Re: [apps-discuss] Question about mailto URI

Martin J. Dürst <duerst@it.aoyama.ac.jp> Sat, 20 February 2016 04:05 UTC

To: Alexey Melnikov <alexey.melnikov@isode.com>, Stephan Bosch <stephan@rename-it.nl>, apps-discuss@ietf.org
References: <56BFD23A.9010601@rename-it.nl> <56C761EC.1000304@isode.com>
From: "Martin J. Dürst" <duerst@it.aoyama.ac.jp>
Organization: Aoyama Gakuin University
Message-ID: <56C7E5F1.7030905@it.aoyama.ac.jp>
Date: Sat, 20 Feb 2016 13:05:05 +0900
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Subject: Re: [apps-discuss] Question about mailto URI
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Hello Stephan,

Sorry for the delay of my answer.

On 2016/02/20 03:41, Alexey Melnikov wrote:
> Hi Stephan,
>
> On 14/02/2016 01:02, Stephan Bosch wrote:
>> Hi,
>>
>> I have a question about the mailto URI specified in RFC 6068. The
>> following syntax is specified for header fields:
>>
>> hfields      = "?" hfield *( "&" hfield )
>> hfield       = hfname "=" hfvalue
>> hfname       = *qchar
>> hfvalue      = *qchar
>>
>> This syntax allows an empty header field name,

I have been able to trace this back to 
https://tools.ietf.org/html/rfc2368, where the rules in question are

      headers    =  "?" header *( "&" header )
      header     =  hname "=" hvalue
      hname      =  *urlc
      hvalue     =  *urlc

>> whereas RFC 5322
>> specifies the following:
>>
>> optional-field  =   field-name ":" unstructured CRLF
>> field-name      =   1*ftext
>> ftext           =   %d33-57 / %d59-126
>>
>> This doesn't allow empty header field names, which makes sense to me.

It makes a lot of sense to me, too.

>> Is there a reason to allow an empty header field name for the mailto
>> URI, or am I just looking at something that warrants an erratum for
>> the RFC?
> I don't know of any reason to allow for empty header field names.
> Although at this point implementations should just ignore empty fields.

I'm thinking about producing an update to RFC 6068 once it is possible 
to use non-ASCII characters in RFCs, which should be "soon". At that 
point, we should re-check this issue.

Looking at RFC 6068, there's already quite some text at the end of 
Section 3 and in Section 4 that makes it clear that MUAs and the like 
have to be careful to not just put all the header fields into an email 
message as-is. This should cover empty header field names, too, but it 
might be a good idea to point this out more specifically in an update.

Regards,   Martin.

[apps-discuss] Question about mailto URI Stephan Bosch
Re: [apps-discuss] Question about mailto URI Alexey Melnikov
Re: [apps-discuss] Question about mailto URI Martin J. Dürst