code quality improvements and improved file error handling

src/components/SettingForms/System/Upload.ts

@@ -0,0 +1,64 @@
+// CORS (server missing Access-Control-Allow-* headers)??
+
+type BlobFileUpload = {
+  file: File | null;
+  opts?: {
+    timeoutMs?: number;
+    fieldName?: string;
+    overrideFileName?: string;
+    uploadUrl: URL | string;
+  };
+};
+
+export async function sendBlobFileUpload({
+  file,
+  opts,
+}: BlobFileUpload): Promise<string> {
+  if (!file) throw new Error("No file supplied");
+  if (!opts?.uploadUrl) throw new Error("No URL supplied");
+
+  if (file?.type !== "text/csv") {
+    throw new Error("This file is not supported, please upload a CSV file.");
+  }
+  const timeoutMs = opts?.timeoutMs ?? 30000;
+  const fieldName = opts?.fieldName ?? "upload";
+  const fileName = opts?.overrideFileName ?? file?.name;
+
+  const controller = new AbortController();
+  const timeout = setTimeout(() => controller.abort(), timeoutMs);
+
+  try {
+    const form = new FormData();
+
+    form.append(fieldName, file, fileName);
+
+    const resp = await fetch(opts?.uploadUrl, {
+      method: "POST",
+      body: form,
+      signal: controller.signal,
+      redirect: "follow",
+    });
+
+    const bodyText = await resp.text();
+
+    if (!resp.ok) {
+      throw new Error(
+        `Upload failed (${resp.status} ${resp.statusText}) from ${opts.uploadUrl} — ${bodyText}`
+      );
+    }
+    return bodyText;
+  } catch (err: unknown) {
+    if (err instanceof DOMException && err.name === "AbortError") {
+      throw new Error(`Timeout uploading to ${opts.uploadUrl}.`);
+    }
+    // In browsers, fetch throws TypeError on network-level failures
+    if (err instanceof TypeError) {
+      throw new Error(
+        `HTTP error uploading to ${opts.uploadUrl}: ${err.message}`
+      );
+    }
+    throw new Error("HTTP method POST is not supported by this URL");
+  } finally {
+    clearTimeout(timeout);
+  }
+}