⚡ Bolt: String.escapeHtml() 단일 패스 StringBuilder 성능 최적화

.jules/bolt.md

@@ -5,3 +5,7 @@
 ## 2024-05-24 - Loop Allocation Hot Paths
 **Learning:** Rendering directory entries with repeated string concatenation and list-based exclusion lookups creates avoidable allocation and lookup cost in large directories.
 **Action:** Use `StringBuilder` for entry rendering and a `Set` for excluded file names.
+
+## 2024-07-25 - Avoid Chained String Replacements
+**Learning:** In Kotlin, using multiple chained `.replace()` calls on a String for frequent operations (like HTML escaping) is inefficient due to multiple intermediate allocations.
+**Action:** Use a single-pass loop with a lazily-initialized `StringBuilder` to prevent intermediate string allocations, significantly improving performance on hot paths.

src/main/kotlin/html4tree/main.kt

@@ -48,13 +48,33 @@ fun go(topDir: String, maxLevel: Int)  {
     }
 }
 
+// ⚡ Bolt Optimization: Replace chained .replace() with single-pass StringBuilder
+// Reduces intermediate allocations and improves performance when escaping strings.
 fun String.escapeHtml(): String {
-    return this.replace("&", "&")
-               .replace("<", "&lt;")
-               .replace(">", "&gt;")
-               .replace("\"", "&quot;")
-               .replace("'", "&#x27;")
-               .replace("`", "&#x60;")
+    var sb: StringBuilder? = null
+    for (i in this.indices) {
+        val char = this[i]
+        val replacement = when (char) {
+            '&' -> "&amp;"
+            '<' -> "&lt;"
+            '>' -> "&gt;"
+            '"' -> "&quot;"
+            '\'' -> "&#x27;"
+            '`' -> "&#x60;"
+            else -> null
+        }
+
+        if (replacement != null) {
+            if (sb == null) {
+                sb = StringBuilder(this.length + 16)
+                sb.append(this, 0, i)
+            }
+            sb.append(replacement)
+        } else {
+            sb?.append(char)
+        }
+    }
+    return sb?.toString() ?: this
 }
 
 fun String.urlEncodePath(): String {

src/test/kotlin/html4tree/MainTest.kt

@@ -39,6 +39,8 @@ class MainTest {
         assertEquals("`", "`".escapeHtml())
         assertEquals("&amp;&lt;&gt;&quot;&#x27;&#x60;", "&<>\"'`".escapeHtml())
         assertEquals("normal text", "normal text".escapeHtml())
+        assertEquals("a&amp;b", "a&b".escapeHtml())
+        assertEquals("hello &amp; world", "hello & world".escapeHtml())
     }
 
     @Test