I am working with the Mandrill Inbound Email API, and when an email has an attachment with one or more spaces in its file name, then the file name is encoded in a format that I do not know how to decode.
Here is a an example string I receive for the file name: =?UTF-8?B?TWlzc2lvbmFyecKgRmFpdGjCoFByb21pc2XCoGFuZMKgQ2FzaMKgUmVjZWlwdHPCoFlURMKgMjUzNQ==?= =?UTF-8?B?OTnCoEp1bHktMjAxNS5jc3Y=?=
I tried Base64.decode64(#{encoded_value})
but that didn't return a readable text.
How do I decode that value into a readable string?
This is MIME encoded-word syntax as defined in RFC-2822. From Wikipedia:
The form is: "
=?
charset?
encoding?
encoded text?=
".
- charset may be any character set registered with IANA. Typically it would be the same charset as the message body.
- encoding can be either "
Q
" denoting Q-encoding that is similar to the quoted-printable encoding, or "B
" denoting base64 encoding.- encoded text is the Q-encoded or base64-encoded text.
Fortunately you don't need to write a decoder for this. The Mail gem comes with a Mail::Encodings.value_decode
method that works perfectly and is very well-tested:
subject = "=?UTF-8?B?TWlzc2lvbmFyecKgRmFpdGjCoFByb21pc2XCoGFuZMKgQ2FzaMKgUmVjZWlwdHPCoFlURMKgMjUzNQ==?= =?UTF-8?B?OTnCoEp1bHktMjAxNS5jc3Y=?="
Mail::Encodings.value_decode(subject)
# => "Missionary Faith Promise and Cash Receipts YTD 253599 July-2015.csv"
It gracefully handles lots of edge cases you probably wouldn't think of (until your app tries to handle them and falls over):
subject = "Re:[=?iso-2022-jp?B?GyRCJTAlayE8JV0lcyEmJTglYyVRJXMzdDwwMnEbKEI=?=\n =?iso-2022-jp?B?GyRCPFIbKEI=?=] =?iso-2022-jp?B?GyRCSlY/LiEnGyhC?=\n =?iso-2022-jp?B?GyRCIVolMCVrITwlXSVzIVskKkxkJCQ5ZyRvJDsbKEI=?=\n =?iso-2022-jp?B?GyRCJE43byRLJEQkJCRGIUolaiUvJSglOSVIGyhC?=#1056273\n =?iso-2022-jp?B?GyRCIUsbKEI=?="
Mail::Encodings.value_decode(subject)
# => "Re:[グルーポン・ジャパン株式会社] 返信:【グルーポン】お問い合わせの件について(リクエスト#1056273\n )"
If you're using Rails you already have the Mail gem. Otherwise just add gem "mail"
to your Gemfile, then bundle install
and, in your script, require "mail"
.