Re: ambiguities in RFC 2821 regarding end of mail data

Keith Moore wrote:

> > The second ambiguity relates to the first, and it concerns the 
> > question: When I receive a period alone in the first line of mail data
> > should I consider that the end of the data?
> you mean, you receive the sequence
>
> 44 41 54 41 0D 0A 2E 0D 0A 
>
> ?
Yes, I suppose that would be the sequence which I am asking about. 
But the way we do our parsing of data I do not see it all together 
that way, since the first OD OA are consumed by a routine which reads 
command lines (which are recognized as lines because they end with OD 
OA).  When DATA is recognized in a command line then the InputStream 
is handed to another parsing routine, specialized for reading data, 
which starts reading where the command-line parser left off, after the 
first OD OA.
> no it's not the end of mail data, since the CR LF after DATA
> cannot be part of the end-of-data marker.  OTOH it's also an SMTP
> protocol error,
This exchange has stimulated me to do the homework which I probably 
should have done before I started.  I have just seen this text in RFC 
2821, section 4.1.1.4, second paragraph:
"The mail data is terminated by a line containing only a period, that 
is, the character sequence "<CRLF>.<CRLF>" (see section 4.5.2).  This 
is the end of mail data indication.  Note that the first <CRLF> of 
this terminating sequence is also the <CRLF> that ends the final line 
of the data (message text) or, if there was no data, ends the DATA 
command itself."
I note two things from this.  First, "if there was no data, ends the 
DATA command itself", allows the possibility that there may be no 
data.  And it seems to answer my second question: a period alone in 
the first line of data ends the data.
Second, turning back now to the first question which I asked, notice 
that the first sentence of that paragraph from RFC 2821 contradicts 
itself.  The character sequence "<CRLF>.<CRLF>" is not "a line 
containing only a period".  It a CRLF -- put there to show that we 
have really reached the end of the prior line -- followed by a line 
containing only a period.  So this sentence gives us two possible "end 
of mail data indication"s.   One is "<CRLF>.<CRLF>" and the other is 
".<CRLF>" alone in a line.  They are not the same.  But I think the 
later is more consistent with other material in this RFC.
Rich