Fix custom MIME type serialization incompatibility (rsocket#260)

rsocket-core/src/commonMain/kotlin/io/rsocket/kotlin/frame/io/mimeType.kt

@@ -47,8 +47,8 @@ internal fun ByteReadPacket.readAuthType(): AuthType = readType(
 
 private fun BytePacketBuilder.writeTextWithLength(text: String) {
     val typeBytes = text.encodeToByteArray()
-    writeByte(typeBytes.size.toByte()) //write length
-    writeFully(typeBytes) //write mime type
+    writeByte((typeBytes.size - 1).toByte())
+    writeFully(typeBytes)
 }
 
 private const val KnownTypeFlag: Byte = Byte.MIN_VALUE
@@ -66,7 +66,7 @@ private inline fun <T> ByteReadPacket.readType(
         val identifier = byte xor KnownTypeFlag
         fromIdentifier(identifier)
     } else {
-        val stringType = readTextExactBytes(byte.toInt())
+        val stringType = readTextExactBytes(byte.toInt() + 1)
         fromText(stringType)
     }
 }

rsocket-core/src/commonTest/kotlin/io/rsocket/kotlin/frame/io/CustomMimeTypeTest.kt

@@ -0,0 +1,36 @@
+/*
+ * Copyright 2015-2024 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package io.rsocket.kotlin.frame.io
+
+import io.ktor.utils.io.core.*
+import io.rsocket.kotlin.core.*
+import kotlin.test.*
+
+class CustomMimeTypeTest {
+    val name = "message/x.foo"
+    private val fooMimeType = CustomMimeType(name)
+
+    @Test
+    fun customMimeTypeSerialization() {
+        val packet = BytePacketBuilder().apply {
+            writeMimeType(fooMimeType)
+        }.build()
+
+        assertEquals((name.length - 1).toByte(), packet.copy().readByte())
+        assertEquals(fooMimeType, packet.copy().readMimeType())
+    }
+}