Blob: convert a type that is not a string in new Blob, new File and slice

packages/bun-types/globals.d.ts

@@ -1566,7 +1566,7 @@ interface Navigator {
 declare var navigator: Navigator;
 
 interface BlobPropertyBag {
-  /** Set a default "type". Not yet implemented. */
+  /** The MIME type of the `Blob`, for example `"text/html"`. */
   type?: string;
   /** Not implemented in Bun yet. */
   // endings?: "transparent" | "native";

src/codegen/builtins/host/web-classes.builtins.ts

@@ -350,7 +350,7 @@ const joinedParts = [
   b.readsContents(),
   b.runsTransitively("OwnValues", "PrototypeChain", "ToPrimitive", b.named("length")),
 ];
-const blobOptions = membersInspected("type");
+const blobOptions = [b.runsTransitively("ToPrimitive", b.named("type"))];
 
 const blobConstruction = [
   {
@@ -451,12 +451,11 @@ const membersOfBlob = {
     },
   },
   size: measuredNumber,
-  // An operand of another kind than a number or a string counts as absent.
   slice: {
-    ...nativeOnly,
+    ...operandCodeOnly,
     args: { start: anythingOrAbsent, end: anythingOrAbsent, contentType: anythingOrAbsent },
     returns: newBlobOverSameBytes,
-    uses: { this: stateRead, start: b.inspected, end: b.inspected, contentType: b.inspected },
+    uses: { this: stateRead, start: converted, end: converted, contentType: converted },
     reads: externalState,
   },
   // The promise is resolved with a Stats object, which looks for `then` on a prototype that is not locked.

src/runtime/webcore/Blob.rs

@@ -1803,7 +1803,8 @@ impl BlobExt for Blob {
         }
 
         let mut blob_content_type = BlobContentType::default();
-        if content_type.is_string() {
+        // A DOMString: ToString converts every value but `undefined`.
+        if !content_type.is_undefined() {
             let content_type_view = content_type.to_js_string_view(global_this)?;
             let slicer = content_type_view.to_utf8();
             let slice = slicer.slice();
@@ -2156,19 +2157,7 @@ impl BlobExt for Blob {
             blob = Blob::get::<false, true>(global_this, parts)?;
 
             if options.is_object() {
-                if let Some(content_type) = options.get(global_this, "type")? {
-                    'inner: {
-                        if content_type.is_string() {
-                            let content_type_str = content_type.to_utf8(global_this)?;
-                            let slice = content_type_str.slice();
-                            if !is_valid_blob_type(slice) {
-                                break 'inner;
-                            }
-                            blob.content_type_was_set.set(true);
-                            blob.content_type.set(BlobContentType::from_script(slice));
-                        }
-                    }
-                }
+                set_type_from_options(global_this, &blob, options)?;
             }
 
             if blob.content_type_slice().is_empty() {
@@ -5268,6 +5257,24 @@ fn write_bytes_to_file_fast<const NEEDS_OPEN: bool>(
     JSPromise::resolved_promise_value(global_this, JSValue::js_number(written as f64))
 }
 
+/// Gives `blob` the `type` of the options of `new Blob()` or `new File()`. The File API declares
+/// it a DOMString: ToString converts every value that is present.
+fn set_type_from_options(
+    global_this: &JSGlobalObject,
+    blob: &Blob,
+    options: JSValue,
+) -> JsResult<()> {
+    if let Some(content_type) = options.fast_get(global_this, jsc::BuiltinName::Type)? {
+        let content_type_str = content_type.to_utf8(global_this)?;
+        let slice = content_type_str.slice();
+        if is_valid_blob_type(slice) {
+            blob.content_type_was_set.set(true);
+            blob.content_type.set(BlobContentType::from_script(slice));
+        }
+    }
+    Ok(())
+}
+
 // ──────────────────────────────────────────────────────────────────────────
 // JSDOMFile constructor
 // ──────────────────────────────────────────────────────────────────────────
@@ -5313,21 +5320,7 @@ pub(crate) fn jsdom_file_construct(
     let mut set_last_modified = false;
 
     if options.is_object() {
-        // type, the ASCII-encoded string in lower case
-        // representing the media type of the Blob.
-        if let Some(content_type) = options.get(global_this, "type")? {
-            'inner: {
-                if content_type.is_string() {
-                    let content_type_str = content_type.to_utf8(global_this)?;
-                    let slice = content_type_str.slice();
-                    if !is_valid_blob_type(slice) {
-                        break 'inner;
-                    }
-                    blob.content_type_was_set.set(true);
-                    blob.content_type.set(BlobContentType::from_script(slice));
-                }
-            }
-        }
+        set_type_from_options(global_this, &blob, options)?;
 
         // WebIDL dictionary member: only `undefined` / not-present falls
         // through to the Date.now() default. Any present value (including

test/aot/parallel/host-classes/a-blob-converts-a-string-object-whose-tostring-nothing-else-calls.js

@@ -0,0 +1,21 @@
+// `slice`, `new Blob()` and `new File()` convert a String object with a toString of its own. Nothing else in the program calls
+// that toString, and nothing uses the results of the calls. In the place of start or end of `slice`, a String object is the contentType.
+let conversions = 0;
+const boxed = Object.assign(new String("x/boxed"), {
+  toString() {
+    conversions++;
+    return "x/own";
+  },
+});
+const blob = new Blob(["abcd"]);
+
+blob.slice(0, 2, boxed);
+console.log(conversions);
+blob.slice(boxed);
+console.log(conversions);
+blob.slice(0, boxed);
+console.log(conversions);
+new Blob(["a"], { type: boxed });
+console.log(conversions);
+new File(["a"], "name", { type: boxed });
+console.log(conversions);

test/aot/parallel/host-classes/a-blob-converts-a-type-that-is-not-a-string.js

@@ -0,0 +1,48 @@
+// `new Blob()` and `new File()` convert the `type` of their options to a string, and `slice` converts its contentType.
+// The conversion runs the code of an object, also in a call whose result nothing uses.
+let conversions = 0;
+const type = {
+  toString() {
+    conversions++;
+    return "x/converted";
+  },
+};
+const blob = new Blob(["abcd"]);
+
+console.log(new Blob(["a"], { type }).type, conversions);
+console.log(new File(["a"], "name", { type }).type, conversions);
+console.log(blob.slice(0, 2, type).type, conversions);
+
+new Blob(["a"], { type });
+console.log(conversions);
+blob.slice(0, 2, type);
+console.log(conversions);
+
+// A string in the place of start is the contentType, and the operand after it is not read.
+console.log(blob.slice("a/b", 1, type).type, conversions);
+console.log(blob.slice(0, 2).type === "", blob.slice(0, 2, "A/B").type, blob.slice(0, 2, 1).type);
+console.log(blob.slice(0, 2, null).type, blob.slice(0, 2, undefined).type === "");
+
+const options = {
+  reads: 0,
+  get type() {
+    this.reads++;
+    return ["x/from-a-getter"];
+  },
+};
+console.log(new Blob(["a"], options).type, options.reads);
+
+for (const value of [Symbol("type"), Object.create(null)]) {
+  try {
+    blob.slice(0, 1, value);
+    console.log("slice did not throw");
+  } catch (error) {
+    console.log(error instanceof TypeError, conversions);
+  }
+  try {
+    new Blob(["a"], { type: value });
+    console.log("new Blob did not throw");
+  } catch (error) {
+    console.log(error instanceof TypeError, conversions);
+  }
+}