Uploading an image using the Dropbox API

I am trying to upload an image to Dropbox using the Dropbox API and Matlab's webwrite function. I get a successful response when running the below code. However, the response says 'size: 215' when I know the size of the image should be lower than that. Furthermore, the image uploaded to Dropbox appears to be corrupted. It does not preview, and after I download and try to open the uploaded image, it does not register as a valid image. I think the issue might have something to do with the encoding, but I can't figure it out. When I use this same code to upload a plain text file with ASCII characters, it works without any problem. Does anyone know what the problem might be?

% Read the file from disk
fid = fopen(dataFile, 'r');
data = char(fread(fid)');
fclose(fid);
 
[~,remoteFName, remoteExt] = fileparts(dataFile);
headerFields = {'Authorization', ['Bearer ', dropboxAccessToken]};
headerFields{2,1} = 'Dropbox-API-Arg';
headerFields{2,2} = sprintf('{"path": "/%s%s", "mode": "add", "autorename": true, "mute": false}',remoteFName, remoteExt);
 
headerFields{3,1} = 'Content-Type';
headerFields{3,2} = 'application/octet-stream';
 
headerFields = string(headerFields);
 
 
% Set the options for WEBWRITE
opt = weboptions;
opt.MediaType = 'application/octet-stream';
opt.CharacterEncoding = 'ISO-8859-1';
opt.RequestMethod = 'post';
opt.HeaderFields = headerFields;
 
 
% Upload the file
try
   tempOutput = webwrite('https://content.dropboxapi.com/2/files/upload', data, opt);
catch someException
   disp(someException);
   throw(addCause(MException('uploadToDropbox:unableToUploadFile','Unable to upload file.'),someException));
end
 
 

Output:

RESPONSE

HTTP/1.1 200 OK

Cache-Control: no-cache

X-Content-Type-Options: nosniff

X-Server-Response-Time: 901

Content-Type: application/json

Accept-Encoding: identity,gzip

Date: Thu, 21 Apr 2022 01:25:01 GMT

Server: envoy

Strict-Transport-Security: max-age=31536000; includeSubDomains; preload

X-Robots-Tag: noindex, nofollow, noimageindex

Content-Encoding: gzip

Vary: Accept-Encoding

X-Dropbox-Response-Origin: far_remote

X-Dropbox-Request-Id: 12cee658f5604167905348fd834c35d5

Transfer-Encoding: chunked

name: 'swiss.png'

path_lower: '/swiss.png'

path_display: '/swiss.png'

id: 'id:B71uxiCfSp4AAAAAAAAAOQ'

client_modified: '2022-04-21T01:25:00Z'

server_modified: '2022-04-21T01:25:01Z'

rev: '015dd1ffa916ba20000000266082110'

size: 215

is_downloadable: 1

content_hash: 'e87f106dcb11834c94b28b84ac739413b24390fae01127db49b81dcad29c62ae'

[Rik]

Maybe the problem is because you have cast your data to char instead of uint8.

I also noticed that the type of the response is JSON. I don't know if that implies the input is interpreted as JSON, or that the response itself was a JSON string.