From 4ccade42b7f87bb07e36de047a12fade0ddeccef Mon Sep 17 00:00:00 2001
From: Luke Wilde <lukew@serenityos.org>
Date: Fri, 11 Feb 2022 21:04:42 +0000
Subject: [PATCH] LibWeb: Implement XMLHttpRequest.overrideMimeType

This allows you to ignore the Content-Type returned by the server and
always parse the content as if it's the given MIME type.

This will currently be used for allowing you to override the charset
of text responses.
---
 .../Libraries/LibWeb/XHR/XMLHttpRequest.cpp     | 17 +++++++++++++++++
 Userland/Libraries/LibWeb/XHR/XMLHttpRequest.h  |  6 ++++++
 .../Libraries/LibWeb/XHR/XMLHttpRequest.idl     |  1 +
 3 files changed, 24 insertions(+)

diff --git a/Userland/Libraries/LibWeb/XHR/XMLHttpRequest.cpp b/Userland/Libraries/LibWeb/XHR/XMLHttpRequest.cpp
index d7224f87a5..309be13573 100644
--- a/Userland/Libraries/LibWeb/XHR/XMLHttpRequest.cpp
+++ b/Userland/Libraries/LibWeb/XHR/XMLHttpRequest.cpp
@@ -291,4 +291,21 @@ String XMLHttpRequest::get_all_response_headers() const
     return builder.to_string();
 }
 
+// https://xhr.spec.whatwg.org/#dom-xmlhttprequest-overridemimetype
+DOM::ExceptionOr<void> XMLHttpRequest::override_mime_type(String const& mime)
+{
+    // 1. If this’s state is loading or done, then throw an "InvalidStateError" DOMException.
+    if (m_ready_state == ReadyState::Loading || m_ready_state == ReadyState::Done)
+        return DOM::InvalidStateError::create("Cannot override MIME type when state is Loading or Done.");
+
+    // 2. Set this’s override MIME type to the result of parsing mime.
+    m_override_mime_type = MimeSniff::MimeType::from_string(mime);
+
+    // 3. If this’s override MIME type is failure, then set this’s override MIME type to application/octet-stream.
+    if (!m_override_mime_type.has_value())
+        m_override_mime_type = MimeSniff::MimeType("application"sv, "octet-stream"sv);
+
+    return {};
+}
+
 }
diff --git a/Userland/Libraries/LibWeb/XHR/XMLHttpRequest.h b/Userland/Libraries/LibWeb/XHR/XMLHttpRequest.h
index 62e7e420b4..5c980701bd 100644
--- a/Userland/Libraries/LibWeb/XHR/XMLHttpRequest.h
+++ b/Userland/Libraries/LibWeb/XHR/XMLHttpRequest.h
@@ -14,6 +14,7 @@
 #include <LibWeb/Bindings/Wrappable.h>
 #include <LibWeb/DOM/EventTarget.h>
 #include <LibWeb/DOM/ExceptionOr.h>
+#include <LibWeb/MimeSniff/MimeType.h>
 #include <LibWeb/XHR/XMLHttpRequestEventTarget.h>
 
 namespace Web::XHR {
@@ -62,6 +63,8 @@ public:
     Bindings::CallbackType* onreadystatechange();
     void set_onreadystatechange(Optional<Bindings::CallbackType>);
 
+    DOM::ExceptionOr<void> override_mime_type(String const& mime);
+
 private:
     virtual void ref_event_target() override { ref(); }
     virtual void unref_event_target() override { unref(); }
@@ -91,6 +94,9 @@ private:
     bool m_timed_out { false };
 
     ByteBuffer m_response_object;
+
+    // https://xhr.spec.whatwg.org/#override-mime-type
+    Optional<MimeSniff::MimeType> m_override_mime_type;
 };
 
 }
diff --git a/Userland/Libraries/LibWeb/XHR/XMLHttpRequest.idl b/Userland/Libraries/LibWeb/XHR/XMLHttpRequest.idl
index 9e1e0ec14c..df794fd04d 100644
--- a/Userland/Libraries/LibWeb/XHR/XMLHttpRequest.idl
+++ b/Userland/Libraries/LibWeb/XHR/XMLHttpRequest.idl
@@ -18,6 +18,7 @@ interface XMLHttpRequest : XMLHttpRequestEventTarget {
 
     ByteString? getResponseHeader(ByteString name);
     ByteString getAllResponseHeaders();
+    undefined overrideMimeType(DOMString mime);
 
     attribute EventHandler onreadystatechange;