SQLite cache

server/cache_sqlite.go

@@ -0,0 +1,127 @@
+package server
+
+import (
+	"database/sql"
+	"errors"
+	_ "github.com/mattn/go-sqlite3" // SQLite driver
+	"time"
+)
+
+const (
+	createTableQuery = `
+		BEGIN;
+		CREATE TABLE IF NOT EXISTS messages (
+			id VARCHAR(20) PRIMARY KEY,
+			time INT NOT NULL,
+			topic VARCHAR(64) NOT NULL,
+			message VARCHAR(1024) NOT NULL
+		);
+		CREATE INDEX IF NOT EXISTS idx_topic ON messages (topic);
+		COMMIT;
+	`
+	insertMessageQuery = `INSERT INTO messages (id, time, topic, message) VALUES (?, ?, ?, ?)`
+	pruneMessagesQuery = `DELETE FROM messages WHERE time < ?`
+	selectMessagesSinceTimeQuery = `
+		SELECT id, time, message 
+		FROM messages 
+		WHERE topic = ? AND time >= ?
+		ORDER BY time ASC
+	`
+	selectMessageCountQuery = `SELECT count(*) FROM messages WHERE topic = ?`
+	selectTopicsQuery       = `SELECT topic, MAX(time) FROM messages GROUP BY TOPIC`
+)
+
+type sqliteCache struct {
+	db *sql.DB
+}
+
+var _ cache = (*sqliteCache)(nil)
+
+func newSqliteCache(filename string) (*sqliteCache, error) {
+	db, err := sql.Open("sqlite3", filename)
+	if err != nil {
+		return nil, err
+	}
+	if _, err := db.Exec(createTableQuery); err != nil {
+		return nil, err
+	}
+	return &sqliteCache{
+		db:     db,
+	}, nil
+}
+
+func (c *sqliteCache) AddMessage(m *message) error {
+	_, err := c.db.Exec(insertMessageQuery, m.ID, m.Time, m.Topic, m.Message)
+	return err
+}
+
+func (c *sqliteCache) Messages(topic string, since time.Time) ([]*message, error) {
+	rows, err := c.db.Query(selectMessagesSinceTimeQuery, topic, since.Unix())
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+	messages := make([]*message, 0)
+	for rows.Next() {
+		var timestamp int64
+		var id, msg string
+		if err := rows.Scan(&id, &timestamp, &msg); err != nil {
+			return nil, err
+		}
+		messages = append(messages, &message{
+			ID:      id,
+			Time:    timestamp,
+			Event:   messageEvent,
+			Topic:   topic,
+			Message: msg,
+		})
+	}
+	if err := rows.Err(); err != nil {
+		return nil, err
+	}
+	return messages, nil
+}
+
+func (c *sqliteCache) MessageCount(topic string) (int, error) {
+	rows, err := c.db.Query(selectMessageCountQuery, topic)
+	if err != nil {
+		return 0, err
+	}
+	defer rows.Close()
+	var count int
+	if !rows.Next() {
+		return 0, errors.New("no rows found")
+	}
+	if err := rows.Scan(&count); err != nil {
+		return 0, err
+	} else if err := rows.Err(); err != nil {
+		return 0, err
+	}
+	return count, nil
+}
+
+func (s *sqliteCache) Topics() (map[string]*topic, error) {
+	rows, err := s.db.Query(selectTopicsQuery)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+	topics := make(map[string]*topic, 0)
+	for rows.Next() {
+		var id string
+		var last int64
+		if err := rows.Scan(&id, &last); err != nil {
+			return nil, err
+		}
+		topics[id] = newTopic(id, time.Unix(last, 0))
+	}
+	if err := rows.Err(); err != nil {
+		return nil, err
+	}
+	return topics, nil
+}
+
+func (c *sqliteCache) Prune(keep time.Duration) error {
+	_, err := c.db.Exec(pruneMessagesQuery, time.Now().Add(-1 * keep).Unix())
+	return err
+}