Blob.slice: type the slice like new Blob(parts, { type })

src/jsc/webcore_types.rs

@@ -120,9 +120,12 @@ impl BlobContentType {
         )
     }
 
-    /// Heap-owned ASCII-lowercased copy of `slice`.
+    /// ASCII-lowercased copy of `slice`, heap-owned unless `slice` is empty.
     #[inline]
     pub fn from_lowercased(slice: &[u8]) -> Self {
+        if slice.is_empty() {
+            return Self::default();
+        }
         let mut buf = vec![0u8; slice.len()];
         bun_core::strings::copy_lowercase(slice, &mut buf);
         Self::Owned(std::sync::Arc::from(buf))

src/runtime/webcore/Blob.rs

@@ -1731,7 +1731,7 @@ impl BlobExt for Blob {
         blob.offset.set(offset);
         blob.size.set(len);
 
-        let content_type_was_allocated = content_type.is_owned() && !content_type.is_empty();
+        let content_type_was_given = !content_type.is_empty();
         // infer the content type if it was not specified
         if content_type.is_empty()
             && !self.content_type.get().is_owned()
@@ -1742,7 +1742,7 @@ impl BlobExt for Blob {
             blob.content_type.set(content_type);
         }
         blob.content_type_was_set
-            .set(self.content_type_was_set.get() || content_type_was_allocated);
+            .set(self.content_type_was_set.get() || content_type_was_given);
 
         let ptr = Blob::new(blob);
         // SAFETY: `ptr` just came from `heap::alloc` in `Blob::new`. Spelled
@@ -1762,13 +1762,7 @@ impl BlobExt for Blob {
     ) -> JsResult<JSValue> {
         let global_this = cx.global();
 
-        if self.size.get() == 0 {
-            let ptr = Blob::new(Blob::init_empty(global_this));
-            // SAFETY: `ptr` just came from `heap::alloc` in `Blob::new`; spelled
-            // `BlobExt::to_js(&*ptr, ..)` to pick the `&self` impl over the
-            // by-value `JsClass::to_js`.
-            return Ok(unsafe { BlobExt::to_js(&*ptr, global_this) });
-        }
+        let receiver_is_empty = self.size.get() == 0;
 
         let size_i64 = i64::try_from(self.size.get()).unwrap_or(i64::MAX);
 
@@ -1802,14 +1796,23 @@ impl BlobExt for Blob {
             }
         }
 
-        let mut blob_content_type = BlobContentType::default();
-        if content_type.is_string() {
+        let blob_content_type = if content_type.is_string() {
             let content_type_view = content_type.to_js_string_view(global_this)?;
             let slicer = content_type_view.to_utf8();
             let slice = slicer.slice();
             if is_valid_blob_type(slice) {
-                blob_content_type = BlobContentType::from_script(slice);
+                BlobContentType::from_script(slice)
+            } else {
+                BlobContentType::default()
             }
+        } else {
+            BlobContentType::default()
+        };
+
+        // Nothing of an empty receiver is kept: the slice is what `new Blob([], { type })` gives.
+        if receiver_is_empty {
+            let parent = Blob::init_empty(global_this);
+            return Ok(parent.get_slice_from(global_this, 0, 0, blob_content_type));
         }
 
         Ok(self.get_slice_from(global_this, relative_start, relative_end, blob_content_type))