closeErr error
for _, pack := range packs {
if err := pack.close(); err != nil && closeErr == nil {
closeErr = err
}
}
for _, index := range indexes {
if err := index.close(); err != nil && closeErr == nil {
closeErr = err
}
}
store.cacheMu.Lock()
store.deltaCache.clear()
store.cacheMu.Unlock()
if err := root.Close(); err != nil && closeErr == nil {
closeErr = err
}
return closeErr
}
// lookup resolves one object ID to its pack location.
func (store *Store) lookup(id objectid.ObjectID) (location, error) {
var zero location
if id.Algorithm() != store.algo {
return zero, errors.New("objectstore/packed: object id algorithm mismatch")
}
if err := store.ensureCandidates(); err != nil {
return zero, err
}
nextPackName := store.firstCandidatePackName()
for nextPackName != "" {
candidate, ok := store.candidateForPack(nextPackName)
if !ok {
nextPackName = store.firstCandidatePackName()
continue
}
nextPackName = store.nextCandidatePackName(candidate.packName)
index, err := store.openIndex(candidate)
if err != nil {
return zero, err
}
offset, ok, err := index.lookup(id)
if err != nil {
return zero, err
}
if ok {
store.touchCandidate(candidate.packName)
return location{packName: index.packName, offset: offset}, nil
}
}
return zero, objectstore.ErrObjectNotFound
}
// openPack returns one opened and validated pack handle.
func (store *Store) openPack(name string) (*packFile, error) {
store.stateMu.RLock()
if pack, ok := store.packs[name]; ok {
store.stateMu.RUnlock()
return pack, nil
}
store.stateMu.RUnlock()
file, err := store.root.Open(name)
if err != nil {
return nil, err
}
info, err := file.Stat()
if err != nil {
_ = file.Close()
return nil, err
}
pack, err := openPackFile(name, file, info.Size())
if err != nil {
_ = file.Close()
return nil, err
}
if err := store.verifyPackMatchesIndexes(pack); err != nil {
_ = pack.close()
return nil, err
}
store.stateMu.Lock()
if existing, ok := store.packs[name]; ok {
store.stateMu.Unlock()
_ = pack.close()
return existing, nil
}
store.packs[name] = pack
store.stateMu.Unlock()
return pack, nil
}
// verifyPackMatchesIndexes checks that one opened pack's trailer hash matches
// every loaded index that references the same pack name.
func (store *Store) verifyPackMatchesIndexes(pack *packFile) error {
if err := store.ensureCandidates(); err != nil {
return err
}
candidate, ok := store.candidateForPack(pack.name)
if !ok {
return fmt.Errorf("objectstore/packed: missing index for pack %q", pack.name)
}
index, err := store.openIndex(candidate)
if err != nil {
return err
}
if err := verifyMappedPackMatchesMappedIdx(pack.data, index.data, store.algo); err != nil {
return fmt.Errorf("objectstore/packed: pack %q does not match idx %q: %w", pack.name, index.idxName, err)
}
return nil
}
// entryMetaAt parses one pack entry header at location.
func (store *Store) entryMetaAt(loc location) (*packFile, entryMeta, error) {
pack, err := store.openPack(loc.packName)
if err != nil {
return nil, entryMeta{}, err
}
meta, err := parseEntryMeta(pack, store.algo, loc.offset)
if err != nil {
return nil, entryMeta{}, err
}
return pack, meta, nil
}
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