Use a more standardized project layout

In #2, mrngm made the point that we should move to a more
standardized project structure. This commit does exactly that.
The new project structure is based on the repository listed at
<https://github.com/golang-standards/project-layout>.

Fixes #2.

internal/db/db.go

@@ -0,0 +1,112 @@
+package db
+
+import (
+	"fmt"
+	"log"
+	"time"
+
+	"github.com/pkg/errors"
+	bolt "go.etcd.io/bbolt"
+
+	"gitea.hashru.nl/dsprenkels/rushlink/pkg/gobmarsh"
+)
+
+var DB *bolt.DB
+
+// The current database version
+//
+// If we alter the database format, we bump this number and write a new
+// database migration in migrateDatabase().
+const CURRENT_MIGRATE_VERSION = 1
+
+// Bucket storing everything that is not a bulk value. This includes stuff like
+// the database version, secret site-wide keys.
+const BUCKET_CONF = "conf"
+
+// The main bucket for paste values and URL redirects
+const BUCKET_PASTES = "pastes"
+
+// This value stores the current migration version. If this value is less than
+// CURRENT_MIGRATE_VERSION, the database has to be migrated.
+const KEY_MIGRATE_VERSION = "migrate_version"
+
+// Open the bolt database
+func Init(name string) error {
+	var err error
+	DB, err = bolt.Open(name, 0666, &bolt.Options{Timeout: 1 * time.Second})
+	if err != nil {
+		return errors.Wrapf(err, "failed to open database at '%v'", name)
+	}
+	return DB.Update(migrateDatabase)
+}
+
+// Initialize and migrate the database to the current version
+func migrateDatabase(tx *bolt.Tx) error {
+	dbVersion, err := dbVersion(tx)
+	if err != nil {
+		return err
+	}
+
+	// Migrate the database to version 1
+	if dbVersion < 1 {
+		log.Println("migrating database to version 1")
+
+		// Create conf bucket
+		_, err := tx.CreateBucket([]byte(BUCKET_CONF))
+		if err != nil {
+			return err
+		}
+
+		// Create paste bucket
+		_, err = tx.CreateBucket([]byte(BUCKET_PASTES))
+		if err != nil {
+			return err
+		}
+
+		// Update the version number
+		if err := setDBVersion(tx, 1); err != nil {
+			return err
+		}
+	}
+
+	return nil
+}
+
+// Get the current migrate version from the database
+func dbVersion(tx *bolt.Tx) (int, error) {
+	conf := tx.Bucket([]byte(BUCKET_CONF))
+	if conf == nil {
+		return 0, nil
+	}
+	dbVersionBytes := conf.Get([]byte(KEY_MIGRATE_VERSION))
+	if dbVersionBytes == nil {
+		return 0, nil
+	}
+
+	// Version was already stored
+	var dbVersion int
+	if err := gobmarsh.Unmarshal(dbVersionBytes, &dbVersion); err != nil {
+		return 0, err
+	}
+	if dbVersion == 0 {
+		return 0, fmt.Errorf("database version is invalid (%v)", dbVersion)
+	}
+	if dbVersion > CURRENT_MIGRATE_VERSION {
+		return 0, fmt.Errorf("database version is too recent (%v > %v)", dbVersion, CURRENT_MIGRATE_VERSION)
+	}
+	return dbVersion, nil
+}
+
+// Update the current migrate version in the database
+func setDBVersion(tx *bolt.Tx, version int) error {
+	conf, err := tx.CreateBucketIfNotExists([]byte(BUCKET_CONF))
+	if err != nil {
+		return err
+	}
+
+	versionBytes, err := gobmarsh.Marshal(version)
+	if err != nil {
+		return err
+	}
+	return conf.Put([]byte(KEY_MIGRATE_VERSION), versionBytes)
+}