Fix custom MIME type serialization incompatibility (rsocket#260)

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

@@ -47,8 +47,13 @@ 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
+    // The first byte of indicates MIME type encoding:
+    // - Values 0x00 to 0x7F represent predefined "well-known" MIME types, directly using the byte as the type ID.
+    // - Values 0x80 to 0xFF denote custom MIME types, where the byte represents the length of the MIME type name that follows.
+    // For custom types, the length stored (byte value minus 0x80) is adjusted by -1 when writing, and adjusted by +1 when reading,
+    // mapping to an effective range of 1 to 128 characters for the MIME type name length.
+    writeByte((typeBytes.size - 1).toByte())
+    writeFully(typeBytes)
 }
 
 private const val KnownTypeFlag: Byte = Byte.MIN_VALUE
@@ -66,7 +71,12 @@ private inline fun <T> ByteReadPacket.readType(
         val identifier = byte xor KnownTypeFlag
         fromIdentifier(identifier)
     } else {
-        val stringType = readTextExactBytes(byte.toInt())
+        // The first byte of indicates MIME type encoding:
+        // - Values 0x00 to 0x7F represent predefined "well-known" MIME types, directly using the byte as the type ID.
+        // - Values 0x80 to 0xFF denote custom MIME types, where the byte represents the length of the MIME type name that follows.
+        // For custom types, the length stored (byte value minus 0x80) is adjusted by -1 when writing, and adjusted by +1 when reading,
+        // mapping to an effective range of 1 to 128 characters for the MIME type name length.
+        val stringType = readTextExactBytes(byte.toInt() + 1)
         fromText(stringType)
     }
 }

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

@@ -0,0 +1,41 @@
+/*
+ * 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.rsocket.kotlin.core.*
+import io.rsocket.kotlin.test.*
+import kotlin.test.*
+
+class MimeTypeTest : TestWithLeakCheck {
+
+    @Test
+    fun customMimeTypeSerialization() {
+        testCustomMimeType("message/x.foo")
+        testCustomMimeType(randomAsciiString(1))
+        testCustomMimeType(randomAsciiString(127))
+        testCustomMimeType(randomAsciiString(128))
+    }
+
+    private fun testCustomMimeType(name: String) {
+        val mimeType = CustomMimeType(name)
+        val packet = packet {
+            writeMimeType(mimeType)
+        }
+        assertEquals(name.length - 1, packet.tryPeek())
+        assertEquals(mimeType, packet.readMimeType())
+    }
+}

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

@@ -0,0 +1,24 @@
+/*
+ * 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
+
+
+private val asciiChars = '!'..'~'
+
+internal fun randomAsciiString(length: Int): String {
+    return (1..length).joinToString(separator = "") { asciiChars.random().toString() }
+}