1 files changed, 162 insertions, 0 deletions
diff --git a/internal/store/store.go b/internal/store/store.go
new file mode 100644
index 00000000..942eeef5
--- /dev/null
+++ b/internal/store/store.go
@@ -0,0 +1,162 @@
+package store
+
+import (
+	"errors"
+	"io/fs"
+	"iter"
+	"os"
+	"strconv"
+	"sync"
+	"syscall"
+
+	"hakurei.app/container/check"
+	"hakurei.app/hst"
+	"hakurei.app/internal/lockedfile"
+)
+
+// storeMutexName is the pathname of the file backing [lockedfile.Mutex] of a stateStore and storeHandle.
+const storeMutexName = "lock"
+
+// A stateStore keeps track of [hst.State] via a well-known filesystem accessible to all hakurei priv-side processes.
+// Access to store data and related resources are synchronised on a per-segment basis via storeHandle.
+type stateStore struct {
+	// Pathname of directory that the store is rooted in.
+	base *check.Absolute
+
+	// All currently known instances of storeHandle, keyed by their identity.
+	handles sync.Map
+
+	// Inter-process mutex to synchronise operations against the entire store.
+	// Held during List and when initialising previously unknown identities during Do.
+	// Must not be accessed directly. Callers should use the bigLock method instead.
+	fileMu *lockedfile.Mutex
+
+	// For creating the base directory.
+	mkdirOnce sync.Once
+	// Stored error value via mkdirOnce.
+	mkdirErr error
+}
+
+// bigLock acquires fileMu on stateStore.
+// A non-nil error returned by bigLock is of type [hst.AppError].
+func (s *stateStore) bigLock() (unlock func(), err error) {
+	s.mkdirOnce.Do(func() { s.mkdirErr = os.MkdirAll(s.base.String(), 0700) })
+	if s.mkdirErr != nil {
+		return nil, &hst.AppError{Step: "create state store directory", Err: s.mkdirErr}
+	}
+
+	if unlock, err = s.fileMu.Lock(); err != nil {
+		return nil, &hst.AppError{Step: "acquire lock on the state store", Err: err}
+	}
+	return
+}
+
+// identityHandle loads or initialises a storeHandle for identity.
+// A non-nil error returned by identityHandle is of type [hst.AppError].
+func (s *stateStore) identityHandle(identity int) (*storeHandle, error) {
+	h := new(storeHandle)
+	h.mu.Lock()
+
+	if v, ok := s.handles.LoadOrStore(identity, h); ok {
+		h = v.(*storeHandle)
+	} else {
+		// acquire big lock to initialise previously unknown segment handle
+		if unlock, err := s.bigLock(); err != nil {
+			return nil, err
+		} else {
+			defer unlock()
+		}
+
+		h.identity = identity
+		h.path = s.base.Append(strconv.Itoa(identity))
+		h.fileMu = lockedfile.MutexAt(h.path.Append(storeMutexName).String())
+
+		err := os.MkdirAll(h.path.String(), 0700)
+		h.mu.Unlock()
+		if err != nil && !errors.Is(err, fs.ErrExist) {
+			// handle methods will likely return ENOENT
+			s.handles.CompareAndDelete(identity, h)
+			return nil, &hst.AppError{Step: "create store segment directory", Err: err}
+		}
+	}
+	return h, nil
+}
+
+// segmentIdentity is produced by the iterator returned by stateStore.segments.
+type segmentIdentity struct {
+	// Identity of the current segment.
+	identity int
+	// Error encountered while processing this segment.
+	err error
+}
+
+// segments returns an iterator over all segmentIdentity known to the store.
+// To obtain a storeHandle on a segment, caller must then call identityHandle.
+// A non-nil error returned by segments is of type [hst.AppError].
+func (s *stateStore) segments() (iter.Seq[segmentIdentity], int, error) {
+	// read directory contents, should only contain storeMutexName and identity
+	var entries []os.DirEntry
+
+	// acquire big lock to read store segment list
+	if unlock, err := s.bigLock(); err != nil {
+		return nil, -1, err
+	} else {
+		entries, err = os.ReadDir(s.base.String())
+		unlock()
+
+		if err != nil && !errors.Is(err, os.ErrNotExist) {
+			return nil, -1, &hst.AppError{Step: "read store segments", Err: err}
+		}
+	}
+
+	// expects lock file
+	l := len(entries)
+	if l > 0 {
+		l--
+	}
+
+	return func(yield func(segmentIdentity) bool) {
+		// for error reporting
+		const step = "process store segment"
+
+		for _, ent := range entries {
+			si := segmentIdentity{identity: -1}
+
+			// should only be the big lock
+			if !ent.IsDir() {
+				if ent.Name() == storeMutexName {
+					continue
+				}
+
+				// this should never happen
+				si.err = &hst.AppError{Step: step, Err: syscall.EISDIR,
+					Msg: "skipped non-directory entry " + strconv.Quote(ent.Name())}
+				goto out
+			}
+
+			// failure paths either indicates a serious bug or external interference
+			if v, err := strconv.Atoi(ent.Name()); err != nil {
+				si.err = &hst.AppError{Step: step, Err: err,
+					Msg: "skipped non-identity entry " + strconv.Quote(ent.Name())}
+				goto out
+			} else if v < hst.IdentityMin || v > hst.IdentityMax {
+				si.err = &hst.AppError{Step: step, Err: syscall.ERANGE,
+					Msg: "skipped out of bounds entry " + strconv.Itoa(v)}
+				goto out
+			} else {
+				si.identity = v
+			}
+
+		out:
+			if !yield(si) {
+				break
+			}
+		}
+	}, l, nil
+}
+
+// newStore returns the address of a new instance of stateStore.
+// Multiple instances of stateStore rooted in the same directory is supported, but discouraged.
+func newStore(base *check.Absolute) *stateStore {
+	return &stateStore{base: base, fileMu: lockedfile.MutexAt(base.Append(storeMutexName).String())}
+}