feat: preserve user-agent header (#2290)

Co-authored-by: Lucio Franco <luciofranco14@gmail.com>

Author: dbolduc

tonic/src/metadata/map.rs

@@ -214,9 +214,8 @@ pub(crate) const GRPC_TIMEOUT_HEADER: &str = "grpc-timeout";
 
 impl MetadataMap {
     // Headers reserved by the gRPC protocol.
-    pub(crate) const GRPC_RESERVED_HEADERS: [HeaderName; 6] = [
+    pub(crate) const GRPC_RESERVED_HEADERS: [HeaderName; 5] = [
         HeaderName::from_static("te"),
-        HeaderName::from_static("user-agent"),
         HeaderName::from_static("content-type"),
         HeaderName::from_static("grpc-message"),
         HeaderName::from_static("grpc-message-type"),

tonic/src/request.rs

@@ -462,6 +462,25 @@ mod tests {
         assert!(http_request.headers().is_empty());
     }
 
+    #[test]
+    fn preserves_user_agent() {
+        let mut r = Request::new(1);
+
+        r.metadata_mut().insert(
+            MetadataKey::from_static("user-agent"),
+            MetadataValue::from_static("Custom/1.2.3"),
+        );
+
+        let http_request = r.into_http(
+            Uri::default(),
+            http::Method::POST,
+            http::Version::HTTP_2,
+            SanitizeHeaders::Yes,
+        );
+        let user_agent = http_request.headers().get("user-agent").unwrap();
+        assert_eq!(user_agent, "Custom/1.2.3");
+    }
+
     #[test]
     fn duration_to_grpc_timeout_less_than_second() {
         let timeout = Duration::from_millis(500);