less buggy urlEncode implementation

Author: jillesvangurp

src/commonMain/kotlin/com/jillesvangurp/geojson/json-helpers.kt

@@ -1,7 +1,6 @@
 package com.jillesvangurp.geojson
 
 import com.jillesvangurp.serializationext.DEFAULT_JSON
-import kotlinx.serialization.encodeToString
 
 
 val FeatureCollection.geoJsonIOUrl: Any
@@ -13,17 +12,20 @@ val FeatureCollection.geoJsonIOUrl: Any
 
 val Geometry.geoJsonIOUrl get() = this.asFeatureCollection.geoJsonIOUrl
 
-fun String.urlEncode(): String {
-    val allowedChars = ('A'..'Z') + ('a'..'z') + ('0'..'9') + listOf('-', '.', '_', '~')
-    return buildString {
-        this@urlEncode.forEach { char ->
-            if (char in allowedChars) {
-                append(char)
-            } else {
-                append(char.code.toByte().toInt().let {
-                    "%${it.shr(4).and(0xF).toString(16)}${it.and(0xF).toString(16)}"
-                }.uppercase())
-            }
+private const val HEX = "0123456789ABCDEF"
+/** Percent-encode according to RFC 3986 (UTF-8) */
+fun String.urlEncode(): String = buildString {
+    for (byte in encodeToByteArray()) {          // UTF-8 bytes
+        val b = byte.toInt() and 0xFF            // 0-255, no sign
+        val c = b.toChar()
+        if (c in "ABCDEFGHIJKLMNOPQRSTUVWXYZ" +
+            "abcdefghijklmnopqrstuvwxyz0123456789-._~"
+        ) {                   // keep unreserved
+            append(c)
+        } else {                                 // escape everything else
+            append('%')
+            append(HEX[b ushr 4])
+            append(HEX[b and 0x0F])
         }
     }
 }

src/commonTest/kotlin/com/jillesvangurp/geojson/JsonHelpersTest.kt

@@ -0,0 +1,40 @@
+package com.jillesvangurp.geojson
+
+import io.kotest.matchers.shouldBe
+import kotlin.test.Test
+
+class JsonHelpersTest {
+
+    @Test
+    fun shouldCorrectlyUrlEncode() {
+        val cases = mapOf(
+            // unreserved chars must stay as-is
+            "AZaz09-._~" to "AZaz09-._~",
+
+            // whitespace
+            "Hello World" to "Hello%20World",
+
+            // German sharp-s (ß) – 2-byte UTF-8
+            "Wattstraße"  to "Wattstra%C3%9Fe",
+
+            // umlaut
+            "München"     to "M%C3%BCnchen",
+
+            // euro sign, ampersand, percent
+            "€ & %"       to "%E2%82%AC%20%26%20%25",
+
+            // plus and equals
+            "a+b=c"       to "a%2Bb%3Dc",
+
+            // slash must be escaped
+            "path/part"   to "path%2Fpart",
+
+            // tilde is unreserved
+            "~tilde"      to "~tilde"
+        )
+
+        cases.forEach { (raw, expected) ->
+            raw.urlEncode() shouldBe expected
+        }
+    }
+}