add Stdout dummy database engine

pkg/persistence/interface.go

@@ -60,6 +60,7 @@ type databaseEngine uint8
 
 const (
 	Sqlite3 databaseEngine = 1
+	Stdout
 )
 
 type Statistics struct {
@@ -112,6 +113,9 @@ func MakeDatabase(rawURL string, logger *zap.Logger) (Database, error) {
 	case "sqlite3":
 		return makeSqlite3Database(url_)
 
+	case "stdout":
+		return makeStdoutDatabase(url_)
+
 	case "postgresql":
 		return nil, fmt.Errorf("postgresql is not yet supported")
 

pkg/persistence/stdout.go

@@ -0,0 +1,85 @@
+package persistence
+
+import (
+	"encoding/json"
+	"net/url"
+	"os"
+
+	"github.com/pkg/errors"
+)
+
+type out struct {
+	InfoHash []byte `json:"infoHash"`
+	Name string     `json:"name"`
+	Files []File    `json:"files"`
+}
+
+var notSupportedError = errors.New("This dummy database engine (\"stdout\") does not support any sort of queries")
+
+func makeStdoutDatabase(_ *url.URL) (Database, error) {
+	s := new(stdout)
+	s.encoder = json.NewEncoder(os.Stdout)
+	return s, nil
+}
+
+type stdout struct {
+	encoder *json.Encoder
+}
+
+func (s *stdout) Engine() databaseEngine {
+	return Stdout
+}
+
+func (s *stdout) DoesTorrentExist(infoHash []byte) (bool, error) {
+	// Always say that "No the torrent does not exist" because we do not have
+	// a way to know if we have seen it before or not.
+	// TODO:
+	// A possible improvement would be using bloom filters (with low false positive
+	// probabilities) to apply some reasonable filtering.
+	return false, nil
+}
+
+func (s *stdout) AddNewTorrent(infoHash []byte, name string, files []File) error {
+	err := s.encoder.Encode(out {
+		InfoHash: infoHash,
+		Name: name,
+		Files: files,
+	})
+	if err != nil {
+		return errors.Wrap(err, "DB engine stdout encode error")
+	}
+
+	return nil
+}
+
+func (s *stdout) Close() error {
+	return os.Stdout.Sync()
+}
+
+func (s *stdout) GetNumberOfTorrents() (uint, error) {
+	return 0, notSupportedError
+}
+
+func (s *stdout) QueryTorrents(
+	query string,
+	epoch int64,
+	orderBy OrderingCriteria,
+	ascending bool,
+	limit uint,
+	lastOrderedValue *float64,
+	lastID *uint64,
+) ([]TorrentMetadata, error) {
+	return nil, notSupportedError
+}
+
+func (s *stdout) GetTorrent(infoHash []byte) (*TorrentMetadata, error) {
+	return nil, notSupportedError
+}
+
+func (s *stdout) GetFiles(infoHash []byte) ([]File, error) {
+	return nil, notSupportedError
+}
+
+func (s *stdout) GetStatistics(from string, n uint) (*Statistics, error) {
+	return nil, notSupportedError
+}