Add Optional match fields support to PI subsystem

Change-Id: Ic458f59cab98340e40c04a0ad060d3c725ac5dbb
diff --git a/core/api/src/main/java/org/onosproject/net/pi/runtime/PiOptionalFieldMatch.java b/core/api/src/main/java/org/onosproject/net/pi/runtime/PiOptionalFieldMatch.java
new file mode 100644
index 0000000..cb34981
--- /dev/null
+++ b/core/api/src/main/java/org/onosproject/net/pi/runtime/PiOptionalFieldMatch.java
@@ -0,0 +1,86 @@
+/*
+ * Copyright 2020-present Open Networking Foundation
+ *
+ * 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.onosproject.net.pi.runtime;
+
+import com.google.common.annotations.Beta;
+import com.google.common.base.Objects;
+import org.onlab.util.ImmutableByteSequence;
+import org.onosproject.net.pi.model.PiMatchFieldId;
+import org.onosproject.net.pi.model.PiMatchType;
+
+import static com.google.common.base.Preconditions.checkArgument;
+import static com.google.common.base.Preconditions.checkNotNull;
+
+/**
+ * Instance of an optional field match in a protocol-independent pipeline.
+ * The optional match field behaves like an exact match if specified, otherwise
+ * it is logically equivalent to a wildcard match.
+ */
+@Beta
+public final class PiOptionalFieldMatch extends PiFieldMatch {
+
+    private final ImmutableByteSequence value;
+
+    /**
+     * Creates an optional field match.
+     *
+     * @param fieldId field identifier
+     * @param value   value
+     */
+    public PiOptionalFieldMatch(PiMatchFieldId fieldId, ImmutableByteSequence value) {
+        super(fieldId);
+        this.value = checkNotNull(value);
+        checkArgument(value.size() > 0, "Value can't have size 0");
+    }
+
+    @Override
+    public PiMatchType type() {
+        return PiMatchType.OPTIONAL;
+    }
+
+    /**
+     * Returns the byte sequence value to be matched.
+     *
+     * @return an immutable byte sequence
+     */
+    public ImmutableByteSequence value() {
+        return value;
+    }
+
+    @Override
+    public boolean equals(Object o) {
+        if (this == o) {
+            return true;
+        }
+        if (o == null || getClass() != o.getClass()) {
+            return false;
+        }
+        PiOptionalFieldMatch that = (PiOptionalFieldMatch) o;
+        return Objects.equal(this.fieldId(), that.fieldId()) &&
+                Objects.equal(value, that.value);
+    }
+
+    @Override
+    public int hashCode() {
+        return Objects.hashCode(this.fieldId(), value);
+    }
+
+    @Override
+    public String toString() {
+        return this.fieldId().toString() + "=" + value.toString();
+    }
+}