How do I send raw binary data via HTTP in node.js? - node.js

Question

From a node.js back end, I need to send an HTTP message to a REST endpoint. The endpoint requires some parameters that it will expect to find in the HTTP message. Some of the parameters are simple enough, just requiring a number or a string as an argument. But one of the parameters is to be "the raw binary file content being uploaded" and this has puzzled me. As far as I understand, the parameters need to be gathered together into a string to put in the body of the HTTP request; How do I add raw binary data to a string? Obviously, for it to be in the string, it cannot be raw binary data; it needs to be encoded into characters.
The endpoint in question is the Twitter media upload API. The "raw binary data" parameter is called media. Below is an incomplete code snippet showing the basic gist of what I've tried. Specifically, the line where I build the requestBody string. I don't believe it is anywhere near correct, because the endpoint is returning a "bad request" message.
var https = require("https");
var base64ImageData = /* (some base 64 string here) */;
var options = {
host: "api.twitter.com",
path: "/1.1/media/upload.json",
method: "POST",
headers: {
"Content-Type": "multipart/form-data"
}
};
var request = https.request(options, function(response) {});
var requestBody = "media_id=18283918294&media=" + Buffer.from(base64ImageData, "base64").toString("binary");
request.write(requestBody);
request.end();
Also worth noting, Twitter themselves note the following extremely confusing statement:
"When posting base64 encoded images, be sure to set the “Content-Transfer-Encoding: base64” on the image part of the message."
Source: https://developer.twitter.com/en/docs/media/upload-media/uploading-media/media-best-practices
That might be part of the answer to my question, but what I don't understand is: How do I apply different headers to different parts of the HTTP message? Because apparently, the image data needs to have a Content-Transfer-Encoding header of "base64" while the rest of the HTTP message does not...

Answer 1

How do I apply different headers to different parts of the HTTP message?
This is the point of the multipart/form-data content type. A multi-part message looks like this:
Content-Type: multipart/form-data; boundary=---foo---
---foo---
Content-Disposition: form-data; name="datafile1"; filename="r.gif"
Content-Transfer-Encoding: base64
Content-Type: image/gif
// data goes here
---foo---
Content-Disposition: form-data; name="datafile2"; filename="g.png"
Content-Transfer-Encoding: base64
Content-Type: image/png
// another file's data goes here
---foo---
You probably don't want to put all this together yourself. There are a bunch of good libraries for putting together complex POSTs. For example: https://www.npmjs.com/package/form-data