if no plugins make middleware no-op (#948)

<!-- The PR description should answer 2 important questions: -->

### What

<!-- What is this PR trying to accomplish (and why, if it's not
obvious)? -->

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<!-- Does this PR introduce new validation that might break old builds?
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Just an improvement to the middleware plugin

### How

<!-- How is it trying to accomplish it (what are the implementation
steps)? -->

We now take a nonempty list of plugins. This ensures that we only do
things if we have plugins.

V3_GIT_ORIGIN_REV_ID: c8fb548f763cdefe3526c67d7c801104ad5c527a

v3/Cargo.lock

@@ -1729,6 +1729,7 @@ dependencies = [
  "json_value_merge",
  "lang-graphql",
  "metadata-resolve",
+ "nonempty",
  "open-dds",
  "opendds-derive",
  "pre-execution-plugin",
@@ -3615,6 +3616,7 @@ dependencies = [
  "axum",
  "hasura-authn-core",
  "lang-graphql",
+ "nonempty",
  "open-dds",
  "reqwest",
  "serde",

v3/crates/engine/Cargo.toml

@@ -40,6 +40,7 @@ axum = { workspace = true }
 base64 = { workspace = true }
 clap = { workspace = true, features = ["derive", "env"] }
 json_value_merge = { workspace = true }
+nonempty = { workspace = true }
 reqwest = { workspace = true, features = ["json", "multipart"] }
 schemars = { workspace = true, features = ["smol_str"] }
 serde = { workspace = true }

v3/crates/engine/bin/engine/main.rs

@@ -656,29 +656,34 @@ async fn handle_explain_request(
     response
 }
 
-async fn pre_execution_plugins_middleware<'a, B>(
+async fn pre_execution_plugins_middleware<'a>(
     State(engine_state): State<Arc<EngineState>>,
     Extension(session): Extension<Session>,
     headers_map: HeaderMap,
-    request: Request<B>,
+    request: Request<axum::body::Body>,
     next: Next<axum::body::Body>,
-) -> axum::response::Result<axum::response::Response>
-where
-    B: HttpBody,
-    B::Error: Display,
-{
-    let (request, response) = pre_execution_plugins_handler(
-        &engine_state.pre_parse_plugins,
-        &engine_state.http_context.client,
-        session,
-        request,
-        headers_map,
-    )
-    .await?;
+) -> axum::response::Result<axum::response::Response> {
+    // Check if the pre_execution_plugins_config is empty
+    match nonempty::NonEmpty::from_slice(&engine_state.pre_parse_plugins) {
+        None => {
+            // If empty, do nothing and pass the request to the next middleware
+            Ok(next.run(request).await)
+        }
+        Some(pre_parse_plugins) => {
+            let (request, response) = pre_execution_plugins_handler(
+                &pre_parse_plugins,
+                &engine_state.http_context.client,
+                session,
+                request,
+                headers_map,
+            )
+            .await?;
 
-    match response {
-        Some(response) => Ok(response),
-        None => Ok(next.run(request).await),
+            match response {
+                Some(response) => Ok(response),
+                None => Ok(next.run(request).await),
+            }
+        }
     }
 }
 

v3/crates/plugins/pre-execution-plugin/Cargo.toml

@@ -12,6 +12,7 @@ tracing-util = { path = "../../utils/tracing-util" }
 open-dds = { path = "../../open-dds" }
 
 axum = { workspace = true }
+nonempty = { workspace = true }
 reqwest = { workspace = true,  features = ["json"] }
 serde = { workspace = true }
 serde_json = { workspace = true }

v3/crates/plugins/pre-execution-plugin/src/execute.rs

@@ -212,7 +212,7 @@ pub async fn execute_plugin(
 }
 
 pub async fn pre_execution_plugins_handler<'a, B>(
-    pre_execution_plugins_config: &Vec<LifecyclePluginHookPreParse>,
+    pre_execution_plugins_config: &nonempty::NonEmpty<LifecyclePluginHookPreParse>,
     http_client: &reqwest::Client,
     session: Session,
     request: Request<B>,