fix(mssql): keep the target usable when the restore drop fails

src/domain/mssql/backup.rs

@@ -14,13 +14,13 @@ pub async fn run(
     logger: Arc<JobLogger>,
 ) -> Result<PathBuf> {
     tokio::task::spawn_blocking(move || -> Result<PathBuf> {
-        logger.log("info", format!("Starting MSSQL backup for database {}", cfg.name));
-
         let (format, unknown_format) = MssqlFormat::from_config(&cfg);
         if let Some(v) = unknown_format {
             logger.log("warn", format!("Unknown backup_format '{}' for {}, falling back to 'dacpac'", v, cfg.name));
         }
 
+        logger.log("info", format!("Starting MSSQL {} backup for database {}", &format.extension()[1..], cfg.name));
+
         let file_path = backup_dir.join(format!("{}{}", cfg.generated_id, file_extension));
         let connection_string = format!(
             "Server=tcp:{},{};Database={};User Id={};Password={};TrustServerCertificate=True;Encrypt=False",

src/domain/mssql/restore.rs

@@ -10,11 +10,24 @@ use std::time::Instant;
 const DROP_DATABASE_SQL: &str = "DECLARE @q nvarchar(258) = QUOTENAME(@P1);
 IF DB_ID(@P1) IS NOT NULL
 BEGIN
-    IF HAS_PERMS_BY_NAME(NULL, 'DATABASE', 'CREATE DATABASE') = 0
+    IF DB_ID(@P1) <= 4
+        THROW 50000, N'Refusing to restore over a system database; nothing was dropped', 1;
+    IF ISNULL(HAS_PERMS_BY_NAME(NULL, 'DATABASE', 'CREATE DATABASE'), 0) = 0
         THROW 50000, N'Restore needs CREATE DATABASE permission (dbcreator) to recreate the target database; nothing was dropped', 1;
+    DECLARE @single bit = 0;
     IF CAST(SERVERPROPERTY('EngineEdition') AS int) <> 5
+    BEGIN
         EXEC(N'ALTER DATABASE ' + @q + N' SET SINGLE_USER WITH ROLLBACK IMMEDIATE');
-    EXEC(N'DROP DATABASE ' + @q);
+        SET @single = 1;
+    END
+    BEGIN TRY
+        EXEC(N'DROP DATABASE ' + @q);
+    END TRY
+    BEGIN CATCH
+        IF @single = 1 AND DB_ID(@P1) IS NOT NULL
+            EXEC(N'ALTER DATABASE ' + @q + N' SET MULTI_USER');
+        THROW;
+    END CATCH
 END";
 
 pub async fn run(cfg: DatabaseConfig, restore_file: PathBuf, logger: Arc<JobLogger>) -> Result<()> {
@@ -80,7 +93,7 @@ pub async fn run(cfg: DatabaseConfig, restore_file: PathBuf, logger: Arc<JobLogg
 }
 
 async fn drop_database(cfg: &DatabaseConfig, logger: &JobLogger) -> Result<()> {
-    logger.log("info", format!("Dropping MSSQL database {} before restore", cfg.database));
+    logger.log("info", format!("Replacing MSSQL database {} (drop if it exists, then recreate from the backup)", cfg.database));
 
     let start = Instant::now();
     let mut client = super::connection::build_client(cfg, Some("master"))
@@ -92,6 +105,6 @@ async fn drop_database(cfg: &DatabaseConfig, logger: &JobLogger) -> Result<()> {
         .with_context(|| format!("Failed to drop MSSQL database {}", cfg.database))?;
 
     let duration_ms = start.elapsed().as_millis() as f64;
-    logger.log_command(format!("DROP DATABASE [{}]", cfg.database), None, Some(0), Some(duration_ms));
+    logger.log_command(format!("DROP DATABASE IF EXISTS [{}]", cfg.database), None, Some(0), Some(duration_ms));
     Ok(())
 }

src/tests/domain/mssql.rs

@@ -373,6 +373,92 @@ async fn mssql_restore_refuses_without_create_database_test() {
     assert_eq!(scalar(&host, port, "ownerdb", "sa", SA_PASSWORD, "SELECT COUNT(*) FROM dbo.users").await, 3);
 }
 
+#[tokio::test]
+async fn mssql_restore_failed_drop_keeps_multi_user_test() {
+    init_tracing_for_test();
+    let (_container, host, port) = start().await;
+    create_user_database(&host, port, "alterdb").await;
+    exec(
+        &host,
+        port,
+        "master",
+        "CREATE LOGIN alter_login WITH PASSWORD = 'Alter!Str0ng1'; GRANT CREATE ANY DATABASE TO alter_login;",
+    )
+    .await;
+    exec(
+        &host,
+        port,
+        "alterdb",
+        "CREATE TABLE dbo.t (id INT PRIMARY KEY); INSERT dbo.t VALUES (1); \
+         CREATE USER alter_user FOR LOGIN alter_login; GRANT ALTER TO alter_user;",
+    )
+    .await;
+
+    let temp_dir = TempDir::new().unwrap();
+    let file_path = temp_dir.path().join("backup.dacpac");
+    std::fs::write(&file_path, b"not a package").unwrap();
+
+    let mut config = make_config(host.clone(), port, "alterdb", "5a445eb4-c2c6-4bde-a423-ee1385dcf6dc");
+    config.username = "alter_login".to_string();
+    config.password = "Alter!Str0ng1".to_string();
+    let result = DatabaseFactory::create_for_restore(config, &file_path)
+        .await
+        .restore(&file_path, Arc::new(JobLogger::new()))
+        .await;
+
+    assert!(!format!("{:#}", result.unwrap_err()).contains("nothing was dropped"));
+    assert_eq!(
+        scalar(&host, port, "master", "sa", SA_PASSWORD, "SELECT CASE WHEN DB_ID('alterdb') IS NULL THEN 0 ELSE 1 END").await,
+        1
+    );
+    assert_eq!(
+        scalar(
+            &host,
+            port,
+            "master",
+            "sa",
+            SA_PASSWORD,
+            "SELECT CASE WHEN DATABASEPROPERTYEX('alterdb', 'UserAccess') = 'MULTI_USER' THEN 1 ELSE 0 END"
+        )
+        .await,
+        1
+    );
+}
+
+#[tokio::test]
+async fn mssql_restore_refuses_system_database_test() {
+    init_tracing_for_test();
+    let (_container, host, port) = start().await;
+
+    let temp_dir = TempDir::new().unwrap();
+    let file_path = temp_dir.path().join("backup.dacpac");
+    std::fs::write(&file_path, b"not a package").unwrap();
+
+    let config = make_config(host.clone(), port, "msdb", "5a445eb4-c2c6-4bde-a423-ee1385dcf6dd");
+    let result = DatabaseFactory::create_for_restore(config, &file_path)
+        .await
+        .restore(&file_path, Arc::new(JobLogger::new()))
+        .await;
+
+    assert!(format!("{:#}", result.unwrap_err()).contains("system database"));
+    assert_eq!(
+        scalar(&host, port, "master", "sa", SA_PASSWORD, "SELECT CASE WHEN DB_ID('msdb') IS NULL THEN 0 ELSE 1 END").await,
+        1
+    );
+    assert_eq!(
+        scalar(
+            &host,
+            port,
+            "master",
+            "sa",
+            SA_PASSWORD,
+            "SELECT CASE WHEN DATABASEPROPERTYEX('msdb', 'UserAccess') = 'MULTI_USER' THEN 1 ELSE 0 END"
+        )
+        .await,
+        1
+    );
+}
+
 mod format_tests {
     use super::{make_config, with_backup_format};
     use crate::domain::mssql::format::MssqlFormat;