LibWeb: Add & use TRY_OR_RETURN_OOM macro

This is a convenient way to return a DOM exception for operations that
return ErrorOr and only have an OOM failure path.

Userland/Libraries/LibWeb/DOM/DOMException.h

@@ -13,6 +13,16 @@
 
 namespace Web::DOM {
 
+#define TRY_OR_RETURN_OOM(expression)                             \
+    ({                                                            \
+        auto _temporary_result = (expression);                    \
+        if (_temporary_result.is_error()) {                       \
+            VERIFY(_temporary_result.error().code() == ENOMEM);   \
+            return DOM::UnknownError::create("Out of memory."sv); \
+        }                                                         \
+        _temporary_result.release_value();                        \
+    })
+
 // The following have a legacy code value but *don't* produce it as
 // DOMException.code value when used as name (and are therefore omitted here):
 // - DOMStringSizeError (DOMSTRING_SIZE_ERR = 2)

Userland/Libraries/LibWeb/FileAPI/Blob.cpp

@@ -28,7 +28,7 @@ DOM::ExceptionOr<NonnullRefPtr<Blob>> Blob::create(Optional<Vector<BlobPart>> co
     ByteBuffer byte_buffer {};
     // 2. Let bytes be the result of processing blob parts given blobParts and options.
     if (blob_parts.has_value()) {
-        byte_buffer = TRY(process_blob_parts(blob_parts.value()));
+        byte_buffer = TRY_OR_RETURN_OOM(process_blob_parts(blob_parts.value()));
     }
 
     String type = String::empty();
@@ -50,14 +50,14 @@ DOM::ExceptionOr<NonnullRefPtr<Blob>> Blob::create_with_global_object(Bindings::
 }
 
 // https://w3c.github.io/FileAPI/#process-blob-parts
-DOM::ExceptionOr<ByteBuffer> Blob::process_blob_parts(Vector<BlobPart> const& blob_parts)
+ErrorOr<ByteBuffer> Blob::process_blob_parts(Vector<BlobPart> const& blob_parts)
 {
     // 1. Let bytes be an empty sequence of bytes.
     ByteBuffer bytes {};
 
     // 2. For each element in parts:
     for (auto const& blob_part : blob_parts) {
-        auto error = blob_part.visit(
+        TRY(blob_part.visit(
             // 1. If element is a USVString, run the following sub-steps:
             [&](String const& string) -> ErrorOr<void> {
                 // NOTE: This step is handled by the lambda expression.
@@ -79,9 +79,7 @@ DOM::ExceptionOr<ByteBuffer> Blob::process_blob_parts(Vector<BlobPart> const& bl
             // 3. If element is a Blob, append the bytes it represents to bytes.
             [&](NonnullRefPtr<Blob> const& blob) -> ErrorOr<void> {
                 return bytes.try_append(blob->m_byte_buffer.bytes());
-            });
-        if (error.is_error())
-            return DOM::UnknownError::create("Out of memory. Failed to process blob parts."sv);
+            }));
     }
     return bytes;
 }
@@ -146,10 +144,8 @@ DOM::ExceptionOr<NonnullRefPtr<Blob>> Blob::slice(Optional<i64> start, Optional<
     // a. S refers to span consecutive bytes from this, beginning with the byte at byte-order position relativeStart.
     // b. S.size = span.
     // c. S.type = relativeContentType.
-    auto byte_buffer_or_error = m_byte_buffer.slice(relative_start, span);
-    if (byte_buffer_or_error.is_error())
-        return DOM::UnknownError::create("Out of memory."sv);
-    return adopt_ref(*new Blob(byte_buffer_or_error.release_value(), move(relative_content_type)));
+    auto byte_buffer = TRY_OR_RETURN_OOM(m_byte_buffer.slice(relative_start, span));
+    return adopt_ref(*new Blob(move(byte_buffer), move(relative_content_type)));
 }
 
 // https://w3c.github.io/FileAPI/#dom-blob-text

Userland/Libraries/LibWeb/FileAPI/Blob.h

@@ -50,7 +50,7 @@ public:
 
 private:
     Blob() = default;
-    static DOM::ExceptionOr<ByteBuffer> process_blob_parts(Vector<BlobPart> const& blob_parts);
+    static ErrorOr<ByteBuffer> process_blob_parts(Vector<BlobPart> const& blob_parts);
 
     ByteBuffer m_byte_buffer {};
     String m_type {};

Userland/Libraries/LibWeb/XHR/XMLHttpRequest.cpp

@@ -118,10 +118,8 @@ DOM::ExceptionOr<JS::Value> XMLHttpRequest::response()
     }
     // 6. Otherwise, if this’s response type is "blob", set this’s response object to a new Blob object representing this’s received bytes with type set to the result of get a final MIME type for this.
     else if (m_response_type == Bindings::XMLHttpRequestResponseType::Blob) {
-        auto blob_part_or_error = try_make_ref_counted<FileAPI::Blob>(m_received_bytes, get_final_mime_type().type());
-        if (blob_part_or_error.is_error())
-            return DOM::UnknownError::create("Out of memory."sv);
-        auto blob = TRY(FileAPI::Blob::create(Vector<FileAPI::BlobPart> { blob_part_or_error.release_value() }));
+        auto blob_part = TRY_OR_RETURN_OOM(try_make_ref_counted<FileAPI::Blob>(m_received_bytes, get_final_mime_type().type()));
+        auto blob = TRY(FileAPI::Blob::create(Vector<FileAPI::BlobPart> { move(blob_part) }));
         m_response_object = JS::make_handle(JS::Value(blob->create_wrapper(global_object)));
     }
     // 7. Otherwise, if this’s response type is "document", set a document response for this.