I will agree that exhaustively defining text protocols is extremely hard, starting from character set / encoding and getting worse from there.
Typically you create message description which is then compiled to code that can serialize/deserialize messages in BER-TLV or PER-TLV.
I know because I wrote a complete parser/serializer for BER-TLV. It is simple protocol and any security issue is in the parser/serializer and not the protocol itself. That for simple reason that the protocol is nothing more than a format to serialize/deserialize the data.
BER-TLV is really nice protocol. I have worked with it for couple of years when I worked on an EMV application. It uses BER-TLV to communicate with the credit card but it is also very convenient format for all sorts of other uses and I would use it wherever I could. Think of it as Json but in binary form. It is not complicated and I would not even bother parsing the messages -- I could interpret hex dumps of them by sight very easily.
>>* a legal notice, here is a blessing:
>>*
>>* May you do good and not evil.
>>* May you find forgiveness for yourself and forgive others.
>>* May you share freely, never taking more than you give.
Above all, this note at the beginning of the source code impressed me.
I don't disagree in principle but I've come across a handful of very poorly documentated binary protocols in my years and that is an extremely painful thing to deal with compared to text-based protocols.
GET /asdfasdfasdfdsaf
X-Asdf-Asdf: 83e7234
HTTP/1.0 202
X-83e7233: 1
X-83f730b: 4
Overall, I think it's kind of a wash. It's basically equally easy to take a documented text or binary protocol and write a working parser. Neither format solves any intrinsic problems -- malicious input has to be accounted for, you have to write fuzz tests, you have to deal with broken producers. It's a wash.
People like text because they can type it into telnet and see something work, which is kind of cool, but probably not a productive use of time. I can type HTTP messages, but use curl anyway. (SMTP was always my favorite. "HELO there / MAIL FROM foo / RCPT TO bar / email body / ." Felt like a real conversation going on. Still not sure how to send an email that consists of a single dot on its own line though.)
It seems you prefix any line of data starting with a period with an additional period, to therefore distinguish it from the end of mail period.
A line starting with a period is escaped by adding an extra period; the receiving side removes the first character of a line if it is a period.