pw_rpc: Create PacketByteFactory

Bug: b/360174359

Test: EXEMPT just wrapping generated code

Change-Id: I16222ca66741cd306910db30bf7fba8bb1c38505
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/230011
Commit-Queue: Kieran Cyphus <[email protected]>
Presubmit-Verified: CQ Bot Account <[email protected]>
Reviewed-by: Wyatt Hepler <[email protected]>
Lint: Lint 🤖 <[email protected]>

pw_rpc/java/main/dev/pigweed/pw_rpc/BUILD.bazel

@@ -31,6 +31,7 @@ RPC_CLIENT_SOURCES = [
     "InvalidRpcStateException.java",
     "Method.java",
     "MethodClient.java",
+    "PacketByteFactory.java",
     "Packets.java",
     "PendingRpc.java",
     "RpcError.java",

pw_rpc/java/main/dev/pigweed/pw_rpc/PacketByteFactory.java

@@ -0,0 +1,75 @@
+// Copyright 2024 The Pigweed Authors
+//
+// 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
+//
+//     https://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 dev.pigweed.pw_rpc;
+
+import com.google.protobuf.MessageLite;
+import dev.pigweed.pw_rpc.internal.Packet.PacketType;
+import dev.pigweed.pw_rpc.internal.Packet.RpcPacket;
+
+/** Util class for creating request / response packets for testing. */
+public final class PacketByteFactory {
+  private PacketByteFactory() {}
+
+  /**
+   * Creates encoded request packet bytes.
+   *
+   * <p>There is no parameter for {@link Status} since request packets always have a status of
+   * {@link Status#OK}.
+   *
+   * @param channelId the channel ID for the packet
+   * @param serviceName the service name for the packet
+   * @param methodName the method name for the packet
+   * @param payload the payload for the packet
+   * @return the encoded packet bytes
+   */
+  public static byte[] requestBytes(
+      int channelId, String serviceName, String methodName, MessageLite payload) {
+    return packetBytes(channelId, Status.OK, serviceName, methodName, payload, PacketType.REQUEST);
+  }
+
+  /**
+   * Creates encoded response packet bytes.
+   *
+   * @param channelId the channel ID for the packet
+   * @param status the status for the packet
+   * @param serviceName the service name for the packet
+   * @param methodName the method name for the packet
+   * @param payload the payload for the packet
+   * @return the encoded packet bytes
+   */
+  public static byte[] responseBytes(
+      int channelId, Status status, String serviceName, String methodName, MessageLite payload) {
+    return packetBytes(channelId, status, serviceName, methodName, payload, PacketType.RESPONSE);
+  }
+
+  private static byte[] packetBytes(int channelId,
+      Status status,
+      String serviceName,
+      String methodName,
+      MessageLite payload,
+      PacketType type) {
+    RpcPacket.Builder builder = RpcPacket.newBuilder()
+                                    .setStatus(status.code())
+                                    .setType(type)
+                                    .setChannelId(channelId)
+                                    .setServiceId(Ids.calculate(serviceName))
+                                    .setMethodId(Ids.calculate(methodName));
+
+    if (payload != null) {
+      builder.setPayload(payload.toByteString());
+    }
+    return builder.build().toByteArray();
+  }
+}