Code review notes

Name macro to reflect underlying NGINX type

src/http/request.rs

@@ -117,12 +117,16 @@ impl Request {
 
     /// Returns the result as an `Option` if it exists, otherwise `None`.
     ///
-    /// The option wraps a pointer to a [`ngx_http_upstream_t`] upstream server object.
+    /// The option wraps an ngx_http_upstream_t instance, it will be none when the underlying NGINX request
+    /// does not have a pointer to a [`ngx_http_upstream_t`] upstream structure.
     ///
     /// [`ngx_http_upstream_t`]: is best described in
     /// https://nginx.org/en/docs/dev/development_guide.html#http_request
     /// https://nginx.org/en/docs/dev/development_guide.html#http_load_balancing
     pub fn upstream(&self) -> Option<*mut ngx_http_upstream_t> {
+        if self.0.upstream.is_null() {
+            return None;
+        }
         Some(self.0.upstream)
     }
 

src/http/upstream.rs

@@ -2,9 +2,15 @@
 ///
 /// Initializes the upstream 'get', 'free', and 'session' callbacks and gives the module writer an
 /// opportunity to set custom data.
+///
+/// This macro will define the NGINX callback type:
+/// `typedef ngx_int_t (*ngx_http_upstream_init_peer_pt)(ngx_http_request_t *r, ngx_http_upstream_srv_conf_t *us)`,
+/// we keep this macro name in-sync with its underlying NGINX type, this callback is required to
+/// initialize your peer.
+///
 /// Load Balancing: <https://nginx.org/en/docs/dev/development_guide.html#http_load_balancing>
 #[macro_export]
-macro_rules! http_upstream_peer_init {
+macro_rules! http_upstream_init_peer_pt {
     ( $name: ident, $handler: expr ) => {
         #[no_mangle]
         extern "C" fn $name(r: *mut ngx_http_request_t, us: *mut ngx_http_upstream_srv_conf_t) -> ngx_int_t {