Subject: [Sip] MIME: MIME when only one body type

From: "Christer Holmberg (JO/LMF)" <[email-masked]>
Date: Wed, 30 May 2007 13:03:15 +0200

Hi,

Chapter 3.2 of Gonzalo's draft says:

"UAs should avoid unnecessarily nesting body parts. Therefore, UAs
SHOULD NOT use a 'multipart' body when there is only one body part."

However, chapter 5.1.1 of RFC2046 says:

"NOTE: Experience has shown that a "multipart" media type with a
single body part is useful for sending non-text media types."

So, I think we need to add some words saying that it can be useful in
some cases.

For example, I THINK I have seen INFO requests with encapsulated ISUP
messages inside a MIME body, eventhough the message doesn't contain any
other body types.

Regards,

Christer

_______________________________________________
Sip mailing list  https://www1.ietf.org/mailman/listinfo/sip
This list is for NEW development of the core SIP Protocol
Use [email-masked] for questions on current sip
Use [email-masked] for new developments on the application of sip

---

From: "Dan Wing" <[email-masked]>
Date: Wed, 30 May 2007 12:45:36 -0700

> single body part is useful for sending non-text media types."

The only reason I could see it being useful for email was when you're
sending the message to a non-MIME-aware mail user agent, and you
included a MIME prologue:

  From: [email-masked]
  Content-Type: multipart/mixed; boundary=A

  You are reading this message with a mailer that doesn't understand
  MIME.  To review the attached content, use 'metamail'.

  --A
  Content-Type: image/jpg
  Content-Transfer-Encoding: base64

  EJKF3849efjkej...

  --A--

> So, I think we need to add some words saying that it can be useful in

Unless there is another case that it's useful for SIP, I think it could
only harm interoperability.

> messages inside a MIME body, eventhough the message doesn't 
> contain any other body types.

-d

---

From: "Christer Holmberg (JO/LMF)" <[email-masked]>
Date: Thu, 31 May 2007 14:27:39 +0200

Hi, 

>The only reason I could see it being useful for email was 
>when you're sending the message to a non-MIME-aware mail user 
>agent, and you included a MIME prologue:
> 
>  From: [email-masked]

Like I said, it may be used for transporting ISUP information. Maybe
Francois has more information?

Also, if a client is going to support multipart anyway, I don't see how
it would harm interoperability. I would be very surprised if a client
supports MIME with multiple bodies, but not with a single body...

Regards,

Christer

---

From: Paul Kyzivat <[email-masked]>
Date: Thu, 31 May 2007 11:17:30 -0400

I was the one who originally raised this issue. I don't have a strong 
opinion on which way it should go, but I think what Gonzalo wrote 
(SHOULD NOT) is about right. The issue is that if there can be one level 
of gratuitous nesting, then what about two, or a hundred levels of 
gratuitous nesting?

I'm inclined to think that people SHOULDN'T do it, but that a recipient 
should deal with it, at least within reason. (Perhaps its ok not to 
support 100 levels of nesting.)

	Paul

---

From: "Dan Wing" <[email-masked]>
Date: Thu, 31 May 2007 10:37:53 -0700

> >Unless there is another case that it's useful for SIP, I 
> >think it could only harm interoperability.
> 

Implementations may well be doing multipart/mixed and including only
one bodypart.  I completely agree that might be happening.  

> Also, if a client is going to support multipart anyway, I 
> don't see how it would harm interoperability.

By doing that, you are teasing fate, and you aren't "being conservative
in what you send".  Afterall, it's the receiver (not the sender) of the
MIME that may have difficulties.  

> I would be very surprised if a client

Yep, but it isn't the client that I'm so worried about.  I expect
if you sent a multipart containing one part (application/sdp), you
would find disasterous interoperability.

-d

---

From: "Francois Audet" <[email-masked]>
Date: Thu, 31 May 2007 13:18:06 -0500

I agree with Dan.

I don't understand the use case in SIP of sending a Multipart with only
one body.

The mail example makes sense for really dumb implementations that don't
support
MIME whatsoever, but for SIP, there is no such thing since MIME has been
in SIP since
day one.

> -----Original Message-----
> From: Dan Wing [mailto:[email-masked]] 
> Sent: Thursday, May 31, 2007 10:38
> To: 'Christer Holmberg (JO/LMF)'; [email-masked]
> Cc: 'Gonzalo Camarillo (JO/LMF)'; Audet, Francois (SC100:3055)
> Subject: RE: [Sip] MIME: MIME when only one body type
> 
>  
> > >Unless there is another case that it's useful for SIP, I think it 
> > >could only harm interoperability.
> > 
> Implementations may well be doing multipart/mixed and 
> including only one bodypart.  I completely agree that might 
> be happening.  
> 
> > Also, if a client is going to support multipart anyway, I don't see 
> > how it would harm interoperability.
> 
> By doing that, you are teasing fate, and you aren't "being 
> conservative in what you send".  Afterall, it's the receiver 
> (not the sender) of the MIME that may have difficulties.  
> 
> Yep, but it isn't the client that I'm so worried about.  I 
> expect if you sent a multipart containing one part 
> (application/sdp), you would find disasterous interoperability.
> 
> -d
>

---

From: "Christer Holmberg (JO/LMF)" <[email-masked]>
Date: Thu, 31 May 2007 21:46:51 +0200

Hi, 

>I agree with Dan.
> 
>I don't understand the use case in SIP of sending a Multipart 
>with only one body.

Again, I think I've seen INFOs and/or BYEs carrying ISUP informatio in
multipart, without any other body (unfortunately I have to use the word
"think", because I don't have any real examples in front of me :)

But, I have nothing against saying that one SHOULD NOT (or even MUST
NOT) SEND it. But, I do think one should be prepared to RECEIVE such
messages, in order to be backward compatible with existing
implementations which may not be fully compliant the draft.

And, regarding Dan's example: if a client is not able to handle
multipart carrying only SDP, I don't think it will be able to handle a
multipart carrying SDP and something else either - and we will have the
problem Francois presented earlier (the multipart, and the SDP innit, is
thrown away).

Regards,

Christer

> including only 
> > conservative in what you send".  Afterall, it's the 
> receiver (not the 
> > sender) of the MIME that may have difficulties.
> > 
> > > I would be very surprised if a client supports MIME with multiple 
> > > bodies, but not with a single body...
> > 
> expect if 
> > you sent a multipart containing one part (application/sdp), 
> you would 
> > find disasterous interoperability.
> > 
> > -d
> > 
>

---

From: "Dan Wing" <[email-masked]>
Date: Thu, 31 May 2007 12:53:18 -0700

> From: Christer Holmberg (JO/LMF) 
> [mailto:[email-masked]] 
> Sent: Thursday, May 31, 2007 12:47 PM
> To: Francois Audet; Dan Wing; [email-masked]
> Cc: Gonzalo Camarillo (JO/LMF)

I agree.

> problem Francois presented earlier (the multipart, and the 
> SDP innit, is thrown away).

Yep.  But that's exactly why I don't think we should encourage
unnecessary use of MIME -- it only tempts fate.

-d