Byte order marks on challenge response

[ytechie]

I set up a Node.js server to respond to the API challange request for a webhook. I can't seem to get it to accept the challenge. I can't tell if it's appending byte order marks, or if Node.js is secretly sending them. I masked out some of the info below, but I kept the key parts.

Notice the extra "\xef\xbb\xbf" prepended to the challenge response.

Error: Incorrect response to challenge. We didn't receive the expected response xxxxx. See the actual response body we received below.

Request:
GET http://xxxx.ngrok.io/api/DropboxWebhook?challenge=xxxxx

Response:
HTTP/1.1 200 OK
Transfer-Encoding: chunked
Server: Microsoft-HTTPAPI/2.0
Connection: keep-alive
Date: Wed, 28 Dec 2016 18:10:30 GMT
Content-Type: text/plain; charset=utf-8

Response Body (First 256 bytes):
\xef\xbb\xbfxxxxx

[Greg-DB]

The Dropbox webhook challenge string doesn't contain a BOM, so the Dropbox webhooks service doesn't expect one in the echoed string. That being the case, it does look like something on your side is adding it.

Unfortunately, that sounds like an issue with Node or your code itself, so I'm afraid I can't offer much insight. Perhaps someone else here is familiar with it though and can help if you share your code.

[ytechie · Accepted solution]

It was an issue specific to Azure Functions. The fix was to use a content type of "application/octet-stream".

Here is code that I confirmed works with dropbox:

res = {
            body: challenge,
            headers: {
                'Content-Type': 'application/octet-stream'
            }
        };