Protobuf notes

Introduction:

• https://protobuf.dev/getting-started/cpptutorial/
• https://protobuf.dev/programming-guides/proto3/

When compiling nanopb Protobuf library as part of C language programs, nested Protobuf messages require use of nanopb defined function type `pb_callback_t` in order to encode and to decode those nested messages. Some examples of this on github:

• https://github.com/particle-iot/device-os/blob/9338b13b1e611f1b57f71f702795c2ca71142c1f/proto_defs/src/cloud/describe.pb.h#L9

• https://github.com/hello/kitsune/blob/6a28afa80dd4547907e58341a84bd0b5bec5d88e/kitsune/protobuf/periodic.pb.h#L11

In the first example an early on file instance of `pb_callback_t` occurs on line 56. Looking further this project has a few dozen protoc generated files . . . switching to a possible smaller project:

• https://github.com/hello/kitsune

In kitsune project, looking at:

(1) file kitsune/kitsune/audio_features_upload_task.c function setup_protbuf( . . . ) (2) file audio_features_upload_task_helpers.c function encode_repeated_streaming_bytes_and_mark_done(pb_ostream_t *stream, const pb_field_t *field, void * const *arg) (3) in same file reviewing function write_streams(pb_ostream_t *stream, const pb_field_t *field,hlo_stream_t * hlo_stream)

^ References To Sort

Protobuf references, somewhat arbitrary starting point yet introduces some key topics of Protobuf standard and use cases:

• https://www.crankuptheamps.com/blog/posts/2017/10/12/protobuf-battle-of-the-syntaxes/
• https://www.educative.io/edpresso/what-is-the-difference-between-protocol-buffers-and-json

• https://developers.google.com/protocol-buffers/docs/proto
• https://spline.de/talks/protobuf.pdf

JSON supported data types:

• https://www.w3schools.com/js/js_json_datatypes.asp

First Protobuf .proto file, compiles using `protoc-c`, part of a package available with Ubuntu 20.04:

// syntax = "proto3";
syntax = "proto2";

// Notes:
// $ protoc-c --c_out=. ./first.proto

message sensorUpdates {
  required int32 message_id = 1;
  optional float vrms = 2;
}

. . . It appears that the integer values which message elements are assigned as tantamount to key names in JSON.

^ Nanopb

2022-01-08 Saturday

• https://github.com/nanopb/nanopb/blob/master/generator/proto/nanopb.proto
• https://jpa.kapsi.fi/nanopb/docs/whats_new.html
• https://jpa.kapsi.fi/nanopb/docs/

• https://docs.python.org/3/tutorial/modules.html

Cmake script to locate Nanopb headers and sources:

• https://chromium.googlesource.com/external/github.com/nanopb/nanopb/+/nanopb-0.2.9.1/extra/FindNanopb.cmake