ASN1Choicepublic abstract class ASN1Choice extends ASN1Type | This abstract class represents ASN.1 Choice type.
To implement custom ASN.1 choice type an application class
must provide implementation for the following methods:
getIndex()
getObjectToEncode()
There are two ways to implement custom ASN.1 choice type:
with application class that represents ASN.1 custom choice type or without.
The key point is how a value of choice type is stored by application classes.
For example, let's consider the following ASN.1 notations
(see http://www.ietf.org/rfc/rfc3280.txt)
Time ::= CHOICE {
utcTime UTCTime,
generalTime GeneralizedTime
}
Validity ::= SEQUENCE {
notBefore Time,
notAfter Time
}
1)First approach:
No application class to represent ASN.1 Time notation
The Time notation is a choice of different time formats: UTC and Generalized.
Both of them are mapped to java.util.Date object, so an application
class that represents ASN.1 Validity notation may keep values
as Date objects.
So a custom ASN.1 Time choice type should map its notation to Date object.
class Time {
// custom ASN.1 choice class: maps Time to is notation
public static final ASN1Choice asn1 = new ASN1Choice(new ASN1Type[] {
ASN1GeneralizedTime.asn1, ASN1UTCTime.asn1 }) {
public int getIndex(java.lang.Object object) {
return 0; // always encode as ASN1GeneralizedTime
}
public Object getObjectToEncode(Object object) {
// A value to be encoded value is a Date object
// pass it to custom time class
return object;
}
};
}
class Validity {
private Date notBefore; // choice as Date
private Date notAfter; // choice as Date
... // constructors and other methods go here
// custom ASN.1 sequence class: maps Validity class to is notation
public static final ASN1Sequence ASN1
= new ASN1Sequence(new ASN1Type[] {Time.asn1, Time.asn1 }) {
protected Object getObject(Object[] values) {
// ASN.1 Time choice passed Data object - use it
return new Validity((Date) values[0], (Date) values[1]);
}
protected void getValues(Object object, Object[] values) {
Validity validity = (Validity) object;
// pass Date objects to ASN.1 Time choice
values[0] = validity.notBefore;
values[1] = validity.notAfter;
}
}
}
2)Second approach:
There is an application class to represent ASN.1 Time notation
If it is a matter what time format should be used to decode/encode
Date objects a class to represent ASN.1 Time notation must be created.
For example,
class Time {
private Date utcTime;
private Date gTime;
... // constructors and other methods go here
// custom ASN.1 choice class: maps Time to is notation
public static final ASN1Choice asn1 = new ASN1Choice(new ASN1Type[] {
ASN1GeneralizedTime.asn1, ASN1UTCTime.asn1 }) {
public Object getDecodedObject(BerInputStream in) {
// create Time object to pass as decoded value
Time time = new Time();
if (in.choiceIndex==0) {
// we decoded GeneralizedTime
// store decoded Date value in corresponding field
time.gTime = in.content;
// return it
return time;
} else {
// we decoded UTCTime
// store decoded Date value in corresponding field
time.utcTime = in.content;
// return it
return time;
}
}
public int getIndex(java.lang.Object object) {
Time time = (Time)object;
if(time.utcTime!=null){
// encode Date as UTCTime
return 1;
} else {
// otherwise encode Date as GeneralizedTime
return 0;
}
}
public Object getObjectToEncode(Object object) {
Time time = (Time)object;
if(time.utcTime!=null){
// encode Date as UTCTime
return 1;
} else {
// otherwise encode Date as GeneralizedTime
return 0;
}
}
};
}
So now Validity class must keep all values in Time object
and its custom ASN.1 sequence class must handle this class of objects
class Validity {
private Time notBefore; // now it is a Time!!!
private Time notAfter; // now it is a Time!!!
... // constructors and other methods go here
// custom ASN.1 sequence class: maps Validity class to is notation
public static final ASN1Sequence ASN1
= new ASN1Sequence(new ASN1Type[] {Time.asn1, Time.asn1 }) {
protected Object getObject(Object[] values) {
// We've gotten Time objects here !!!
return new Validity((Time) values[0], (Time) values[1]);
}
protected void getValues(Object object, Object[] values) {
Validity validity = (Validity) object;
// pass Time objects to ASN.1 Time choice
values[0] = validity.notBefore;
values[1] = validity.notAfter;
}
}
} |
| Fields Summary |
|---|
| public final ASN1Type[] | type | | private final int[] | identifiers |
| Constructors Summary |
|---|
public ASN1Choice(ASN1Type[] type)Constructs ASN.1 choice type.
super(TAG_CHOICE); // has not tag number
if (type.length == 0) {
throw new IllegalArgumentException(Messages.getString("security.10E", //$NON-NLS-1$
getClass().getName()));
}
// create map of all identifiers
TreeMap map = new TreeMap();
for (int index = 0; index < type.length; index++) {
ASN1Type t = type[index];
if (t instanceof ASN1Any) {
// ASN.1 ANY is not allowed,
// even it is a single component (not good for nested choices)
throw new IllegalArgumentException(Messages.getString("security.10F", //$NON-NLS-1$
getClass().getName())); // FIXME name
} else if (t instanceof ASN1Choice) {
// add all choice's identifiers
int[][] choiceToAdd = ((ASN1Choice) t).identifiers;
for (int j = 0; j < choiceToAdd[0].length; j++) {
addIdentifier(map, choiceToAdd[0][j], index);
}
continue;
}
// add primitive identifier
if (t.checkTag(t.id)) {
addIdentifier(map, t.id, index);
}
// add constructed identifier
if (t.checkTag(t.constrId)) {
addIdentifier(map, t.constrId, index);
}
}
// fill identifiers array
int size = map.size();
identifiers = new int[2][size];
Iterator it = map.keySet().iterator();
for (int i = 0; i < size; i++) {
BigInteger identifier = (BigInteger) it.next();
identifiers[0][i] = identifier.intValue();
identifiers[1][i] = ((BigInteger) map.get(identifier)).intValue();
}
this.type = type;
|
| Methods Summary |
|---|
| private void | addIdentifier(java.util.TreeMap map, int identifier, int index)
if (map.put(BigInteger.valueOf(identifier), BigInteger.valueOf(index)) != null) {
throw new IllegalArgumentException(Messages.getString("security.10F", //$NON-NLS-1$
getClass().getName())); // FIXME name
}
| | public final boolean | checkTag(int identifier)Tests whether one of choice alternatives has the same identifier or not.
return Arrays.binarySearch(identifiers[0], identifier) >= 0;
| | public java.lang.Object | decode(BerInputStream in)
int index = Arrays.binarySearch(identifiers[0], in.tag);
if (index < 0) {
throw new ASN1Exception(Messages.getString("security.110", //$NON-NLS-1$
getClass().getName()));// FIXME message
}
index = identifiers[1][index];
in.content = type[index].decode(in);
// set index for getDecodedObject method
in.choiceIndex = index;
if (in.isVerify) {
return null;
}
return getDecodedObject(in);
| | public void | encodeASN(BerOutputStream out)
encodeContent(out);
| | public final void | encodeContent(BerOutputStream out)
out.encodeChoice(this);
| | public abstract int | getIndex(java.lang.Object object)TODO Put method description here
| | public abstract java.lang.Object | getObjectToEncode(java.lang.Object object)
| | public final void | setEncodingContent(BerOutputStream out)
out.getChoiceLength(this);
|
|
