Wyatt Hepler | f9fb90f | 2020-09-30 18:59:33 -0700 | [diff] [blame] | 1 | .. _module-pw_rpc: |
Alexei Frolov | 26e3ae6 | 2020-05-04 17:06:17 -0700 | [diff] [blame] | 2 | |
| 3 | ------ |
| 4 | pw_rpc |
| 5 | ------ |
| 6 | The ``pw_rpc`` module provides a system for defining and invoking remote |
| 7 | procedure calls (RPCs) on a device. |
| 8 | |
Wyatt Hepler | 830d26d | 2021-02-17 09:07:43 -0800 | [diff] [blame] | 9 | This document discusses the ``pw_rpc`` protocol and its C++ implementation. |
| 10 | ``pw_rpc`` implementations for other languages are described in their own |
| 11 | documents: |
| 12 | |
| 13 | .. toctree:: |
| 14 | :maxdepth: 1 |
| 15 | |
| 16 | py/docs |
Jared Weinstein | d464911 | 2021-08-19 12:27:23 -0700 | [diff] [blame] | 17 | ts/docs |
Wyatt Hepler | 830d26d | 2021-02-17 09:07:43 -0800 | [diff] [blame] | 18 | |
Wyatt Hepler | 455b492 | 2020-09-18 00:19:21 -0700 | [diff] [blame] | 19 | .. admonition:: Try it out! |
| 20 | |
Wyatt Hepler | f9fb90f | 2020-09-30 18:59:33 -0700 | [diff] [blame] | 21 | For a quick intro to ``pw_rpc``, see the |
Alexei Frolov | d3e5cb7 | 2021-01-08 13:08:45 -0800 | [diff] [blame] | 22 | :ref:`module-pw_hdlc-rpc-example` in the :ref:`module-pw_hdlc` module. |
Wyatt Hepler | 455b492 | 2020-09-18 00:19:21 -0700 | [diff] [blame] | 23 | |
Wyatt Hepler | 592b5a1 | 2022-02-01 17:55:21 -0800 | [diff] [blame] | 24 | .. warning:: |
Alexei Frolov | 26e3ae6 | 2020-05-04 17:06:17 -0700 | [diff] [blame] | 25 | |
Wyatt Hepler | 592b5a1 | 2022-02-01 17:55:21 -0800 | [diff] [blame] | 26 | This documentation is under construction. Many sections are outdated or |
| 27 | incomplete. The content needs to be reorgnanized. |
Wyatt Hepler | 455b492 | 2020-09-18 00:19:21 -0700 | [diff] [blame] | 28 | |
Wyatt Hepler | 3b4f89a | 2021-12-06 16:18:53 -0800 | [diff] [blame] | 29 | Implementations |
| 30 | =============== |
| 31 | Pigweed provides several client and server implementations of ``pw_rpc``. |
| 32 | |
| 33 | .. list-table:: |
| 34 | :header-rows: 1 |
| 35 | |
| 36 | * - Language |
| 37 | - Server |
| 38 | - Client |
| 39 | * - C++ (raw) |
| 40 | - ✅ |
| 41 | - ✅ |
| 42 | * - C++ (Nanopb) |
| 43 | - ✅ |
| 44 | - ✅ |
| 45 | * - C++ (pw_protobuf) |
| 46 | - planned |
| 47 | - planned |
| 48 | * - Java |
| 49 | - |
| 50 | - in development |
| 51 | * - Python |
| 52 | - |
| 53 | - ✅ |
| 54 | * - TypeScript |
| 55 | - |
| 56 | - in development |
| 57 | |
Wyatt Hepler | 85e9140 | 2021-08-05 12:48:03 -0700 | [diff] [blame] | 58 | RPC semantics |
| 59 | ============= |
| 60 | The semantics of ``pw_rpc`` are similar to `gRPC |
| 61 | <https://grpc.io/docs/what-is-grpc/core-concepts/>`_. |
| 62 | |
| 63 | RPC call lifecycle |
| 64 | ------------------ |
| 65 | In ``pw_rpc``, an RPC begins when the client sends a request packet. The server |
| 66 | receives the request, looks up the relevant service method, then calls into the |
| 67 | RPC function. The RPC is considered active until the server sends a response |
| 68 | packet with the RPC's status. The client may terminate an ongoing RPC by |
| 69 | cancelling it. |
| 70 | |
| 71 | ``pw_rpc`` supports only one RPC invocation per service/method/channel. If a |
| 72 | client calls an ongoing RPC on the same channel, the server cancels the ongoing |
| 73 | call and reinvokes the RPC with the new request. This applies to unary and |
| 74 | streaming RPCs, though the server may not have an opportunity to cancel a |
| 75 | synchronously handled unary RPC before it completes. The same RPC may be invoked |
| 76 | multiple times simultaneously if the invocations are on different channels. |
| 77 | |
Wyatt Hepler | 592b5a1 | 2022-02-01 17:55:21 -0800 | [diff] [blame] | 78 | Status codes |
| 79 | ------------ |
| 80 | ``pw_rpc`` call objects (``ClientReaderWriter``, ``ServerReaderWriter``, etc.) |
| 81 | use certain status codes to indicate what occurred. These codes are returned |
| 82 | from functions like ``Write()`` or ``Finish()``. |
| 83 | |
| 84 | * ``OK`` -- The operation succeeded. |
| 85 | * ``UNAVAILABLE`` -- The channel is not currently registered with the server or |
| 86 | client. |
| 87 | * ``UNKNOWN`` -- Sending a packet failed due to an unrecoverable |
| 88 | :cpp:func:`pw::rpc::ChannelOutput::Send` error. |
| 89 | |
Wyatt Hepler | 5a3a36b | 2021-09-08 11:15:05 -0700 | [diff] [blame] | 90 | Unrequested responses |
| 91 | --------------------- |
| 92 | ``pw_rpc`` supports sending responses to RPCs that have not yet been invoked by |
| 93 | a client. This is useful in testing and in situations like an RPC that triggers |
| 94 | reboot. After the reboot, the device opens the writer object and sends its |
| 95 | response to the client. |
| 96 | |
Wyatt Hepler | d95e1e9 | 2021-09-14 22:10:51 -0700 | [diff] [blame] | 97 | The C++ API for opening a server reader/writer takes the generated RPC function |
| 98 | as a template parameter. The server to use, channel ID, and service instance are |
| 99 | passed as arguments. The API is the same for all RPC types, except the |
| 100 | appropriate reader/writer class must be used. |
Wyatt Hepler | 5a3a36b | 2021-09-08 11:15:05 -0700 | [diff] [blame] | 101 | |
Wyatt Hepler | d95e1e9 | 2021-09-14 22:10:51 -0700 | [diff] [blame] | 102 | .. code-block:: c++ |
| 103 | |
| 104 | // Open a ServerWriter for a server streaming RPC. |
| 105 | auto writer = RawServerWriter::Open<pw_rpc::raw::ServiceName::MethodName>( |
| 106 | server, channel_id, service_instance); |
| 107 | |
| 108 | // Send some responses, even though the client has not yet called this RPC. |
| 109 | CHECK_OK(writer.Write(encoded_response_1)); |
| 110 | CHECK_OK(writer.Write(encoded_response_2)); |
| 111 | |
| 112 | // Finish the RPC. |
| 113 | CHECK_OK(writer.Finish(OkStatus())); |
Wyatt Hepler | 5a3a36b | 2021-09-08 11:15:05 -0700 | [diff] [blame] | 114 | |
Wyatt Hepler | 455b492 | 2020-09-18 00:19:21 -0700 | [diff] [blame] | 115 | Creating an RPC |
| 116 | =============== |
| 117 | |
| 118 | 1. RPC service declaration |
| 119 | -------------------------- |
| 120 | Pigweed RPCs are declared in a protocol buffer service definition. |
| 121 | |
| 122 | * `Protocol Buffer service documentation |
| 123 | <https://developers.google.com/protocol-buffers/docs/proto3#services>`_ |
| 124 | * `gRPC service definition documentation |
| 125 | <https://grpc.io/docs/what-is-grpc/core-concepts/#service-definition>`_ |
| 126 | |
| 127 | .. code-block:: protobuf |
| 128 | |
| 129 | syntax = "proto3"; |
| 130 | |
| 131 | package foo.bar; |
| 132 | |
| 133 | message Request {} |
| 134 | |
| 135 | message Response { |
| 136 | int32 number = 1; |
| 137 | } |
| 138 | |
| 139 | service TheService { |
| 140 | rpc MethodOne(Request) returns (Response) {} |
| 141 | rpc MethodTwo(Request) returns (stream Response) {} |
| 142 | } |
| 143 | |
| 144 | This protocol buffer is declared in a ``BUILD.gn`` file as follows: |
| 145 | |
| 146 | .. code-block:: python |
| 147 | |
| 148 | import("//build_overrides/pigweed.gni") |
| 149 | import("$dir_pw_protobuf_compiler/proto.gni") |
| 150 | |
| 151 | pw_proto_library("the_service_proto") { |
| 152 | sources = [ "foo_bar/the_service.proto" ] |
| 153 | } |
| 154 | |
Wyatt Hepler | 830d26d | 2021-02-17 09:07:43 -0800 | [diff] [blame] | 155 | .. admonition:: proto2 or proto3 syntax? |
| 156 | |
| 157 | Always use proto3 syntax rather than proto2 for new protocol buffers. Proto2 |
| 158 | protobufs can be compiled for ``pw_rpc``, but they are not as well supported |
| 159 | as proto3. Specifically, ``pw_rpc`` lacks support for non-zero default values |
| 160 | in proto2. When using Nanopb with ``pw_rpc``, proto2 response protobufs with |
| 161 | non-zero field defaults should be manually initialized to the default struct. |
| 162 | |
| 163 | In the past, proto3 was sometimes avoided because it lacked support for field |
| 164 | presence detection. Fortunately, this has been fixed: proto3 now supports |
| 165 | ``optional`` fields, which are equivalent to proto2 ``optional`` fields. |
| 166 | |
| 167 | If you need to distinguish between a default-valued field and a missing field, |
| 168 | mark the field as ``optional``. The presence of the field can be detected |
| 169 | with a ``HasField(name)`` or ``has_<field>`` member, depending on the library. |
| 170 | |
| 171 | Optional fields have some overhead --- default-valued fields are included in |
| 172 | the encoded proto, and, if using Nanopb, the proto structs have a |
| 173 | ``has_<field>`` flag for each optional field. Use plain fields if field |
| 174 | presence detection is not needed. |
| 175 | |
| 176 | .. code-block:: protobuf |
| 177 | |
| 178 | syntax = "proto3"; |
| 179 | |
| 180 | message MyMessage { |
| 181 | // Leaving this field unset is equivalent to setting it to 0. |
| 182 | int32 number = 1; |
| 183 | |
| 184 | // Setting this field to 0 is different from leaving it unset. |
| 185 | optional int32 other_number = 2; |
| 186 | } |
| 187 | |
Wyatt Hepler | 8779bcd | 2020-11-25 07:25:16 -0800 | [diff] [blame] | 188 | 2. RPC code generation |
| 189 | ---------------------- |
| 190 | ``pw_rpc`` generates a C++ header file for each ``.proto`` file. This header is |
| 191 | generated in the build output directory. Its exact location varies by build |
| 192 | system and toolchain, but the C++ include path always matches the sources |
| 193 | declaration in the ``pw_proto_library``. The ``.proto`` extension is replaced |
| 194 | with an extension corresponding to the protobuf library in use. |
Wyatt Hepler | 455b492 | 2020-09-18 00:19:21 -0700 | [diff] [blame] | 195 | |
Wyatt Hepler | 8779bcd | 2020-11-25 07:25:16 -0800 | [diff] [blame] | 196 | ================== =============== =============== ============= |
| 197 | Protobuf libraries Build subtarget Protobuf header pw_rpc header |
| 198 | ================== =============== =============== ============= |
| 199 | Raw only .raw_rpc (none) .raw_rpc.pb.h |
| 200 | Nanopb or raw .nanopb_rpc .pb.h .rpc.pb.h |
| 201 | pw_protobuf or raw .pwpb_rpc .pwpb.h .rpc.pwpb.h |
| 202 | ================== =============== =============== ============= |
| 203 | |
| 204 | For example, the generated RPC header for ``"foo_bar/the_service.proto"`` is |
| 205 | ``"foo_bar/the_service.rpc.pb.h"`` for Nanopb or |
| 206 | ``"foo_bar/the_service.raw_rpc.pb.h"`` for raw RPCs. |
| 207 | |
| 208 | The generated header defines a base class for each RPC service declared in the |
| 209 | ``.proto`` file. A service named ``TheService`` in package ``foo.bar`` would |
Wyatt Hepler | d249632 | 2021-09-10 17:22:14 -0700 | [diff] [blame] | 210 | generate the following base class for Nanopb: |
Wyatt Hepler | 455b492 | 2020-09-18 00:19:21 -0700 | [diff] [blame] | 211 | |
Wyatt Hepler | d249632 | 2021-09-10 17:22:14 -0700 | [diff] [blame] | 212 | .. cpp:class:: template <typename Implementation> foo::bar::pw_rpc::nanopb::TheService::Service |
Wyatt Hepler | 455b492 | 2020-09-18 00:19:21 -0700 | [diff] [blame] | 213 | |
Wyatt Hepler | 8779bcd | 2020-11-25 07:25:16 -0800 | [diff] [blame] | 214 | 3. RPC service definition |
| 215 | ------------------------- |
| 216 | The serivce class is implemented by inheriting from the generated RPC service |
| 217 | base class and defining a method for each RPC. The methods must match the name |
| 218 | and function signature for one of the supported protobuf implementations. |
| 219 | Services may mix and match protobuf implementations within one service. |
| 220 | |
| 221 | .. tip:: |
| 222 | |
| 223 | The generated code includes RPC service implementation stubs. You can |
| 224 | reference or copy and paste these to get started with implementing a service. |
| 225 | These stub classes are generated at the bottom of the pw_rpc proto header. |
| 226 | |
Wyatt Hepler | df38ed1 | 2021-03-24 08:42:48 -0700 | [diff] [blame] | 227 | To use the stubs, do the following: |
| 228 | |
| 229 | #. Locate the generated RPC header in the build directory. For example: |
| 230 | |
| 231 | .. code-block:: sh |
| 232 | |
| 233 | find out/ -name <proto_name>.rpc.pb.h |
| 234 | |
| 235 | #. Scroll to the bottom of the generated RPC header. |
| 236 | #. Copy the stub class declaration to a header file. |
| 237 | #. Copy the member function definitions to a source file. |
| 238 | #. Rename the class or change the namespace, if desired. |
| 239 | #. List these files in a build target with a dependency on the |
| 240 | ``pw_proto_library``. |
| 241 | |
Wyatt Hepler | 455b492 | 2020-09-18 00:19:21 -0700 | [diff] [blame] | 242 | A Nanopb implementation of this service would be as follows: |
| 243 | |
| 244 | .. code-block:: cpp |
| 245 | |
Wyatt Hepler | 8779bcd | 2020-11-25 07:25:16 -0800 | [diff] [blame] | 246 | #include "foo_bar/the_service.rpc.pb.h" |
| 247 | |
Wyatt Hepler | 455b492 | 2020-09-18 00:19:21 -0700 | [diff] [blame] | 248 | namespace foo::bar { |
| 249 | |
Wyatt Hepler | d249632 | 2021-09-10 17:22:14 -0700 | [diff] [blame] | 250 | class TheService : public pw_rpc::nanopb::TheService::Service<TheService> { |
Wyatt Hepler | 455b492 | 2020-09-18 00:19:21 -0700 | [diff] [blame] | 251 | public: |
Wyatt Hepler | 8e756e3 | 2021-11-18 09:59:27 -0800 | [diff] [blame] | 252 | pw::Status MethodOne(const foo_bar_Request& request, |
Wyatt Hepler | 455b492 | 2020-09-18 00:19:21 -0700 | [diff] [blame] | 253 | foo_bar_Response& response) { |
| 254 | // implementation |
Wyatt Hepler | 1b3da3a | 2021-01-07 13:26:57 -0800 | [diff] [blame] | 255 | return pw::OkStatus(); |
Wyatt Hepler | 455b492 | 2020-09-18 00:19:21 -0700 | [diff] [blame] | 256 | } |
| 257 | |
Wyatt Hepler | 8e756e3 | 2021-11-18 09:59:27 -0800 | [diff] [blame] | 258 | void MethodTwo(const foo_bar_Request& request, |
Wyatt Hepler | 455b492 | 2020-09-18 00:19:21 -0700 | [diff] [blame] | 259 | ServerWriter<foo_bar_Response>& response) { |
| 260 | // implementation |
| 261 | response.Write(foo_bar_Response{.number = 123}); |
| 262 | } |
| 263 | }; |
| 264 | |
| 265 | } // namespace foo::bar |
| 266 | |
| 267 | The Nanopb implementation would be declared in a ``BUILD.gn``: |
| 268 | |
| 269 | .. code-block:: python |
| 270 | |
| 271 | import("//build_overrides/pigweed.gni") |
| 272 | |
| 273 | import("$dir_pw_build/target_types.gni") |
| 274 | |
| 275 | pw_source_set("the_service") { |
| 276 | public_configs = [ ":public" ] |
| 277 | public = [ "public/foo_bar/service.h" ] |
Wyatt Hepler | 8779bcd | 2020-11-25 07:25:16 -0800 | [diff] [blame] | 278 | public_deps = [ ":the_service_proto.nanopb_rpc" ] |
Wyatt Hepler | 455b492 | 2020-09-18 00:19:21 -0700 | [diff] [blame] | 279 | } |
| 280 | |
| 281 | .. attention:: |
| 282 | |
| 283 | pw_rpc's generated classes will support using ``pw_protobuf`` or raw buffers |
| 284 | (no protobuf library) in the future. |
| 285 | |
Wyatt Hepler | 8779bcd | 2020-11-25 07:25:16 -0800 | [diff] [blame] | 286 | 4. Register the service with a server |
Wyatt Hepler | 455b492 | 2020-09-18 00:19:21 -0700 | [diff] [blame] | 287 | ------------------------------------- |
Alexei Frolov | d3e5cb7 | 2021-01-08 13:08:45 -0800 | [diff] [blame] | 288 | This example code sets up an RPC server with an :ref:`HDLC<module-pw_hdlc>` |
Wyatt Hepler | f9fb90f | 2020-09-30 18:59:33 -0700 | [diff] [blame] | 289 | channel output and the example service. |
Wyatt Hepler | 455b492 | 2020-09-18 00:19:21 -0700 | [diff] [blame] | 290 | |
| 291 | .. code-block:: cpp |
| 292 | |
| 293 | // Set up the output channel for the pw_rpc server to use. This configures the |
| 294 | // pw_rpc server to use HDLC over UART; projects not using UART and HDLC must |
| 295 | // adapt this as necessary. |
| 296 | pw::stream::SysIoWriter writer; |
| 297 | pw::rpc::RpcChannelOutput<kMaxTransmissionUnit> hdlc_channel_output( |
Alexei Frolov | d3e5cb7 | 2021-01-08 13:08:45 -0800 | [diff] [blame] | 298 | writer, pw::hdlc::kDefaultRpcAddress, "HDLC output"); |
Wyatt Hepler | 455b492 | 2020-09-18 00:19:21 -0700 | [diff] [blame] | 299 | |
| 300 | pw::rpc::Channel channels[] = { |
| 301 | pw::rpc::Channel::Create<1>(&hdlc_channel_output)}; |
| 302 | |
| 303 | // Declare the pw_rpc server with the HDLC channel. |
| 304 | pw::rpc::Server server(channels); |
| 305 | |
Wyatt Hepler | 7566bc8 | 2022-02-15 15:09:00 -0800 | [diff] [blame] | 306 | foo::bar::TheService the_service; |
| 307 | pw::rpc::SomeOtherService some_other_service; |
Wyatt Hepler | 455b492 | 2020-09-18 00:19:21 -0700 | [diff] [blame] | 308 | |
| 309 | void RegisterServices() { |
Wyatt Hepler | 7566bc8 | 2022-02-15 15:09:00 -0800 | [diff] [blame] | 310 | // Register the foo.bar.TheService example service and another service. |
| 311 | server.RegisterService(the_service, some_other_service); |
Wyatt Hepler | 455b492 | 2020-09-18 00:19:21 -0700 | [diff] [blame] | 312 | } |
| 313 | |
| 314 | int main() { |
| 315 | // Set up the server. |
| 316 | RegisterServices(); |
| 317 | |
| 318 | // Declare a buffer for decoding incoming HDLC frames. |
| 319 | std::array<std::byte, kMaxTransmissionUnit> input_buffer; |
| 320 | |
| 321 | PW_LOG_INFO("Starting pw_rpc server"); |
Alexei Frolov | d3e5cb7 | 2021-01-08 13:08:45 -0800 | [diff] [blame] | 322 | pw::hdlc::ReadAndProcessPackets( |
Wyatt Hepler | 455b492 | 2020-09-18 00:19:21 -0700 | [diff] [blame] | 323 | server, hdlc_channel_output, input_buffer); |
| 324 | } |
Wyatt Hepler | 948f547 | 2020-06-02 16:52:28 -0700 | [diff] [blame] | 325 | |
Alexei Frolov | 1c670a2 | 2021-04-09 10:18:17 -0700 | [diff] [blame] | 326 | Channels |
| 327 | ======== |
| 328 | ``pw_rpc`` sends all of its packets over channels. These are logical, |
| 329 | application-layer routes used to tell the RPC system where a packet should go. |
| 330 | |
| 331 | Channels over a client-server connection must all have a unique ID, which can be |
| 332 | assigned statically at compile time or dynamically. |
| 333 | |
| 334 | .. code-block:: cpp |
| 335 | |
| 336 | // Creating a channel with the static ID 3. |
| 337 | pw::rpc::Channel static_channel = pw::rpc::Channel::Create<3>(&output); |
| 338 | |
| 339 | // Grouping channel IDs within an enum can lead to clearer code. |
| 340 | enum ChannelId { |
| 341 | kUartChannel = 1, |
| 342 | kSpiChannel = 2, |
| 343 | }; |
| 344 | |
| 345 | // Creating a channel with a static ID defined within an enum. |
| 346 | pw::rpc::Channel another_static_channel = |
| 347 | pw::rpc::Channel::Create<ChannelId::kUartChannel>(&output); |
| 348 | |
| 349 | // Creating a channel with a dynamic ID (note that no output is provided; it |
| 350 | // will be set when the channel is used. |
| 351 | pw::rpc::Channel dynamic_channel; |
| 352 | |
Alexei Frolov | 567e670 | 2021-04-13 09:13:02 -0700 | [diff] [blame] | 353 | Sometimes, the ID and output of a channel are not known at compile time as they |
| 354 | depend on information stored on the physical device. To support this use case, a |
| 355 | dynamically-assignable channel can be configured once at runtime with an ID and |
| 356 | output. |
| 357 | |
| 358 | .. code-block:: cpp |
| 359 | |
| 360 | // Create a dynamic channel without a compile-time ID or output. |
| 361 | pw::rpc::Channel dynamic_channel; |
| 362 | |
| 363 | void Init() { |
| 364 | // Called during boot to pull the channel configuration from the system. |
| 365 | dynamic_channel.Configure(GetChannelId(), some_output); |
| 366 | } |
| 367 | |
Wyatt Hepler | 3d57eaa | 2022-02-01 18:31:07 -0800 | [diff] [blame] | 368 | Adding and removing channels |
| 369 | ---------------------------- |
| 370 | New channels may be registered with the ``OpenChannel`` function. If dynamic |
| 371 | allocation is enabled (:c:macro:`PW_RPC_DYNAMIC_ALLOCATION` is 1), any number of |
| 372 | channels may be registered. If dynamic allocation is disabled, new channels may |
| 373 | only be registered if there are availale channel slots in the span provided to |
| 374 | the RPC endpoint at construction. |
| 375 | |
Erik Gilling | 3b7159a | 2022-01-20 20:37:01 +0000 | [diff] [blame] | 376 | A channel may be closed and unregistered with an endpoint by calling |
| 377 | ``ChannelClose`` on the endpoint with the corresponding channel ID. This |
| 378 | will terminate any pending calls and call their ``on_error`` callback |
| 379 | with the ``ABORTED`` status. |
| 380 | |
| 381 | .. code-block:: cpp |
| 382 | |
| 383 | // When a channel is closed, any pending calls will receive |
| 384 | // on_error callbacks with ABORTED status. |
| 385 | client->CloseChannel(1); |
| 386 | |
Alexei Frolov | 7c7a386 | 2020-07-16 15:36:02 -0700 | [diff] [blame] | 387 | Services |
| 388 | ======== |
| 389 | A service is a logical grouping of RPCs defined within a .proto file. ``pw_rpc`` |
| 390 | uses these .proto definitions to generate code for a base service, from which |
| 391 | user-defined RPCs are implemented. |
| 392 | |
| 393 | ``pw_rpc`` supports multiple protobuf libraries, and the generated code API |
| 394 | depends on which is used. |
| 395 | |
Wyatt Hepler | f9fb90f | 2020-09-30 18:59:33 -0700 | [diff] [blame] | 396 | .. _module-pw_rpc-protobuf-library-apis: |
Alexei Frolov | 4d2adde | 2020-08-04 10:19:24 -0700 | [diff] [blame] | 397 | |
| 398 | Protobuf library APIs |
| 399 | ===================== |
| 400 | |
Alexei Frolov | 7c7a386 | 2020-07-16 15:36:02 -0700 | [diff] [blame] | 401 | .. toctree:: |
| 402 | :maxdepth: 1 |
| 403 | |
| 404 | nanopb/docs |
| 405 | |
| 406 | Testing a pw_rpc integration |
| 407 | ============================ |
| 408 | After setting up a ``pw_rpc`` server in your project, you can test that it is |
| 409 | working as intended by registering the provided ``EchoService``, defined in |
Wyatt Hepler | 752d7d3 | 2021-03-02 09:02:23 -0800 | [diff] [blame] | 410 | ``echo.proto``, which echoes back a message that it receives. |
Alexei Frolov | 7c7a386 | 2020-07-16 15:36:02 -0700 | [diff] [blame] | 411 | |
Wyatt Hepler | 752d7d3 | 2021-03-02 09:02:23 -0800 | [diff] [blame] | 412 | .. literalinclude:: echo.proto |
Alexei Frolov | 7c7a386 | 2020-07-16 15:36:02 -0700 | [diff] [blame] | 413 | :language: protobuf |
| 414 | :lines: 14- |
| 415 | |
| 416 | For example, in C++ with nanopb: |
| 417 | |
| 418 | .. code:: c++ |
| 419 | |
| 420 | #include "pw_rpc/server.h" |
| 421 | |
| 422 | // Include the apporpriate header for your protobuf library. |
| 423 | #include "pw_rpc/echo_service_nanopb.h" |
| 424 | |
| 425 | constexpr pw::rpc::Channel kChannels[] = { /* ... */ }; |
| 426 | static pw::rpc::Server server(kChannels); |
| 427 | |
| 428 | static pw::rpc::EchoService echo_service; |
| 429 | |
| 430 | void Init() { |
Wyatt Hepler | 31b16ea | 2021-07-21 08:52:02 -0700 | [diff] [blame] | 431 | server.RegisterService(echo_service); |
Alexei Frolov | 7c7a386 | 2020-07-16 15:36:02 -0700 | [diff] [blame] | 432 | } |
| 433 | |
Wyatt Hepler | 31b16ea | 2021-07-21 08:52:02 -0700 | [diff] [blame] | 434 | Benchmarking and stress testing |
| 435 | ------------------------------- |
| 436 | |
| 437 | .. toctree:: |
| 438 | :maxdepth: 1 |
| 439 | :hidden: |
| 440 | |
| 441 | benchmark |
| 442 | |
| 443 | ``pw_rpc`` provides an RPC service and Python module for stress testing and |
| 444 | benchmarking a ``pw_rpc`` deployment. See :ref:`module-pw_rpc-benchmark`. |
| 445 | |
Wyatt Hepler | 05d860d | 2021-09-22 09:43:10 -0700 | [diff] [blame] | 446 | Naming |
| 447 | ====== |
| 448 | |
| 449 | Reserved names |
| 450 | -------------- |
| 451 | ``pw_rpc`` reserves a few service method names so they can be used for generated |
| 452 | classes. The following names cannnot be used for service methods: |
| 453 | |
| 454 | - ``Client`` |
| 455 | - ``Service`` |
| 456 | - Any reserved words in the languages ``pw_rpc`` supports (e.g. ``class``). |
| 457 | |
| 458 | ``pw_rpc`` does not reserve any service names, but the restriction of avoiding |
| 459 | reserved words in supported languages applies. |
| 460 | |
| 461 | Service naming style |
| 462 | -------------------- |
| 463 | ``pw_rpc`` service names should use capitalized camel case and should not use |
| 464 | the term "Service". Appending "Service" to a service name is redundant, similar |
| 465 | to appending "Class" or "Function" to a class or function name. The |
| 466 | C++ implementation class may use "Service" in its name, however. |
| 467 | |
| 468 | For example, a service for accessing a file system should simply be named |
| 469 | ``service FileSystem``, rather than ``service FileSystemService``, in the |
| 470 | ``.proto`` file. |
| 471 | |
| 472 | .. code-block:: protobuf |
| 473 | |
| 474 | // file.proto |
| 475 | package pw.file; |
| 476 | |
| 477 | service FileSystem { |
| 478 | rpc List(ListRequest) returns (stream ListResponse); |
| 479 | } |
| 480 | |
| 481 | The C++ service implementation class may append "Service" to the name. |
| 482 | |
| 483 | .. code-block:: cpp |
| 484 | |
| 485 | // file_system_service.h |
| 486 | #include "pw_file/file.raw_rpc.pb.h" |
| 487 | |
| 488 | namespace pw::file { |
| 489 | |
| 490 | class FileSystemService : public pw_rpc::raw::FileSystem::Service<FileSystemService> { |
Wyatt Hepler | 8e756e3 | 2021-11-18 09:59:27 -0800 | [diff] [blame] | 491 | void List(ConstByteSpan request, RawServerWriter& writer); |
Wyatt Hepler | 05d860d | 2021-09-22 09:43:10 -0700 | [diff] [blame] | 492 | }; |
| 493 | |
| 494 | } |
| 495 | |
| 496 | For upstream Pigweed services, this naming style is a requirement. Note that |
| 497 | some services created before this was established may use non-compliant |
| 498 | names. For Pigweed users, this naming style is a suggestion. |
| 499 | |
Wyatt Hepler | 067dd7e | 2020-07-14 19:34:32 -0700 | [diff] [blame] | 500 | Protocol description |
| 501 | ==================== |
| 502 | Pigweed RPC servers and clients communicate using ``pw_rpc`` packets. These |
| 503 | packets are used to send requests and responses, control streams, cancel ongoing |
| 504 | RPCs, and report errors. |
| 505 | |
| 506 | Packet format |
| 507 | ------------- |
| 508 | Pigweed RPC packets consist of a type and a set of fields. The packets are |
| 509 | encoded as protocol buffers. The full packet format is described in |
Wyatt Hepler | ba325e4 | 2021-03-08 14:23:34 -0800 | [diff] [blame] | 510 | ``pw_rpc/pw_rpc/internal/packet.proto``. |
Wyatt Hepler | 067dd7e | 2020-07-14 19:34:32 -0700 | [diff] [blame] | 511 | |
Wyatt Hepler | 752d7d3 | 2021-03-02 09:02:23 -0800 | [diff] [blame] | 512 | .. literalinclude:: internal/packet.proto |
Wyatt Hepler | 067dd7e | 2020-07-14 19:34:32 -0700 | [diff] [blame] | 513 | :language: protobuf |
| 514 | :lines: 14- |
| 515 | |
| 516 | The packet type and RPC type determine which fields are present in a Pigweed RPC |
Wyatt Hepler | 0f26235 | 2020-07-29 09:51:27 -0700 | [diff] [blame] | 517 | packet. Each packet type is only sent by either the client or the server. |
| 518 | These tables describe the meaning of and fields included with each packet type. |
Wyatt Hepler | 067dd7e | 2020-07-14 19:34:32 -0700 | [diff] [blame] | 519 | |
Wyatt Hepler | 0f26235 | 2020-07-29 09:51:27 -0700 | [diff] [blame] | 520 | Client-to-server packets |
| 521 | ^^^^^^^^^^^^^^^^^^^^^^^^ |
Wyatt Hepler | a921116 | 2021-06-12 15:40:11 -0700 | [diff] [blame] | 522 | +-------------------+-------------------------------------+ |
| 523 | | packet type | description | |
| 524 | +===================+=====================================+ |
| 525 | | REQUEST | Invoke an RPC | |
| 526 | | | | |
| 527 | | | .. code-block:: text | |
| 528 | | | | |
| 529 | | | - channel_id | |
| 530 | | | - service_id | |
| 531 | | | - method_id | |
| 532 | | | - payload | |
| 533 | | | (unary & server streaming only) | |
Alexei Frolov | 86e05de | 2021-10-19 16:52:31 -0700 | [diff] [blame] | 534 | | | - call_id (optional) | |
Wyatt Hepler | a921116 | 2021-06-12 15:40:11 -0700 | [diff] [blame] | 535 | | | | |
| 536 | +-------------------+-------------------------------------+ |
| 537 | | CLIENT_STREAM | Message in a client stream | |
| 538 | | | | |
| 539 | | | .. code-block:: text | |
| 540 | | | | |
| 541 | | | - channel_id | |
| 542 | | | - service_id | |
| 543 | | | - method_id | |
| 544 | | | - payload | |
Alexei Frolov | 86e05de | 2021-10-19 16:52:31 -0700 | [diff] [blame] | 545 | | | - call_id (if set in REQUEST) | |
Wyatt Hepler | a921116 | 2021-06-12 15:40:11 -0700 | [diff] [blame] | 546 | | | | |
| 547 | +-------------------+-------------------------------------+ |
Wyatt Hepler | 5ba8064 | 2021-06-18 12:56:17 -0700 | [diff] [blame] | 548 | | CLIENT_STREAM_END | Client stream is complete | |
| 549 | | | | |
| 550 | | | .. code-block:: text | |
| 551 | | | | |
| 552 | | | - channel_id | |
| 553 | | | - service_id | |
| 554 | | | - method_id | |
Alexei Frolov | 86e05de | 2021-10-19 16:52:31 -0700 | [diff] [blame] | 555 | | | - call_id (if set in REQUEST) | |
Wyatt Hepler | 5ba8064 | 2021-06-18 12:56:17 -0700 | [diff] [blame] | 556 | | | | |
| 557 | +-------------------+-------------------------------------+ |
Wyatt Hepler | 1716915 | 2021-10-20 18:46:08 -0700 | [diff] [blame] | 558 | | CLIENT_ERROR | Abort an ongoing RPC | |
Wyatt Hepler | a921116 | 2021-06-12 15:40:11 -0700 | [diff] [blame] | 559 | | | | |
| 560 | | | .. code-block:: text | |
| 561 | | | | |
| 562 | | | - channel_id | |
| 563 | | | - service_id | |
| 564 | | | - method_id | |
| 565 | | | - status | |
Alexei Frolov | 86e05de | 2021-10-19 16:52:31 -0700 | [diff] [blame] | 566 | | | - call_id (if set in REQUEST) | |
Wyatt Hepler | a921116 | 2021-06-12 15:40:11 -0700 | [diff] [blame] | 567 | | | | |
| 568 | +-------------------+-------------------------------------+ |
Wyatt Hepler | 067dd7e | 2020-07-14 19:34:32 -0700 | [diff] [blame] | 569 | |
Wyatt Hepler | 82db4b1 | 2021-09-23 09:10:12 -0700 | [diff] [blame] | 570 | **Client errors** |
Wyatt Hepler | 067dd7e | 2020-07-14 19:34:32 -0700 | [diff] [blame] | 571 | |
Wyatt Hepler | 0f26235 | 2020-07-29 09:51:27 -0700 | [diff] [blame] | 572 | The client sends ``CLIENT_ERROR`` packets to a server when it receives a packet |
Wyatt Hepler | 82db4b1 | 2021-09-23 09:10:12 -0700 | [diff] [blame] | 573 | it did not request. If possible, the server should abort it. |
Wyatt Hepler | 0f26235 | 2020-07-29 09:51:27 -0700 | [diff] [blame] | 574 | |
Wyatt Hepler | a921116 | 2021-06-12 15:40:11 -0700 | [diff] [blame] | 575 | The status code indicates the type of error. The status code is logged, but all |
| 576 | status codes result in the same action by the server: aborting the RPC. |
Wyatt Hepler | 0f26235 | 2020-07-29 09:51:27 -0700 | [diff] [blame] | 577 | |
Wyatt Hepler | 1716915 | 2021-10-20 18:46:08 -0700 | [diff] [blame] | 578 | * ``CANCELLED`` -- The client requested that the RPC be cancelled. |
Erik Gilling | 3b7159a | 2022-01-20 20:37:01 +0000 | [diff] [blame] | 579 | * ``ABORTED`` -- The RPC was aborted due its channel being closed. |
Wyatt Hepler | 0f26235 | 2020-07-29 09:51:27 -0700 | [diff] [blame] | 580 | * ``NOT_FOUND`` -- Received a packet for a service method the client does not |
| 581 | recognize. |
| 582 | * ``FAILED_PRECONDITION`` -- Received a packet for a service method that the |
| 583 | client did not invoke. |
Wyatt Hepler | 35240da | 2021-07-21 08:51:22 -0700 | [diff] [blame] | 584 | * ``DATA_LOSS`` -- Received a corrupt packet for a pending service method. |
Wyatt Hepler | 82db4b1 | 2021-09-23 09:10:12 -0700 | [diff] [blame] | 585 | * ``INVALID_ARGUMENT`` -- The server sent a packet type to an RPC that does not |
| 586 | support it (a ``SERVER_STREAM`` was sent to an RPC with no server stream). |
Wyatt Hepler | 3d57eaa | 2022-02-01 18:31:07 -0800 | [diff] [blame] | 587 | * ``UNAVAILABLE`` -- Received a packet for an unknown channel. |
Wyatt Hepler | 0f26235 | 2020-07-29 09:51:27 -0700 | [diff] [blame] | 588 | |
| 589 | Server-to-client packets |
| 590 | ^^^^^^^^^^^^^^^^^^^^^^^^ |
Wyatt Hepler | a921116 | 2021-06-12 15:40:11 -0700 | [diff] [blame] | 591 | +-------------------+-------------------------------------+ |
| 592 | | packet type | description | |
| 593 | +===================+=====================================+ |
Wyatt Hepler | 5ba8064 | 2021-06-18 12:56:17 -0700 | [diff] [blame] | 594 | | RESPONSE | The RPC is complete | |
| 595 | | | | |
| 596 | | | .. code-block:: text | |
| 597 | | | | |
| 598 | | | - channel_id | |
| 599 | | | - service_id | |
| 600 | | | - method_id | |
| 601 | | | - status | |
| 602 | | | - payload | |
| 603 | | | (unary & client streaming only) | |
Alexei Frolov | 86e05de | 2021-10-19 16:52:31 -0700 | [diff] [blame] | 604 | | | - call_id (if set in REQUEST) | |
Wyatt Hepler | 5ba8064 | 2021-06-18 12:56:17 -0700 | [diff] [blame] | 605 | | | | |
| 606 | +-------------------+-------------------------------------+ |
| 607 | | SERVER_STREAM | Message in a server stream | |
Wyatt Hepler | a921116 | 2021-06-12 15:40:11 -0700 | [diff] [blame] | 608 | | | | |
| 609 | | | .. code-block:: text | |
| 610 | | | | |
| 611 | | | - channel_id | |
| 612 | | | - service_id | |
| 613 | | | - method_id | |
| 614 | | | - payload | |
Alexei Frolov | 86e05de | 2021-10-19 16:52:31 -0700 | [diff] [blame] | 615 | | | - call_id (if set in REQUEST) | |
Wyatt Hepler | a921116 | 2021-06-12 15:40:11 -0700 | [diff] [blame] | 616 | | | | |
| 617 | +-------------------+-------------------------------------+ |
| 618 | | SERVER_ERROR | Received unexpected packet | |
| 619 | | | | |
| 620 | | | .. code-block:: text | |
| 621 | | | | |
| 622 | | | - channel_id | |
| 623 | | | - service_id (if relevant) | |
| 624 | | | - method_id (if relevant) | |
| 625 | | | - status | |
Alexei Frolov | 86e05de | 2021-10-19 16:52:31 -0700 | [diff] [blame] | 626 | | | - call_id (if set in REQUEST) | |
Wyatt Hepler | a921116 | 2021-06-12 15:40:11 -0700 | [diff] [blame] | 627 | | | | |
| 628 | +-------------------+-------------------------------------+ |
Wyatt Hepler | 0f26235 | 2020-07-29 09:51:27 -0700 | [diff] [blame] | 629 | |
Erik Gilling | 1f9e355 | 2022-01-21 18:49:20 +0000 | [diff] [blame] | 630 | All server packets contain the same ``call_id`` that was set in the initial |
Alexei Frolov | 86e05de | 2021-10-19 16:52:31 -0700 | [diff] [blame] | 631 | request made by the client, if any. |
| 632 | |
Wyatt Hepler | 82db4b1 | 2021-09-23 09:10:12 -0700 | [diff] [blame] | 633 | **Server errors** |
Wyatt Hepler | 0f26235 | 2020-07-29 09:51:27 -0700 | [diff] [blame] | 634 | |
| 635 | The server sends ``SERVER_ERROR`` packets when it receives a packet it cannot |
| 636 | process. The client should abort any RPC for which it receives an error. The |
| 637 | status field indicates the type of error. |
| 638 | |
| 639 | * ``NOT_FOUND`` -- The requested service or method does not exist. |
Wyatt Hepler | a921116 | 2021-06-12 15:40:11 -0700 | [diff] [blame] | 640 | * ``FAILED_PRECONDITION`` -- A client stream or cancel packet was sent for an |
| 641 | RPC that is not pending. |
Wyatt Hepler | 01fc15b | 2021-06-10 18:15:59 -0700 | [diff] [blame] | 642 | * ``INVALID_ARGUMENT`` -- The client sent a packet type to an RPC that does not |
Wyatt Hepler | 82db4b1 | 2021-09-23 09:10:12 -0700 | [diff] [blame] | 643 | support it (a ``CLIENT_STREAM`` was sent to an RPC with no client stream). |
Wyatt Hepler | 067dd7e | 2020-07-14 19:34:32 -0700 | [diff] [blame] | 644 | * ``RESOURCE_EXHAUSTED`` -- The request came on a new channel, but a channel |
| 645 | could not be allocated for it. |
Erik Gilling | 3b7159a | 2022-01-20 20:37:01 +0000 | [diff] [blame] | 646 | * ``ABORTED`` -- The RPC was aborted due its channel being closed. |
Wyatt Hepler | 712d367 | 2020-07-13 15:52:11 -0700 | [diff] [blame] | 647 | * ``INTERNAL`` -- The server was unable to respond to an RPC due to an |
| 648 | unrecoverable internal error. |
Wyatt Hepler | 3d57eaa | 2022-02-01 18:31:07 -0800 | [diff] [blame] | 649 | * ``UNAVAILABLE`` -- Received a packet for an unknown channel. |
Wyatt Hepler | 067dd7e | 2020-07-14 19:34:32 -0700 | [diff] [blame] | 650 | |
| 651 | Inovking a service method |
| 652 | ------------------------- |
| 653 | Calling an RPC requires a specific sequence of packets. This section describes |
| 654 | the protocol for calling service methods of each type: unary, server streaming, |
| 655 | client streaming, and bidirectional streaming. |
| 656 | |
Wyatt Hepler | 5ba8064 | 2021-06-18 12:56:17 -0700 | [diff] [blame] | 657 | The basic flow for all RPC invocations is as follows: |
| 658 | |
| 659 | * Client sends a ``REQUEST`` packet. Includes a payload for unary & server |
| 660 | streaming RPCs. |
| 661 | * For client and bidirectional streaming RPCs, the client may send any number |
| 662 | of ``CLIENT_STREAM`` packets with payloads. |
| 663 | * For server and bidirectional streaming RPCs, the server may send any number |
| 664 | of ``SERVER_STREAM`` packets. |
| 665 | * The server sends a ``RESPONSE`` packet. Includes a payload for unary & |
| 666 | client streaming RPCs. The RPC is complete. |
| 667 | |
Wyatt Hepler | 1716915 | 2021-10-20 18:46:08 -0700 | [diff] [blame] | 668 | The client may cancel an ongoing RPC at any time by sending a ``CLIENT_ERROR`` |
| 669 | packet with status ``CANCELLED``. The server may finish an ongoing RPC at any |
| 670 | time by sending the ``RESPONSE`` packet. |
Wyatt Hepler | 5ba8064 | 2021-06-18 12:56:17 -0700 | [diff] [blame] | 671 | |
Wyatt Hepler | 067dd7e | 2020-07-14 19:34:32 -0700 | [diff] [blame] | 672 | Unary RPC |
| 673 | ^^^^^^^^^ |
| 674 | In a unary RPC, the client sends a single request and the server sends a single |
| 675 | response. |
| 676 | |
Wyatt Hepler | 1d22124 | 2021-09-07 15:42:21 -0700 | [diff] [blame] | 677 | .. image:: unary_rpc.svg |
Wyatt Hepler | 067dd7e | 2020-07-14 19:34:32 -0700 | [diff] [blame] | 678 | |
Wyatt Hepler | 1716915 | 2021-10-20 18:46:08 -0700 | [diff] [blame] | 679 | The client may attempt to cancel a unary RPC by sending a ``CLIENT_ERROR`` |
| 680 | packet with status ``CANCELLED``. The server sends no response to a cancelled |
| 681 | RPC. If the server processes the unary RPC synchronously (the handling thread |
| 682 | sends the response), it may not be possible to cancel the RPC. |
Wyatt Hepler | a921116 | 2021-06-12 15:40:11 -0700 | [diff] [blame] | 683 | |
Wyatt Hepler | 1d22124 | 2021-09-07 15:42:21 -0700 | [diff] [blame] | 684 | .. image:: unary_rpc_cancelled.svg |
Wyatt Hepler | a921116 | 2021-06-12 15:40:11 -0700 | [diff] [blame] | 685 | |
Wyatt Hepler | 067dd7e | 2020-07-14 19:34:32 -0700 | [diff] [blame] | 686 | Server streaming RPC |
| 687 | ^^^^^^^^^^^^^^^^^^^^ |
| 688 | In a server streaming RPC, the client sends a single request and the server |
Wyatt Hepler | 5ba8064 | 2021-06-18 12:56:17 -0700 | [diff] [blame] | 689 | sends any number of ``SERVER_STREAM`` packets followed by a ``RESPONSE`` packet. |
Wyatt Hepler | 067dd7e | 2020-07-14 19:34:32 -0700 | [diff] [blame] | 690 | |
Wyatt Hepler | 1d22124 | 2021-09-07 15:42:21 -0700 | [diff] [blame] | 691 | .. image:: server_streaming_rpc.svg |
Wyatt Hepler | 067dd7e | 2020-07-14 19:34:32 -0700 | [diff] [blame] | 692 | |
Wyatt Hepler | 1716915 | 2021-10-20 18:46:08 -0700 | [diff] [blame] | 693 | The client may terminate a server streaming RPC by sending a ``CLIENT_STREAM`` |
| 694 | packet with status ``CANCELLED``. The server sends no response. |
Wyatt Hepler | 067dd7e | 2020-07-14 19:34:32 -0700 | [diff] [blame] | 695 | |
Wyatt Hepler | 1d22124 | 2021-09-07 15:42:21 -0700 | [diff] [blame] | 696 | .. image:: server_streaming_rpc_cancelled.svg |
Wyatt Hepler | 067dd7e | 2020-07-14 19:34:32 -0700 | [diff] [blame] | 697 | |
| 698 | Client streaming RPC |
| 699 | ^^^^^^^^^^^^^^^^^^^^ |
Wyatt Hepler | a921116 | 2021-06-12 15:40:11 -0700 | [diff] [blame] | 700 | In a client streaming RPC, the client starts the RPC by sending a ``REQUEST`` |
| 701 | packet with no payload. It then sends any number of messages in |
| 702 | ``CLIENT_STREAM`` packets, followed by a ``CLIENT_STREAM_END``. The server sends |
Wyatt Hepler | 5ba8064 | 2021-06-18 12:56:17 -0700 | [diff] [blame] | 703 | a single ``RESPONSE`` to finish the RPC. |
Wyatt Hepler | 067dd7e | 2020-07-14 19:34:32 -0700 | [diff] [blame] | 704 | |
Wyatt Hepler | 1d22124 | 2021-09-07 15:42:21 -0700 | [diff] [blame] | 705 | .. image:: client_streaming_rpc.svg |
Wyatt Hepler | 067dd7e | 2020-07-14 19:34:32 -0700 | [diff] [blame] | 706 | |
Wyatt Hepler | a921116 | 2021-06-12 15:40:11 -0700 | [diff] [blame] | 707 | The server may finish the RPC at any time by sending its ``RESPONSE`` packet, |
| 708 | even if it has not yet received the ``CLIENT_STREAM_END`` packet. The client may |
Wyatt Hepler | 1716915 | 2021-10-20 18:46:08 -0700 | [diff] [blame] | 709 | terminate the RPC at any time by sending a ``CLIENT_ERROR`` packet with status |
| 710 | ``CANCELLED``. |
Wyatt Hepler | 067dd7e | 2020-07-14 19:34:32 -0700 | [diff] [blame] | 711 | |
Wyatt Hepler | 1d22124 | 2021-09-07 15:42:21 -0700 | [diff] [blame] | 712 | .. image:: client_streaming_rpc_cancelled.svg |
Wyatt Hepler | 067dd7e | 2020-07-14 19:34:32 -0700 | [diff] [blame] | 713 | |
| 714 | Bidirectional streaming RPC |
| 715 | ^^^^^^^^^^^^^^^^^^^^^^^^^^^ |
| 716 | In a bidirectional streaming RPC, the client sends any number of requests and |
Wyatt Hepler | a921116 | 2021-06-12 15:40:11 -0700 | [diff] [blame] | 717 | the server sends any number of responses. The client invokes the RPC by sending |
| 718 | a ``REQUEST`` with no payload. It sends a ``CLIENT_STREAM_END`` packet when it |
Wyatt Hepler | 5ba8064 | 2021-06-18 12:56:17 -0700 | [diff] [blame] | 719 | has finished sending requests. The server sends a ``RESPONSE`` packet to finish |
| 720 | the RPC. |
Wyatt Hepler | 067dd7e | 2020-07-14 19:34:32 -0700 | [diff] [blame] | 721 | |
Wyatt Hepler | 1d22124 | 2021-09-07 15:42:21 -0700 | [diff] [blame] | 722 | .. image:: bidirectional_streaming_rpc.svg |
Wyatt Hepler | 067dd7e | 2020-07-14 19:34:32 -0700 | [diff] [blame] | 723 | |
Wyatt Hepler | 5ba8064 | 2021-06-18 12:56:17 -0700 | [diff] [blame] | 724 | The server may finish the RPC at any time by sending the ``RESPONSE`` packet, |
| 725 | even if it has not received the ``CLIENT_STREAM_END`` packet. The client may |
Wyatt Hepler | 1716915 | 2021-10-20 18:46:08 -0700 | [diff] [blame] | 726 | terminate the RPC at any time by sending a ``CLIENT_ERROR`` packet with status |
| 727 | ``CANCELLED``. |
Wyatt Hepler | 067dd7e | 2020-07-14 19:34:32 -0700 | [diff] [blame] | 728 | |
Wyatt Hepler | 1d22124 | 2021-09-07 15:42:21 -0700 | [diff] [blame] | 729 | .. image:: bidirectional_streaming_rpc_cancelled.svg |
Wyatt Hepler | 067dd7e | 2020-07-14 19:34:32 -0700 | [diff] [blame] | 730 | |
Wyatt Hepler | 948f547 | 2020-06-02 16:52:28 -0700 | [diff] [blame] | 731 | RPC server |
| 732 | ========== |
| 733 | Declare an instance of ``rpc::Server`` and register services with it. |
| 734 | |
| 735 | .. admonition:: TODO |
| 736 | |
| 737 | Document the public interface |
| 738 | |
Alexei Frolov | bf33d21 | 2020-09-15 17:13:45 -0700 | [diff] [blame] | 739 | Size report |
| 740 | ----------- |
| 741 | The following size report showcases the memory usage of the core RPC server. It |
| 742 | is configured with a single channel using a basic transport interface that |
| 743 | directly reads from and writes to ``pw_sys_io``. The transport has a 128-byte |
| 744 | packet buffer, which comprises the plurality of the example's RAM usage. This is |
| 745 | not a suitable transport for an actual product; a real implementation would have |
| 746 | additional overhead proportional to the complexity of the transport. |
| 747 | |
| 748 | .. include:: server_size |
| 749 | |
Wyatt Hepler | 948f547 | 2020-06-02 16:52:28 -0700 | [diff] [blame] | 750 | RPC server implementation |
| 751 | ------------------------- |
| 752 | |
| 753 | The Method class |
| 754 | ^^^^^^^^^^^^^^^^ |
| 755 | The RPC Server depends on the ``pw::rpc::internal::Method`` class. ``Method`` |
| 756 | serves as the bridge between the ``pw_rpc`` server library and the user-defined |
Wyatt Hepler | e95bd72 | 2020-11-23 07:49:47 -0800 | [diff] [blame] | 757 | RPC functions. Each supported protobuf implementation extends ``Method`` to |
| 758 | implement its request and response proto handling. The ``pw_rpc`` server |
| 759 | calls into the ``Method`` implementation through the base class's ``Invoke`` |
| 760 | function. |
Wyatt Hepler | 948f547 | 2020-06-02 16:52:28 -0700 | [diff] [blame] | 761 | |
Wyatt Hepler | e95bd72 | 2020-11-23 07:49:47 -0800 | [diff] [blame] | 762 | ``Method`` implementations store metadata about each method, including a |
| 763 | function pointer to the user-defined method implementation. They also provide |
| 764 | ``static constexpr`` functions for creating each type of method. ``Method`` |
| 765 | implementations must satisfy the ``MethodImplTester`` test class in |
Wyatt Hepler | fa6edcc | 2021-08-20 08:30:08 -0700 | [diff] [blame] | 766 | ``pw_rpc/internal/method_impl_tester.h``. |
Wyatt Hepler | 948f547 | 2020-06-02 16:52:28 -0700 | [diff] [blame] | 767 | |
Wyatt Hepler | e95bd72 | 2020-11-23 07:49:47 -0800 | [diff] [blame] | 768 | See ``pw_rpc/internal/method.h`` for more details about ``Method``. |
Wyatt Hepler | 948f547 | 2020-06-02 16:52:28 -0700 | [diff] [blame] | 769 | |
| 770 | Packet flow |
| 771 | ^^^^^^^^^^^ |
| 772 | |
| 773 | Requests |
| 774 | ~~~~~~~~ |
| 775 | |
Wyatt Hepler | 1d22124 | 2021-09-07 15:42:21 -0700 | [diff] [blame] | 776 | .. image:: request_packets.svg |
Wyatt Hepler | 948f547 | 2020-06-02 16:52:28 -0700 | [diff] [blame] | 777 | |
| 778 | Responses |
| 779 | ~~~~~~~~~ |
| 780 | |
Wyatt Hepler | 1d22124 | 2021-09-07 15:42:21 -0700 | [diff] [blame] | 781 | .. image:: response_packets.svg |
Alexei Frolov | 4d2adde | 2020-08-04 10:19:24 -0700 | [diff] [blame] | 782 | |
| 783 | RPC client |
| 784 | ========== |
| 785 | The RPC client is used to send requests to a server and manages the contexts of |
| 786 | ongoing RPCs. |
| 787 | |
| 788 | Setting up a client |
| 789 | ------------------- |
| 790 | The ``pw::rpc::Client`` class is instantiated with a list of channels that it |
| 791 | uses to communicate. These channels can be shared with a server, but multiple |
| 792 | clients cannot use the same channels. |
| 793 | |
| 794 | To send incoming RPC packets from the transport layer to be processed by a |
| 795 | client, the client's ``ProcessPacket`` function is called with the packet data. |
| 796 | |
| 797 | .. code:: c++ |
| 798 | |
| 799 | #include "pw_rpc/client.h" |
| 800 | |
| 801 | namespace { |
| 802 | |
| 803 | pw::rpc::Channel my_channels[] = { |
| 804 | pw::rpc::Channel::Create<1>(&my_channel_output)}; |
| 805 | pw::rpc::Client my_client(my_channels); |
| 806 | |
| 807 | } // namespace |
| 808 | |
| 809 | // Called when the transport layer receives an RPC packet. |
| 810 | void ProcessRpcPacket(ConstByteSpan packet) { |
| 811 | my_client.ProcessPacket(packet); |
| 812 | } |
| 813 | |
Alexei Frolov | 5a3a61c | 2020-10-01 18:51:41 -0700 | [diff] [blame] | 814 | .. _module-pw_rpc-making-calls: |
| 815 | |
Alexei Frolov | 4d2adde | 2020-08-04 10:19:24 -0700 | [diff] [blame] | 816 | Making RPC calls |
| 817 | ---------------- |
| 818 | RPC calls are not made directly through the client, but using one of its |
| 819 | registered channels instead. A service client class is generated from a .proto |
| 820 | file for each selected protobuf library, which is then used to send RPC requests |
| 821 | through a given channel. The API for this depends on the protobuf library; |
Wyatt Hepler | f9fb90f | 2020-09-30 18:59:33 -0700 | [diff] [blame] | 822 | please refer to the |
| 823 | :ref:`appropriate documentation<module-pw_rpc-protobuf-library-apis>`. Multiple |
| 824 | service client implementations can exist simulatenously and share the same |
| 825 | ``Client`` class. |
Alexei Frolov | 4d2adde | 2020-08-04 10:19:24 -0700 | [diff] [blame] | 826 | |
| 827 | When a call is made, a ``pw::rpc::ClientCall`` object is returned to the caller. |
| 828 | This object tracks the ongoing RPC call, and can be used to manage it. An RPC |
| 829 | call is only active as long as its ``ClientCall`` object is alive. |
| 830 | |
| 831 | .. tip:: |
| 832 | Use ``std::move`` when passing around ``ClientCall`` objects to keep RPCs |
| 833 | alive. |
| 834 | |
Alexei Frolov | 2d737bc | 2021-04-27 23:03:09 -0700 | [diff] [blame] | 835 | Example |
| 836 | ^^^^^^^ |
| 837 | .. code-block:: c++ |
| 838 | |
| 839 | #include "pw_rpc/echo_service_nanopb.h" |
| 840 | |
| 841 | namespace { |
Alexei Frolov | 2b54ee6 | 2021-04-29 14:58:21 -0700 | [diff] [blame] | 842 | // Generated clients are namespaced with their proto library. |
Alexei Frolov | 39d8c5c | 2021-11-24 10:16:31 -0800 | [diff] [blame] | 843 | using EchoClient = pw_rpc::nanopb::EchoService::Client; |
Alexei Frolov | 2b54ee6 | 2021-04-29 14:58:21 -0700 | [diff] [blame] | 844 | |
Alexei Frolov | 73687fb | 2021-09-03 11:22:33 -0700 | [diff] [blame] | 845 | // RPC channel ID on which to make client calls. |
| 846 | constexpr uint32_t kDefaultChannelId = 1; |
| 847 | |
Alexei Frolov | 39d8c5c | 2021-11-24 10:16:31 -0800 | [diff] [blame] | 848 | EchoClient::EchoCall echo_call; |
Alexei Frolov | bebba90 | 2021-06-09 17:03:52 -0700 | [diff] [blame] | 849 | |
| 850 | // Callback invoked when a response is received. This is called synchronously |
| 851 | // from Client::ProcessPacket. |
| 852 | void EchoResponse(const pw_rpc_EchoMessage& response, |
| 853 | pw::Status status) { |
| 854 | if (status.ok()) { |
| 855 | PW_LOG_INFO("Received echo response: %s", response.msg); |
| 856 | } else { |
| 857 | PW_LOG_ERROR("Echo failed with status %d", |
| 858 | static_cast<int>(status.code())); |
| 859 | } |
| 860 | } |
Alexei Frolov | 2d737bc | 2021-04-27 23:03:09 -0700 | [diff] [blame] | 861 | |
| 862 | } // namespace |
| 863 | |
| 864 | void CallEcho(const char* message) { |
Alexei Frolov | 73687fb | 2021-09-03 11:22:33 -0700 | [diff] [blame] | 865 | // Create a client to call the EchoService. |
Alexei Frolov | 39d8c5c | 2021-11-24 10:16:31 -0800 | [diff] [blame] | 866 | EchoClient echo_client(my_rpc_client, kDefaultChannelId); |
Alexei Frolov | 73687fb | 2021-09-03 11:22:33 -0700 | [diff] [blame] | 867 | |
Alexei Frolov | 2d737bc | 2021-04-27 23:03:09 -0700 | [diff] [blame] | 868 | pw_rpc_EchoMessage request = pw_rpc_EchoMessage_init_default; |
| 869 | pw::string::Copy(message, request.msg); |
| 870 | |
| 871 | // By assigning the returned ClientCall to the global echo_call, the RPC |
| 872 | // call is kept alive until it completes. When a response is received, it |
| 873 | // will be logged by the handler function and the call will complete. |
Alexei Frolov | 73687fb | 2021-09-03 11:22:33 -0700 | [diff] [blame] | 874 | echo_call = echo_client.Echo(request, EchoResponse); |
| 875 | if (!echo_call.active()) { |
| 876 | // The RPC call was not sent. This could occur due to, for example, an |
| 877 | // invalid channel ID. Handle if necessary. |
| 878 | } |
Alexei Frolov | 2d737bc | 2021-04-27 23:03:09 -0700 | [diff] [blame] | 879 | } |
| 880 | |
Alexei Frolov | 4d2adde | 2020-08-04 10:19:24 -0700 | [diff] [blame] | 881 | Client implementation details |
| 882 | ----------------------------- |
| 883 | |
| 884 | The ClientCall class |
| 885 | ^^^^^^^^^^^^^^^^^^^^ |
| 886 | ``ClientCall`` stores the context of an active RPC, and serves as the user's |
| 887 | interface to the RPC client. The core RPC library provides a base ``ClientCall`` |
| 888 | class with common functionality, which is then extended for RPC client |
| 889 | implementations tied to different protobuf libraries to provide convenient |
| 890 | interfaces for working with RPCs. |
| 891 | |
| 892 | The RPC server stores a list of all of active ``ClientCall`` objects. When an |
| 893 | incoming packet is recieved, it dispatches to one of its active calls, which |
| 894 | then decodes the payload and presents it to the user. |
Alexei Frolov | 3e28092 | 2021-04-12 14:53:06 -0700 | [diff] [blame] | 895 | |
| 896 | ClientServer |
| 897 | ============ |
| 898 | Sometimes, a device needs to both process RPCs as a server, as well as making |
| 899 | calls to another device as a client. To do this, both a client and server must |
| 900 | be set up, and incoming packets must be sent to both of them. |
| 901 | |
| 902 | Pigweed simplifies this setup by providing a ``ClientServer`` class which wraps |
| 903 | an RPC client and server with the same set of channels. |
| 904 | |
| 905 | .. code-block:: cpp |
| 906 | |
| 907 | pw::rpc::Channel channels[] = { |
| 908 | pw::rpc::Channel::Create<1>(&channel_output)}; |
| 909 | |
| 910 | // Creates both a client and a server. |
| 911 | pw::rpc::ClientServer client_server(channels); |
| 912 | |
| 913 | void ProcessRpcData(pw::ConstByteSpan packet) { |
| 914 | // Calls into both the client and the server, sending the packet to the |
| 915 | // appropriate one. |
Alexei Frolov | ba93a43 | 2021-12-02 13:36:26 -0800 | [diff] [blame] | 916 | client_server.ProcessPacket(packet); |
Alexei Frolov | 3e28092 | 2021-04-12 14:53:06 -0700 | [diff] [blame] | 917 | } |
Wyatt Hepler | 9732a8e | 2021-11-10 16:31:41 -0800 | [diff] [blame] | 918 | |
Wyatt Hepler | 1215a9d | 2021-11-10 08:55:47 -0800 | [diff] [blame] | 919 | Testing |
| 920 | ======= |
Wyatt Hepler | 9732a8e | 2021-11-10 16:31:41 -0800 | [diff] [blame] | 921 | ``pw_rpc`` provides utilities for unit testing RPC services and client calls. |
| 922 | |
Wyatt Hepler | 1215a9d | 2021-11-10 08:55:47 -0800 | [diff] [blame] | 923 | Client unit testing in C++ |
| 924 | -------------------------- |
Wyatt Hepler | 9732a8e | 2021-11-10 16:31:41 -0800 | [diff] [blame] | 925 | ``pw_rpc`` supports invoking RPCs, simulating server responses, and checking |
| 926 | what packets are sent by an RPC client in tests. Both raw and Nanopb interfaces |
| 927 | are supported. Code that uses the raw API may be tested with the Nanopb test |
| 928 | helpers, and vice versa. |
| 929 | |
| 930 | To test code that invokes RPCs, declare a ``RawClientTestContext`` or |
| 931 | ``NanopbClientTestContext``. These test context objects provide a |
| 932 | preconfigured RPC client, channel, server fake, and buffer for encoding packets. |
| 933 | These test classes are defined in ``pw_rpc/raw/client_testing.h`` and |
| 934 | ``pw_rpc/nanopb/client_testing.h``. |
| 935 | |
| 936 | Use the context's ``client()`` and ``channel()`` to invoke RPCs. Use the |
| 937 | context's ``server()`` to simulate responses. To verify that the client sent the |
| 938 | expected data, use the context's ``output()``, which is a ``FakeChannelOutput``. |
| 939 | |
| 940 | For example, the following tests a class that invokes an RPC. It checks that |
| 941 | the expected data was sent and then simulates a response from the server. |
| 942 | |
| 943 | .. code-block:: cpp |
| 944 | |
| 945 | #include "pw_rpc/raw/client_testing.h" |
| 946 | |
| 947 | class ThingThatCallsRpcs { |
| 948 | public: |
| 949 | // To support injecting an RPC client for testing, classes that make RPC |
| 950 | // calls should take an RPC client and channel ID or an RPC service client |
| 951 | // (e.g. pw_rpc::raw::MyService::Client). |
| 952 | ThingThatCallsRpcs(pw::rpc::Client& client, uint32_t channel_id); |
| 953 | |
| 954 | void DoSomethingThatInvokesAnRpc(); |
| 955 | |
| 956 | bool SetToTrueWhenRpcCompletes(); |
| 957 | }; |
| 958 | |
| 959 | TEST(TestAThing, InvokesRpcAndHandlesResponse) { |
| 960 | RawClientTestContext context; |
| 961 | ThingThatCallsRpcs thing(context.client(), context.channel().id()); |
| 962 | |
| 963 | // Execute the code that invokes the MyService.TheMethod RPC. |
| 964 | things.DoSomethingThatInvokesAnRpc(); |
| 965 | |
| 966 | // Find and verify the payloads sent for the MyService.TheMethod RPC. |
| 967 | auto msgs = context.output().payloads<pw_rpc::raw::MyService::TheMethod>(); |
| 968 | ASSERT_EQ(msgs.size(), 1u); |
| 969 | |
| 970 | VerifyThatTheExpectedMessageWasSent(msgs.back()); |
| 971 | |
| 972 | // Send the response packet from the server and verify that the class reacts |
| 973 | // accordingly. |
| 974 | EXPECT_FALSE(thing.SetToTrueWhenRpcCompletes()); |
| 975 | |
| 976 | context_.server().SendResponse<pw_rpc::raw::MyService::TheMethod>( |
| 977 | final_message, OkStatus()); |
| 978 | |
| 979 | EXPECT_TRUE(thing.SetToTrueWhenRpcCompletes()); |
| 980 | } |
Ewout van Bekkum | 7f5b305 | 2021-11-11 17:35:23 -0800 | [diff] [blame] | 981 | |
Wyatt Hepler | 1215a9d | 2021-11-10 08:55:47 -0800 | [diff] [blame] | 982 | Integration testing with ``pw_rpc`` |
| 983 | ----------------------------------- |
| 984 | ``pw_rpc`` provides utilities to simplify writing integration tests for systems |
| 985 | that communicate with ``pw_rpc``. The integration test utitilies set up a socket |
| 986 | to use for IPC between an RPC server and client process. |
| 987 | |
| 988 | The server binary uses the system RPC server facade defined |
| 989 | ``pw_rpc_system_server/rpc_server.h``. The client binary uses the functions |
| 990 | defined in ``pw_rpc/integration_testing.h``: |
| 991 | |
| 992 | .. cpp:var:: constexpr uint32_t kChannelId |
| 993 | |
| 994 | The RPC channel for integration test RPCs. |
| 995 | |
| 996 | .. cpp:function:: pw::rpc::Client& pw::rpc::integration_test::Client() |
| 997 | |
| 998 | Returns the global RPC client for integration test use. |
| 999 | |
| 1000 | .. cpp:function:: pw::Status pw::rpc::integration_test::InitializeClient(int argc, char* argv[], const char* usage_args = "PORT") |
| 1001 | |
| 1002 | Initializes logging and the global RPC client for integration testing. Starts |
| 1003 | a background thread that processes incoming. |
| 1004 | |
Ewout van Bekkum | 7f5b305 | 2021-11-11 17:35:23 -0800 | [diff] [blame] | 1005 | Module Configuration Options |
| 1006 | ============================ |
| 1007 | The following configurations can be adjusted via compile-time configuration of |
| 1008 | this module, see the |
| 1009 | :ref:`module documentation <module-structure-compile-time-configuration>` for |
| 1010 | more details. |
| 1011 | |
| 1012 | .. c:macro:: PW_RPC_CLIENT_STREAM_END_CALLBACK |
| 1013 | |
| 1014 | In client and bidirectional RPCs, pw_rpc clients may signal that they have |
| 1015 | finished sending requests with a CLIENT_STREAM_END packet. While this can be |
| 1016 | useful in some circumstances, it is often not necessary. |
| 1017 | |
| 1018 | This option controls whether or not include a callback that is called when |
| 1019 | the client stream ends. The callback is included in all ServerReader/Writer |
| 1020 | objects as a pw::Function, so may have a significant cost. |
| 1021 | |
| 1022 | This is disabled by default. |
| 1023 | |
| 1024 | .. c:macro:: PW_RPC_NANOPB_STRUCT_MIN_BUFFER_SIZE |
| 1025 | |
| 1026 | The Nanopb-based pw_rpc implementation allocates memory to use for Nanopb |
| 1027 | structs for the request and response protobufs. The template function that |
| 1028 | allocates these structs rounds struct sizes up to this value so that |
| 1029 | different structs can be allocated with the same function. Structs with sizes |
| 1030 | larger than this value cause an extra function to be created, which slightly |
| 1031 | increases code size. |
| 1032 | |
| 1033 | Ideally, this value will be set to the size of the largest Nanopb struct used |
| 1034 | as an RPC request or response. The buffer can be stack or globally allocated |
| 1035 | (see ``PW_RPC_NANOPB_STRUCT_BUFFER_STACK_ALLOCATE``). |
| 1036 | |
| 1037 | This defaults to 64 Bytes. |
| 1038 | |
| 1039 | .. c:macro:: PW_RPC_USE_GLOBAL_MUTEX |
| 1040 | |
| 1041 | Enable global synchronization for RPC calls. If this is set, a backend must |
| 1042 | be configured for pw_sync:mutex. |
| 1043 | |
| 1044 | This is disabled by default. |
| 1045 | |
Wyatt Hepler | 3d57eaa | 2022-02-01 18:31:07 -0800 | [diff] [blame] | 1046 | .. c:macro:: PW_RPC_DYNAMIC_ALLOCATION |
| 1047 | |
| 1048 | Whether pw_rpc should use dynamic memory allocation internally. If enabled, |
| 1049 | pw_rpc dynamically allocates channels and its encoding buffers. RPC users may |
| 1050 | use dynamic allocation independently of this option (e.g. to allocate pw_rpc |
| 1051 | call objects). |
| 1052 | |
| 1053 | The semantics for allocating and initializing channels change depending on |
| 1054 | this option. If dynamic allocation is disabled, pw_rpc endpoints (servers or |
| 1055 | clients) use an externally-allocated, fixed-size array of channels. |
| 1056 | That array must include unassigned channels or existing channels must be |
| 1057 | closed to add new channels. |
| 1058 | |
| 1059 | If dynamic allocation is enabled, an span of channels may be passed to the |
| 1060 | endpoint at construction, but these channels are only used to initialize its |
| 1061 | internal std::vector of channels. External channel objects are NOT used by |
| 1062 | the endpoint cannot be updated if dynamic allocation is enabled. No |
| 1063 | unassigned channels should be passed to the endpoint; they will be ignored. |
| 1064 | Any number of channels may be added to the endpoint, without closing existing |
| 1065 | channels, but adding channels will use more memory. |
| 1066 | |
Ewout van Bekkum | 7f5b305 | 2021-11-11 17:35:23 -0800 | [diff] [blame] | 1067 | .. c:macro:: PW_RPC_CONFIG_LOG_LEVEL |
| 1068 | |
| 1069 | The log level to use for this module. Logs below this level are omitted. |
| 1070 | |
| 1071 | This defaults to ``PW_LOG_LEVEL_INFO``. |
| 1072 | |
| 1073 | .. c:macro:: PW_RPC_CONFIG_LOG_MODULE_NAME |
| 1074 | |
| 1075 | The log module name to use for this module. |
| 1076 | |
| 1077 | This defaults to ``"PW_RPC"``. |
| 1078 | |
| 1079 | .. c:macro:: PW_RPC_NANOPB_STRUCT_BUFFER_STACK_ALLOCATE |
| 1080 | |
| 1081 | This option determines whether to allocate the Nanopb structs on the stack or |
| 1082 | in a global variable. Globally allocated structs are NOT thread safe, but |
| 1083 | work fine when the RPC server's ProcessPacket function is only called from |
| 1084 | one thread. |
| 1085 | |
| 1086 | This is enabled by default. |
Wyatt Hepler | 1443976 | 2021-11-09 09:16:32 -0800 | [diff] [blame] | 1087 | |
| 1088 | Sharing server and client code |
| 1089 | ============================== |
| 1090 | Streaming RPCs support writing multiple requests or responses. To facilitate |
| 1091 | sharing code between servers and clients, ``pw_rpc`` provides the |
| 1092 | ``pw::rpc::Writer`` interface. On the client side, a client or bidirectional |
| 1093 | streaming RPC call object (``ClientWriter`` or ``ClientReaderWriter``) can be |
| 1094 | used as a ``pw::rpc::Writer&``. On the server side, a server or bidirectional |
| 1095 | streaming RPC call object (``ServerWriter`` or ``ServerReaderWriter``) can be |
| 1096 | used as a ``pw::rpc::Writer&``. |
Yuval Peress | b8f3ad2 | 2021-10-26 22:55:27 -0600 | [diff] [blame] | 1097 | |
| 1098 | Zephyr |
| 1099 | ====== |
| 1100 | To enable ``pw_rpc.*`` for Zephyr add ``CONFIG_PIGWEED_RPC=y`` to the project's |
| 1101 | configuration. This will enable the Kconfig menu for the following: |
| 1102 | |
| 1103 | * ``pw_rpc.server`` which can be enabled via ``CONFIG_PIGWEED_RPC_SERVER=y``. |
| 1104 | * ``pw_rpc.client`` which can be enabled via ``CONFIG_PIGWEED_RPC_CLIENT=y``. |
| 1105 | * ``pw_rpc.client_server`` which can be enabled via |
| 1106 | ``CONFIG_PIGWEED_RPC_CLIENT_SERVER=y``. |
| 1107 | * ``pw_rpc.common` which can be enabled via ``CONFIG_PIGWEED_RPC_COMMON=y``. |
Wyatt Hepler | 5fdaeac | 2022-01-20 18:00:40 -0800 | [diff] [blame] | 1108 | |
Wyatt Hepler | cfedcc4 | 2022-01-26 15:08:39 -0800 | [diff] [blame] | 1109 | Encoding and sending packets |
| 1110 | ============================ |
| 1111 | ``pw_rpc`` has to manage interactions among multiple RPC clients, servers, |
| 1112 | client calls, and server calls. To safely synchronize these interactions with |
| 1113 | minimal overhead, ``pw_rpc`` uses a single, global mutex (when |
| 1114 | ``PW_RPC_USE_GLOBAL_MUTEX`` is enabled). |
| 1115 | |
| 1116 | Because ``pw_rpc`` uses a global mutex, it also uses a global buffer to encode |
| 1117 | outgoing packets. The size of the buffer is set with |
| 1118 | ``PW_RPC_ENCODING_BUFFER_SIZE``, which defaults to 512 B. |
| 1119 | |
| 1120 | Users of ``pw_rpc`` must implement the :cpp:class:`pw::rpc::ChannelOutput` |
Wyatt Hepler | 5fdaeac | 2022-01-20 18:00:40 -0800 | [diff] [blame] | 1121 | interface. |
| 1122 | |
Chad Norvell | ee40edd | 2022-02-25 13:29:53 -0800 | [diff] [blame] | 1123 | .. _module-pw_rpc-ChannelOutput: |
Wyatt Hepler | 5fdaeac | 2022-01-20 18:00:40 -0800 | [diff] [blame] | 1124 | .. cpp:class:: pw::rpc::ChannelOutput |
| 1125 | |
Wyatt Hepler | cfedcc4 | 2022-01-26 15:08:39 -0800 | [diff] [blame] | 1126 | ``pw_rpc`` endpoints use :cpp:class:`ChannelOutput` instances to send packets. |
| 1127 | Systems that integrate pw_rpc must use one or more :cpp:class:`ChannelOutput` |
| 1128 | instances. |
| 1129 | |
| 1130 | .. cpp:member:: static constexpr size_t kUnlimited = std::numeric_limits<size_t>::max() |
| 1131 | |
| 1132 | Value returned from :cpp:func:`MaximumTransmissionUnit` to indicate an |
| 1133 | unlimited MTU. |
Wyatt Hepler | 5fdaeac | 2022-01-20 18:00:40 -0800 | [diff] [blame] | 1134 | |
| 1135 | .. cpp:function:: virtual size_t MaximumTransmissionUnit() |
| 1136 | |
Wyatt Hepler | cfedcc4 | 2022-01-26 15:08:39 -0800 | [diff] [blame] | 1137 | Returns the size of the largest packet the :cpp:class:`ChannelOutput` can |
| 1138 | send. :cpp:class:`ChannelOutput` implementations should only override this |
| 1139 | function if they impose a limit on the MTU. The default implementation |
| 1140 | returns :cpp:member:`kUnlimited`, which indicates that there is no MTU |
| 1141 | limit. |
Wyatt Hepler | 5fdaeac | 2022-01-20 18:00:40 -0800 | [diff] [blame] | 1142 | |
Wyatt Hepler | cfedcc4 | 2022-01-26 15:08:39 -0800 | [diff] [blame] | 1143 | .. cpp:function:: virtual pw::Status Send(std::span<std::byte> packet) |
Wyatt Hepler | 5fdaeac | 2022-01-20 18:00:40 -0800 | [diff] [blame] | 1144 | |
Wyatt Hepler | cfedcc4 | 2022-01-26 15:08:39 -0800 | [diff] [blame] | 1145 | Sends an encoded RPC packet. Returns OK if further packets may be sent, even |
| 1146 | if the current packet could not be sent. Returns any other status if the |
| 1147 | Channel is no longer able to send packets. |
Wyatt Hepler | 5fdaeac | 2022-01-20 18:00:40 -0800 | [diff] [blame] | 1148 | |
Wyatt Hepler | cfedcc4 | 2022-01-26 15:08:39 -0800 | [diff] [blame] | 1149 | The RPC system's internal lock is held while this function is called. Avoid |
| 1150 | long-running operations, since these will delay any other users of the RPC |
| 1151 | system. |
Wyatt Hepler | 5fdaeac | 2022-01-20 18:00:40 -0800 | [diff] [blame] | 1152 | |
Wyatt Hepler | cfedcc4 | 2022-01-26 15:08:39 -0800 | [diff] [blame] | 1153 | .. danger:: |
| 1154 | |
| 1155 | No ``pw_rpc`` APIs may be accessed in this function! Implementations MUST |
| 1156 | NOT access any RPC endpoints (:cpp:class:`pw::rpc::Client`, |
| 1157 | :cpp:class:`pw::rpc::Server`) or call objects |
| 1158 | (:cpp:class:`pw::rpc::ServerReaderWriter`, |
| 1159 | :cpp:class:`pw::rpc::ClientReaderWriter`, etc.) inside the :cpp:func:`Send` |
| 1160 | function or any descendent calls. Doing so will result in deadlock! RPC APIs |
| 1161 | may be used by other threads, just not within :cpp:func:`Send`. |
| 1162 | |
| 1163 | The buffer provided in ``packet`` must NOT be accessed outside of this |
| 1164 | function. It must be sent immediately or copied elsewhere before the |
| 1165 | function returns. |