Improve resource loader error reporting and thumbnail uploads

assets/scripts/pages/resource-loader.js

@@ -107,10 +107,26 @@
     els.syncStatus.querySelector("small").textContent = label;
   }
 
+  async function responseError(response, prefix) {
+    let detail = "";
+    try {
+      const contentType = response.headers.get("Content-Type") || "";
+      if (contentType.includes("application/json")) {
+        const body = await response.json();
+        detail = body && body.message ? body.message : "";
+      } else {
+        detail = (await response.text()).trim().slice(0, 240);
+      }
+    } catch (_) {
+      detail = "";
+    }
+    return new Error(`${prefix} (${response.status})${detail ? `: ${detail}` : ""}`);
+  }
+
   async function fetchServerLibrary() {
     const response = await fetch(API_URL, { cache: "no-store", credentials: "same-origin" });
     if (response.status === 404) return null;
-    if (!response.ok) throw new Error(`Server library request failed (${response.status}).`);
+    if (!response.ok) throw await responseError(response, "Server library request failed");
     const library = Model.normaliseLibrary(await response.json());
     state.serverEtag = response.headers.get("ETag");
     return library;
@@ -128,7 +144,7 @@
         headers: { "Content-Type": attachment.type || attachment.blob.type || "image/jpeg" },
         body: attachment.blob,
       });
-      if (!response.ok) throw new Error(`Thumbnail upload failed (${response.status}).`);
+      if (!response.ok) throw await responseError(response, "Thumbnail upload failed");
       await deleteAttachment(id);
       state.uploadedThumbnails.add(id);
     }));
@@ -153,10 +169,13 @@
       toast("Changes from another device were merged.");
       return pushServerLibrary(merged, false);
     }
-    if (!response.ok) throw new Error(`Server save failed (${response.status}).`);
+    if (!response.ok) throw await responseError(response, "Server save failed");
     state.serverEtag = response.headers.get("ETag");
-    await uploadLocalThumbnails(library);
     setSyncStatus("synced", "synced to server");
+    uploadLocalThumbnails(library).catch((error) => {
+      console.warn("Resource Loader metadata was saved, but a cover could not be uploaded.", error);
+      toast(`Saved to the server. Cover upload pending: ${error.message}`, true);
+    });
   }
 
   async function saveLibrary() {