Issue #4890 - Do not index large HTTP2 Fields

jetty-http2/http2-hpack/src/main/java/org/eclipse/jetty/http2/hpack/HpackEncoder.java

@@ -299,11 +299,11 @@ public void encode(ByteBuffer buffer, HttpField field)
 
         String encoding = null;
 
-        // Is there an entry for the field?
+        // Is there an index entry for the field?
         Entry entry = _context.get(field);
         if (entry != null)
         {
-            // Known field entry, so encode it as indexed
+            // This is a known indexed field, send as static or dynamic indexed.
             if (entry.isStatic())
             {
                 buffer.put(((StaticEntry)entry).getEncodedField());
@@ -321,10 +321,10 @@ public void encode(ByteBuffer buffer, HttpField field)
         }
         else
         {
-            // Unknown field entry, so we will have to send literally.
+            // Unknown field entry, so we will have to send literally, but perhaps add an index.
             final boolean indexed;
 
-            // But do we know it's name?
+            // Do we know it's name?
             HttpHeader header = field.getHeader();
 
             // Select encoding strategy
@@ -342,12 +342,12 @@ public void encode(ByteBuffer buffer, HttpField field)
                     if (_debug)
                         encoding = indexed ? "PreEncodedIdx" : "PreEncoded";
                 }
-                // has the custom header name been seen before?
-                else if (name == null)
+                // has the custom header name been seen before and will it fit in dynamic table?
+                else if (name == null && fieldSize < _context.getMaxDynamicTableSize())
                 {
-                    // unknown name and value, so let's index this just in case it is
-                    // the first time we have seen a custom name or a custom field.
-                    // unless the name is changing, this is worthwhile
+                    // unknown name and value that will fit in dynamic table, so let's index
+                    // this just in case it is the first time we have seen a custom name or a
+                    // custom field.  Unless the name is once only, this is worthwhile
                     indexed = true;
                     encodeName(buffer, (byte)0x40, 6, field.getName(), null);
                     encodeValue(buffer, true, field.getValue());

jetty-http2/http2-hpack/src/test/java/org/eclipse/jetty/http2/hpack/HpackEncoderTest.java

@@ -145,6 +145,32 @@ public void testUnknownFieldsContextManagement() throws Exception
         assertEquals(5, encoder.getHpackContext().size());
     }
 
+    @Test
+    public void testLargeFieldsNotIndexed()
+    {
+        HpackEncoder encoder = new HpackEncoder(38 * 5);
+        HpackContext ctx = encoder.getHpackContext();
+
+        ByteBuffer buffer = BufferUtil.allocate(4096);
+
+        // Index little fields
+        int pos = BufferUtil.flipToFill(buffer);
+        encoder.encode(buffer, new HttpField("Name", "Value"));
+        BufferUtil.flipToFlush(buffer, pos);
+        int dynamicTableSize = ctx.getDynamicTableSize();
+        assertThat(dynamicTableSize, Matchers.greaterThan(0));
+
+        // Do not index big field
+        StringBuilder largeName = new StringBuilder("largeName-");
+        String filler = "XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX";
+        while (largeName.length() < ctx.getMaxDynamicTableSize())
+            largeName.append(filler, 0, Math.min(filler.length(), ctx.getMaxDynamicTableSize() - largeName.length()));
+        pos = BufferUtil.flipToFill(buffer);
+        encoder.encode(buffer, new HttpField(largeName.toString(), "Value"));
+        BufferUtil.flipToFlush(buffer, pos);
+        assertThat(ctx.getDynamicTableSize(), Matchers.is(dynamicTableSize));
+    }
+
     @Test
     public void testNeverIndexSetCookie() throws Exception
     {