feat(ext/fetch): support fetching local files

Closes denoland#11925
Closes denoland#2150

Author: kitsonk

cli/tests/unit/fetch_test.ts

@@ -23,7 +23,7 @@ unitTest(
 unitTest({ permissions: { net: true } }, async function fetchProtocolError() {
   await assertRejects(
     async () => {
-      await fetch("file:///");
+      await fetch("ftp://localhost:21/a/file");
     },
     TypeError,
     "not supported",
@@ -1360,3 +1360,59 @@ unitTest(
     client.close();
   },
 );
+
+unitTest(async function fetchFilePerm() {
+  await assertRejects(async () => {
+    await fetch(new URL("../testdata/subdir/json_1.json", import.meta.url));
+  }, Deno.errors.PermissionDenied);
+});
+
+unitTest(async function fetchFilePermDoesNotExist() {
+  await assertRejects(async () => {
+    await fetch(new URL("./bad.json", import.meta.url));
+  }, Deno.errors.PermissionDenied);
+});
+
+unitTest(
+  { permissions: { read: true } },
+  async function fetchFileBadMethod() {
+    await assertRejects(
+      async () => {
+        await fetch(
+          new URL("../testdata/subdir/json_1.json", import.meta.url),
+          {
+            method: "POST",
+          },
+        );
+      },
+      TypeError,
+      "Fetching files only supports the GET method. Received POST.",
+    );
+  },
+);
+
+unitTest(
+  { permissions: { read: true } },
+  async function fetchFileDoesNotExist() {
+    await assertRejects(
+      async () => {
+        await fetch(new URL("./bad.json", import.meta.url));
+      },
+      TypeError,
+    );
+  },
+);
+
+unitTest(
+  { permissions: { read: true } },
+  async function fetchFile() {
+    const res = await fetch(
+      new URL("../testdata/subdir/json_1.json", import.meta.url),
+    );
+    assert(res.ok);
+    const fixture = await Deno.readTextFile(
+      "cli/tests/testdata/subdir/json_1.json",
+    );
+    assertEquals(await res.text(), fixture);
+  },
+);

ext/fetch/lib.rs

@@ -164,6 +164,36 @@ where
   // Check scheme before asking for net permission
   let scheme = url.scheme();
   let (request_rid, request_body_rid, cancel_handle_rid) = match scheme {
+    "file" => {
+      let permissions = state.borrow_mut::<FP>();
+      let path = url
+        .to_file_path()
+        .map_err(|_| type_error(format!("Invalid file URL: {}", url)))?;
+      permissions.check_read(&path)?;
+      if method != Method::GET {
+        return Err(type_error(format!(
+          "Fetching files only supports the GET method. Received {}.",
+          method
+        )));
+      }
+      if !path.is_file() {
+        return Err(type_error(format!("Unable to fetch \"{}\".", url)));
+      }
+
+      let body = std::fs::read(&path)?;
+
+      let response = http::Response::builder()
+        .status(http::StatusCode::OK)
+        .body(reqwest::Body::from(body))?;
+
+      let fut = async move { Ok(Ok(Response::from(response))) };
+
+      let request_rid = state
+        .resource_table
+        .add(FetchRequestResource(Box::pin(fut)));
+
+      (request_rid, None, None)
+    }
     "http" | "https" => {
       let permissions = state.borrow_mut::<FP>();
       permissions.check_net_url(&url)?;