chore: Make codegen independent from protoc (#1953)

Author: tottoto

.github/workflows/CI.yml

@@ -46,10 +46,6 @@ jobs:
     steps:
     - uses: actions/checkout@v4
     - uses: hecrj/setup-rust-action@v2
-    - name: Install protoc
-      uses: taiki-e/install-action@v2
-      with:
-        tool: [email protected]
     - uses: Swatinem/rust-cache@v2
     - run: cargo run --package codegen
     - run: git diff --exit-code

CONTRIBUTING.md

@@ -211,8 +211,7 @@ example would explicitly use `Timeout::new`. For example:
 When making changes to `tonic-build` that affects the generated code you will
 need to ensure that each of the sub crates gets updated as well. Each of the sub
 crates like, for example `tonic-health`, generate their gRPC code via `codegen`
-crate. This requires `Protocol Buffers Compiler` of which version is same as the
-one used in the GitHub Action (see [`codegen` job](./.github/workflows/CI.yml)).
+crate.
 
 ```
 cargo run --package codegen

codegen/Cargo.toml

@@ -8,4 +8,5 @@ version = "0.1.0"
 
 [dependencies]
 tempfile = "3.8.0"
+protox = "0.7"
 tonic-build = {path = "../tonic-build", default-features = false, features = ["prost", "cleanup-markdown"]}

codegen/src/main.rs

@@ -1,4 +1,11 @@
-use std::path::{Path, PathBuf};
+use std::{
+    fs::File,
+    io::{BufWriter, Write as _},
+    path::{Path, PathBuf},
+};
+
+use protox::prost::{bytes::BytesMut, Message as _};
+use tonic_build::FileDescriptorSet;
 
 fn main() {
     // tonic-health
@@ -82,12 +89,15 @@ fn codegen(
     let out_dir = root_dir.join(out_dir);
     let file_descriptor_set_path = root_dir.join(file_descriptor_set_path);
 
+    let fds = protox::compile(&iface_files, &include_dirs).unwrap();
+
+    write_fds(&fds, &file_descriptor_set_path);
+
     tonic_build::configure()
         .build_client(build_client)
         .build_server(build_server)
         .out_dir(&tempdir)
-        .file_descriptor_set_path(file_descriptor_set_path)
-        .compile_protos(&iface_files, &include_dirs)
+        .compile_fds(fds)
         .unwrap();
 
     for path in std::fs::read_dir(tempdir.path()).unwrap() {
@@ -105,3 +115,10 @@ fn codegen(
         std::fs::copy(&path, &to).unwrap();
     }
 }
+
+fn write_fds(fds: &FileDescriptorSet, path: &Path) {
+    let mut writer = BufWriter::new(File::create(path).unwrap());
+    let mut buf = BytesMut::with_capacity(fds.encoded_len());
+    fds.encode(&mut buf).unwrap();
+    writer.write_all(&buf).unwrap();
+}