Function mail::mime::create_structured_random_boundary

pub fn create_structured_random_boundary(count: usize) -> String

Generate a boundary from a counter, "=_^" and a random sequence of boundary chars.

Usage Note

Be aware that it might be required to quote the boundary.

Implementation Details

The boundary will start with =_^ which is neither valid for base64 nor quoted-printable encoding followed by a hex repr. of the given count, a . and a random sequence of boundary chars.

The boundary will be 66 chars long, this is so that if a boundary parameter is placed on it's own line it won't be more then 78 chars. (66 chars boundary, + 2 chars quotation + 9 chars for 'boundary=' + 1 char because of \r\n<WS> == 78 chars)

The remaining characters will be picked based one the grammar defined in rfc2046, which relevant part is:

boundary := 0*69<bchars> bcharsnospace
bchars := bcharsnospace / " "
bcharsnospace := DIGIT / ALPHA / "'" / "(" / ")" /
                 "+" / "_" / "," / "-" / "." /
                 "/" / ":" / "=" / "?"

Note that ' ' isn't used for simplicity.