Rust App Config Serializer

[ipetr0v]

We need to add a Rust version of the App Config Serializer for creating binary configuration files for Oak applications.
C++ version of the Serializer was implemented in #459 as a part of #412.

Blocks #723

[ipetr0v]

Currently I have not found that Prost allows to read textproto files and to serialize protobuf structures into files, compared to the C++ version of ProtoBuf:
https://github.com/protocolbuffers/protobuf/blob/70fc0f0275389a99b0c654778ef937f904921be0/src/google/protobuf/text_format.h#L448-L452
https://github.com/protocolbuffers/protobuf/blob/70fc0f0275389a99b0c654778ef937f904921be0/src/google/protobuf/message_lite.cc#L466-L474

I will continue searching but another possibility is to use non-protobuf (non-textproto) formats for textual config files, use them to create Rust structures and then serialize everything with Serde (Rust serialization).

cc @tiziano88

[daviddrysdale]

Why does this block #723? There's nothing stopping us having a C++ tool that generates a binary serialized protobuf file that the Rust runtime can then read (language interoperability being the point of protobuf, after all).

[tiziano88]

I agree this does not block anything, the current C++ serializer should work perfectly for both the C++ and Rust runtime. We may want to have different scripts / Bazel rules to make it easier to invoke perhaps, in the short term.

[ipetr0v]

Deleted "Blocks"

[tiziano88]

Probably worth starting work on this, since we know it will necessary for #1183 , @ipetr0v WDYT?

[ipetr0v]

We already have TOML files with example info:

oak/examples/abitest/example.toml

Lines 1 to 12 in 08c6a60

	name = "abitest"
	[modules]
	module_0 = { Cargo = { cargo_manifest = "examples/abitest/module_0/rust/Cargo.toml" } }
	module_1 = { Cargo = { cargo_manifest = "examples/abitest/module_1/rust/Cargo.toml" } }
	[clients]
	cpp = { Bazel = { bazel_target = "//examples/abitest/client:client" }, additional_args = [
	"--test_exclude=Storage",
	"--cert_chain=../../../../../../../../examples/certs/local/local.pem",
	"--private_key=../../../../../../../../examples/certs/local/local.key",
	] }

Should this be a separate file with a list of Wasm files, or it's better to keep everything together?
I personally prefer a separate file, because in this case it would be possible to just have a file with URLs and no source code.

WDYT?

[tiziano88]

The example manifests are and should stay separate; they are used to organize how examples are built and run, including clients and other example-specific stuff.

We need an application config manifest that is essentially a replacement for the textproto application definition, and also allow specifying the mapping from names to files (which is currently provided via flags to the app serializer).

The example TOML file then should probably be modified so that it points to the example manifest file, which runner or whatever other mechanism would then pass to the app serializer, after having actually built the local Wasm modules (the app serializer does not build the modules directly)

This should be the first version.

Next, separately, we should add support for specifying a URL as the source for the modules.

[ipetr0v]

Should serialized files be put into out (#719) directory, or it's better to create something inside target?

[tiziano88]

I think we should create an out dir as part of this. target is specific to Rust, I would leave it alone.