fix: Detect more kinds of FormData objects (#11)

src/__tests__/index.test.ts

@@ -4,7 +4,7 @@ import FormData from 'form-data';
 import nock from 'nock';
 import { Headers } from 'node-fetch';
 import { buildCall } from '../index';
-import { buildUrl, unwrapError } from '../common';
+import { buildUrl, isFormData, unwrapError } from '../common';
 import invariant from 'ts-invariant';
 import { createReadStream } from 'fs';
 import { TypicalHttpError } from '../types';
@@ -1195,7 +1195,6 @@ describe('call builder', () => {
         .method('get')
         .mapError((_) => 'error!')
         .mapError(async (err) => {
-          console.log(err);
           await new Promise((res) => setTimeout(res, 1));
           return err.toUpperCase();
         })
@@ -1311,4 +1310,16 @@ describe('buildUrl', () => {
       expect(scope.isDone()).toEqual(true);
     });
   });
+
+  describe('isFormData', () => {
+    it('smoke test', () => {
+      expect(isFormData(Buffer.from('asdf'))).toEqual(false);
+      expect(isFormData(new URLSearchParams())).toEqual(false);
+      expect(isFormData(undefined)).toEqual(false);
+      expect(isFormData(new FormData())).toEqual(true);
+      expect(
+        isFormData({ toString: () => '[object FormData]' } as any),
+      ).toEqual(true);
+    });
+  });
 });

src/common.ts

@@ -5,6 +5,21 @@ import { BodyInit, Headers, HeadersInit } from 'node-fetch';
 import invariant from 'ts-invariant';
 import { BodyType, CallRecord, QueryParam, TypicalWrappedError } from './types';
 
+/**
+ * Tries to detect if something is a FormData object. Since the consuming code
+ * may be using a different version of form-data than this lib, we can't trust
+ * the instanceof check to always work. The `form-data` package explicitly sets
+ * the return value of `someFormData.toString()` to `[object FormData]`, so we
+ * use that for the extra check.
+ * @param thing
+ * @returns
+ */
+export function isFormData(thing: BodyType | undefined): thing is FormData {
+  return thing == null
+    ? false
+    : thing instanceof FormData || thing.toString() === '[object FormData]';
+}
+
 export function getBodyInfo(data: BodyType | undefined): {
   body?: BodyInit;
   contentType?: string;
@@ -17,7 +32,7 @@ export function getBodyInfo(data: BodyType | undefined): {
     Buffer.isBuffer(data) ||
     data instanceof Readable ||
     data instanceof URLSearchParams ||
-    data instanceof FormData
+    isFormData(data)
   ) {
     return { body: data };
   } else {