[fleet] fix Base64 usages: allow non-padded input

Follows-up aff75c5e3eae2d6d33b65a18c1d89815e23bf997 which introduced an implicit mandatory padding by use of default `kotlin.io.encoding.Base64` object.

Utility decoder is now provided to make the choice explicit.

Also reverts PluginSerialization.kt, it seems withPadding isn't supported (probably used somewhere in plugin with kotlin version < 2.0, while it's marked `@SinceKotlin("2.0")`)

GitOrigin-RevId: 3f9a639e2cbf58e30293da9c87e3e4bd0824796b

fleet/rpc/src/fleet/rpc/core/Serialization.kt

@@ -24,7 +24,6 @@ import kotlinx.serialization.modules.SerializersModule
 import kotlinx.serialization.serializer
 import java.util.concurrent.ConcurrentHashMap
 import kotlin.coroutines.CoroutineContext
-import kotlin.io.encoding.Base64
 import kotlin.io.encoding.ExperimentalEncodingApi
 import kotlin.reflect.KClass
 import kotlin.reflect.KClassifier
@@ -360,12 +359,12 @@ class Blob(val bytes: ByteArray) {
 object BlobSerializer : DataSerializer<Blob, String>(String.serializer()) {
   @OptIn(ExperimentalEncodingApi::class)
   override fun fromData(data: String): Blob {
-    return Blob(Base64.decode(data))
+    return Blob(Base64WithOptionalPadding.decode(data))
   }
 
   @OptIn(ExperimentalEncodingApi::class)
   override fun toData(value: Blob): String {
-    return Base64.encode(value.bytes)
+    return Base64WithOptionalPadding.encode(value.bytes)
   }
 }
 

fleet/util/core/src/fleet/util/Bytes.kt

@@ -1,6 +1,9 @@
 // Copyright 2000-2024 JetBrains s.r.o. and contributors. Use of this source code is governed by the Apache 2.0 license.
 package fleet.util
 
+import kotlin.io.encoding.Base64
+import kotlin.io.encoding.ExperimentalEncodingApi
+
 /*
  * Following functions are used to replace jvm specific byte array to string conversion that explicitly specified UTF-8 as charset.
  */
@@ -15,3 +18,11 @@ fun ByteArray.decodeToStringUtf8(
   endIndex: Int = this.size,
   throwOnInvalidSequence: Boolean = false
 ): String = decodeToString(startIndex, endIndex, throwOnInvalidSequence)
+
+// Replaces java.util.Base64.getDecoder(), which did not require padding on decoding
+@OptIn(ExperimentalEncodingApi::class)
+val Base64WithOptionalPadding = Base64.withPadding(Base64.PaddingOption.PRESENT_OPTIONAL)
+
+// Replaces java.util.Base64.getUrlDecoder(), which did not require padding on decoding
+@OptIn(ExperimentalEncodingApi::class)
+val UrlSafeBase64WithOptionalPadding = Base64.UrlSafe.withPadding(Base64.PaddingOption.PRESENT_OPTIONAL)