Base64 decoding of MIME email not working (GMail A

问题:

I'm using the GMail API to retrieve an email contents. I am getting the following base64 encoded data for the body: http://hastebin.com/ovucoranam.md

But when I run it through a base64 decoder, it either returns an empty string (error) or something that resembles the HTML data but with a bunch of weird characters.

Help?

回答1:

I'm not sure if you've solved it yet, but GmailGuy is correct. You need to convert the body to the Base64 RFC 4648 standard. The jist is you'll need to replace - with + and _ with /.

I've taken your original input and did the replacement: http://hastebin.com/ukanavudaz

And used base64decode.org to decode it, and it was fine.

回答2:

You need to use URL (aka "web") safe base64 decoding alphabet (see rfc 4648), which it doesn't appear you're doing. Using the standard base64 alphabet may work sometimes but not always (2 of the characters are different).

Docs don't seem to consistently mention this important detail. Here's one where it does though: https://developers.google.com/gmail/api/guides/drafts

Also, if your particular library doesn't support the "URL safe" alphabet then you can do string substitution on the string first ("-" with "+" and "_" with "/") and then do normal base64 decoding on it.

回答3:

I had the same issue decoding the 'data' fields in the message object response from the Gmail API. The Google Ruby API library wasn't decoding the text correctly either. I found I needed to do a url-safe base64 decode:

@data = Base64.urlsafe_decode64(JSON.parse(@result.data.to_json)["payload"]["body"]["data"])

Hope that helps!

回答4:

There is an example for python 2.x and 3.x:

decodedContents = base64.urlsafe_b64decode(payload["body"]["data"].encode('ASCII'))

回答5:

If you only need to decode for displaying purposes, consider using atob to decode the messages in JavaScript frontend (see ref).

回答6:

I found whilst playing with the API result, once I had drilled down to the body I was given an option to decode in the available methods.

  val message = mService!!.users().messages().get(user, id).setFormat("full").execute()

  println("Message snippet: " + message.snippet)
  if(message.payload.mimeType == "text/plain"){
        val body = message.payload.body.decodeData()  // getValue("body")

        Log.i("BODY", body.toString(Charset.defaultCharset()))
  }

The result:-
com.example.quickstart I/BODY: ISOLATE NORMAL: 514471,Fap, South Point Rolleston, 55 Faringdon Boulevard , Rolleston, 30 May 2018 20:59:21

回答7:

I coped the base64 test to a file (b64.txt), then base64-decoded it using base64 (from coreutils) with the -d option (see http://linux.die.net/man/1/base64) and I got text that was perfectly readable. The command I used was:

cat b64.txt | base64 -d