From e5cdd89edc4f085d227a11719e0333b8ed07754c Mon Sep 17 00:00:00 2001
From: Paul Schaub <vanitasvitae@fsfe.org>
Date: Thu, 4 Jan 2018 15:15:43 +0100
Subject: [PATCH] Ignore stale devices when encrypting

---
 .../smackx/omemo/OmemoService.java            | 17 +++++++-
 .../exceptions/StaleDeviceException.java      | 41 +++++++++++++++++++
 2 files changed, 57 insertions(+), 1 deletion(-)
 create mode 100644 smack-omemo/src/main/java/org/jivesoftware/smackx/omemo/exceptions/StaleDeviceException.java

diff --git a/smack-omemo/src/main/java/org/jivesoftware/smackx/omemo/OmemoService.java b/smack-omemo/src/main/java/org/jivesoftware/smackx/omemo/OmemoService.java
index 0e39e0dc9..8b0231878 100644
--- a/smack-omemo/src/main/java/org/jivesoftware/smackx/omemo/OmemoService.java
+++ b/smack-omemo/src/main/java/org/jivesoftware/smackx/omemo/OmemoService.java
@@ -53,6 +53,7 @@ import org.jivesoftware.smackx.omemo.exceptions.CannotEstablishOmemoSessionExcep
 import org.jivesoftware.smackx.omemo.exceptions.CorruptedOmemoKeyException;
 import org.jivesoftware.smackx.omemo.exceptions.CryptoFailedException;
 import org.jivesoftware.smackx.omemo.exceptions.NoIdentityKeyException;
+import org.jivesoftware.smackx.omemo.exceptions.StaleDeviceException;
 import org.jivesoftware.smackx.omemo.exceptions.UndecidedOmemoIdentityException;
 import org.jivesoftware.smackx.omemo.exceptions.UntrustedOmemoIdentityException;
 import org.jivesoftware.smackx.omemo.internal.OmemoCachedDeviceList;
@@ -384,6 +385,19 @@ public abstract class OmemoService<T_IdKeyPair, T_IdKey, T_PreKey, T_SigPreKey,
                 }
             }
 
+            // Ignore stale devices
+            if (OmemoConfiguration.getIgnoreStaleDevices()) {
+
+                Date lastActivity = getOmemoStoreBackend().getDateOfLastReceivedMessage(userDevice, contactsDevice);
+
+                if (isStale(userDevice, contactsDevice, lastActivity, OmemoConfiguration.getIgnoreStaleDevicesAfterHours())) {
+                    LOGGER.log(Level.FINE, "Device " + contactsDevice + " seems to be stale (last message received "
+                            + lastActivity + "). Ignore it.");
+                    skippedRecipients.put(contactsDevice, new StaleDeviceException(contactsDevice, lastActivity));
+                    continue;
+                }
+            }
+
             // Add recipients
             try {
                 builder.addRecipient(contactsDevice);
@@ -393,7 +407,8 @@ public abstract class OmemoService<T_IdKeyPair, T_IdKey, T_PreKey, T_SigPreKey,
                 skippedRecipients.put(contactsDevice, e);
             }
             catch (UndecidedOmemoIdentityException e) {
-                throw new AssertionError("At this point, devices cannot be undecided. " + e);
+                throw new AssertionError("Recipients device seems to be undecided, even though we should have thrown" +
+                        " an exception earlier in that case. " + e);
             }
             catch (UntrustedOmemoIdentityException e) {
                 LOGGER.log(Level.WARNING, "Device " + contactsDevice + " is untrusted. Message is not encrypted for it.");
diff --git a/smack-omemo/src/main/java/org/jivesoftware/smackx/omemo/exceptions/StaleDeviceException.java b/smack-omemo/src/main/java/org/jivesoftware/smackx/omemo/exceptions/StaleDeviceException.java
new file mode 100644
index 000000000..2d51a94f2
--- /dev/null
+++ b/smack-omemo/src/main/java/org/jivesoftware/smackx/omemo/exceptions/StaleDeviceException.java
@@ -0,0 +1,41 @@
+/**
+ *
+ * Copyright 2018 Paul Schaub
+ *
+ * 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 org.jivesoftware.smackx.omemo.exceptions;
+
+import java.util.Date;
+
+import org.jivesoftware.smackx.omemo.internal.OmemoDevice;
+
+public class StaleDeviceException extends Exception {
+    private static final long serialVersionUID = 1L;
+
+    private final OmemoDevice device;
+    private final Date lastActivity;
+
+    public StaleDeviceException(OmemoDevice device, Date lastActivity) {
+        this.device = device;
+        this.lastActivity = lastActivity;
+    }
+
+    public Date getLastActivity() {
+        return lastActivity;
+    }
+
+    public OmemoDevice getDevice() {
+        return device;
+    }
+}