Decode URL safe base64 correctly (#4721)

* Add unit test for encoding/decoding a string containing all base64 characters This also checks decoding of URL-safe base64 strings, which currently does not work, but will be changed in a separate commit. * Change base64 decoder, so it can also handle URL-safe base64 strings * Fix code formatting using the `formatKotlin` task --------- Co-authored-by: Bruce Hamilton <150327496+bjhham@users.noreply.github.com>

Decode URL safe base64 correctly (#4721)
* Add unit test for encoding/decoding a string containing all base64 characters This also checks decoding of URL-safe base64 strings, which currently does not work, but will be changed in a separate commit. * Change base64 decoder, so it can also handle URL-safe base64 strings * Fix code formatting using the `formatKotlin` task --------- Co-authored-by: Bruce Hamilton <150327496+bjhham@users.noreply.github.com>
37c67245 · Florian Schäfer · GitHub · acbb25d1 · 37c67245 · 37c67245
--- a/ktor-utils/common/src/io/ktor/util/Base64.kt
+++ b/ktor-utils/common/src/io/ktor/util/Base64.kt
@@ -15,6 +15,10 @@ private const val BASE64_PAD = '='

 private val BASE64_INVERSE_ALPHABET = IntArray(256) {
    BASE64_ALPHABET.indexOf(it.toChar())
+}.also {
+    // correctly decode URL-safe Base64
+    it['-'.code] = it['+'.code]
+    it['_'.code] = it['/'.code]
 }

 /**

--- a/ktor-utils/common/test/io/ktor/util/Base64Test.kt
+++ b/ktor-utils/common/test/io/ktor/util/Base64Test.kt
@@ -51,4 +51,22 @@ class Base64Test {
            assertEquals(text, encodedText.decodeBase64String())
        }
    }
+
+    @Test
+    fun testEncodeDecodeAllCharacters() {
+        val commonChars: List<Char> = ('a'..'z') + ('A'..'Z') + ('0'..'9')
+        val allBase64Chars: String = (commonChars + '+' + '/').joinToString("")
+        val allUrlSafeBase64Chars: String = (commonChars + '-' + '_').joinToString("")
+
+        val expectedBytes: List<Byte> = listOf(
+            105, -73, 29, 121, -8, 33, -118, 57, 37, -102, 122, 41, -86, -69, 45, -70, -4, 49, -53, 48, 1, 8, 49, 5,
+            24, 114, 9, 40, -77, 13, 56, -12, 17, 73, 53, 21, 89, 118, 25, -45, 93, -73, -29, -98, -69, -13, -33, -65,
+        )
+
+        // Check encode
+        assertEquals(allBase64Chars, expectedBytes.toByteArray().encodeBase64())
+        // Check decode
+        assertEquals(expectedBytes, allBase64Chars.decodeBase64Bytes().toList())
+        assertEquals(expectedBytes, allUrlSafeBase64Chars.decodeBase64Bytes().toList())
+    }
 }