LibWeb: Implement more CSS serializers and make them more ergonomic

This implements these algorithms from the CSSOM-1 spec:
- serialize a string
- serialize a URL

Also, we now have two versions of each of the serialization functions:
One that returns a String as before, and the other that takes a
StringBuilder to write into. This saves creating extra StringBuilders
when they are not needed. :^)

2 files changed, 94 insertions, 13 deletions

diff --git a/Userland/Libraries/LibWeb/CSS/Serialize.cpp b/Userland/Libraries/LibWeb/CSS/Serialize.cpp
index 3989f64787..7e1d6f3a19 100644
--- a/Userland/Libraries/LibWeb/CSS/Serialize.cpp
+++ b/Userland/Libraries/LibWeb/CSS/Serialize.cpp
@@ -11,24 +11,21 @@
 namespace Web::CSS {
 
 // https://www.w3.org/TR/cssom-1/#escape-a-character
-String escape_a_character(u32 character)
+void escape_a_character(StringBuilder builder, u32 character)
 {
-    StringBuilder builder;
     builder.append('\\');
     builder.append_code_point(character);
-    return builder.to_string();
 }
 
 // https://www.w3.org/TR/cssom-1/#escape-a-character-as-code-point
-String escape_a_character_as_code_point(u32 character)
+void escape_a_character_as_code_point(StringBuilder builder, u32 character)
 {
-    return String::formatted("\\{:x} ", character);
+    builder.appendff("\\{:x} ", character);
 }
 
 // https://www.w3.org/TR/cssom-1/#serialize-an-identifier
-String serialize_an_identifier(StringView const& ident)
+void serialize_an_identifier(StringBuilder builder, StringView const& ident)
 {
-    StringBuilder builder;
     Utf8View characters { ident };
     auto first_character = characters.is_empty() ? 0 : *characters.begin();
 
@@ -43,25 +40,25 @@ String serialize_an_identifier(StringView const& ident)
         // If the character is in the range [\1-\1f] (U+0001 to U+001F) or is U+007F,
         // then the character escaped as code point.
         if ((character >= 0x0001 && character <= 0x001F) || (character == 0x007F)) {
-            builder.append(escape_a_character_as_code_point(character));
+            escape_a_character_as_code_point(builder, character);
             continue;
         }
         // If the character is the first character and is in the range [0-9] (U+0030 to U+0039),
         // then the character escaped as code point.
         if (builder.is_empty() && character >= '0' && character <= '9') {
-            builder.append(escape_a_character_as_code_point(character));
+            escape_a_character_as_code_point(builder, character);
             continue;
         }
         // If the character is the second character and is in the range [0-9] (U+0030 to U+0039)
         // and the first character is a "-" (U+002D), then the character escaped as code point.
         if (builder.length() == 1 && first_character == '-' && character >= '0' && character <= '9') {
-            builder.append(escape_a_character_as_code_point(character));
+            escape_a_character_as_code_point(builder, character);
             continue;
         }
         // If the character is the first character and is a "-" (U+002D), and there is no second
         // character, then the escaped character.
         if (builder.is_empty() && character == '-' && characters.length() == 1) {
-            builder.append(escape_a_character(character));
+            escape_a_character(builder, character);
             continue;
         }
         // If the character is not handled by one of the above rules and is greater than or equal to U+0080, is "-" (U+002D) or "_" (U+005F), or is in one of the ranges [0-9] (U+0030 to U+0039), [A-Z] (U+0041 to U+005A), or \[a-z] (U+0061 to U+007A), then the character itself.
@@ -74,8 +71,84 @@ String serialize_an_identifier(StringView const& ident)
             continue;
         }
         // Otherwise, the escaped character.
-        builder.append(escape_a_character(character));
+        escape_a_character(builder, character);
     }
+}
+
+// https://www.w3.org/TR/cssom-1/#serialize-a-string
+void serialize_a_string(StringBuilder builder, StringView const& string)
+{
+    Utf8View characters { string };
+
+    // To serialize a string means to create a string represented by '"' (U+0022), followed by the result
+    // of applying the rules below to each character of the given string, followed by '"' (U+0022):
+    builder.append('"');
+
+    for (auto character : characters) {
+        // If the character is NULL (U+0000), then the REPLACEMENT CHARACTER (U+FFFD).
+        if (character == 0) {
+            builder.append_code_point(0xFFFD);
+            continue;
+        }
+        // If the character is in the range [\1-\1f] (U+0001 to U+001F) or is U+007F, the character escaped as code point.
+        if ((character >= 0x0001 && character <= 0x001F) || (character == 0x007F)) {
+            escape_a_character_as_code_point(builder, character);
+            continue;
+        }
+        // If the character is '"' (U+0022) or "\" (U+005C), the escaped character.
+        if (character == 0x0022 || character == 0x005C) {
+            escape_a_character(builder, character);
+            continue;
+        }
+        // Otherwise, the character itself.
+        builder.append_code_point(character);
+    }
+
+    builder.append('"');
+}
+
+// https://www.w3.org/TR/cssom-1/#serialize-a-url
+void serialize_a_url(StringBuilder builder, StringView const& url)
+{
+    // To serialize a URL means to create a string represented by "url(",
+    // followed by the serialization of the URL as a string, followed by ")".
+    builder.append("url(");
+    serialize_a_string(builder, url.to_string());
+    builder.append(')');
+}
+
+String escape_a_character(u32 character)
+{
+    StringBuilder builder;
+    escape_a_character(builder, character);
+    return builder.to_string();
+}
+
+String escape_a_character_as_code_point(u32 character)
+{
+    StringBuilder builder;
+    escape_a_character_as_code_point(builder, character);
+    return builder.to_string();
+}
+
+String serialize_an_identifier(StringView const& ident)
+{
+    StringBuilder builder;
+    serialize_an_identifier(builder, ident);
+    return builder.to_string();
+}
+
+String serialize_a_string(StringView const& string)
+{
+    StringBuilder builder;
+    serialize_a_string(builder, string);
+    return builder.to_string();
+}
+
+String serialize_a_url(StringView const& url)
+{
+    StringBuilder builder;
+    serialize_a_url(builder, url);
     return builder.to_string();
 }
 
diff --git a/Userland/Libraries/LibWeb/CSS/Serialize.h b/Userland/Libraries/LibWeb/CSS/Serialize.h
index 08264ebc81..8b0f240008 100644
--- a/Userland/Libraries/LibWeb/CSS/Serialize.h
+++ b/Userland/Libraries/LibWeb/CSS/Serialize.h
@@ -7,13 +7,21 @@
 #pragma once
 
 #include <AK/String.h>
+#include <AK/StringBuilder.h>
 #include <AK/StringView.h>
 
 namespace Web::CSS {
 
+void escape_a_character(StringBuilder, u32 character);
+void escape_a_character_as_code_point(StringBuilder, u32 character);
+void serialize_an_identifier(StringBuilder, StringView const& ident);
+void serialize_a_string(StringBuilder, StringView const& string);
+void serialize_a_url(StringBuilder, StringView const& url);
+
 String escape_a_character(u32 character);
 String escape_a_character_as_code_point(u32 character);
-
 String serialize_an_identifier(StringView const& ident);
+String serialize_a_string(StringView const& string);
+String serialize_a_url(StringView const& url);
 
 }