1 files changed, 105 insertions, 0 deletions
diff --git a/core/extensions.rs b/core/extensions.rs
new file mode 100644
index 000000000..eb6f6f719
--- /dev/null
+++ b/core/extensions.rs
@@ -0,0 +1,105 @@
+use crate::error::AnyError;
+use crate::{OpFn, OpState};
+
+pub type SourcePair = (&'static str, &'static str);
+pub type OpPair = (&'static str, Box<OpFn>);
+pub type OpMiddlewareFn = dyn Fn(&'static str, Box<OpFn>) -> Box<OpFn>;
+pub type OpStateFn = dyn Fn(&mut OpState) -> Result<(), AnyError>;
+
+#[derive(Default)]
+pub struct Extension {
+  js_files: Option<Vec<SourcePair>>,
+  ops: Option<Vec<OpPair>>,
+  opstate_fn: Option<Box<OpStateFn>>,
+  middleware_fn: Option<Box<OpMiddlewareFn>>,
+  initialized: bool,
+}
+
+impl Extension {
+  pub fn new(
+    js_files: Option<Vec<SourcePair>>,
+    ops: Option<Vec<OpPair>>,
+    opstate_fn: Option<Box<OpStateFn>>,
+    middleware_fn: Option<Box<OpMiddlewareFn>>,
+  ) -> Self {
+    Self {
+      js_files,
+      ops,
+      opstate_fn,
+      middleware_fn,
+      initialized: false,
+    }
+  }
+
+  pub fn pure_js(js_files: Vec<SourcePair>) -> Self {
+    Self::new(Some(js_files), None, None, None)
+  }
+
+  pub fn with_ops(
+    js_files: Vec<SourcePair>,
+    ops: Vec<OpPair>,
+    opstate_fn: Option<Box<OpStateFn>>,
+  ) -> Self {
+    Self::new(Some(js_files), Some(ops), opstate_fn, None)
+  }
+}
+
+// Note: this used to be a trait, but we "downgraded" it to a single concrete type
+// for the initial iteration, it will likely become a trait in the future
+impl Extension {
+  /// returns JS source code to be loaded into the isolate (either at snapshotting,
+  /// or at startup).  as a vector of a tuple of the file name, and the source code.
+  pub(crate) fn init_js(&self) -> Vec<SourcePair> {
+    match &self.js_files {
+      Some(files) => files.clone(),
+      None => vec![],
+    }
+  }
+
+  /// Called at JsRuntime startup to initialize ops in the isolate.
+  pub(crate) fn init_ops(&mut self) -> Option<Vec<OpPair>> {
+    // TODO(@AaronO): maybe make op registration idempotent
+    if self.initialized {
+      panic!("init_ops called twice: not idempotent or correct");
+    }
+    self.initialized = true;
+
+    self.ops.take()
+  }
+
+  /// Allows setting up the initial op-state of an isolate at startup.
+  pub(crate) fn init_state(&self, state: &mut OpState) -> Result<(), AnyError> {
+    match &self.opstate_fn {
+      Some(ofn) => ofn(state),
+      None => Ok(()),
+    }
+  }
+
+  /// init_middleware lets us middleware op registrations, it's called before init_ops
+  pub(crate) fn init_middleware(&mut self) -> Option<Box<OpMiddlewareFn>> {
+    self.middleware_fn.take()
+  }
+}
+
+/// Helps embed JS files in an extension. Returns Vec<(&'static str, &'static str)>
+/// representing the filename and source code.
+///
+/// Example:
+/// ```ignore
+/// include_js_files!(
+///   prefix "deno:op_crates/hello",
+///   "01_hello.js",
+///   "02_goodbye.js",
+/// )
+/// ```
+#[macro_export]
+macro_rules! include_js_files {
+  (prefix $prefix:literal, $($file:literal,)+) => {
+    vec![
+      $((
+        concat!($prefix, "/", $file),
+        include_str!($file),
+      ),)+
+    ]
+  };
+}