RPC: Support reconnect for linux rpc server (#21185)

Fork default Pigweed rpc server implementation and change the
behaviour on disconnect from closing and returning, to awaiting a
reconnect.

examples/chef/linux/BUILD.gn

@@ -66,7 +66,7 @@ executable("${sample_name}") {
 
     sources += [
       "${chip_root}/examples/platform/linux/Rpc.cpp",
-      "${dir_pigweed}/targets/host/system_rpc_server.cc",
+      "${chip_root}/examples/platform/linux/system_rpc_server.cc",
     ]
 
     deps += [

examples/lighting-app/linux/BUILD.gn

@@ -61,7 +61,7 @@ executable("chip-lighting-app") {
 
     sources += [
       "${chip_root}/examples/platform/linux/Rpc.cpp",
-      "${dir_pigweed}/targets/host/system_rpc_server.cc",
+      "${chip_root}/examples/platform/linux/system_rpc_server.cc",
     ]
 
     deps += [

examples/lighting-app/linux/main.cpp

@@ -26,10 +26,6 @@
 #include <lib/support/logging/CHIPLogging.h>
 #include <platform/Linux/NetworkCommissioningDriver.h>
 
-#if defined(PW_RPC_ENABLED)
-#include "Rpc.h"
-#endif // PW_RPC_ENABLED
-
 using namespace chip;
 using namespace chip::app;
 using namespace chip::app::Clusters;
@@ -79,10 +75,6 @@ void ApplicationInit()
 
 int main(int argc, char * argv[])
 {
-#if PW_RPC_ENABLED
-    chip::rpc::Init();
-#endif
-
     if (ChipLinuxAppInit(argc, argv) != 0)
     {
         return -1;

examples/platform/linux/system_rpc_server.cc

@@ -0,0 +1,118 @@
+/*
+ *
+ *    Copyright (c) 2021 Project CHIP Authors
+ *    All rights reserved.
+ *
+ *    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.
+ *
+ *    This file is a fork from: third_party/pigweed/repo/targets/host/system_rpc_server.cc
+ *    But changes the disconnect behaviour from closing and returning, to awaiting a
+ *    reconnection.
+ */
+
+#include <cstddef>
+#include <cstdint>
+#include <cstdio>
+
+#include "pw_assert/check.h"
+#include "pw_hdlc/rpc_channel.h"
+#include "pw_hdlc/rpc_packets.h"
+#include "pw_log/log.h"
+#include "pw_rpc_system_server/rpc_server.h"
+#include "pw_stream/socket_stream.h"
+
+namespace pw::rpc::system_server {
+namespace {
+
+constexpr size_t kMaxTransmissionUnit = 512;
+uint16_t socket_port                  = 33000;
+
+stream::SocketStream socket_stream;
+
+hdlc::RpcChannelOutput hdlc_channel_output(socket_stream, hdlc::kDefaultRpcAddress, "HDLC channel");
+Channel channels[] = { rpc::Channel::Create<1>(&hdlc_channel_output) };
+rpc::Server server(channels);
+
+} // namespace
+
+void set_socket_port(uint16_t new_socket_port)
+{
+    socket_port = new_socket_port;
+}
+
+int GetServerSocketFd()
+{
+    return socket_stream.connection_fd();
+}
+
+void Init()
+{
+    log_basic::SetOutput([](std::string_view log) {
+        std::fprintf(stderr, "%.*s\n", static_cast<int>(log.size()), log.data());
+        hdlc::WriteUIFrame(1, as_bytes(span(log)), socket_stream).IgnoreError(); // TODO(pwbug/387): Handle Status properly
+    });
+
+    PW_LOG_INFO("Starting pw_rpc server on port %d", socket_port);
+    PW_CHECK_OK(socket_stream.Serve(socket_port));
+}
+
+rpc::Server & Server()
+{
+    return server;
+}
+
+Status Start()
+{
+    // Declare a buffer for decoding incoming HDLC frames.
+    std::array<std::byte, kMaxTransmissionUnit> input_buffer;
+    hdlc::Decoder decoder(input_buffer);
+
+    while (true)
+    {
+        std::array<std::byte, kMaxTransmissionUnit> data;
+        auto ret_val = socket_stream.Read(data);
+        if (!ret_val.ok())
+        {
+            if (ret_val.status() == Status::OutOfRange())
+            {
+                // An out of range status indicates the remote end has disconnected.
+                // Start to serve the connection again, which will allow another
+                // remote to connect.
+                PW_CHECK_OK(socket_stream.Serve(socket_port));
+            }
+            continue;
+        }
+
+        for (std::byte byte : ret_val.value())
+        {
+            auto result = decoder.Process(byte);
+            if (!result.ok())
+            {
+                // Non-OK means there isn't a complete packet yet, or there was some
+                // other issue. Wait for more bytes that form a complete packet.
+                continue;
+            }
+            hdlc::Frame & frame = result.value();
+            if (frame.address() != hdlc::kDefaultRpcAddress)
+            {
+                // Wrong address; ignore the packet for now. In the future, this branch
+                // could expand to add packet routing or metrics.
+                continue;
+            }
+
+            server.ProcessPacket(frame.data(), hdlc_channel_output).IgnoreError();
+        }
+    }
+}
+
+} // namespace pw::rpc::system_server