Decode RFC 2047 quoted-printable and base64 MIME encoded text

Usage

decode_mime_text(string, charset = NULL)

Arguments

string: A character vector containing a string to be decoded.
charset: A character string with the charset declared in the MIME Content-Type. When supplied it is honored (via apply_charset()) instead of the legacy heuristic detection.

Value

A decoded character vector if applicable.

Note

The RFC 2047 (Moore, 1996) presents an encoded-word syntax to be used by e-mail clients to display body text and header information in character sets other than ASCII. According to the manual, non-ASCII content is encoded as an ASCII text string as follows: =?<charset>?<encoding>?<encoded-text>?=. The encoding can be of two types: "B" for "BASE64", or "Q" for quoted- printable content (Freed and Borenstein, 1996). Besides the standard RFC 2047 decoding, this function also enables users to decode content that does not strictly follow the =?<charset>?<encoding>?<encoded-text>?= RFC 2047 syntax, i.e. cases where only the encoded text part is present, such as the quoted-printable pattern in the string "Estat=EDstica" (Estatística, which is the equivalent word, in Portuguese, for Statistics).

References

Moore, K. (1996), MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text, RFC 2047, November 1996, https://tools.ietf.org/html/rfc2047.

Freed, N., Borenstein, N. (1996), Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies, RFC 2045, November 1996, https://tools.ietf.org/html/rfc2045.

Internal parts of this object, regarding the quoted printable type, were borrowed from https://github.com/hrbrmstr/hrbrmisc/blob/master/R/qp.r with slight modifications.