fix(multipart): optional content-disposition for non-form-data requests (#3416)

actix-multipart/examples/form.rs

@@ -0,0 +1,36 @@
+use actix_multipart::form::{json::Json as MpJson, tempfile::TempFile, MultipartForm};
+use actix_web::{middleware::Logger, post, App, HttpServer, Responder};
+use serde::Deserialize;
+
+#[derive(Debug, Deserialize)]
+struct Metadata {
+    name: String,
+}
+
+#[derive(Debug, MultipartForm)]
+struct UploadForm {
+    #[multipart(limit = "100MB")]
+    file: TempFile,
+    json: MpJson<Metadata>,
+}
+
+#[post("/videos")]
+async fn post_video(MultipartForm(form): MultipartForm<UploadForm>) -> impl Responder {
+    format!(
+        "Uploaded file {}, with size: {}\ntemporary file ({}) was deleted\n",
+        form.json.name,
+        form.file.size,
+        form.file.file.path().display(),
+    )
+}
+
+#[actix_web::main]
+async fn main() -> std::io::Result<()> {
+    env_logger::init_from_env(env_logger::Env::new().default_filter_or("info"));
+
+    HttpServer::new(move || App::new().service(post_video).wrap(Logger::default()))
+        .workers(2)
+        .bind(("127.0.0.1", 8080))?
+        .run()
+        .await
+}