feat: Implement gRPC Reflection Service (#340)

Co-authored-by: Samani G. Gikandi <[email protected]>

tonic/src/macros.rs

@@ -33,3 +33,43 @@ macro_rules! include_proto {
         include!(concat!(env!("OUT_DIR"), concat!("/", $package, ".rs")));
     };
 }
+
+/// Include an encoded `prost_types::FileDescriptorSet` as a `&'static [u8]`. The parameter must be
+/// the stem of the filename passed to `file_descriptor_set_path` for the `tonic-build::Builder`,
+/// excluding the `.bin` extension.
+///
+/// For example, a file descriptor set compiled like this in `build.rs`:
+///
+/// ```rust,ignore
+/// let descriptor_path = PathBuf::from(env::var("OUT_DIR").unwrap()).join("my_descriptor.bin")
+/// tonic_build::configure()
+///     .file_descriptor_set_path(&descriptor_path)
+///     .format(true)
+///     .compile(&["proto/reflection.proto"], &["proto/"])?;
+/// ```
+///
+/// Can be included like this:
+///
+/// ```rust,ignore
+/// mod pb {
+///     pub(crate) const FILE_DESCRIPTOR_SET: &[u8] = tonic::include_file_descriptor_set!("my_descriptor");
+/// }
+/// ```
+///
+/// # Note:
+/// **This only works if the tonic-build output directory has been unmodified**.
+/// The default output directory is set to the [`OUT_DIR`] environment variable.
+/// If the output directory has been modified, the following pattern may be used
+/// instead of this macro.
+///
+/// ```rust,ignore
+/// mod pb {
+///     pub(crate) const FILE_DESCRIPTOR_SET: &[u8] = include_bytes!("/relative/protobuf/directory/descriptor_name.bin");
+/// }
+/// ```
+#[macro_export]
+macro_rules! include_file_descriptor_set {
+    ($package: tt) => {
+        include_bytes!(concat!(env!("OUT_DIR"), concat!("/", $package, ".bin")))
+    };
+}