[ONOS-7602]Implement support for P4Data in PI framework and P4Runtime southbound

Change-Id: I9c0c76fb29b8c3aa36f39bde62e825f0f0094253
diff --git a/core/api/src/main/java/org/onosproject/net/pi/runtime/data/PiStruct.java b/core/api/src/main/java/org/onosproject/net/pi/runtime/data/PiStruct.java
new file mode 100644
index 0000000..7c60c16
--- /dev/null
+++ b/core/api/src/main/java/org/onosproject/net/pi/runtime/data/PiStruct.java
@@ -0,0 +1,89 @@
+/*
+ * Copyright 2018-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.data;
+
+import com.google.common.annotations.Beta;
+import com.google.common.base.Objects;
+import com.google.common.collect.ImmutableList;
+import org.onosproject.net.pi.model.PiData;
+
+import java.util.List;
+import java.util.StringJoiner;
+
+/**
+ * Struct entity in a protocol-independent pipeline.
+ */
+@Beta
+public final class PiStruct implements PiData {
+    private final ImmutableList<PiData> struct;
+
+    /**
+     * Creates a new protocol-independent struct instance for the given collection of PiData.
+     *
+     * @param struct the collection of PiData
+     */
+    private PiStruct(List<PiData> struct) {
+        this.struct = ImmutableList.copyOf(struct);
+    }
+
+    /**
+     * Returns a new protocol-independent struct.
+     * @param struct the list of PiData
+     * @return struct
+     */
+    public static PiStruct of(List<PiData> struct) {
+        return new PiStruct(struct);
+    }
+
+    /**
+     * Return protocol-independent struct instance.
+     *
+     * @return the list of PiData
+     */
+    public List<PiData> struct() {
+        return this.struct;
+    }
+
+    @Override
+    public Type type() {
+        return Type.STRUCT;
+    }
+
+    @Override
+    public boolean equals(Object o) {
+        if (this == o) {
+            return true;
+        }
+        if (o == null || getClass() != o.getClass()) {
+            return false;
+        }
+        PiStruct st = (PiStruct) o;
+        return Objects.equal(struct, st.struct);
+    }
+
+    @Override
+    public int hashCode() {
+        return Objects.hashCode(struct);
+    }
+
+    @Override
+    public String toString() {
+        StringJoiner stringParams = new StringJoiner(", ", "(", ")");
+        this.struct().forEach(p -> stringParams.add(p.toString()));
+        return stringParams.toString();
+    }
+}
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