Re: [ietf-smtp] Stray <LF> in the middle of messages
Dave Crocker <dhc@dcrocker.net> Sat, 06 June 2020 17:22 UTC
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Reply-To: dcrocker@bbiw.net
To: Leo Gaspard <ietf=40leo.gaspard.io@dmarc.ietf.org>
References: <87ftb8p1ii.fsf@llwynog.ekleog.org>
From: Dave Crocker <dhc@dcrocker.net>
Organization: Brandenburg InternetWorking
Cc: ietf-smtp@ietf.org
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Date: Sat, 06 Jun 2020 10:22:29 -0700
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Subject: Re: [ietf-smtp] Stray <LF> in the middle of messages
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On 6/6/2020 10:06 AM, Leo Gaspard wrote: >> In addition, the appearance of "bare" "CR" or "LF" characters in text >> (i.e., either without the other) has a long history of causing >> problems in mail implementations and applications that use the mail >> system as a tool. SMTP client implementations MUST NOT transmit >> these characters except when they are intended as line terminators >> and then MUST, as indicated above, transmit them only as a <CRLF> >> sequence. > Should I understand this paragraph as meaning that if I ever receive > such an ill-formed message, I… can? should? must? accept it and… can? > should? must? convert the <LF> into proper <CRLF>? Encountering practice that differs from theory -- or, in this case, specification -- can be an excellent teachable moment. I think your opportunity, here, is to appreciate the pragmatics of Postel's Law. It is often taken to mean that one can send whatever one wants, but Jon was never that sloppy. You should try to generate only according to the strictest interpretation of the spec. But there are realities of different interpretations and some tolerable sloppiness that apply to this case, given a long history of systems that do use LF as line terminator and network software that fails to map it to the network standard CRLF. I believe systems still vary on how they respond to an incoming LF. I even suspect there are arguments for treating it only as data and arguments for treating it as newline. I suspect, therefore, the answer to your question will be how you assess the benefits and detriments of each choice. This being an IETF list, we should expect strong, differing comments from others. d/ -- Dave Crocker Brandenburg InternetWorking bbiw.net
- [ietf-smtp] Stray <LF> in the middle of messages Leo Gaspard
- Re: [ietf-smtp] Stray <LF> in the middle of messa… Dave Crocker
- Re: [ietf-smtp] Stray <LF> in the middle of messa… Claus Assmann
- Re: [ietf-smtp] Stray <LF> in the middle of messa… John C Klensin
- Re: [ietf-smtp] Stray <LF> in the middle of messa… Valdis Kl ē tnieks
- Re: [ietf-smtp] Stray <LF> in the middle of messa… Paul Smith
- Re: [ietf-smtp] Stray <LF> in the middle of messa… John C Klensin
- Re: [ietf-smtp] Stray <LF> in the middle of messa… Valdis Kl ē tnieks
- Re: [ietf-smtp] Stray <LF> in the middle of messa… John C Klensin
- Re: [ietf-smtp] Stray <LF> in the middle of messa… John Levine
- Re: [ietf-smtp] Stray <LF> in the middle of messa… John C Klensin
- Re: [ietf-smtp] Stray <LF> in the middle of messa… Hector Santos
- Re: [ietf-smtp] Stray <LF> in the middle of messa… Alessandro Vesely
- Re: [ietf-smtp] Stray <LF> in the middle of messa… Keith Moore
- Re: [ietf-smtp] Stray <LF> in the middle of messa… Valdis Kl ē tnieks
- Re: [ietf-smtp] Stray <LF> in the middle of messa… Paul Smith
- Re: [ietf-smtp] Stray <LF> in the middle of messa… Dave Crocker
- Re: [ietf-smtp] Stray <LF> in the middle of messa… John C Klensin
- Re: [ietf-smtp] Stray <LF> in the middle of messa… Dave Crocker
- Re: [ietf-smtp] Stray <LF> in the middle of messa… John Levine
- Re: [ietf-smtp] Stray <LF> in the middle of messa… Ned Freed
- Re: [ietf-smtp] Stray <LF> in the middle of messa… Hector Santos
- Re: [ietf-smtp] Stray <LF> in the middle of messa… Hector Santos
- Re: [ietf-smtp] Stray <LF> in the middle of messa… Valdis Kl ē tnieks
- Re: [ietf-smtp] Stray <LF> in the middle of messa… John C Klensin
- Re: [ietf-smtp] Stray <LF> in the middle of messa… Viktor Dukhovni