improved error messages on missing omemo keys

src/main/java/eu/siacs/conversations/ui/TrustKeysActivity.java

@@ -228,7 +228,15 @@ public class TrustKeysActivity extends OmemoActivity implements OnKeyStatusUpdat
 				}
 				if (fingerprints.size() == 0) {
 					informNoKeys.setVisibility(View.VISIBLE);
-					informNoKeys.setText(getString(R.string.no_keys_just_confirm,mAccount.getRoster().getContact(jid).getDisplayName()));
+					if (hasNoOtherTrustedKeys(jid)) {
+						if (!mAccount.getRoster().getContact(jid).mutualPresenceSubscription()) {
+							informNoKeys.setText(R.string.error_no_keys_to_trust_presence);
+						} else {
+							informNoKeys.setText(R.string.error_no_keys_to_trust_server_error);
+						}
+					} else {
+						informNoKeys.setText(getString(R.string.no_keys_just_confirm, mAccount.getRoster().getContact(jid).getDisplayName()));
+					}
 				} else {
 					informNoKeys.setVisibility(View.GONE);
 				}
@@ -251,7 +259,11 @@ public class TrustKeysActivity extends OmemoActivity implements OnKeyStatusUpdat
 				keyErrorMessageCard.setVisibility(View.VISIBLE);
 				if (lastFetchReport == AxolotlService.FetchStatus.ERROR
 						|| mAccount.getAxolotlService().fetchMapHasErrors(contactJids)) {
+					if (anyWithoutMutualPresenceSubscription(contactJids)) {
+						keyErrorMessage.setText(R.string.error_no_keys_to_trust_presence);
+					} else {
 						keyErrorMessage.setText(R.string.error_no_keys_to_trust_server_error);
+					}
 				} else {
 					keyErrorMessage.setText(R.string.error_no_keys_to_trust);
 				}
@@ -265,6 +277,15 @@ public class TrustKeysActivity extends OmemoActivity implements OnKeyStatusUpdat
 		}
 	}
 
+	private boolean anyWithoutMutualPresenceSubscription(List<Jid> contactJids){
+		for(Jid jid : contactJids) {
+			if (!mAccount.getRoster().getContact(jid).mutualPresenceSubscription()) {
+				return true;
+			}
+		}
+		return false;
+	}
+
 	private boolean foreignActuallyHasKeys() {
 		synchronized (this.foreignKeysToTrust) {
 			for (Map.Entry<Jid, Map<String, Boolean>> entry : foreignKeysToTrust.entrySet()) {

src/main/res/values/strings.xml

@@ -434,6 +434,7 @@
 	<string name="clear_other_devices">Clear devices</string>
 	<string name="clear_other_devices_desc">Are you sure you want to clear all other devices from the OMEMO announcement? The next time your devices connect, they will reannounce themselves, but they might not receive messages sent in the meantime.</string>
 	<string name="error_no_keys_to_trust_server_error">There are no usable keys available for this contact.\nFetching new keys from the server has been unsuccessful. Maybe there is something wrong with your contacts server.</string>
+	<string name="error_no_keys_to_trust_presence">There are no usable keys available for this contact.\nMake sure you have mutual presence subscription.</string>
 	<string name="error_no_keys_to_trust">There are no usable keys available for this contact. If you have purged any of their keys, they need to generate new ones.</string>
 	<string name="error_trustkeys_title">Error</string>
 	<string name="fetching_history_from_server">Fetching history from server</string>