refactor: Use Kotlin's Base64-encoding

Use Kotlin's built-in functionality as much as possible for portability.

Signed-off-by: Sebastian Schuberth <[email protected]>

buildSrc/src/main/kotlin/ort-kotlin-conventions.gradle.kts

@@ -161,6 +161,7 @@ tasks.withType<KotlinCompile>().configureEach {
 
     val customCompilerArgs = buildList {
         add("-opt-in=kotlin.contracts.ExperimentalContracts")
+        add("-opt-in=kotlin.io.encoding.ExperimentalEncodingApi")
         add("-opt-in=kotlin.io.path.ExperimentalPathApi")
         add("-opt-in=kotlin.time.ExperimentalTime")
         if (hasSerialization) add("-opt-in=kotlinx.serialization.ExperimentalSerializationApi")

clients/fossid-webapp/src/main/kotlin/Extensions.kt

@@ -22,7 +22,8 @@
 package org.ossreviewtoolkit.clients.fossid
 
 import java.io.File
-import java.util.Base64
+
+import kotlin.io.encoding.Base64
 
 import okio.buffer
 import okio.sink
@@ -41,8 +42,6 @@ internal const val SCAN_GROUP = "scans"
 private const val FILES_AND_FOLDERS_GROUP = "files_and_folders"
 private const val PROJECT_GROUP = "projects"
 
-private val base64Encoder = Base64.getEncoder()
-
 /**
  * Verify that a request for the given [operation] was successful. [operation] is a free label describing the operation.
  * If [withDataCheck] is true, also the payload data is checked, otherwise that check is skipped.
@@ -260,7 +259,7 @@ suspend fun FossIdRestService.listSnippets(
     scanCode: String,
     path: String
 ): PolymorphicResponseBody<Snippet> {
-    val base64Path = base64Encoder.encodeToString(path.toByteArray())
+    val base64Path = Base64.encode(path.toByteArray())
     return listSnippets(
         PostRequestBody(
             "get_fossid_results",

model/src/main/kotlin/Hash.kt

@@ -23,7 +23,8 @@ import com.fasterxml.jackson.databind.annotation.JsonSerialize
 import com.fasterxml.jackson.databind.util.StdConverter
 
 import java.io.File
-import java.util.Base64
+
+import kotlin.io.encoding.Base64
 
 import org.ossreviewtoolkit.utils.common.decodeHex
 import org.ossreviewtoolkit.utils.common.encodeHex
@@ -59,7 +60,7 @@ data class Hash(
                 // Support Subresource Integrity (SRI) hashes, see
                 // https://w3c.github.io/webappsec-subresource-integrity/
                 Hash(
-                    value = Base64.getDecoder().decode(splitValue.last()).encodeHex(),
+                    value = Base64.decode(splitValue.last()).encodeHex(),
                     algorithm = HashAlgorithm.fromString(splitValue.first())
                 )
             } else {
@@ -82,7 +83,7 @@ data class Hash(
     /**
      * Return the hash in Support Subresource Integrity (SRI) format.
      */
-    fun toSri() = algorithm.name.lowercase() + "-" + Base64.getEncoder().encodeToString(value.decodeHex())
+    fun toSri() = algorithm.name.lowercase() + "-" + Base64.encode(value.decodeHex())
 
     /**
      * Verify that the [file] matches this hash.