From ee27d8cdfd747b482dd7379c8b2d4c7179c25e11 Mon Sep 17 00:00:00 2001
From: networkException <git@nwex.de>
Date: Sun, 23 Oct 2022 04:02:56 +0200
Subject: [PATCH] LibWeb: Add is_code_unit_prefix() function

---
 Userland/Libraries/LibWeb/Infra/Strings.cpp | 36 +++++++++++++++++++++
 Userland/Libraries/LibWeb/Infra/Strings.h   |  2 ++
 2 files changed, 38 insertions(+)

diff --git a/Userland/Libraries/LibWeb/Infra/Strings.cpp b/Userland/Libraries/LibWeb/Infra/Strings.cpp
index 3b415bd6d3..b881b753e5 100644
--- a/Userland/Libraries/LibWeb/Infra/Strings.cpp
+++ b/Userland/Libraries/LibWeb/Infra/Strings.cpp
@@ -1,10 +1,12 @@
 /*
  * Copyright (c) 2022, Linus Groh <linusg@serenityos.org>
+ * Copyright (c) 2022, networkException <networkexception@serenityos.org>
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
 
 #include <AK/String.h>
+#include <AK/Utf16View.h>
 #include <AK/Utf8View.h>
 #include <LibWeb/Infra/CharacterTypes.h>
 #include <LibWeb/Infra/Strings.h>
@@ -29,4 +31,38 @@ String strip_and_collapse_whitespace(StringView string)
     return builder.string_view().trim(Infra::ASCII_WHITESPACE);
 }
 
+// https://infra.spec.whatwg.org/#code-unit-prefix
+bool is_code_unit_prefix(StringView potential_prefix, StringView input)
+{
+    auto potential_prefix_utf16 = utf8_to_utf16(potential_prefix);
+    auto input_utf16 = utf8_to_utf16(input);
+
+    // 1. Let i be 0.
+    size_t i = 0;
+
+    // 2. While true:
+    while (true) {
+        // 1. If i is greater than or equal to potentialPrefix’s length, then return true.
+        if (i >= potential_prefix.length())
+            return true;
+
+        // 2. If i is greater than or equal to input’s length, then return false.
+        if (i >= input.length())
+            return false;
+
+        // 3. Let potentialPrefixCodeUnit be the ith code unit of potentialPrefix.
+        auto potential_prefix_code_unit = Utf16View(potential_prefix_utf16).code_unit_at(i);
+
+        // 4. Let inputCodeUnit be the ith code unit of input.
+        auto input_code_unit = Utf16View(input_utf16).code_unit_at(i);
+
+        // 5. Return false if potentialPrefixCodeUnit is not inputCodeUnit.
+        if (potential_prefix_code_unit != input_code_unit)
+            return false;
+
+        // 6. Set i to i + 1.
+        ++i;
+    }
+}
+
 }
diff --git a/Userland/Libraries/LibWeb/Infra/Strings.h b/Userland/Libraries/LibWeb/Infra/Strings.h
index f73b435519..aef8cf4b5c 100644
--- a/Userland/Libraries/LibWeb/Infra/Strings.h
+++ b/Userland/Libraries/LibWeb/Infra/Strings.h
@@ -1,5 +1,6 @@
 /*
  * Copyright (c) 2022, Linus Groh <linusg@serenityos.org>
+ * Copyright (c) 2022, networkException <networkexception@serenityos.org>
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
@@ -11,5 +12,6 @@
 namespace Web::Infra {
 
 String strip_and_collapse_whitespace(StringView string);
+bool is_code_unit_prefix(StringView potential_prefix, StringView input);
 
 }