Use prost instead of rust-protobuf

Main differences:

- use `::default` instead of `::new` to create instances
- use native field accessors
- use native Option and Vec types for optional and repeated fields
- dispatcher struct has a more qualified name
- gRPC generator code is encapsulated in a prost ServiceGenerator
- use `quote!` macros instead of string concatenation in the generator

Cargo.toml

@@ -63,5 +63,3 @@ split_grpc_proxy = { path = "experimental/split_grpc/proxy" }
 split_grpc_server = { path = "experimental/split_grpc/server" }
 # Third party.
 expect = { path = "third_party/expect" }
-grpc-compiler = { path = "third_party/grpc-rust/grpc-compiler" }
-protoc-rust-grpc = { path = "third_party/grpc-rust/protoc-rust-grpc" }

docs/programming-oak.md

@@ -123,7 +123,7 @@ generated file appearing in `src/proto/<service>_grpc.rs`.
 [embedmd]:# (../examples/hello_world/module/rust/build.rs Rust /fn main/ /^}/)
 ```Rust
 fn main() {
-    oak_utils::run_protoc_rust_grpc(protoc_rust_grpc::Args {
+    oak_utils::compile_protobuf_grpc(protoc_rust_grpc::Args {
         out_dir: "src/proto",
         input: &["../../proto/hello_world.proto"],
         includes: &["../../proto", "../../../../third_party"],

examples/abitest/module_0/rust/Cargo.toml

@@ -15,7 +15,7 @@ hex = "*"
 log = "*"
 oak = "=0.1.0"
 oak_abi = "=0.1.0"
-protobuf = "*"
+prost = "*"
 rand_core = "*"
 rand = "*"
 regex = "*"
@@ -24,4 +24,3 @@ serde_json = "*"
 
 [build-dependencies]
 oak_utils = "*"
-protoc-rust-grpc = { path = "../../../../third_party/grpc-rust/protoc-rust-grpc" }

examples/abitest/module_0/rust/build.rs

@@ -15,12 +15,8 @@
 //
 
 fn main() {
-    oak_utils::run_protoc_rust_grpc(protoc_rust_grpc::Args {
-        out_dir: "src/proto",
-        input: &["../../proto/abitest.proto"],
-        includes: &["../../proto", "../../../../third_party"],
-        rust_protobuf: true, // also generate protobuf messages, not just services
-        ..Default::default()
-    })
-    .expect("protoc-rust-grpc");
+    oak_utils::compile_protobuf(
+        &["../../proto/abitest.proto"],
+        &["../../proto", "../../../../third_party"],
+    );
 }