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package sun.security.provider.certpath;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Iterator;
import java.util.List;
An AdjacencyList is used to store the history of certification paths
attempted in constructing a path from an initiator to a target. The
AdjacencyList is initialized with a List of
Lists, where each sub-List contains objects of
type Vertex. A Vertex describes one possible or
actual step in the chain building process, and the associated
Certificate. Specifically, a Vertex object
contains a Certificate and an index value referencing the
next sub-list in the process. If the index value is -1 then this
Vertex doesn't continue the attempted build path.
Example:
Attempted Paths:
- C1->C2->C3
- C1->C4->C5
- C1->C4->C6
- C1->C4->C7
- C1->C8->C9
- C1->C10->C11
AdjacencyList structure:
- AL[0] = C1,1
- AL[1] = C2,2 =>C4,3 =>C8,4 =>C10,5
- AL[2] = C3,-1
- AL[3] = C5,-1 =>C6,-1 =>C7,-1
- AL[4] = C9,-1
- AL[5] = C11,-1
The iterator method returns objects of type BuildStep, not
objects of type Vertex.
A BuildStep contains a Vertex and a result code,
accessible via getResult method. There are five result values.
POSSIBLE denotes that the current step represents a
Certificate that the builder is considering at this point in
the build. FOLLOW denotes a Certificate (one of
those noted as POSSIBLE) that the builder is using to try
extending the chain. BACK represents that a
FOLLOW was incorrect, and is being removed from the chain.
There is exactly one FOLLOW for each BACK. The
values SUCCEED and FAIL mean that we've come to
the end of the build process, and there will not be any more entries in
the list.
Author: seth proctor See Also: - BuildStep
- Vertex
Since: 1.4
/**
* An AdjacencyList is used to store the history of certification paths
* attempted in constructing a path from an initiator to a target. The
* AdjacencyList is initialized with a <code>List</code> of
* <code>List</code>s, where each sub-<code>List</code> contains objects of
* type <code>Vertex</code>. A <code>Vertex</code> describes one possible or
* actual step in the chain building process, and the associated
* <code>Certificate</code>. Specifically, a <code>Vertex</code> object
* contains a <code>Certificate</code> and an index value referencing the
* next sub-list in the process. If the index value is -1 then this
* <code>Vertex</code> doesn't continue the attempted build path.
* <p>
* Example:
* <p>
* Attempted Paths:<ul>
* <li>C1->C2->C3
* <li>C1->C4->C5
* <li>C1->C4->C6
* <li>C1->C4->C7
* <li>C1->C8->C9
* <li>C1->C10->C11
* </ul>
* <p>
* AdjacencyList structure:<ul>
* <li>AL[0] = C1,1
* <li>AL[1] = C2,2 =>C4,3 =>C8,4 =>C10,5
* <li>AL[2] = C3,-1
* <li>AL[3] = C5,-1 =>C6,-1 =>C7,-1
* <li>AL[4] = C9,-1
* <li>AL[5] = C11,-1
* </ul>
* <p>
* The iterator method returns objects of type <code>BuildStep</code>, not
* objects of type <code>Vertex</code>.
* A <code>BuildStep</code> contains a <code>Vertex</code> and a result code,
* accessible via getResult method. There are five result values.
* <code>POSSIBLE</code> denotes that the current step represents a
* <code>Certificate</code> that the builder is considering at this point in
* the build. <code>FOLLOW</code> denotes a <code>Certificate</code> (one of
* those noted as <code>POSSIBLE</code>) that the builder is using to try
* extending the chain. <code>BACK</code> represents that a
* <code>FOLLOW</code> was incorrect, and is being removed from the chain.
* There is exactly one <code>FOLLOW</code> for each <code>BACK</code>. The
* values <code>SUCCEED</code> and <code>FAIL</code> mean that we've come to
* the end of the build process, and there will not be any more entries in
* the list.
*
* @see sun.security.provider.certpath.BuildStep
* @see sun.security.provider.certpath.Vertex
*
* @author seth proctor
* @since 1.4
*/
public class AdjacencyList {
// the actual set of steps the AdjacencyList represents
private ArrayList<BuildStep> mStepList;
// the original list, just for the toString method
private List<List<Vertex>> mOrigList;
Constructs a new AdjacencyList based on the specified
List. See the example above.
Params: - list – a
List of Lists of
Vertex objects
/**
* Constructs a new <code>AdjacencyList</code> based on the specified
* <code>List</code>. See the example above.
*
* @param list a <code>List</code> of <code>List</code>s of
* <code>Vertex</code> objects
*/
public AdjacencyList(List<List<Vertex>> list) {
mStepList = new ArrayList<BuildStep>();
mOrigList = list;
buildList(list, 0, null);
}
Gets an Iterator to iterate over the set of
BuildSteps in build-order. Any attempts to change
the list through the remove method will fail.
Returns: an Iterator over the BuildSteps
/**
* Gets an <code>Iterator</code> to iterate over the set of
* <code>BuildStep</code>s in build-order. Any attempts to change
* the list through the remove method will fail.
*
* @return an <code>Iterator</code> over the <code>BuildStep</code>s
*/
public Iterator<BuildStep> iterator() {
return Collections.unmodifiableList(mStepList).iterator();
}
Recursive, private method which actually builds the step list from
the given adjacency list. Follow is the parent BuildStep
that we followed to get here, and if it's null, it means that we're
at the start.
/**
* Recursive, private method which actually builds the step list from
* the given adjacency list. <code>Follow</code> is the parent BuildStep
* that we followed to get here, and if it's null, it means that we're
* at the start.
*/
private boolean buildList(List<List<Vertex>> theList, int index,
BuildStep follow) {
// Each time this method is called, we're examining a new list
// from the global list. So, we have to start by getting the list
// that contains the set of Vertexes we're considering.
List<Vertex> l = theList.get(index);
// we're interested in the case where all indexes are -1...
boolean allNegOne = true;
// ...and in the case where every entry has a Throwable
boolean allXcps = true;
for (Vertex v : l) {
if (v.getIndex() != -1) {
// count an empty list the same as an index of -1...this
// is to patch a bug somewhere in the builder
if (theList.get(v.getIndex()).size() != 0)
allNegOne = false;
} else {
if (v.getThrowable() == null)
allXcps = false;
}
// every entry, regardless of the final use for it, is always
// entered as a possible step before we take any actions
mStepList.add(new BuildStep(v, BuildStep.POSSIBLE));
}
if (allNegOne) {
// There are two cases that we could be looking at here. We
// may need to back up, or the build may have succeeded at
// this point. This is based on whether or not any
// exceptions were found in the list.
if (allXcps) {
// we need to go back...see if this is the last one
if (follow == null)
mStepList.add(new BuildStep(null, BuildStep.FAIL));
else
mStepList.add(new BuildStep(follow.getVertex(),
BuildStep.BACK));
return false;
} else {
// we succeeded...now the only question is which is the
// successful step? If there's only one entry without
// a throwable, then that's the successful step. Otherwise,
// we'll have to make some guesses...
List<Vertex> possibles = new ArrayList<>();
for (Vertex v : l) {
if (v.getThrowable() == null)
possibles.add(v);
}
if (possibles.size() == 1) {
// real easy...we've found the final Vertex
mStepList.add(new BuildStep(possibles.get(0),
BuildStep.SUCCEED));
} else {
// ok...at this point, there is more than one Cert
// which might be the succeed step...how do we know
// which it is? I'm going to assume that our builder
// algorithm is good enough to know which is the
// correct one, and put it first...but a FIXME goes
// here anyway, and we should be comparing to the
// target/initiator Cert...
mStepList.add(new BuildStep(possibles.get(0),
BuildStep.SUCCEED));
}
return true;
}
} else {
// There's at least one thing that we can try before we give
// up and go back. Run through the list now, and enter a new
// BuildStep for each path that we try to follow. If none of
// the paths we try produce a successful end, we're going to
// have to back out ourselves.
boolean success = false;
for (Vertex v : l) {
// Note that we'll only find a SUCCEED case when we're
// looking at the last possible path, so we don't need to
// consider success in the while loop
if (v.getIndex() != -1) {
if (theList.get(v.getIndex()).size() != 0) {
// If the entry we're looking at doesn't have an
// index of -1, and doesn't lead to an empty list,
// then it's something we follow!
BuildStep bs = new BuildStep(v, BuildStep.FOLLOW);
mStepList.add(bs);
success = buildList(theList, v.getIndex(), bs);
}
}
}
if (success) {
// We're already finished!
return true;
} else {
// We failed, and we've exhausted all the paths that we
// could take. The only choice is to back ourselves out.
if (follow == null)
mStepList.add(new BuildStep(null, BuildStep.FAIL));
else
mStepList.add(new BuildStep(follow.getVertex(),
BuildStep.BACK));
return false;
}
}
}
Prints out a string representation of this AdjacencyList.
Returns: String representation
/**
* Prints out a string representation of this AdjacencyList.
*
* @return String representation
*/
@Override
public String toString() {
StringBuilder sb = new StringBuilder("[\n");
int i = 0;
for (List<Vertex> l : mOrigList) {
sb.append("LinkedList[").append(i++).append("]:\n");
for (Vertex step : l) {
sb.append(step.toString()).append("\n");
}
}
sb.append("]\n");
return sb.toString();
}
}