isle/go/secrets/store_fs.go

package secrets

import (
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"io/fs"
	"os"
	"path/filepath"
)

type fsStore struct {
	dirPath string
}

type fsStorePayload[Body any] struct {
	Version int
	Body    Body
}

// NewFSStore returns a Store which will store secrets to the given directory.
// The directory must already exist.
func NewFSStore(dirPath string) Store {
	return &fsStore{dirPath}
}

func (s *fsStore) path(id ID) string {
	return filepath.Join(s.dirPath, string(id))
}

func (s *fsStore) Set(_ context.Context, id ID, payload any) error {
	path := s.path(id)

	f, err := os.Create(path)
	if err != nil {
		return fmt.Errorf("creating file %q: %w", path, err)
	}
	defer f.Close()

	if err := json.NewEncoder(f).Encode(fsStorePayload[any]{
		Version: 1,
		Body:    payload,
	}); err != nil {
		return fmt.Errorf("writing JSON encoded payload to %q: %w", path, err)
	}

	return nil
}

func (s *fsStore) Get(_ context.Context, into any, id ID) error {
	path := s.path(id)

	f, err := os.Open(path)
	if errors.Is(err, fs.ErrNotExist) {
		return ErrNotFound
	} else if err != nil {
		return fmt.Errorf("creating file %q: %w", path, err)
	}
	defer f.Close()

	var fullPayload fsStorePayload[json.RawMessage]
	if err := json.NewDecoder(f).Decode(&fullPayload); err != nil {
		return fmt.Errorf("decoding JSON payload from %q: %w", path, err)
	}

	if fullPayload.Version != 1 {
		return fmt.Errorf(
			"unexpected JSON payload version %d", fullPayload.Version,
		)
	}

	if err := json.Unmarshal(fullPayload.Body, into); err != nil {
		return fmt.Errorf(
			"decoding JSON payload body from %q into %T: %w", path, into, err,
		)
	}

	return nil
}