pw_rpc: Consolidate functions that encode to the payload buffer

Create a EncodeToPayloadBuffer() function template that is used by
both Nanopb and pwpb. Place it in a pw_rpc/internal/encoding_buffer.h
header.

Change-Id: I454ef814743c48a0cf50acf98636a57cfc3afc3d
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/129573
Pigweed-Auto-Submit: Wyatt Hepler <hepler@google.com>
Commit-Queue: Auto-Submit <auto-submit@pigweed.google.com.iam.gserviceaccount.com>
Reviewed-by: Alexei Frolov <frolv@google.com>

2 files changed, 42 insertions, 7 deletions

diff --git a/pw_rpc/public/pw_rpc/internal/channel.h b/pw_rpc/public/pw_rpc/internal/channel.h
index a74f4bb5d..a3161d05d 100644
--- a/pw_rpc/public/pw_rpc/internal/channel.h
+++ b/pw_rpc/public/pw_rpc/internal/channel.h
@@ -13,20 +13,13 @@
 // the License.
 #pragma once
 
-#include "pw_assert/assert.h"
-#include "pw_bytes/span.h"
 #include "pw_rpc/channel.h"
 #include "pw_rpc/internal/lock.h"
 #include "pw_rpc/internal/packet.h"
-#include "pw_span/span.h"
 #include "pw_status/status.h"
 
 namespace pw::rpc::internal {
 
-// Returns a portion of the encoding buffer that may be used to encode an
-// outgoing payload.
-ByteSpan GetPayloadBuffer() PW_EXCLUSIVE_LOCKS_REQUIRED(rpc_lock());
-
 class Channel : public rpc::Channel {
  public:
   Channel() = delete;
diff --git a/pw_rpc/public/pw_rpc/internal/encoding_buffer.h b/pw_rpc/public/pw_rpc/internal/encoding_buffer.h
new file mode 100644
index 000000000..3c81bbf86
--- /dev/null
+++ b/pw_rpc/public/pw_rpc/internal/encoding_buffer.h
@@ -0,0 +1,42 @@
+// Copyright 2023 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.
+
+// Definitions for the static and dynamic versions of the pw_rpc encoding
+// buffer. Both version are compiled rot, but only one is instantiated,
+// depending on the PW_RPC_DYNAMIC_ALLOCATION config option.
+#pragma once
+
+#include "pw_bytes/span.h"
+#include "pw_rpc/internal/lock.h"
+#include "pw_status/status_with_size.h"
+
+namespace pw::rpc::internal {
+
+ByteSpan GetPayloadBuffer() PW_EXCLUSIVE_LOCKS_REQUIRED(rpc_lock());
+
+// Successful calls to EncodeToPayloadBuffer MUST send the returned buffer,
+// without releasing the RPC lock.
+template <typename Proto, typename Encoder>
+static Result<ByteSpan> EncodeToPayloadBuffer(Proto& payload,
+                                              const Encoder& encoder)
+    PW_EXCLUSIVE_LOCKS_REQUIRED(rpc_lock()) {
+  ByteSpan buffer = GetPayloadBuffer();
+  StatusWithSize result = encoder.Encode(payload, buffer);
+  if (!result.ok()) {
+    return result.status();
+  }
+  return buffer.first(result.size());
+}
+
+}  // namespace pw::rpc::internal