Get size without authenticating?

Shared links like this (generally) don't require you to authenticate to access the content, so you can get the content and check the length. For example, using this link:

https://www.dropbox.com/s/vv7us05r9z46lwt/hello_world.txt?dl=0

We can ask for the raw file content by modifying the parameters as shown here:

https://www.dropbox.com/help/201

This gives us this version of the link:

https://www.dropbox.com/s/vv7us05r9z46lwt/hello_world.txt?raw=1

We can then access the content programmatically, e.g., using curl:

curl -L https://www.dropbox.com/s/vv7us05r9z46lwt/hello_world.txt?raw=1

(The -L is necessary to follow redirects.)

The response contains the length in the "Content-Length" header, e.g.:

Content-Length: 14

Alternatively, you can check the length of the returned file yourself.

Or, here's a more advanced method, using the Python requests library, to get the Content-Length without downloading the file, by using a HEAD request:

import requests

url = "https://www.dropbox.com/s/vv7us05r9z46lwt/hello_world.txt?raw=1"

redirected_url = requests.head(url).headers['location']

content_length = requests.head(redirected_url).headers['Content-Length']

print content_length

(Just don't re-use redirected_url. Always get a new one from the original link.)