feat: Implement gRPC Reflection Service (#340)

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

tonic-build/src/prost.rs

@@ -12,6 +12,7 @@ pub fn configure() -> Builder {
     Builder {
         build_client: true,
         build_server: true,
+        file_descriptor_set_path: None,
         out_dir: None,
         extern_path: Vec::new(),
         field_attributes: Vec::new(),
@@ -189,6 +190,7 @@ impl prost_build::ServiceGenerator for ServiceGenerator {
 pub struct Builder {
     pub(crate) build_client: bool,
     pub(crate) build_server: bool,
+    pub(crate) file_descriptor_set_path: Option<PathBuf>,
     pub(crate) extern_path: Vec<(String, String)>,
     pub(crate) field_attributes: Vec<(String, String)>,
     pub(crate) type_attributes: Vec<(String, String)>,
@@ -213,6 +215,13 @@ impl Builder {
         self
     }
 
+    /// Generate a file containing the encoded `prost_types::FileDescriptorSet` for protocol buffers
+    /// modules. This is required for implementing gRPC Server Reflection.
+    pub fn file_descriptor_set_path(mut self, path: impl AsRef<Path>) -> Self {
+        self.file_descriptor_set_path = Some(path.as_ref().to_path_buf());
+        self
+    }
+
     /// Enable the output to be formated by rustfmt.
     #[cfg(feature = "rustfmt")]
     pub fn format(mut self, run: bool) -> Self {
@@ -305,6 +314,9 @@ impl Builder {
         let format = self.format;
 
         config.out_dir(out_dir.clone());
+        if let Some(path) = self.file_descriptor_set_path.as_ref() {
+            config.file_descriptor_set_path(path);
+        }
         for (proto_path, rust_path) in self.extern_path.iter() {
             config.extern_path(proto_path, rust_path);
         }