Decoding base64 while using GitHub API to Download a File

Question

I am using the GitHub API to download a file from GitHub. I have been able to successfully authenticate as well as get a response from github, and see a base64 encoded stri

Answer 1

After much experimenting, I think I nailed down the difference between the working and broken base64 decoding.

It appears GitHub Base-64 encodes with:

• UTF-8 charset
• Base 64 MIME encoder (RFC2045)

As opposed to a "basic" (RFC4648) Base64 encoder. Several languages seem to default to the basic encoder (including Java, which I was using). When I switched to a MIME encoder, I got the full contents of the file un-garbled. This would explain why switching libraries in some cases fixed the issue.

I will note the contents field contained newline characters - decoders are supposed to ignore them, but not all do, so if you still get errors, you may need to try removing them.

The media-type header will do the job better, however in my case I am trying to use the API via a GitHub App - at time of writing, GitHub requires a specific media type be used when doing that, and it returns the JSON response.