Update StatusBody to support gRPC trailers

Change StatusBody from a tuple struct to a struct containing both data
and trailers. Update the codegen to use the new StatusBody::new
constructor to specify gRPC status codes.

Also remove the temp_test_project.

roto-tonic/Cargo.toml

@@ -12,3 +12,4 @@ http-body = "1.0"
 http-body-util = "0.1"
 tower = "0.4"
 futures-util = "0.3"
+http = "1.1"

roto-tonic/src/lib.rs

@@ -101,7 +101,21 @@ impl BufferPool {
     }
 }
 
-pub struct StatusBody(pub Option<Bytes>);
+pub struct StatusBody {
+    pub data: Option<Bytes>,
+    pub trailers: Option<http::HeaderMap>,
+}
+
+impl StatusBody {
+    pub fn new(data: Option<Bytes>, status: u8) -> Self {
+        let mut trailers = http::HeaderMap::new();
+        trailers.insert("grpc-status", status.to_string().parse().unwrap());
+        Self {
+            data,
+            trailers: Some(trailers),
+        }
+    }
+}
 
 impl Body for StatusBody {
     type Data = Bytes;
@@ -111,8 +125,10 @@ impl Body for StatusBody {
         mut self: Pin<&mut Self>,
         cx: &mut Context<'_>,
     ) -> Poll<Option<Result<http_body::Frame<Self::Data>, Self::Error>>> {
-        if let Some(data) = self.0.take() {
+        if let Some(data) = self.data.take() {
             Poll::Ready(Some(Ok(http_body::Frame::data(data))))
+        } else if let Some(trailers) = self.trailers.take() {
+            Poll::Ready(Some(Ok(http_body::Frame::trailers(trailers))))
         } else {
             Poll::Ready(None)
         }