feat: add durable client command spool

internal/client/spool/identity.go

@@ -0,0 +1,75 @@
+package spool
+
+import (
+	"errors"
+	"fmt"
+	"os"
+	"path/filepath"
+
+	"github.com/rvbox/rvbox/internal/domain"
+)
+
+func loadOrCreateIdentity(path string, generate func() (domain.UUID, error)) (domain.UUID, error) {
+	data, err := os.ReadFile(path)
+	if err == nil {
+		return parseIdentity(data)
+	}
+	if !errors.Is(err, os.ErrNotExist) {
+		return domain.UUID{}, fmt.Errorf("read client instance identity: %w", err)
+	}
+	identity, err := generate()
+	if err != nil {
+		return domain.UUID{}, fmt.Errorf("generate client instance identity: %w", err)
+	}
+	if err := writeIdentityAtomically(path, []byte(identity.String()+"\n")); err != nil {
+		return domain.UUID{}, err
+	}
+	return identity, nil
+}
+
+func parseIdentity(data []byte) (domain.UUID, error) {
+	if len(data) != 37 || data[36] != '\n' {
+		return domain.UUID{}, ErrIdentityCorrupt
+	}
+	identity, err := domain.ParseUUIDv7(string(data[:36]))
+	if err != nil {
+		return domain.UUID{}, fmt.Errorf("%w: %v", ErrIdentityCorrupt, err)
+	}
+	return identity, nil
+}
+
+func writeIdentityAtomically(path string, data []byte) (result error) {
+	directory := filepath.Dir(path)
+	temporary, err := os.CreateTemp(directory, ".client-instance-id-*")
+	if err != nil {
+		return fmt.Errorf("create client identity temporary file: %w", err)
+	}
+	temporaryPath := temporary.Name()
+	defer func() {
+		if result != nil {
+			_ = os.Remove(temporaryPath)
+		}
+	}()
+	if err := temporary.Chmod(0o600); err != nil {
+		_ = temporary.Close()
+		return fmt.Errorf("secure client identity temporary file: %w", err)
+	}
+	if _, err := temporary.Write(data); err != nil {
+		_ = temporary.Close()
+		return fmt.Errorf("write client identity: %w", err)
+	}
+	if err := temporary.Sync(); err != nil {
+		_ = temporary.Close()
+		return fmt.Errorf("sync client identity: %w", err)
+	}
+	if err := temporary.Close(); err != nil {
+		return fmt.Errorf("close client identity: %w", err)
+	}
+	if err := replaceIdentityFile(temporaryPath, path); err != nil {
+		return fmt.Errorf("install client identity: %w", err)
+	}
+	if err := syncDirectory(directory); err != nil {
+		return fmt.Errorf("sync client identity directory: %w", err)
+	}
+	return nil
+}