Simplify the request limiting

src/api/client_server/media.rs

@@ -13,7 +13,6 @@ use {
     webpage::HTML,
     reqwest::Url,
     std::{io::Cursor, net::IpAddr, sync::Arc},
-    tokio::sync::Notify,
     image::io::Reader as ImgReader,
 };
 
@@ -198,49 +197,21 @@ async fn get_url_preview(url: &str) -> Result<UrlPreviewData> {
         return Ok(preview);
     }
 
-    let notif_opt = services()
+    // ensure that only one request is made per URL
-        .media
+    let mutex_request = Arc::clone(
-        .url_preview_requests
+        services()
-        .read()
+            .media
-        .unwrap()
+            .url_preview_mutex
-        .get(url)
+            .write()
-        .cloned();
+            .unwrap()
+            .entry(url.to_owned())
+            .or_default(),
+    );
+    let _request_lock = mutex_request.lock().await;
 
-    match notif_opt {
+    match services().media.get_url_preview(url).await {
-        None => {
+        Some(preview) => Ok(preview),
-            let notifier = Arc::new(Notify::new());
+        None => request_url_preview(url).await
-            {
-                services().media
-                    .url_preview_requests
-                    .write()
-                    .unwrap()
-                    .insert(url.to_owned(), notifier.clone());
-            }
-
-            let data = request_url_preview(url).await;
-
-            notifier.notify_waiters();
-
-            {
-                services().media.url_preview_requests.write().unwrap().remove(url);
-            }
-
-            data
-        }
-        Some(notifier) => {
-            // wait until being notified that request is finished
-            let notifier = notifier.clone();
-            let notifier = notifier.notified();
-            notifier.await;
-
-            services().media
-                .get_url_preview(url)
-                .await
-                .ok_or(Error::BadRequest(
-                    ErrorKind::Unknown,
-                    "No Preview available",
-                ))
-        }
     }
 }
 

src/service/media/mod.rs

@@ -14,7 +14,7 @@ use image::imageops::FilterType;
 use tokio::{
     fs::File,
     io::{AsyncReadExt, AsyncWriteExt, BufReader},
-    sync::Notify,
+    sync::Mutex,
 };
 use serde::Serialize;
 
@@ -60,7 +60,7 @@ pub struct UrlPreviewData {
 
 pub struct Service {
     pub db: &'static dyn Data,
-    pub url_preview_requests: RwLock<HashMap<String, Arc<Notify>>>,
+    pub url_preview_mutex: RwLock<HashMap<String, Arc<Mutex<()>>>>,
 }
 
 impl Service {

src/service/mod.rs

@@ -120,7 +120,7 @@ impl Services {
             key_backups: key_backups::Service { db },
             media: media::Service {
                 db,
-                url_preview_requests: StdRwLock::new(HashMap::new())
+                url_preview_mutex: StdRwLock::new(HashMap::new()),
             },
             sending: sending::Service::build(db, &config),