Request for refactoring: Config.getXXX()

Weijun Wang weijun.wang at oracle.com
Mon Jun 18 19:07:54 PDT 2012


This is about the internal class sun.security.krb5.Config.

If you want to get a value from inside krb5.conf, you can call 
getDefault(String). This might be good to get a value from the 
[libdefaults] section. However, the method was designed to be so smart 
that it can recursively search for key/value pairs no matter how deep it is.

For example, given a krb5.conf

    [s1]
    a=b

    [s2]
    c=d

    [s3]
    e = {
      f = g
    }

getDefault("a") = "b", getDefault("c") = "d", and astonishingly, 
getDefault("f") = "g".

I don't think this is a good design, for several reasons:

1. It depends on the order of sections if there are key/value pairs with 
the same key.

2. It ignores wrong settings. For example, when doing a cross-realm 
auth, the Realm.getRealmsList(from,to) is used to get a path which 
should be defined in [capaths]. However, the method simply crawls 
recursively into any subsection it found and won't notice the [capaths] 
being mistakenly typed as [capath]

3. It lacks certain features. Because the function always return a 
String (same with the getDefault(String,String) method), getDefault("e") 
can only return a null. Therefore there is no way to find out the 
existence of the subsection e unless we also know it contains a key f.

4. The current Config class needs to know what subsections contains more 
subsections, and it hardcodes names like [capaths] and [realms].

In short, it's just too smart and becomes unsafe to use. I suggest 
removing all this smartness and a user must use the full paths to get a 
value, say,

    kdc = config.get("realms", "SUN.COM", "kdc")

My full spec is:

1. The Config class should understand a krb5.conf without knowing any 
specific section names. All it maintains is a Value, which can be either of

     String
     List<Value>
     TreeMap<String,Value>

Here I use TreeMap to preserve the order (might not be necessary).

2. The basic retrieval method will be

     Value get(String... key)

3. There are simply methods if you already know what the type in your 
case is

     String getAsString(String... key)
     List<String> getAsStringList(String... key)

The compatibility risk will be low, and if there really comes a 
compatibility issue, most likely it will be because the caller had 
written his krb5.conf wrong.

One of the advantages of the original design is that when a key is 
provided in both [libdefaults] and a given realm, the method can find it 
anyway. This will be useful for keys like kdc_timeout, max_retries. 
However, I think this automatic retrieval is confusing and error-prone, 
I'd rather manually call the get() method twice.

Thanks
Max




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