connection: add allow_attach to config

Default is false, which means connections are blocked from attaching
databases. If allowed, colocated databases can be attached in readonly
mode.

Example:
→  attach another as another; select * from another.sqlite_master;
TYPE      NAME     TBL NAME     ROOTPAGE     SQL
table     t3       t3           2            CREATE TABLE t3(id)

Author: psarna

libsql-server/src/connection/config.rs

@@ -18,6 +18,8 @@ pub struct DatabaseConfig {
     pub heartbeat_url: Option<Url>,
     #[serde(default)]
     pub bottomless_db_id: Option<String>,
+    #[serde(default)]
+    pub allow_attach: bool,
 }
 
 const fn default_max_size() -> u64 {
@@ -33,6 +35,7 @@ impl Default for DatabaseConfig {
             max_db_pages: default_max_size(),
             heartbeat_url: None,
             bottomless_db_id: None,
+            allow_attach: Default::default(),
         }
     }
 }

libsql-server/src/connection/libsql.rs

@@ -693,7 +693,7 @@ impl<W: Wal> Connection<W> {
             StmtKind::Read | StmtKind::TxnBegin | StmtKind::Other => config.block_reads,
             StmtKind::Write => config.block_reads || config.block_writes,
             StmtKind::TxnEnd | StmtKind::Release | StmtKind::Savepoint => false,
-            StmtKind::Attach | StmtKind::Detach => false,
+            StmtKind::Attach | StmtKind::Detach => !config.allow_attach,
         };
         if blocked {
             return Err(Error::Blocked(config.block_reason.clone()));

libsql-server/src/http/admin/mod.rs

@@ -177,6 +177,7 @@ async fn handle_get_config<M: MakeNamespace, C: Connector>(
         block_reason: config.block_reason.clone(),
         max_db_size: Some(max_db_size),
         heartbeat_url: config.heartbeat_url.clone().map(|u| u.into()),
+        allow_attach: config.allow_attach,
     };
 
     Ok(Json(resp))
@@ -219,6 +220,8 @@ struct HttpDatabaseConfig {
     max_db_size: Option<bytesize::ByteSize>,
     #[serde(default)]
     heartbeat_url: Option<String>,
+    #[serde(default)]
+    allow_attach: bool,
 }
 
 async fn handle_post_config<M: MakeNamespace, C>(
@@ -234,6 +237,7 @@ async fn handle_post_config<M: MakeNamespace, C>(
     config.block_reads = req.block_reads;
     config.block_writes = req.block_writes;
     config.block_reason = req.block_reason;
+    config.allow_attach = req.allow_attach;
     if let Some(size) = req.max_db_size {
         config.max_db_pages = size.as_u64() / LIBSQL_PAGE_SIZE;
     }

libsql-server/tests/namespaces/meta.rs

@@ -81,6 +81,45 @@ fn meta_store() {
             foo_conn.execute("select 1", ()).await.unwrap();
         }
 
+        // STEP 4: try attaching a database
+        {
+            let foo = Database::open_remote_with_connector(
+                "http://foo.primary:8080",
+                "",
+                TurmoilConnector,
+            )?;
+            let foo_conn = foo.connect()?;
+
+            foo_conn.execute("attach foo as foo", ()).await.unwrap_err();
+        }
+
+        // STEP 5: update config to allow attaching databases
+        client
+            .post(
+                "http://primary:9090/v1/namespaces/foo/config",
+                json!({
+                    "block_reads": false,
+                    "block_writes": false,
+                    "allow_attach": true,
+                }),
+            )
+            .await?;
+
+        {
+            let foo = Database::open_remote_with_connector(
+                "http://foo.primary:8080",
+                "",
+                TurmoilConnector,
+            )?;
+            let foo_conn = foo.connect()?;
+
+            foo_conn.execute("attach foo as foo", ()).await.unwrap();
+            foo_conn
+                .execute("select * from foo.sqlite_master", ())
+                .await
+                .unwrap();
+        }
+
         Ok(())
     });