feat: accept third-party Blobs in FormData

lib/fetch/formdata.js

@@ -1,9 +1,8 @@
 'use strict'
 
-const { Blob } = require('buffer')
+const { isBlobLike, toUSVString } = require('./util')
 const { kState } = require('./symbols')
 const { File } = require('./file')
-const { toUSVString } = require('./util')
 
 class FormData {
   constructor (...args) {
@@ -25,7 +24,7 @@ class FormData {
         `Failed to execute 'append' on 'FormData': 2 arguments required, but only ${args.length} present.`
       )
     }
-    if (args.length === 3 && !(args[1] instanceof Blob)) {
+    if (args.length === 3 && !isBlobLike(args[1])) {
       throw new TypeError(
         "Failed to execute 'append' on 'FormData': parameter 2 is not of type 'Blob'"
       )
@@ -34,7 +33,7 @@ class FormData {
     const filename = args.length === 3 ? toUSVString(args[2]) : undefined
 
     // 1. Let value be value if given; otherwise blobValue.
-    const value = args[1] instanceof Blob ? args[1] : toUSVString(args[1])
+    const value = isBlobLike(args[1]) ? args[1] : toUSVString(args[1])
 
     // 2. Let entry be the result of creating an entry with
     // name, value, and filename if given.
@@ -135,7 +134,7 @@ class FormData {
         `Failed to execute 'set' on 'FormData': 2 arguments required, but only ${args.length} present.`
       )
     }
-    if (args.length === 3 && !(args[1] instanceof Blob)) {
+    if (args.length === 3 && !isBlobLike(args[1])) {
       throw new TypeError(
         "Failed to execute 'set' on 'FormData': parameter 2 is not of type 'Blob'"
       )
@@ -147,7 +146,7 @@ class FormData {
     // are:
 
     // 1. Let value be value if given; otherwise blobValue.
-    const value = args[1] instanceof Blob ? args[1] : toUSVString(args[1])
+    const value = isBlobLike(args[1]) ? args[1] : toUSVString(args[1])
 
     // 2. Let entry be the result of creating an entry with name, value, and
     // filename if given.
@@ -214,7 +213,7 @@ function makeEntry (name, value, filename) {
 
   // 3. If value is a Blob object and not a File object, then set value to a new File
   // object, representing the same bytes, whose name attribute value is "blob".
-  if (value instanceof Blob && !(value instanceof File)) {
+  if (isBlobLike(value) && !(value instanceof File)) {
     value = new File([value], 'blob')
   }
 

lib/fetch/util.js

@@ -2,6 +2,7 @@
 
 const { redirectStatus } = require('./constants')
 const { performance } = require('perf_hooks')
+const { Blob } = require('buffer')
 const nodeUtil = require('util')
 
 let ReadableStream
@@ -68,6 +69,18 @@ function requestBadPort (request) {
   return 'allowed'
 }
 
+// based on https://github.com/node-fetch/fetch-blob/blob/8ab587d34080de94140b54f07168451e7d0b655e/index.js#L229-L241 (MIT License)
+function isBlobLike (object) {
+  return object instanceof Blob || (
+    object &&
+    typeof object === 'object' &&
+    typeof object.constructor === 'function' &&
+    (typeof object.stream === 'function' ||
+      typeof object.arrayBuffer === 'function') &&
+    /^(Blob|File)$/.test(object[Symbol.toStringTag])
+  )
+}
+
 // Check whether |statusText| is a ByteString and
 // matches the Reason-Phrase token production.
 // RFC 2616: https://tools.ietf.org/html/rfc2616
@@ -349,5 +362,6 @@ module.exports = {
   requestCurrentURL,
   responseURL,
   responseLocationURL,
+  isBlobLike,
   isValidReasonPhrase
 }

package.json

@@ -63,6 +63,7 @@
     "cronometro": "^0.8.0",
     "delay": "^5.0.0",
     "docsify-cli": "^4.4.3",
+    "formdata-node": "^4.3.1",
     "https-pem": "^2.0.0",
     "husky": "^7.0.2",
     "jest": "^27.2.0",

test/fetch/formdata.js

@@ -2,6 +2,7 @@
 
 const { test } = require('tap')
 const { FormData, File } = require('../../')
+const { Blob: ThirdPartyBlob } = require('formdata-node')
 const { Blob } = require('buffer')
 
 test('arg validation', (t) => {
@@ -104,6 +105,18 @@ test('append blob', async (t) => {
   t.end()
 })
 
+test('append third-party blob', async (t) => {
+  const form = new FormData()
+  form.set('asd', new ThirdPartyBlob(['asd1']))
+
+  t.equal(form.has('asd'), true)
+  t.equal(await form.get('asd').text(), 'asd1')
+  form.delete('asd')
+  t.equal(form.get('asd'), null)
+
+  t.end()
+})
+
 test('append string', (t) => {
   const form = new FormData()
   form.set('k1', 'v1')