001 /*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements. See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License. You may obtain a copy of the License at
008 *
009 * http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017
018
019 package org.apache.commons.net.nntp;
020
021 /**
022 * This is an implementation of a message threading algorithm, as originally devised by Zamie Zawinski.
023 * See <a href="http://www.jwz.org/doc/threading.html">http://www.jwz.org/doc/threading.html</a> for details.
024 * For his Java implementation, see <a href="http://lxr.mozilla.org/mozilla/source/grendel/sources/grendel/view/Threader.java">http://lxr.mozilla.org/mozilla/source/grendel/sources/grendel/view/Threader.java</a>
025 *
026 * @author rwinston <rwinston@checkfree.com>
027 *
028 */
029
030 import java.util.Arrays;
031 import java.util.HashMap;
032 import java.util.Iterator;
033 import java.util.List;
034
035 public class Threader {
036 private ThreadContainer root;
037 private HashMap<String,ThreadContainer> idTable;
038 private int bogusIdCount = 0;
039
040 /**
041 * The main threader entry point - The client passes in an array of Threadable objects, and
042 * the Threader constructs a connected 'graph' of messages
043 * @param messages array of messages to thread
044 * @return null if messages == null or root.child == null
045 * @deprecated (2.2) prefer {@link #thread(List)}
046 */
047 @Deprecated
048 public Threadable thread(Threadable[] messages) {
049 return thread(Arrays.asList(messages));
050 }
051
052 /**
053 * The main threader entry point - The client passes in a list of Threadable objects, and
054 * the Threader constructs a connected 'graph' of messages
055 * @param messages list of messages to thread
056 * @return null if messages == null or root.child == null
057 * @since 2.2
058 */
059 public Threadable thread(List<? extends Threadable> messages) {
060 if (messages == null)
061 return null;
062
063 idTable = new HashMap<String,ThreadContainer>();
064
065 // walk through each Threadable element
066 for (Threadable t : messages) {
067 if (!t.isDummy())
068 buildContainer(t);
069 }
070
071 root = findRootSet();
072 idTable.clear();
073 idTable = null;
074
075 pruneEmptyContainers(root);
076
077 root.reverseChildren();
078 gatherSubjects();
079
080 if (root.next != null)
081 throw new RuntimeException("root node has a next:" + root);
082
083 for (ThreadContainer r = root.child; r != null; r = r.next) {
084 if (r.threadable == null)
085 r.threadable = r.child.threadable.makeDummy();
086 }
087
088 Threadable result = (root.child == null ? null : root.child.threadable);
089 root.flush();
090 root = null;
091
092 return result;
093 }
094
095 /**
096 *
097 * @param threadable
098 */
099 private void buildContainer(Threadable threadable) {
100 String id = threadable.messageThreadId();
101 ThreadContainer container = idTable.get(id);
102
103 // A ThreadContainer exists for this id already. This should be a forward reference, but may
104 // be a duplicate id, in which case we will need to generate a bogus placeholder id
105 if (container != null) {
106 if (container.threadable != null) { // oops! duplicate ids...
107 id = "<Bogus-id:" + (bogusIdCount++) + ">";
108 container = null;
109 } else {
110 // The container just contained a forward reference to this message, so let's
111 // fill in the threadable field of the container with this message
112 container.threadable = threadable;
113 }
114 }
115
116 // No container exists for that message Id. Create one and insert it into the hash table.
117 if (container == null) {
118 container = new ThreadContainer();
119 container.threadable = threadable;
120 idTable.put(id, container);
121 }
122
123 // Iterate through all of the references and create ThreadContainers for any references that
124 // don't have them.
125 ThreadContainer parentRef = null;
126 {
127 String[] references = threadable.messageThreadReferences();
128 for (int i = 0; i < references.length; ++i) {
129 String refString = references[i];
130 ThreadContainer ref = idTable.get(refString);
131
132 // if this id doesnt have a container, create one
133 if (ref == null) {
134 ref = new ThreadContainer();
135 idTable.put(refString, ref);
136 }
137
138 // Link references together in the order they appear in the References: header,
139 // IF they dont have a have a parent already &&
140 // IF it will not cause a circular reference
141 if ((parentRef != null)
142 && (ref.parent == null)
143 && (parentRef != ref)
144 && !(parentRef.findChild(ref))) {
145 // Link ref into the parent's child list
146 ref.parent = parentRef;
147 ref.next = parentRef.child;
148 parentRef.child = ref;
149 }
150 parentRef = ref;
151 }
152 }
153
154 // parentRef is now set to the container of the last element in the references field. make that
155 // be the parent of this container, unless doing so causes a circular reference
156 if (parentRef != null
157 && (parentRef == container || container.findChild(parentRef)))
158 parentRef = null;
159
160 // if it has a parent already, its because we saw this message in a References: field, and presumed
161 // a parent based on the other entries in that field. Now that we have the actual message, we can
162 // throw away the old parent and use this new one
163 if (container.parent != null) {
164 ThreadContainer rest, prev;
165
166 for (prev = null, rest = container.parent.child;
167 rest != null;
168 prev = rest, rest = rest.next) {
169 if (rest == container)
170 break;
171 }
172
173 if (rest == null) {
174 throw new RuntimeException(
175 "Didnt find "
176 + container
177 + " in parent"
178 + container.parent);
179 }
180
181 // Unlink this container from the parent's child list
182 if (prev == null)
183 container.parent.child = container.next;
184 else
185 prev.next = container.next;
186
187 container.next = null;
188 container.parent = null;
189 }
190
191 // If we have a parent, link container into the parents child list
192 if (parentRef != null) {
193 container.parent = parentRef;
194 container.next = parentRef.child;
195 parentRef.child = container;
196 }
197 }
198
199 /**
200 * Find the root set of all existing ThreadContainers
201 * @return root the ThreadContainer representing the root node
202 */
203 private ThreadContainer findRootSet() {
204 ThreadContainer root = new ThreadContainer();
205 Iterator<String> iter = idTable.keySet().iterator();
206
207 while (iter.hasNext()) {
208 Object key = iter.next();
209 ThreadContainer c = idTable.get(key);
210 if (c.parent == null) {
211 if (c.next != null)
212 throw new RuntimeException(
213 "c.next is " + c.next.toString());
214 c.next = root.child;
215 root.child = c;
216 }
217 }
218 return root;
219 }
220
221 /**
222 * Delete any empty or dummy ThreadContainers
223 * @param parent
224 */
225 private void pruneEmptyContainers(ThreadContainer parent) {
226 ThreadContainer container, prev, next;
227 for (prev = null, container = parent.child, next = container.next;
228 container != null;
229 prev = container,
230 container = next,
231 next = (container == null ? null : container.next)) {
232
233 // Is it empty and without any children? If so,delete it
234 if (container.threadable == null && container.child == null) {
235 if (prev == null)
236 parent.child = container.next;
237 else
238 prev.next = container.next;
239
240 // Set container to prev so that prev keeps its same value the next time through the loop
241 container = prev;
242 }
243
244 // Else if empty, with kids, and (not at root or only one kid)
245 else if (
246 container.threadable == null
247 && container.child != null
248 && (container.parent != null
249 || container.child.next == null)) {
250 // We have an invalid/expired message with kids. Promote the kids to this level.
251 ThreadContainer tail;
252 ThreadContainer kids = container.child;
253
254 // Remove this container and replace with 'kids'.
255 if (prev == null)
256 parent.child = kids;
257 else
258 prev.next = kids;
259
260 // Make each child's parent be this level's parent -> i.e. promote the children. Make the last child's next point to this container's next
261 // i.e. splice kids into the list in place of container
262 for (tail = kids; tail.next != null; tail = tail.next)
263 tail.parent = container.parent;
264
265 tail.parent = container.parent;
266 tail.next = container.next;
267
268 // next currently points to the item after the inserted items in the chain - reset that so we process the newly
269 // promoted items next time round
270 next = kids;
271
272 // Set container to prev so that prev keeps its same value the next time through the loop
273 container = prev;
274 } else if (container.child != null) {
275 // A real message , with kids
276 // Iterate over the children
277 pruneEmptyContainers(container);
278 }
279 }
280 }
281
282 /**
283 * If any two members of the root set have the same subject, merge them. This is to attempt to accomodate messages without References: headers.
284 */
285 private void gatherSubjects() {
286
287 int count = 0;
288
289 for (ThreadContainer c = root.child; c != null; c = c.next)
290 count++;
291
292 // TODO verify this will avoid rehashing
293 HashMap<String, ThreadContainer> subjectTable = new HashMap<String, ThreadContainer>((int) (count * 1.2), (float) 0.9);
294 count = 0;
295
296 for (ThreadContainer c = root.child; c != null; c = c.next) {
297 Threadable threadable = c.threadable;
298
299 // No threadable? If so, it is a dummy node in the root set.
300 // Only root set members may be dummies, and they alway have at least 2 kids
301 // Take the first kid as representative of the subject
302 if (threadable == null)
303 threadable = c.child.threadable;
304
305 String subj = threadable.simplifiedSubject();
306
307 if (subj == null || subj == "")
308 continue;
309
310 ThreadContainer old = subjectTable.get(subj);
311
312 // Add this container to the table iff:
313 // - There exists no container with this subject
314 // - or this is a dummy container and the old one is not - the dummy one is
315 // more interesting as a root, so put it in the table instead
316 // - The container in the table has a "Re:" version of this subject, and
317 // this container has a non-"Re:" version of this subject. The non-"Re:" version
318 // is the more interesting of the two.
319 if (old == null
320 || (c.threadable == null && old.threadable != null)
321 || (old.threadable != null
322 && old.threadable.subjectIsReply()
323 && c.threadable != null
324 && !c.threadable.subjectIsReply())) {
325 subjectTable.put(subj, c);
326 count++;
327 }
328 }
329
330 // If the table is empty, we're done
331 if (count == 0)
332 return;
333
334 // subjectTable is now populated with one entry for each subject which occurs in the
335 // root set. Iterate over the root set, and gather together the difference.
336 ThreadContainer prev, c, rest;
337 for (prev = null, c = root.child, rest = c.next;
338 c != null;
339 prev = c, c = rest, rest = (rest == null ? null : rest.next)) {
340 Threadable threadable = c.threadable;
341
342 // is it a dummy node?
343 if (threadable == null)
344 threadable = c.child.threadable;
345
346 String subj = threadable.simplifiedSubject();
347
348 // Dont thread together all subjectless messages
349 if (subj == null || subj == "")
350 continue;
351
352 ThreadContainer old = subjectTable.get(subj);
353
354 if (old == c) // That's us
355 continue;
356
357 // We have now found another container in the root set with the same subject
358 // Remove the "second" message from the root set
359 if (prev == null)
360 root.child = c.next;
361 else
362 prev.next = c.next;
363 c.next = null;
364
365 if (old.threadable == null && c.threadable == null) {
366 // both dummies - merge them
367 ThreadContainer tail;
368 for (tail = old.child;
369 tail != null && tail.next != null;
370 tail = tail.next);
371
372 tail.next = c.child;
373
374 for (tail = c.child; tail != null; tail = tail.next)
375 tail.parent = old;
376
377 c.child = null;
378 } else if (
379 old.threadable == null
380 || (c.threadable != null
381 && c.threadable.subjectIsReply()
382 && !old.threadable.subjectIsReply())) {
383 // Else if old is empty, or c has "Re:" and old does not ==> make this message a child of old
384 c.parent = old;
385 c.next = old.child;
386 old.child = c;
387 } else {
388 // else make the old and new messages be children of a new dummy container.
389 // We create a new container object for old.msg and empty the old container
390 ThreadContainer newc = new ThreadContainer();
391 newc.threadable = old.threadable;
392 newc.child = old.child;
393
394 for (ThreadContainer tail = newc.child;
395 tail != null;
396 tail = tail.next)
397 tail.parent = newc;
398
399 old.threadable = null;
400 old.child = null;
401
402 c.parent = old;
403 newc.parent = old;
404
405 // Old is now a dummy- give it 2 kids , c and newc
406 old.child = c;
407 c.next = newc;
408 }
409 // We've done a merge, so keep the same prev
410 c = prev;
411 }
412
413 subjectTable.clear();
414 subjectTable = null;
415
416 }
417 }