Mention option to pass streams into FormData (#3086)

README.md

@@ -248,6 +248,18 @@ const data = {
 await fetch('https://example.com', { body: data, method: 'POST', duplex: 'half' })
 ```
 
+[FormData](https://developer.mozilla.org/en-US/docs/Web/API/FormData) besides text data and buffers can also utilize streams via [Blob](https://developer.mozilla.org/en-US/docs/Web/API/Blob) objects:
+
+```js
+import { openAsBlob } from 'node:fs'
+
+const file = await openAsBlob('./big.csv')
+const body = new FormData()
+body.set('file', file, 'big.csv')
+
+await fetch('http://example.com', { method: 'POST', body })
+```
+
 #### `request.duplex`
 
 - half

docs/examples/README.md

@@ -71,6 +71,33 @@ async function postFormRequest (port = 3001) {
 }
 ```
 
+### A FormData request with file stream, read the response body as text
+
+```js
+const { request } = require('undici')
+const { openAsBlob } = require('fs')
+
+async function formDataBlobRequest () {
+  // Make a FormData request with file stream:
+
+  const formData = new FormData()
+  formData.append('field', 42)
+  formData.set('file', await openAsBlob('./index.mjs'))
+
+  const response = await request('http://127.0.0.1:3000', {
+    method: 'POST',
+    body: formData
+  })
+  console.log(await response.body.text())
+
+  const data = await body.text()
+  console.log('response received', statusCode)
+  console.log('headers', headers)
+  console.log('data', data)
+}
+
+```
+
 ### A DELETE request
 ```js
 const { request } = require('undici')