fix(core): panic on big string allocation

core/bindings.rs

@@ -658,9 +658,22 @@ fn decode(
     )
   };
 
-  let text_str =
-    v8::String::new_from_utf8(scope, &buf, v8::NewStringType::Normal).unwrap();
-  rv.set(text_str.into())
+  // If `String::new_from_utf8()` returns `None`, this means that the
+  // length of the decoded string would be longer than what V8 can
+  // handle. In this case we return `RangeError`.
+  //
+  // For more details see:
+  // - https://encoding.spec.whatwg.org/#dom-textdecoder-decode
+  // - https://github.com/denoland/deno/issues/6649
+  // - https://github.com/v8/v8/blob/d68fb4733e39525f9ff0a9222107c02c28096e2a/include/v8.h#L3277-L3278
+  match v8::String::new_from_utf8(scope, &buf, v8::NewStringType::Normal) {
+    Some(text) => rv.set(text.into()),
+    None => {
+      let msg = v8::String::new(scope, "string too long").unwrap();
+      let exception = v8::Exception::range_error(scope, msg);
+      scope.throw_exception(exception);
+    }
+  };
 }
 
 fn queue_microtask(

core/encode_decode_test.js

@@ -41,6 +41,17 @@ function main() {
 
   assert(Deno.core.decode(new Uint8Array(fixture1)) === "𝓽𝓮𝔁𝓽");
   assert(Deno.core.decode(new Uint8Array(fixture2)) === "Hello �� World");
+
+  // See https://github.com/denoland/deno/issues/6649
+  let thrown = false;
+  try {
+    Deno.core.decode(new Uint8Array(2 ** 29));
+  } catch (e) {
+    thrown = true;
+    assert(e instanceof RangeError);
+    assert(e.message === "string too long");
+  }
+  assert(thrown);
 }
 
 main();