(2nd round) Proposed API Changes for JEP 114: TLS Server Name Indication (SNI) Extension

[Xuelei Fan]

More comments about whether we are able to override the default value.

On 8/15/2012 10:45 AM, Xuelei Fan wrote:
>>> >> Thought more about the design, I would have to say that we cannot return
>>> >> the default value in sslParameters.getServerNames().  Otherwise, the
>>> >> following two block of codes look very weird to me:
>>> >>      // case one:
>>> >> 1   SSLparameters sslParameters = sslSocket.getSSLParameters();
>>> >> 2   sslParameters.clearServerName("host_name");
>>> >> 3   Map<String, String> names = sslParameters.getServerNames();
>>> >> 4   sslSocket.setSSLParameters(sslParameters);
>>> >> 5   sslParameters = sslSocket.getSSLParameters();
>>> >> 6   names = sslParameters.getServerNames();
>>> >>
>>> >> In line 3, the returned map does not contain "host_name" entry. But in
>>> >> line 6, it may be expected that no "host_name" in the returned map. But
>>> >> if we want to return default values, line 6 do need to return a map
>>> >> containing "host_name".  The behavior is pretty confusing. We may want
>>> >> to try avoid the confusion.
>> > 
>> > I'm not following your confusion, it seemed pretty straightforward to
>> > me, it works much like CipherSuites.  We have a set of ciphersuites
>> > which are enabled by default.  We can turn some off by using
>> > SSLParameters.
Compatibility is my concerns here.

When the SSLParameters class was was introduced in JDK 6,
set/getCipherSuites() and set/getProtocols were new, so there was no
compatibility issue for these two pairs methods at that time, as they
were not used in old applications.

In JDK 7, we introduced two new methods, set/getAlgorithmConstraints().
We were luck that we cannot allow the override of default constraints
because of security consideration, and the concept of algorithm
constraints was new in JDK 7. So we needed not to consider the
compatibility issue too much between JDK 6 and 7 for this pair of methods.

However, things get changed for the Server Name Inidication (SNI),
because in JDK 7 we have already support default SNI extension implicit.
We have to consider the compatibility issues more between JDK 7 and JDK
8, we need to make sure the behaviors are consistent whenever we call
the set/getServerName(). If we allow override of default value, the
application may run into corner trap as the description in my previous mail.

That's the background of my thoughts. Hope it helps you understand the
current design.

Thanks,
Xuelei

>> >  Expanding a bit on your example here, I'll describe what
>> > I think would happen internally/externally:
>> > 
>> > 1    SSLSocket sslSocket = mySSLSocketFactory.createSocket(
>> >         "www.example.com", 443);
>> > 
>> > mySSLSocketFactory sets any initial parameters as usual.  SSLSocketImpl
>> > knows it's connecting to www.example.com and automatically stores
>> > "host_name" -> "www.example.com" in its local host data (map or separate
>> > variables).
>> > 
>> > 2   SSLparameters sslParameters = sslSocket.getSSLParameters();
>> > 
>> > SSLSocketImpl.getSSLParameters() creates a SSLParameters, and sets the
>> > hostmap to the one value "host_name" -> "www.example.com"
>> > 
>> > If the application want to get the "default values", they just pull them
>> > out of the SSLParameters here
>> > 
>> > 3   sslParameters.clearServerName("host_name");
>> > 
>> > Or sslParameters.setServerName("host_name", null)?
>> > 
>> > User just decided to clear it.  Ok, that's what we do.  It becomes an
>> > empty map in SSLParameters.
>> > 
>> > 4   Map<String, String> names = sslParameters.getServerNames();
>> > 
>> > Returns empty Map.
>> > 
> As far as good.
> 
>> > 5   sslSocket.setSSLParameters(sslParameters);
>> > 
>> > SSLSocketImpl.setSSLParameters is empty, so SSLSocketImpl takes this
>> > SSLParameters and as a result, clears it's internal "host_name" map to
>> > null, and thus won't send anything out since it's empty.
>> > 
> We have problems here.  We need to support that if an application does
> not specified host_name value, we should use default values.
>   I.   SSLParameters sslParameters = new SSLParameters();
>   II.  sslParameters.setCipherSuites(...);
>   III. SSLSocket sslSocket =
>           sslSocketFactory.createSocket("www.example.com", 443)
>   IV.  sslSocket.setSSLParameters(sslParameters);
> 
> Before line IV and after line II, the sslParameters.getServerNames() are
> empty. In line IV, we need to make sure the internal "host_name",
> "www.example.com" is used as default value, and send it to server in
> SNI.  That's the default behaviors in JDK 7.  We cannot break it without
> strong desires.
> 
> I think it means that we cannot clear the internal "host_name" when the
> sslParameters.getServerNames() return empty.
> 
> Does it make sense to you?
> 
> Thanks,
> Xuelei
> 
>> > 6   sslParameters = sslSocket.getSSLParameters();
>> > 
>> > SSLSocketImpl.getSSLParameters() creates a SSLParameters, which sees
>> > that there's no name indication, so it creates an empty name map and
>> > stores in SSLParameters.
>> > 
>> > 7   names = sslParameters.getServerNames();
>> > 
>> > returns empty.
>> > 
>> > It's no longer the default value, because they have specifically set the
>> > value.
>> > 
>> > HTH,
>> > 
>> > Brad