feat: add envelopes api (#2105)

packages/trpc/utils/zod-form-data.ts

@@ -0,0 +1,32 @@
+import type { ZodRawShape } from 'zod';
+import z from 'zod';
+
+/**
+ * This helper takes the place of the `z.object` at the root of your schema.
+ * It wraps your schema in a `z.preprocess` that extracts all the data out of a `FormData`
+ * and transforms it into a regular object.
+ * If the `FormData` contains multiple entries with the same field name,
+ * it will automatically turn that field into an array.
+ *
+ * This is used instead of `zfd.formData()` because it receives `undefined`
+ * somewhere in the pipeline of our openapi schema generation and throws
+ * an error. This provides the same functionality as `zfd.formData()` but
+ * can be considered somewhat safer.
+ */
+export const zodFormData = <T extends ZodRawShape>(schema: T) => {
+  return z.preprocess((data) => {
+    if (data instanceof FormData) {
+      const formData: Record<string, unknown> = {};
+
+      for (const key of data.keys()) {
+        const values = data.getAll(key);
+
+        formData[key] = values.length > 1 ? values : values[0];
+      }
+
+      return formData;
+    }
+
+    return data;
+  }, z.object(schema));
+};