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

Wed Aug 7 14:13:46 UTC 2013

On 8/7/2013 10:05 PM, Michael McMahon wrote:
> Resolvers seem to accept queries using trailing dots.
> 
> eg nslookup www.oracle.com.
> 
> or InetAddress.getByName("www.oracle.com.");
> 
> The part of RFC3490 quoted below seems to me to be saying
> that the empty label implied by the trailing dot is not regarded
> as a label so that you don't end up calling toAscii() or toUnicode()
> with an empty string. I don't think it's saying the trailing dot can't
> be there.
> 
It makes sense.

What's your preference to return for IDN.toASCII("www.oracle.com."),
"www.oracle.com." or "www.oracle.com"? The current returned value is
"www.oracle.com".  I would like to reserve the behavior in this update.

I think we are on same page soon.

Thanks,
Xuelei

> Michael
> 
> On 07/08/13 13:44, Xuelei Fan wrote:
>> 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
>>>>>
> 