From 520bf6c9beedf83916837848ec6164eddac2d41c Mon Sep 17 00:00:00 2001
From: Timothy Flynn <trflynn89@pm.me>
Date: Tue, 10 Dec 2024 11:13:40 -0500
Subject: [PATCH] LibWeb: Return a better error message for invalid byte
 strings

We are currently returning LibJS's invalid code point message, but not
formatting it with the bad value. So we get something like:

    Unhandled JavaScript exception: [TypeError] Invalid code point {},
    must be an integer no less than 0 and no greater than 0x10FFFF

So not only is the error unformatted, but it's inaccurate; in this case,
the byte cannot be larger than 255.
---
 Libraries/LibWeb/WebIDL/AbstractOperations.cpp | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/Libraries/LibWeb/WebIDL/AbstractOperations.cpp b/Libraries/LibWeb/WebIDL/AbstractOperations.cpp
index 5476c6cc790..0054fb51194 100644
--- a/Libraries/LibWeb/WebIDL/AbstractOperations.cpp
+++ b/Libraries/LibWeb/WebIDL/AbstractOperations.cpp
@@ -7,6 +7,7 @@
  */
 
 #include <AK/ByteBuffer.h>
+#include <AK/Enumerate.h>
 #include <AK/Math.h>
 #include <AK/NumericLimits.h>
 #include <LibJS/Runtime/AbstractOperations.h>
@@ -232,9 +233,9 @@ JS::ThrowCompletionOr<String> to_byte_string(JS::VM& vm, JS::Value value)
     auto x = TRY(value.to_string(vm));
 
     // 2. If the value of any element of x is greater than 255, then throw a TypeError.
-    for (auto character : x.code_points()) {
+    for (auto [i, character] : enumerate(x.code_points())) {
         if (character > 0xFF)
-            return vm.throw_completion<JS::TypeError>(JS::ErrorType::InvalidCodePoint);
+            return vm.throw_completion<JS::TypeError>(MUST(String::formatted("Invalid byte 0x{:X} at index {}, must be an integer no less than 0 and no greater than 0xFF", character, x.code_points().byte_offset_of(i))));
     }
 
     // 3. Return an IDL ByteString value whose length is the length of x, and where the value of each element is the value of the corresponding element of x.