chore: add convenience function for decoding URL components (#607)

Author: ianbotsf

runtime/utils/common/src/aws/smithy/kotlin/runtime/util/text/Text.kt

@@ -129,3 +129,13 @@ public fun String.splitAsQueryString(): Map<String, List<String>> {
         }
     return entries
 }
+
+private val percentEncodedParam = """%([A-Fa-f0-9]{2})""".toRegex()
+
+/**
+ * Decode a URL's query string, resolving percent-encoding (e.g., "%3B" → ";").
+ */
+@InternalApi
+public fun String.urlDecodeComponent(): String = this
+    .replace('+', ' ')
+    .replace(percentEncodedParam) { it.groupValues[1].toInt(radix = 16).toChar().toString() }

runtime/utils/common/test/aws/smithy/kotlin/runtime/util/text/TextTest.kt

@@ -112,4 +112,11 @@ class TextTest {
             actualValueWithEquals.shouldContain(entry.key, entry.value)
         }
     }
+
+    @Test
+    fun decodeUrlComponent() {
+        val component = "a%3Bb+c%7Ed%20e%2Bf"
+        val expected = "a;b c~d e+f"
+        assertEquals(expected, component.urlDecodeComponent())
+    }
 }