fix: ensure SQLite has a writable temporary directory (#876)

Co-authored-by: Elias Schneider <login@eliasschneider.com>

backend/internal/bootstrap/db_bootstrap.go

@@ -5,6 +5,8 @@ import (
 	"fmt"
 	"log/slog"
 	"net/url"
+	"os"
+	"path/filepath"
 	"strings"
 	"time"
 
@@ -21,6 +23,7 @@ import (
 	gormLogger "gorm.io/gorm/logger"
 
 	"github.com/pocket-id/pocket-id/backend/internal/common"
+	"github.com/pocket-id/pocket-id/backend/internal/utils"
 	sqliteutil "github.com/pocket-id/pocket-id/backend/internal/utils/sqlite"
 	"github.com/pocket-id/pocket-id/backend/resources"
 )
@@ -140,11 +143,20 @@ func connectDatabase() (db *gorm.DB, err error) {
 		if common.EnvConfig.DbConnectionString == "" {
 			return nil, errors.New("missing required env var 'DB_CONNECTION_STRING' for SQLite database")
 		}
+
 		sqliteutil.RegisterSqliteFunctions()
-		connString, err := parseSqliteConnectionString(common.EnvConfig.DbConnectionString)
+
+		connString, dbPath, err := parseSqliteConnectionString(common.EnvConfig.DbConnectionString)
 		if err != nil {
 			return nil, err
 		}
+
+		// Before we connect, also make sure that there's a temporary folder for SQLite to write its data
+		err = ensureSqliteTempDir(filepath.Dir(dbPath))
+		if err != nil {
+			return nil, err
+		}
+
 		dialector = sqlite.Open(connString)
 	case common.DbProviderPostgres:
 		if common.EnvConfig.DbConnectionString == "" {
@@ -174,7 +186,7 @@ func connectDatabase() (db *gorm.DB, err error) {
 	return nil, err
 }
 
-func parseSqliteConnectionString(connString string) (string, error) {
+func parseSqliteConnectionString(connString string) (parsedConnString string, dbPath string, err error) {
 	if !strings.HasPrefix(connString, "file:") {
 		connString = "file:" + connString
 	}
@@ -185,7 +197,7 @@ func parseSqliteConnectionString(connString string) (string, error) {
 	// Parse the connection string
 	connStringUrl, err := url.Parse(connString)
 	if err != nil {
-		return "", fmt.Errorf("failed to parse SQLite connection string: %w", err)
+		return "", "", fmt.Errorf("failed to parse SQLite connection string: %w", err)
 	}
 
 	// Convert options for the old SQLite driver to the new one
@@ -194,10 +206,19 @@ func parseSqliteConnectionString(connString string) (string, error) {
 	// Add the default and required params
 	err = addSqliteDefaultParameters(connStringUrl, isMemoryDB)
 	if err != nil {
-		return "", fmt.Errorf("invalid SQLite connection string: %w", err)
+		return "", "", fmt.Errorf("invalid SQLite connection string: %w", err)
 	}
 
-	return connStringUrl.String(), nil
+	// Get the absolute path to the database
+	// Here, we know for a fact that the ? is present
+	parsedConnString = connStringUrl.String()
+	idx := strings.IndexRune(parsedConnString, '?')
+	dbPath, err = filepath.Abs(parsedConnString[len("file:"):idx])
+	if err != nil {
+		return "", "", fmt.Errorf("failed to determine absolute path to the database: %w", err)
+	}
+
+	return parsedConnString, dbPath, nil
 }
 
 // The official C implementation of SQLite allows some additional properties in the connection string
@@ -350,6 +371,48 @@ func isSqliteInMemory(connString string) bool {
 	return len(qs["mode"]) > 0 && qs["mode"][0] == "memory"
 }
 
+// ensureSqliteTempDir ensures that SQLite has a directory where it can write temporary files if needed
+// The default directory may not be writable when using a container with a read-only root file system
+// See: https://www.sqlite.org/tempfiles.html
+func ensureSqliteTempDir(dbPath string) error {
+	// Per docs, SQLite tries these folders in order (excluding those that aren't applicable to us):
+	//
+	// - The SQLITE_TMPDIR environment variable
+	// - The TMPDIR environment variable
+	// - /var/tmp
+	// - /usr/tmp
+	// - /tmp
+	//
+	// Source: https://www.sqlite.org/tempfiles.html#temporary_file_storage_locations
+	//
+	// First, let's check if SQLITE_TMPDIR or TMPDIR are set, in which case we trust the user has taken care of the problem already
+	if os.Getenv("SQLITE_TMPDIR") != "" || os.Getenv("TMPDIR") != "" {
+		return nil
+	}
+
+	// Now, let's check if /var/tmp, /usr/tmp, or /tmp exist and are writable
+	for _, dir := range []string{"/var/tmp", "/usr/tmp", "/tmp"} {
+		ok, err := utils.IsWritableDir(dir)
+		if err != nil {
+			return fmt.Errorf("failed to check if %s is writable: %w", dir, err)
+		}
+		if ok {
+			// We found a folder that's writable
+			return nil
+		}
+	}
+
+	// If we're here, there's no temporary directory that's writable (not unusual for containers with a read-only root file system), so we set SQLITE_TMPDIR to the folder where the SQLite database is set
+	err := os.Setenv("SQLITE_TMPDIR", dbPath)
+	if err != nil {
+		return fmt.Errorf("failed to set SQLITE_TMPDIR environmental variable: %w", err)
+	}
+
+	slog.Debug("Set SQLITE_TMPDIR to the database directory", "path", dbPath)
+
+	return nil
+}
+
 func getGormLogger() gormLogger.Interface {
 	loggerOpts := make([]slogGorm.Option, 0, 5)
 	loggerOpts = append(loggerOpts,

backend/internal/utils/file_util.go

@@ -1,12 +1,15 @@
 package utils
 
 import (
+	"crypto/rand"
+	"encoding/hex"
 	"errors"
 	"fmt"
 	"io"
 	"mime/multipart"
 	"os"
 	"path/filepath"
+	"syscall"
 
 	"github.com/google/uuid"
 	"github.com/pocket-id/pocket-id/backend/resources"
@@ -136,3 +139,41 @@ func FileExists(path string) (bool, error) {
 	}
 	return !s.IsDir(), nil
 }
+
+// IsWritableDir checks if a directory exists and is writable
+func IsWritableDir(dir string) (bool, error) {
+	// Check if directory exists and it's actually a directory
+	info, err := os.Stat(dir)
+	if os.IsNotExist(err) {
+		return false, nil
+	} else if err != nil {
+		return false, fmt.Errorf("failed to stat '%s': %w", dir, err)
+	}
+	if !info.IsDir() {
+		return false, nil
+	}
+
+	// Generate a random suffix for the test file to avoid conflicts
+	randomBytes := make([]byte, 8)
+	_, err = io.ReadFull(rand.Reader, randomBytes)
+	if err != nil {
+		return false, fmt.Errorf("failed to generate random bytes: %w", err)
+	}
+
+	// Check if directory is writable by trying to create a temporary file
+	testFile := filepath.Join(dir, ".pocketid_test_write_"+hex.EncodeToString(randomBytes))
+	defer os.Remove(testFile)
+
+	file, err := os.Create(testFile)
+	if err != nil {
+		if os.IsPermission(err) || errors.Is(err, syscall.EROFS) {
+			return false, nil
+		}
+
+		return false, fmt.Errorf("failed to create test file: %w", err)
+	}
+
+	_ = file.Close()
+
+	return true, nil
+}