Index: lucene/CHANGES.txt
===================================================================
--- lucene/CHANGES.txt	(revision 1491345)
+++ lucene/CHANGES.txt	(working copy)
@@ -143,6 +143,10 @@
 
 * LUCENE-5045: DrillSideways.search did not work on an empty index. (Shai Erera)
 
+* LUCENE-5048: Creating CategoryPath with large components (larger than 65,535
+  characters) could result in NegativeArraySizeException or categories being
+  added multiple times to the taxonomy. (Mike McCandless, Shai Erera)
+
 Optimizations
 
 * LUCENE-4936: Improve numeric doc values compression in case all values share
Index: lucene/facet/src/java/org/apache/lucene/facet/taxonomy/CategoryPath.java
===================================================================
--- lucene/facet/src/java/org/apache/lucene/facet/taxonomy/CategoryPath.java	(revision 1491345)
+++ lucene/facet/src/java/org/apache/lucene/facet/taxonomy/CategoryPath.java	(working copy)
@@ -64,9 +64,7 @@
   public CategoryPath(final String... components) {
     assert components.length > 0 : "use CategoryPath.EMPTY to create an empty path";
     for (String comp : components) {
-      if (comp == null || comp.isEmpty()) {
-        throw new IllegalArgumentException("empty or null components not allowed: " + Arrays.toString(components));
-      }
+      verifyComponent(comp, components);
     }
     this.components = components;
     length = components.length;
@@ -80,15 +78,23 @@
       length = 0;
     } else {
       for (String comp : comps) {
-        if (comp == null || comp.isEmpty()) {
-          throw new IllegalArgumentException("empty or null components not allowed: " + Arrays.toString(comps));
-        }
+        verifyComponent(comp, comps);
       }
       components = comps;
       length = components.length;
     }
   }
 
+  private void verifyComponent(String comp, String[] comps) {
+    if (comp == null || comp.isEmpty()) {
+      throw new IllegalArgumentException("empty or null component not allowed: " + Arrays.toString(comps));
+    }
+    if (comp.length() > 65535) {
+      // this results in incorrect behavior in e.g. Cl2oTaxoWriterCache; see TestDirectoryTaxonomyWriter.testHugeLabel
+      throw new IllegalArgumentException("component too large (max=65535, actual=" + comp.length() + "): " + Arrays.toString(comps));
+    }
+  }
+  
   /**
    * Returns the number of characters needed to represent the path, including
    * delimiter characters, for using with
Index: lucene/facet/src/java/org/apache/lucene/facet/taxonomy/writercache/cl2o/CategoryPathUtils.java
===================================================================
--- lucene/facet/src/java/org/apache/lucene/facet/taxonomy/writercache/cl2o/CategoryPathUtils.java	(revision 1491345)
+++ lucene/facet/src/java/org/apache/lucene/facet/taxonomy/writercache/cl2o/CategoryPathUtils.java	(working copy)
@@ -39,14 +39,14 @@
    * {@link #serialize(CategoryPath, CharBlockArray)}.
    */
   public static int hashCodeOfSerialized(CharBlockArray charBlockArray, int offset) {
-    int length = (short) charBlockArray.charAt(offset++);
+    int length = charBlockArray.charAt(offset++);
     if (length == 0) {
       return 0;
     }
     
     int hash = length;
     for (int i = 0; i < length; i++) {
-      int len = (short) charBlockArray.charAt(offset++);
+      int len = charBlockArray.charAt(offset++);
       hash = hash * 31 + charBlockArray.subSequence(offset, offset + len).hashCode();
       offset += len;
     }
@@ -67,7 +67,7 @@
     }
     
     for (int i = 0; i < cp.length; i++) {
-      int len = (short) charBlockArray.charAt(offset++);
+      int len = charBlockArray.charAt(offset++);
       if (len != cp.components[i].length()) {
         return false;
       }
Index: lucene/facet/src/test/org/apache/lucene/facet/taxonomy/TestCategoryPath.java
===================================================================
--- lucene/facet/src/test/org/apache/lucene/facet/taxonomy/TestCategoryPath.java	(revision 1491345)
+++ lucene/facet/src/test/org/apache/lucene/facet/taxonomy/TestCategoryPath.java	(working copy)
@@ -3,6 +3,7 @@
 import java.util.Arrays;
 
 import org.apache.lucene.facet.FacetTestCase;
+import org.apache.lucene.util._TestUtil;
 import org.junit.Test;
 
 /*
@@ -274,5 +275,31 @@
       // expected
     }
   }
+
+  @Test
+  public void testLargeComponent() throws Exception {
+    String bigComp = null;
+    while (true) {
+      bigComp = _TestUtil.randomRealisticUnicodeString(random(), 65536, 65536);
+      if (bigComp.indexOf('\u001f') != -1) {
+        continue;
+      }
+      break;
+    }
+
+    try {
+      assertNotNull(new CategoryPath("dim", bigComp));
+      fail("large components should not be allowed; len=" + bigComp.length());
+    } catch (IllegalArgumentException e) {
+      // expected
+    }
+
+    try {
+      assertNotNull(new CategoryPath("dim\u001f" + bigComp, '\u001f'));
+      fail("large components should not be allowed; len=" + bigComp.length());
+    } catch (IllegalArgumentException e) {
+      // expected
+    }
+  }
   
 }
Index: lucene/facet/src/test/org/apache/lucene/facet/taxonomy/directory/TestDirectoryTaxonomyWriter.java
===================================================================
--- lucene/facet/src/test/org/apache/lucene/facet/taxonomy/directory/TestDirectoryTaxonomyWriter.java	(revision 1491345)
+++ lucene/facet/src/test/org/apache/lucene/facet/taxonomy/directory/TestDirectoryTaxonomyWriter.java	(working copy)
@@ -17,11 +17,12 @@
 import org.apache.lucene.index.DirectoryReader;
 import org.apache.lucene.index.IndexReader;
 import org.apache.lucene.index.IndexWriter;
+import org.apache.lucene.index.IndexWriterConfig.OpenMode;
 import org.apache.lucene.index.IndexWriterConfig;
-import org.apache.lucene.index.IndexWriterConfig.OpenMode;
 import org.apache.lucene.index.SegmentInfos;
 import org.apache.lucene.store.AlreadyClosedException;
 import org.apache.lucene.store.Directory;
+import org.apache.lucene.util._TestUtil;
 import org.junit.Test;
 
 /*
@@ -412,5 +413,37 @@
     taxoWriter.close();
     dir.close();
   }
-  
+
+  @Test
+  public void testHugeLabel() throws Exception {
+    Directory dir = newDirectory();
+    DirectoryTaxonomyWriter taxoWriter = new DirectoryTaxonomyWriter(dir, OpenMode.CREATE, new Cl2oTaxonomyWriterCache(2, 1f, 1));
+    
+    // Add one huge label:
+    String bigs = null;
+    int ordinal = -1;
+    while (true) {
+      bigs = _TestUtil.randomRealisticUnicodeString(random(), 32767, 32767);
+      if (bigs.indexOf('\u001f') != -1) {
+        continue;
+      }
+      ordinal = taxoWriter.addCategory(new CategoryPath("dim", bigs));
+      break;
+    }
+
+    // Add tiny ones to cause a re-hash
+    for (int i = 0; i < 3; i++) {
+      String s = _TestUtil.randomUnicodeString(random());
+      if (s.isEmpty() || s.indexOf('\u001f') != -1) {
+        continue;
+      }
+      taxoWriter.addCategory(new CategoryPath("dim", s));
+    }
+
+    // when too large components were allowed to be added, this resulted in a new added category
+    assertEquals(ordinal, taxoWriter.addCategory(new CategoryPath("dim", bigs)));
+    
+    taxoWriter.close();
+    dir.close();
+  }
 }