LotusRPC 🌼

RPC framework for embedded systems based on ETL. Generates C++ code for your device with no dynamic memory allocations, no exceptions, no RTTI, etc.

WARNING: This project is work in progress

Features

Supported data types

basic types: (u)intx_t, float, double, bool
string
- Fixed size: e.g., string_10 for a maximum size of 10 characters (excluding termination character)
- Automatic size: string. For this type the number of bytes that is transferred is determined by how long the actual string is. This can be different for every RPC function call, contrary to the fixed size string.
array
- Array can be of any type except string
- Enabled by using the count setting in the definition file with any value larger than 1
optional
- Can be used with any type
- Translated to etl::optional in the generated C++ code
- Enabled by using the count setting in the definition file with a value ?
custom
- struct
  - A custom struct can have any number of fields of any type except string, even other custom types
  - A custom struct can be used as a function argument or function return type by referencing it with a @-prefix
- enum
  - A custom enum can have any number of fields
  - Translated to an enum class in the generated C++ code

Multiple return values

Multiple return values for a function are supported. In the generated C++ code this feature is translated to a function returning a std::tuple

Interface definition file

The interface definition file is in YAML format. This makes it easy to parse in many languages and use it for any other purpose that you may need. There is a schema for the interface definition file to provide code completion and error checking in editors that support JSON schema.

Code generation in a namespace

All code is generated in the namespace specified in the interface definition file. If no namespace is specified, all code is generated in the global namespace

Configuration of receive and transmit buffer size

Receive and transmit buffer sizes can be configured in the interface definition file. If not specified, both take the value of 256 bytes

Fully configurable service and function IDs

Every LRPC service has an ID with a value between 0 and 254 (ID 255 is reserved for). This means that LRPC supports a maximum of 255 services. Duplicate service IDs are not allowed. The service ID can optionally be specified in the definition file. If it is not specified an ID is generated, starting with 0 for the first service, 1 for the second service, etc. It is possible to specify only some service IDs and let the rest be generated automatically. For example, if a definition contains 4 services, but only the third service has a specified ID of 17, then the resulting service IDs are [0, 1, 17, 18]

The same applies to LRPC functions inside a service.

Platform independent

LRPC uses Python to generate code and can therefore be used on all platforms that support Python. The generated C++ code is C++11 compatible and can be compiled for any platform with a suitable compiler.

DISCLAIMER: All development is done on Windows. Continuous integration is done with Github Actions on Ubuntu.

Example definition

services:
  - name: "battery"
    functions:
      - name: "get"
        params:
          - name: "option"
            type: "@VoltageScales"
        returns:
          - name: "voltage"
            type: double
enums:
  - name: "VoltageScales"
    fields:
        name: "microvolts"
        name: "millivolts"
        name: "volts"

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