From 71dc6a3e9053d22ab6b0fe7a6e6960653813fcd0 Mon Sep 17 00:00:00 2001
From: Simon Rettberg
Date: Fri, 15 May 2020 15:28:04 +0200
Subject: Check if remote host actually repies with RFB handshake

---
 src/main/java/de/bwlehrpool/bwlp_guac/AvailableClient.java | 11 ++++++++---
 src/main/java/de/bwlehrpool/bwlp_guac/VncConnection.java   |  6 ++++++
 2 files changed, 14 insertions(+), 3 deletions(-)

diff --git a/src/main/java/de/bwlehrpool/bwlp_guac/AvailableClient.java b/src/main/java/de/bwlehrpool/bwlp_guac/AvailableClient.java
index 8798813..c60db10 100644
--- a/src/main/java/de/bwlehrpool/bwlp_guac/AvailableClient.java
+++ b/src/main/java/de/bwlehrpool/bwlp_guac/AvailableClient.java
@@ -161,18 +161,23 @@ public class AvailableClient implements Cloneable {
 			if (now < this.lastConnectionCheck) {
 				this.lastConnectionCheck = 0;
 			}
-			if (now - this.lastConnectionCheck < 1000)
+			if (now - this.lastConnectionCheck < 2000)
 				return this.connectionOk;
 			for (;;) {
 				try (VncConnection vnc = new VncConnection(this.clientip, 5900)) {
-					LOGGER.debug("VNC Version for " + this.clientip + " is " + vnc.handshake());
+					String version = vnc.handshake();
+					if (version == null) {
+						LOGGER.info("Host " + this.clientip + " doesn't speak RFB protocol");
+						break;
+					}
+					LOGGER.debug("VNC Version for " + this.clientip + " is " + version);
 					if (vnc.tryLogin(this.password)) {
 						LOGGER.info("Connection to " + this + " is OK");
 						this.lastConnectionCheck = now;
 						return this.connectionOk = true;
 					}
 				} catch (IOException e) {
-					LOGGER.info("Connection error VNC @ " + this, e);
+					LOGGER.info("Connection error VNC @ " + this);
 					if (retries-- > 0) {
 						try {
 							Thread.sleep(1000);
diff --git a/src/main/java/de/bwlehrpool/bwlp_guac/VncConnection.java b/src/main/java/de/bwlehrpool/bwlp_guac/VncConnection.java
index 8bd4bd0..06a7013 100644
--- a/src/main/java/de/bwlehrpool/bwlp_guac/VncConnection.java
+++ b/src/main/java/de/bwlehrpool/bwlp_guac/VncConnection.java
@@ -36,9 +36,15 @@ public class VncConnection implements Closeable {
 		in = new DataInputStream(sock.getInputStream());
 	}
 
+	/**
+	 * @return Version string on success, null if not RFB
+	 * @throws IOException
+	 */
 	public String handshake() throws IOException {
 		byte[] buffer = new byte[12];
 		in.readFully(buffer);
+		if (buffer[0] != 'R' || buffer[1] != 'F' || buffer[2] != 'B')
+			return null;
 		out.write("RFB 003.008\n".getBytes());
 		out.flush();
 		return new String(buffer).substring(4, 11);
-- 
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