Fix NoClassDefFoundError on Android due to JDK11's WebSocketHandshake…

…Exception

Resolves:
#246

krossbow-websocket-ktor-legacy/src/jvmMain/kotlin/org/hildan/krossbow/websocket/ktor/HandshakeExceptionsJvm.kt

@@ -3,13 +3,21 @@ package org.hildan.krossbow.websocket.ktor
 import java.net.ProtocolException
 import java.net.UnknownHostException
 import java.net.http.WebSocketHandshakeException
+import kotlin.contracts.ExperimentalContracts
+import kotlin.contracts.contract
 
-internal actual fun extractHandshakeStatusCode(handshakeException: Exception): Int? = when (handshakeException) {
-    is WebSocketHandshakeException -> handshakeException.response.statusCode()
-    // with OkHttp engine, we get ProtocolException with itself as cause - we can only parse the message
-    is ProtocolException -> extractHandshakeStatusCode(handshakeException)
-    is UnknownHostException -> null
-    else -> null
+internal actual fun extractHandshakeStatusCode(handshakeException: Exception): Int? {
+    val e = handshakeException
+    return when {
+        // no status code if we can't even contact the host
+        e is UnknownHostException -> null
+        // with OkHttp engine, we get ProtocolException with itself as cause - we can only parse the message
+        e is ProtocolException -> extractHandshakeStatusCode(e)
+        e.safeIs<WebSocketHandshakeException>("java.net.http.WebSocketHandshakeException") -> {
+            extractHandshakeStatusCode(e)
+        }
+        else -> null
+    }
 }
 
 private val protocolExceptionMessageRegex = Regex("""Expected HTTP 101 response but was '(\d{3}) [^']+'""")
@@ -18,3 +26,38 @@ private fun extractHandshakeStatusCode(handshakeException: ProtocolException): I
     val message = handshakeException.message ?: return null
     return protocolExceptionMessageRegex.matchEntire(message)?.groupValues?.get(1)?.toInt()
 }
+
+private fun extractHandshakeStatusCode(webSocketHandshakeException: WebSocketHandshakeException) =
+    webSocketHandshakeException.response.statusCode()
+
+/**
+ * Returns true if [C] is on the classpath and `this` is an instance of [C].
+ * The given [className] must match the fully qualified name of [C].
+ *
+ * Doesn't fail with [NoClassDefFoundError] if [C] is not present.
+ */
+@OptIn(ExperimentalContracts::class)
+private inline fun <reified C : Any> Any.safeIs(className: String): Boolean {
+    contract {
+        returns(true) implies(this@safeIs is C)
+    }
+    if (!classExists(className)) {
+        return false
+    }
+    checkMatches<C>(className) // prevent developer mistakes
+    return this is C
+}
+
+private inline fun <reified T : Any> checkMatches(className: String) {
+    val typeName = T::class.qualifiedName
+    require(typeName == className) {
+        "Mismatch between the given class name '$className' and the actual parameter type of the action lambda '$typeName"
+    }
+}
+
+private fun classExists(className: String): Boolean = try {
+    Class.forName(className)
+    true
+} catch (e: ClassNotFoundException) {
+    false
+}

krossbow-websocket-ktor/src/jvmMain/kotlin/org/hildan/krossbow/websocket/ktor/HandshakeExceptionsJvm.kt

@@ -3,13 +3,21 @@ package org.hildan.krossbow.websocket.ktor
 import java.net.ProtocolException
 import java.net.UnknownHostException
 import java.net.http.WebSocketHandshakeException
+import kotlin.contracts.ExperimentalContracts
+import kotlin.contracts.contract
 
-internal actual fun extractHandshakeStatusCode(handshakeException: Exception): Int? = when (handshakeException) {
-    is WebSocketHandshakeException -> handshakeException.response.statusCode()
-    // with OkHttp engine, we get ProtocolException with itself as cause - we can only parse the message
-    is ProtocolException -> extractHandshakeStatusCode(handshakeException)
-    is UnknownHostException -> null
-    else -> null
+internal actual fun extractHandshakeStatusCode(handshakeException: Exception): Int? {
+    val e = handshakeException
+    return when {
+        // no status code if we can't even contact the host
+        e is UnknownHostException -> null
+        // with OkHttp engine, we get ProtocolException with itself as cause - we can only parse the message
+        e is ProtocolException -> extractHandshakeStatusCode(e)
+        e.safeIs<WebSocketHandshakeException>("java.net.http.WebSocketHandshakeException") -> {
+            extractHandshakeStatusCode(e)
+        }
+        else -> null
+    }
 }
 
 private val protocolExceptionMessageRegex = Regex("""Expected HTTP 101 response but was '(\d{3}) [^']+'""")
@@ -18,3 +26,38 @@ private fun extractHandshakeStatusCode(handshakeException: ProtocolException): I
     val message = handshakeException.message ?: return null
     return protocolExceptionMessageRegex.matchEntire(message)?.groupValues?.get(1)?.toInt()
 }
+
+private fun extractHandshakeStatusCode(webSocketHandshakeException: WebSocketHandshakeException) =
+    webSocketHandshakeException.response.statusCode()
+
+/**
+ * Returns true if [C] is on the classpath and `this` is an instance of [C].
+ * The given [className] must match the fully qualified name of [C].
+ *
+ * Doesn't fail with [NoClassDefFoundError] if [C] is not present.
+ */
+@OptIn(ExperimentalContracts::class)
+private inline fun <reified C : Any> Any.safeIs(className: String): Boolean {
+    contract {
+        returns(true) implies(this@safeIs is C)
+    }
+    if (!classExists(className)) {
+        return false
+    }
+    checkMatches<C>(className) // prevent developer mistakes
+    return this is C
+}
+
+private inline fun <reified T : Any> checkMatches(className: String) {
+    val typeName = T::class.qualifiedName
+    require(typeName == className) {
+        "Mismatch between the given class name '$className' and the actual parameter type of the action lambda '$typeName"
+    }
+}
+
+private fun classExists(className: String): Boolean = try {
+    Class.forName(className)
+    true
+} catch (e: ClassNotFoundException) {
+    false
+}