From 7c71a68da5cd412bd6be4c19e542b0ffa1d11934 Mon Sep 17 00:00:00 2001
From: Christian Muehlhaeuser <muesli@gmail.com>
Date: Thu, 19 Nov 2020 01:49:54 +0100
Subject: [PATCH] Add database schema versioning & migration skeleton (#382)

---
 core/data/data.go | 71 +++++++++++++++++++++++++++++++++++++++++++++--
 main.go           |  5 +++-
 2 files changed, 72 insertions(+), 4 deletions(-)

diff --git a/core/data/data.go b/core/data/data.go
index 1f0f214e9..6b8634763 100644
--- a/core/data/data.go
+++ b/core/data/data.go
@@ -6,6 +6,7 @@ package data
 
 import (
 	"database/sql"
+	"fmt"
 	"os"
 
 	"github.com/owncast/owncast/config"
@@ -13,13 +14,17 @@ import (
 	log "github.com/sirupsen/logrus"
 )
 
+const (
+	schemaVersion = 0
+)
+
 var _db *sql.DB
 
 func GetDatabase() *sql.DB {
 	return _db
 }
 
-func SetupPersistence() {
+func SetupPersistence() error {
 	file := config.Config.DatabaseFilePath
 
 	// Create empty DB file if it doesn't exist.
@@ -32,6 +37,66 @@ func SetupPersistence() {
 		}
 	}
 
-	sqliteDatabase, _ := sql.Open("sqlite3", file)
-	_db = sqliteDatabase
+	db, err := sql.Open("sqlite3", file)
+	if err != nil {
+		return err
+	}
+
+	if _, err := db.Exec(`CREATE TABLE IF NOT EXISTS config (
+		"key" string NOT NULL PRIMARY KEY,
+		"value" TEXT
+	);`); err != nil {
+		return err
+	}
+
+	var version int
+	err = db.QueryRow("SELECT value FROM config WHERE key='version'").
+		Scan(&version)
+	if err != nil {
+		if err != sql.ErrNoRows {
+			return err
+		}
+
+		// fresh database: initialize it with the current schema version
+		_, err := db.Exec("INSERT INTO config(key, value) VALUES(?, ?)", "version", schemaVersion)
+		if err != nil {
+			return err
+		}
+		version = schemaVersion
+	}
+
+	// is database from a newer Owncast version?
+	if version > schemaVersion {
+		return fmt.Errorf("incompatible database version %d (versions up to %d are supported)",
+			version, schemaVersion)
+	}
+
+	// is database schema outdated?
+	if version < schemaVersion {
+		if err := migrateDatabase(db, version, schemaVersion); err != nil {
+			return err
+		}
+	}
+
+	_db = db
+	return nil
+}
+
+func migrateDatabase(db *sql.DB, from, to int) error {
+	log.Printf("Migrating database from version %d to %d\n", from, to)
+	for v := from; v < to; v++ {
+		switch v {
+		case 0:
+			log.Printf("Migration step from %d to %d\n", v, v+1)
+		default:
+			panic("missing database migration step")
+		}
+	}
+
+	_, err := db.Exec("UPDATE config SET value = ? WHERE key = ?", to, "version")
+	if err != nil {
+		return err
+	}
+
+	return nil
 }
diff --git a/main.go b/main.go
index d6d197046..f852ef156 100644
--- a/main.go
+++ b/main.go
@@ -63,7 +63,10 @@ func main() {
 
 	go metrics.Start()
 
-	data.SetupPersistence()
+	err := data.SetupPersistence()
+	if err != nil {
+		log.Fatalln("failed to open database", err)
+	}
 
 	// starts the core
 	if err := core.Start(); err != nil {