Replace LogEntry Rust struct with a protobuf object

[tiziano88]

oak/sdk/rust/oak_log/src/lib.rs

Lines 31 to 37 in 1528e03

	/// An object representing a log entry. Currently just a wrapper around a string, but it may be
	/// extended in the future with additional fields, e.g. level or file / line information, though
	/// that would probably require defining a cross-language schema such as protobuf or FIDL for it,
	/// rather than just a Rust struct.
	struct LogEntry {
	message: String,
	}

Currently LogEntry is a Rust struct wrapping a string, and on the C++ side of the logging pseudo-node, this is de-serialized as a string, but there is no "schema" to keep the two sides in sync, especially if we wanted to add more fields to it (e.g. log level).

@daviddrysdale : it looks like protobuf is going to be the de facto IDL, at least for the time being, so perhaps we should replace this object (and others) with corresponding protobuf ones. What are your thoughts?

[daviddrysdale]

Yeah, I think that makes sense for now. Something like the following?

message LogMessage {
  string file = 1;
  int32 line = 2;
  int32 level = 3;
  string message = 4;
}

[tiziano88]

For reference, this is the corresponding Rust struct: https://docs.rs/log/0.4.10/log/struct.Record.html (not that we have to necessarily stick to that though).

[tiziano88]

Assigning to @rbehjati to investigate, I think it makes sense to go ahead with that proto definition, which perhaps should live near or inside oak_abi (especially after #666 ).

FYI the log crate is in the process of adding key/value support (see https://docs.rs/log/0.4.10/log/kv/index.html ), so we may look into supporting that in the future.

[rbehjati]

The change list in (#697) relies on rust-protobuf for generating rust structs from proto file. The use of rust-protobuf in the entire crate will later be replaced with prost in a separate task.