ONOS-2513 Fix entire MP2SP intent failing on partial connectivity loss

 * Added PartialFailureContraint to MP2SP intent to allow partial connectivity.
   This means the intent remains installed as long as at least one ingress point
   can reach the egress point.
 * Intents with this constraint are recompiled on ObjectiveTracker triggers
   even if not in FAILED state
 * MP2SP intent compiler can compute a partial tree if constraint is set
 * ObjectiveTracker recompiles intents on any link event
 * SDN-IP MP2SP intents now use PartialFailureConstraint

Ported from onos-1.2 branch.

Change-Id: I32eaa198fae1dfba021d9251c8f855573f0e1d7d
diff --git a/core/net/src/main/java/org/onosproject/net/intent/impl/compiler/MultiPointToSinglePointIntentCompiler.java b/core/net/src/main/java/org/onosproject/net/intent/impl/compiler/MultiPointToSinglePointIntentCompiler.java
index 5c158e0..8fad769 100644
--- a/core/net/src/main/java/org/onosproject/net/intent/impl/compiler/MultiPointToSinglePointIntentCompiler.java
+++ b/core/net/src/main/java/org/onosproject/net/intent/impl/compiler/MultiPointToSinglePointIntentCompiler.java
@@ -26,13 +26,14 @@
 import org.onosproject.net.DeviceId;
 import org.onosproject.net.Link;
 import org.onosproject.net.Path;
+import org.onosproject.net.device.DeviceService;
 import org.onosproject.net.intent.Intent;
 import org.onosproject.net.intent.IntentCompiler;
+import org.onosproject.net.intent.IntentException;
 import org.onosproject.net.intent.IntentExtensionService;
 import org.onosproject.net.intent.LinkCollectionIntent;
 import org.onosproject.net.intent.MultiPointToSinglePointIntent;
 import org.onosproject.net.intent.PointToPointIntent;
-import org.onosproject.net.intent.impl.PathNotFoundException;
 import org.onosproject.net.resource.link.LinkResourceAllocations;
 import org.onosproject.net.topology.PathService;
 
@@ -42,6 +43,9 @@
 import java.util.Map;
 import java.util.Set;
 
+import static org.onosproject.net.intent.constraint.PartialFailureConstraint.intentAllowsPartialFailure;
+
+
 /**
  * An intent compiler for
  * {@link org.onosproject.net.intent.MultiPointToSinglePointIntent}.
@@ -56,6 +60,9 @@
     @Reference(cardinality = ReferenceCardinality.MANDATORY_UNARY)
     protected PathService pathService;
 
+    @Reference(cardinality = ReferenceCardinality.MANDATORY_UNARY)
+    protected DeviceService deviceService;
+
     @Activate
     public void activate() {
         intentManager.registerCompiler(MultiPointToSinglePointIntent.class, this);
@@ -72,23 +79,44 @@
         Map<DeviceId, Link> links = new HashMap<>();
         ConnectPoint egressPoint = intent.egressPoint();
 
+        final boolean allowMissingPaths = intentAllowsPartialFailure(intent);
+        boolean partialTree = false;
+        boolean anyMissingPaths = false;
         for (ConnectPoint ingressPoint : intent.ingressPoints()) {
             if (ingressPoint.deviceId().equals(egressPoint.deviceId())) {
-                continue;
-            }
-            Path path = getPath(ingressPoint, intent.egressPoint());
-            for (Link link : path.links()) {
-                if (links.containsKey(link.src().deviceId())) {
-                    // We've already reached the existing tree with the first
-                    // part of this path. Add the merging point with different
-                    // incoming port, but don't add the remainder of the path
-                    // in case it differs from the path we already have.
-                    links.put(link.src().deviceId(), link);
-                    break;
+                if (deviceService.isAvailable(ingressPoint.deviceId())) {
+                    partialTree = true;
+                } else {
+                    anyMissingPaths = true;
                 }
 
-                links.put(link.src().deviceId(), link);
+                continue;
             }
+
+            Path path = getPath(ingressPoint, intent.egressPoint());
+            if (path != null) {
+                partialTree = true;
+
+                for (Link link : path.links()) {
+                    if (links.containsKey(link.src().deviceId())) {
+                        // We've already reached the existing tree with the first
+                        // part of this path. Add the merging point with different
+                        // incoming port, but don't add the remainder of the path
+                        // in case it differs from the path we already have.
+                        links.put(link.src().deviceId(), link);
+                        break;
+                    }
+                    links.put(link.src().deviceId(), link);
+                }
+            } else {
+                anyMissingPaths = true;
+            }
+        }
+
+        if (!partialTree) {
+            throw new IntentException("Could not find any paths between ingress and egress points.");
+        } else if (!allowMissingPaths && anyMissingPaths) {
+            throw new IntentException("Missing some paths between ingress and egress ports.");
         }
 
         Intent result = LinkCollectionIntent.builder()
@@ -111,12 +139,11 @@
      * @param one start of the path
      * @param two end of the path
      * @return Path between the two
-     * @throws org.onosproject.net.intent.impl.PathNotFoundException if a path cannot be found
      */
     private Path getPath(ConnectPoint one, ConnectPoint two) {
         Set<Path> paths = pathService.getPaths(one.deviceId(), two.deviceId());
         if (paths.isEmpty()) {
-            throw new PathNotFoundException(one.elementId(), two.elementId());
+            return null;
         }
         // TODO: let's be more intelligent about this eventually
         return paths.iterator().next();