Subject: [MMUSIC] An error in SDP syntax regarding r= lines?

From: Federico Montesino Pouzols <[email-masked]>
Date: Thu, 27 Jun 2002 22:31:09 +0200

Hello everyone,

  On section 6 in draft-ietf-mmusic-sdp-new-10.txt the following
examples of r= lines are given:

# r=604800 3600 0 90000
# r=7d 1h 0 25h

  From this examples, I understand that "0" is a valid value for the
offsets. However on appendix A r= lines are defined like this:

# repeat-fields =       "r=" repeat-interval SP typed-time
#                      1*(SP typed-time)

# repeat-interval =     typed-time

# typed-time =          POS-DIGIT *DIGIT [fixed-len-time-unit]

# POS-DIGIT =           %x31-39 ; 1 - 9

  The two examples above would violate this syntax, since the first
offset is "0", which is not a POS-DIGIT. In RFC 2327, typed-time
started with DIGIT, so there was no problem.

  It seems to me, correct me please if I am wrong, that the first
offset, "0", is not necessary and could be assumed. Anyway, to keep
backward compatibility it has to be there. Would the following rule
solve the problem?

# repeat-fields =       "r=" repeat-interval SP typed-time SP "0"
#                      1*(SP typed-time)

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From: Colin Perkins <[email-masked]>
Date: Sun, 30 Jun 2002 14:58:25 -0400

># repeat-fields =       "r=" repeat-interval SP typed-time SP "0"

I agree that it looks like a bug in the ABNF. A better fix might be to
change typed-time to be

	typed-time = 1*DIGIT [fixed-len-time-unit]

to avoid mandating a leading zero?

Colin