feat(encoder): add util createBytesWriter

Author: iseki0

src/commonMain/kotlin/space/iseki/bencoding/BWriter.kt

@@ -7,6 +7,8 @@ internal interface BWriter {
         writeByte('e'.code)
     }
 
+    fun getByteArray(): ByteArray = throw UnsupportedOperationException("Not implemented")
+
     fun writeDictBegin() {
         writeByte('d'.code)
     }

src/commonMain/kotlin/space/iseki/bencoding/Utils.kt

@@ -12,3 +12,5 @@ internal expect fun string2BytesIso88591(s: String): ByteArray
 @OptIn(ExperimentalSerializationApi::class)
 internal fun SerialDescriptor.binaryStringAnnotation(childIndex: Int) =
     getElementAnnotations(childIndex).firstOrNull { it is BinaryString } as BinaryString?
+
+internal expect fun createBytesWriter(): BWriter

src/jvmMain/kotlin/space/iseki/bencoding/Utils.jvm.kt

@@ -1,9 +1,22 @@
 package space.iseki.bencoding
 
+import java.io.ByteArrayOutputStream
 import java.nio.charset.StandardCharsets
 
 internal actual fun bytes2Long(bytes: ByteArray, off: Int, len: Int): Long = String(bytes, off, len).toLong()
 internal actual fun bytes2StringIso88591(bytes: ByteArray, off: Int, len: Int): String =
     String(bytes, off, len, StandardCharsets.ISO_8859_1)
-
 internal actual fun string2BytesIso88591(s: String): ByteArray = s.toByteArray(StandardCharsets.ISO_8859_1)
+
+internal actual fun createBytesWriter(): BWriter = object : BWriter {
+    private val bytes = ByteArrayOutputStream()
+    override fun writeByte(b: Int) {
+        bytes.write(b)
+    }
+
+    override fun writeBytes(b: ByteArray) {
+        bytes.writeBytes(b)
+    }
+
+    override fun getByteArray(): ByteArray = bytes.toByteArray()
+}