问题
I ran into a bug in a mime parsing library where it blows up on subject lines that contain foreign characters beyond a certain length. It turns out that it would convert the subject into a Quoted-Printable MIME "Encoded-Word" and then try to word-wrap the whole thing to 78 characters. Because MIME-Word encoding has no spaces (they are replaced with underscores) it failed to wrap.
Example line being wrapped:
Subject: =?UTF-8?Q?lalalla_=E7=84=A1=E6=AD=A4=E7=84=A1=E6=AD=A4=E9=A0=85=E7=9B=AE=AE=AE=AE=AE=AE=AE=AE=AE?=
I thought I might contribute a patch to the library to wrap the line correctly but I couldn't find a reference as to how to break up a MIME-Word as part of a word-wrapping algorithm.
The RFC 5322 says to word-wrap at spaces but doesn't provide any guidance about what to do if there's a string of characters with no white-space that exceeds the target width.
Anyone know the correct action to take here?
回答1:
Just split the line where you need to, and continue with a 2nd wrapped line. For example:
Subject: =?UTF-8?Q?lalalla_=E7=84=A1=E6=AD=A4=E7=84=A1=E6=AD=A4?=
=?UTF-8?Q?=E9=A0=85=E7=9B=AE=AE=AE=AE=AE=AE=AE=AE=AE?=
Just be sure to make sure the 2nd (and following) wrapped lines start with either a space or a tab.
hth,
--Dave
来源：https://stackoverflow.com/questions/8132599/how-should-quoted-printable-mime-words-be-wrapped-to-the-correct-line-length