Add local repo contents

backend/src/lib/upload.ts

@@ -0,0 +1,36 @@
+import type { RequestHandler } from "express";
+import multer from "multer";
+
+export const MAX_UPLOAD_SIZE_BYTES = 100 * 1024 * 1024;
+export const MAX_UPLOAD_SIZE_MB = Math.round(
+  MAX_UPLOAD_SIZE_BYTES / (1024 * 1024),
+);
+
+const memoryUpload = multer({
+  storage: multer.memoryStorage(),
+  limits: {
+    fileSize: MAX_UPLOAD_SIZE_BYTES,
+    files: 1,
+  },
+});
+
+export function singleFileUpload(fieldName: string): RequestHandler {
+  return (req, res, next) => {
+    memoryUpload.single(fieldName)(req, res, (err) => {
+      if (!err) return next();
+
+      if (err instanceof multer.MulterError) {
+        if (err.code === "LIMIT_FILE_SIZE") {
+          return void res.status(413).json({
+            detail: `File too large. Maximum size is ${MAX_UPLOAD_SIZE_MB} MB.`,
+          });
+        }
+        return void res.status(400).json({
+          detail: `Upload failed: ${err.message}`,
+        });
+      }
+
+      return next(err);
+    });
+  };
+}