Split Base64 utility to reduce reflection

Author: akonradi-signal

java/android/src/androidTest/java/org/signal/libsignal/util/AndroidBase64.kt

@@ -0,0 +1,16 @@
+package org.signal.libsignal.util
+
+import android.util.Base64
+
+public class AndroidBase64 : org.signal.libsignal.util.Base64.Impl {
+  public override fun decode(encoded: ByteArray): ByteArray = Base64.decode(encoded, 0)
+
+  public override fun decodeUrl(encoded: ByteArray): ByteArray = Base64.decode(encoded, Base64.URL_SAFE)
+
+  public override fun encode(raw: ByteArray): String = Base64.encodeToString(raw, Base64.NO_WRAP)
+
+  public override fun encodeUrl(raw: ByteArray): String = Base64.encodeToString(
+    raw,
+    Base64.NO_WRAP or Base64.NO_PADDING or Base64.URL_SAFE,
+  )
+}

java/client/src/test/java/org/signal/libsignal/util/Base64.java

@@ -0,0 +1,59 @@
+//
+// Copyright 2024 Signal Messenger, LLC.
+// SPDX-License-Identifier: AGPL-3.0-only
+//
+
+package org.signal.libsignal.util
+
+import java.nio.charset.StandardCharsets
+
+// This whole helper can go away when we reach Android 26, which supports java.util.Base64.
+public class Base64 {
+  public interface Impl {
+    public fun decode(encoded: ByteArray): ByteArray
+    public fun decodeUrl(encoded: ByteArray): ByteArray
+    public fun encode(raw: ByteArray): String
+    public fun encodeUrl(raw: ByteArray): String
+  }
+
+  companion object {
+    @JvmStatic
+    public fun decode(str: String): ByteArray = impl.decode(str.toByteArray(StandardCharsets.UTF_8))
+
+    @JvmStatic
+    public fun decodeUrl(str: String): ByteArray = impl.decodeUrl(str.toByteArray(StandardCharsets.UTF_8))
+
+    @JvmStatic
+    public fun encodeToString(input: ByteArray): String = impl.encode(input)
+
+    @JvmStatic
+    public fun encodeToStringUrl(input: ByteArray): String = impl.encodeUrl(input)
+
+    val impl: Impl = run {
+      // Prefer the Android class. If we preferred the JRE one, we'd only test the Android
+      // codepath when testing on older emulators.
+      try {
+        try {
+          var androidImpl = Class.forName("org.signal.libsignal.util.AndroidBase64")
+          Impl::class.java.cast(androidImpl.getConstructor().newInstance())
+        } catch (notFoundException: ClassNotFoundException) {
+          JavaBase64
+        }
+      } catch (e: Exception) {
+        throw AssertionError(e)
+      }
+    }
+  }
+
+  private object JavaBase64 : Impl {
+    public override fun decode(encoded: ByteArray): ByteArray = java.util.Base64.getDecoder().decode(encoded)
+
+    public override fun decodeUrl(encoded: ByteArray): ByteArray = java.util.Base64.getUrlDecoder().decode(encoded)
+
+    public override fun encode(raw: ByteArray): String = java.util.Base64.getEncoder().encodeToString(raw)
+
+    public override fun encodeUrl(
+      raw: ByteArray,
+    ): String = java.util.Base64.getUrlEncoder().withoutPadding().encodeToString(raw)
+  }
+}