Sending Multipart form using string body

Question

I have seen almost all answers in relation to this suggest to use some variant of FormData within nodejs to build a multipart form.

I wish to achieve the same without using the FormData library, but instead just using request headers and a string for the request body.

Only one answer hints at how this can be achieved, but the solution uses a stringify function on the string payload so I am not sure how the correct stringified body should look like.

Regardless, I have gotten this far;

import { RequestOptions } from "http"

const path: 'url/'
const method: 'POST'

const body = `--BOUNDARY
\nContent-Disposition: form-data; name="file"; filename="test.txt"
\nContent-Type: text/plain
\nThis is the content of the file
\n--BOUNDARY
\nContent-Disposition: form-data; name="form-field-one"
\nexample1
\n--BOUNDARY
\nContent-Disposition: form-data; name="form-field-two"
\nexample2
\n--BOUNDARY--`

const headers = {
  'content-type': 'multipart/form-data; boundary=BOUNDARY',
  'content-length': String(Buffer.byteLength(body))
}

const options = {
  path,
  method,
  headers,
  body
}

const response = await execute(options)

I cannot create a fully minimal reproduction as I am not permitted to post the execute function contents, but I can describe the function signature I need to use (which is why I need to use this string approach).

For what its worth, i think the function is simply using the basic builtin nodejs http library.

import { RequestOptions } from "http"

const execute = async (options: RequestOptions): Promise<any> => { ... }

I get an error using this, but the error is not helpful at all due to the internals of the function.

Regardless, I believe it should be possible to replicate sending a multi-part form (with file and form fields) using just the body and headers of a POST request without an additional library to transform the data of the body.

My string is a modified output from a successful Postman request multipart form request.

Can someone point out what I am doing incorrectly?

Heiko Theißen · Accepted Answer · 2022-12-22 13:53:32Z

1

Several points:

Every line in your `...` already ends with a newline, but the next starts with \n, which contributes another newline, leading to an unwanted blank line.
You do need a blank line between the headers and content.
Lines must end with CRLF, so you must add a \r as the last character on each line.

Try this:

const body = `--BOUNDARY\r
Content-Disposition: form-data; name="file"; filename="test.txt"\r
Content-Type: text/plain\r
\r
This is the content of the file\r
--BOUNDARY\r
Content-Disposition: form-data; name="form-field-one"\r
\r
example1\r
--BOUNDARY\r
Content-Disposition: form-data; name="form-field-two"\r
\r
example2\r
--BOUNDARY--`

edited Dec 22, 2022 at 13:53

answered Dec 22, 2022 at 13:47

Heiko Theißen

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