feat: add support for multipart/form-data

lib/fetch/body.js

@@ -1,5 +1,6 @@
 'use strict'
 
+const Busboy = require('busboy')
 const util = require('../core/util')
 const { ReadableStreamFrom, toUSVString, isBlobLike } = require('./util')
 const { FormData } = require('./formdata')
@@ -8,9 +9,9 @@ const { webidl } = require('./webidl')
 const { Blob } = require('buffer')
 const { kBodyUsed } = require('../core/symbols')
 const assert = require('assert')
-const { NotSupportedError } = require('../core/errors')
 const { isErrored } = require('../core/util')
 const { isUint8Array, isArrayBuffer } = require('util/types')
+const { File } = require('./file')
 
 let ReadableStream
 
@@ -397,7 +398,40 @@ function bodyMixinMethods (instance) {
 
       // If mimeType’s essence is "multipart/form-data", then:
       if (/multipart\/form-data/.test(contentType)) {
-        throw new NotSupportedError('multipart/form-data not supported')
+        const headers = {}
+        for (const [key, value] of this.headers) headers[key.toLowerCase()] = value
+
+        const responseFormData = new FormData()
+
+        try {
+          const busboy = Busboy({ headers })
+          busboy.on('field', (name, value) => {
+            responseFormData.append(name, value)
+          })
+          busboy.on('file', (name, value, info) => {
+            const { filename, encoding, mimeType } = info
+            const base64 = encoding.toLowerCase() === 'base64'
+            const chunks = []
+            value.on('data', (chunk) => {
+              if (base64) chunk = Buffer.from(chunk.toString(), 'base64')
+              chunks.push(chunk)
+            })
+            value.on('end', () => {
+              const file = new File(chunks, filename, { type: mimeType })
+              responseFormData.append(name, file)
+            })
+          })
+          const busboyResolve = new Promise((resolve) => busboy.on('finish', resolve))
+
+          if (this.body !== null) for await (const chunk of consumeBody(this[kState].body)) busboy.write(chunk)
+          busboy.end()
+          await busboyResolve
+        } catch (err) {
+          // busboy may fail to parse a malformed body, so throw a type error
+          throw Object.assign(new TypeError(), { cause: err })
+        }
+
+        return responseFormData
       } else if (/application\/x-www-form-urlencoded/.test(contentType)) {
         // Otherwise, if mimeType’s essence is "application/x-www-form-urlencoded", then:
 

test/fetch/client-fetch.js

@@ -165,21 +165,38 @@ test('unsupported formData 1', (t) => {
   })
 })
 
-test('unsupported formData 2', (t) => {
-  t.plan(1)
+test('multipart formdata', async (t) => {
+  t.plan(2)
+
+  // Construct example form data, with text and file fields
+  const formData = new FormData()
+  formData.append('field1', 'value1')
+  const blob = new Blob(['example\ntext file'], { type: 'text/plain' })
+  formData.append('field2', blob, 'file.txt')
+
+  const tempRes = new Response(formData)
+  const boundary = tempRes.headers.get('content-type').split('boundary=')[1]
+  const formRaw = await tempRes.text()
 
   const server = createServer((req, res) => {
-    res.setHeader('content-type', 'multipart/form-data')
+    res.setHeader('content-type', 'multipart/form-data; boundary=' + boundary)
+    res.write(formRaw)
     res.end()
   })
   t.teardown(server.close.bind(server))
 
-  server.listen(0, () => {
-    fetch(`http://localhost:${server.address().port}`)
-      .then(res => res.formData())
-      .catch(err => {
-        t.equal(err.name, 'NotSupportedError')
-      })
+  await new Promise((resolve) => {
+    server.listen(0, () => {
+      fetch(`http://localhost:${server.address().port}`)
+        .then(res => res.formData())
+        .then(formData => {
+          t.equal(formData.get('field1'), 'value1')
+          return formData.get('field2').text()
+        }).then(text => {
+          t.equal(text, 'example\ntext file')
+          resolve()
+        })
+    })
   })
 })