Code review request, 8020842 IDN do not throw IAE when hostname ends with a trailing dot

[Xuelei Fan]

On 8/7/2013 12:06 AM, Matthew Hall wrote:
> Trailing dots are allowed in plain DNS (thus almost surely in IDN),
> and the single dot represents the root zone. So you have to be
> careful making this sort of change to check the DNS RFCs first.

That's the first question we need to answer, whether IDN allow tailling
dots ("com."), zero-length root label ("."), and zero-length label ("",
for example ""example..com")?

Per the specification of IDN.toASCII():
=======================================
"ToASCII operation can fail. ToASCII fails if any step of it fails. If
ToASCII operation fails, an IllegalArgumentException will be thrown. In
this case, the input string should not be used in an internationalized
domain name.

A label is an individual part of a domain name. The original ToASCII
operation, as defined in RFC 3490, only operates on a single label. This
method can handle both label and entire domain name, by assuming that
labels in a domain name are always separated by dots. ...

Throws IllegalArgumentException - if the input string doesn't conform to
RFC 3490 specification"

Per the specification of RFC 3490:
==================================
[section 2]
"A label is an individual part of a domain name.  Labels are usually
 shown separated by dots; for example, the domain name
 "www.example.com" is composed of three labels: "www", "example", and
 "com".  (The zero-length root label described in [STD13], which can
 be explicit as in "www.example.com." or implicit as in
 "www.example.com", is not considered a label in this specification.)"

"An "internationalized label" is a label to which the ToASCII
 operation (see section 4) can be applied without failing (with the
 UseSTD3ASCIIRules flag unset).  ...
 Although most Unicode characters can appear in
 internationalized labels, ToASCII will fail for some input strings,
 and such strings are not valid internationalized labels."

"An "internationalized domain name" (IDN) is a domain name in which
 every label is an internationalized label."

[Section 4.1]
"ToASCII consists of the following steps:

 ...

 8. Verify that the number of code points is in the range 1 to 63
      inclusive."


Here are the questions:
1. whether "example..com" is an valid IDN?
   As dot is used as label separators, there are three labels,
"example", "", "com".  Per RFC 3490, "" is not a valid label. Hence,
"example..com" is not a valid IDN.

   We need to address the issue in IDN.

2. whether "xyz." is an valid IDN?
   It's an gray area, I think. We can treat the trailing "." as root
label, or a label separator.
   If the trailing "." is treated as label separator, "xyz." is invalid
per RFC 3490.
   if the trailing "." is treated as root label, what's the expected
return value of IDN.toASCII("xyz.")?  I think the return value can be
either "xyz." or "xyz".  The current implementation returns "xyz".

   We may need not to update the implementation if tailing "." is
treated as root label.

3. whether "." is an valid IDN?
   It's an gray area again, I think.
   As above, if the trailing "." is treated as root label, I think the
return value can be either "." or "".  The current implementation throws
a StringIndexOutOfBoundsException.

   However, what empty domain name ("") really means?  I would prefer to
return "." for "." instead.

   We need to address the issue in IDN.


Here comes the solution, the IDN.toASCII() returns:
1. "." for ".";
2. "xyz" for "xyz.";
3. IAE for "example..com".

Does it make sense?

Thanks,
Xuelei


On 8/7/2013 1:35 AM, Michael McMahon wrote:
> I don't really understand the reason for the restriction in SNIHostName
> But, I guess that is where it should be enforced if it is required.
> 
> Michael.
> 
> On 06/08/13 17:43, Dmitry Samersoff wrote:
>> Xuelei,
>>
>> . (dot) is perfectly valid domain name and it means root domain so com.
>> is valid domain name as well.
>>
>> It thinks to me that in context of methods your change we should ignore
>> trailing dots, rather than throw exception.
>>
>> -Dmitry
>>
>>
>>
>> On 2013-08-06 15:44, Xuelei Fan wrote:
>>> Hi,
>>>
>>> Please review the bug fix to strict the illegal input checking in IDN.
>>>
>>> webrev: http://cr.openjdk.java.net./~xuelei/8020842/webrev.00/
>>>
>>> Here is two test cases, which are expected to get IAE.
>>>
>>> Case 1:
>>> String host = IDN.toASCII(".", IDN.USE_STD3_ASCII_RULES);
>>> Exception in thread "main" java.lang.StringIndexOutOfBoundsException:
>>> String index out of range: 0
>>>          at java.lang.StringBuffer.charAt(StringBuffer.java:204)
>>>          at java.net.IDN.toASCIIInternal(IDN.java:279)
>>>          at java.net.IDN.toASCII(IDN.java:118)
>>>
>>> Case 2:
>>> String host = IDN.toASCII("com.", IDN.USE_STD3_ASCII_RULES);
>>>
>>> Thanks,
>>> Xuelei
>>>
>>
>