Plugins! (#420)

* Some queries

* Plugins!!

* cleanup

* actual names

* the actual plugins

* comment

* fix tests

* Tests

* unused errors

* Increase reaper rate to actually enforce settings

* ok

src/plugins/mod.rs

@@ -0,0 +1,40 @@
+//! The plugin ecosystem.
+//!
+//! Currently plugins only grant access or deny access to the database for a particual query.
+//! Example use cases:
+//!   - block known bad queries
+//!   - block access to system catalogs
+//!   - block dangerous modifications like `DROP TABLE`
+//!   - etc
+//!
+
+pub mod intercept;
+pub mod table_access;
+
+use crate::{errors::Error, query_router::QueryRouter};
+use async_trait::async_trait;
+use bytes::BytesMut;
+use sqlparser::ast::Statement;
+
+pub use intercept::Intercept;
+pub use table_access::TableAccess;
+
+#[derive(Clone, Debug, PartialEq)]
+pub enum PluginOutput {
+    Allow,
+    Deny(String),
+    Overwrite(Vec<Statement>),
+    Intercept(BytesMut),
+}
+
+#[async_trait]
+pub trait Plugin {
+    // Custom output is allowed because we want to extend this system
+    // to rewriting queries some day. So an output of a plugin could be
+    // a rewritten AST.
+    async fn run(
+        &mut self,
+        query_router: &QueryRouter,
+        ast: &Vec<Statement>,
+    ) -> Result<PluginOutput, Error>;
+}