add sqlite main storage example

Author: pilcrowonpaper

code/faroe-main-storage-sql-sqlite_go

@@ -0,0 +1,81 @@
+package main
+
+/*
+CREATE TABLE main_storage (
+	key TEXT NOT NULL PRIMARY KEY,
+	value BLOB NOT NULL,
+	counter INTEGER NOT NULL,
+	expires_at INTEGER NOT NULL
+) STRICT;
+*/
+
+import (
+	"database/sql"
+	"errors"
+	"fmt"
+	"time"
+
+	"github.com/faroedev/faroe"
+)
+
+type mainStorageStruct struct {
+	db *sql.DB
+}
+
+func newMainStorage(db *sql.DB) *mainStorageStruct {
+	storage := &mainStorageStruct{
+		db: db,
+	}
+	return storage
+}
+
+func (mainStorage *mainStorageStruct) Get(key string) ([]byte, int32, error) {
+	row := mainStorage.db.QueryRow("SELECT value, counter FROM main_storage WHERE key = ?", key)
+
+	var value []byte
+    var counter int32
+	err := row.Scan(&value, &counter)
+	if err != nil && errors.Is(err, sql.ErrNoRows) {
+		return nil, 0, faroe.ErrMainStorageEntryNotFound
+	}
+	if err != nil {
+		return nil, 0, fmt.Errorf("failed to run query: %s", err.Error())
+	}
+
+	return value, counter, nil
+}
+
+func (mainStorage *mainStorageStruct) Set(key string, value []byte, expiresAt time.Time) error {
+	_, err := mainStorage.db.Exec("INSERT INTO main_storage (key, value, counter, expires_at) VALUES (?, ?, ?, ?)", key, value, 0, expiresAt.Unix())
+	if err != nil {
+		return fmt.Errorf("failed to run query: %s", err.Error())
+	}
+
+	return nil
+}
+
+func (mainStorage *mainStorageStruct) Update(key string, value []byte, expiresAt time.Time, counter int32) error {
+	result, err := mainStorage.db.Exec("UPDATE main_storage SET value = ?, counter = counter + 1, expires_at = ? WHERE key = ? AND counter = ?", value, expiresAt, key, counter)
+	if err != nil {
+		return fmt.Errorf("failed to run query: %s", err.Error())
+	}
+	rowsAffected, _ := result.RowsAffected()
+	if rowsAffected < 1 {
+		return faroe.ErrMainStorageEntryNotFound
+	}
+
+	return nil
+}
+
+func (mainStorage *mainStorageStruct) Delete(key string) error {
+	result, err := mainStorage.db.Exec("DELETE FROM main_storage WHERE key = ?", key)
+	if err != nil {
+		return fmt.Errorf("failed to run query: %s", err.Error())
+	}
+	rowsAffected, _ := result.RowsAffected()
+	if rowsAffected < 1 {
+		return faroe.ErrMainStorageEntryNotFound
+	}
+
+	return nil
+}