feat: initial scaffold of unibus message bus (membership service + client lib + demo peers)

pkg/blobstore/blobstore.go

@@ -0,0 +1,81 @@
+// Package blobstore is a content-addressed object store on local disk.
+//
+// The bus transports messages, not blobs. Media (images, files, large payloads)
+// is encrypted by the client BEFORE being stored here, so the store only ever
+// sees ciphertext. Objects are addressed by the sha256 hex of their (encrypted)
+// bytes, which makes Put idempotent and deduplicating.
+package blobstore
+
+import (
+	"crypto/sha256"
+	"encoding/hex"
+	"fmt"
+	"os"
+	"path/filepath"
+)
+
+// Store is a directory-backed content-addressed blob store.
+type Store struct {
+	dir string
+}
+
+// New creates a Store rooted at dir, creating the directory if needed.
+func New(dir string) (*Store, error) {
+	if err := os.MkdirAll(dir, 0o755); err != nil {
+		return nil, fmt.Errorf("blobstore: mkdir %q: %w", dir, err)
+	}
+	return &Store{dir: dir}, nil
+}
+
+// path returns the on-disk path for a given content hash.
+func (s *Store) path(hash string) string {
+	return filepath.Join(s.dir, hash)
+}
+
+// Put writes data to the store and returns its sha256 hex hash. If an object
+// with the same content already exists, Put is a no-op and returns the hash.
+func (s *Store) Put(data []byte) (string, error) {
+	sum := sha256.Sum256(data)
+	hash := hex.EncodeToString(sum[:])
+	p := s.path(hash)
+
+	if _, err := os.Stat(p); err == nil {
+		return hash, nil // already present (content-addressed: identical bytes)
+	}
+
+	// Write atomically: temp file + rename, so readers never see a partial blob.
+	tmp, err := os.CreateTemp(s.dir, ".tmp-*")
+	if err != nil {
+		return "", fmt.Errorf("blobstore: create temp: %w", err)
+	}
+	tmpName := tmp.Name()
+	if _, err := tmp.Write(data); err != nil {
+		tmp.Close()
+		os.Remove(tmpName)
+		return "", fmt.Errorf("blobstore: write temp: %w", err)
+	}
+	if err := tmp.Close(); err != nil {
+		os.Remove(tmpName)
+		return "", fmt.Errorf("blobstore: close temp: %w", err)
+	}
+	if err := os.Rename(tmpName, p); err != nil {
+		os.Remove(tmpName)
+		return "", fmt.Errorf("blobstore: rename: %w", err)
+	}
+	return hash, nil
+}
+
+// Get reads the object with the given hash.
+func (s *Store) Get(hash string) ([]byte, error) {
+	data, err := os.ReadFile(s.path(hash))
+	if err != nil {
+		return nil, fmt.Errorf("blobstore: get %q: %w", hash, err)
+	}
+	return data, nil
+}
+
+// Has reports whether an object with the given hash exists.
+func (s *Store) Has(hash string) bool {
+	_, err := os.Stat(s.path(hash))
+	return err == nil
+}