Implement the QpackFieldPreEncoder allowing it to use static table references.

Signed-off-by: Lachlan Roberts <lachlan@webtide.com>

jetty-http3/http3-qpack/src/main/java/org/eclipse/jetty/http3/qpack/EncodableEntry.java

@@ -68,7 +68,6 @@ class EncodableEntry
         {
             byte allowIntermediary = 0x00; // TODO: this is 0x20 bit, when should this be set?
             byte staticBit = _referencedName.isStatic() ? (byte)0x10 : (byte)0x00;
-            String value = (Objects.requireNonNull(_field).getValue() == null) ? "" : _field.getValue();
 
             // Encode the prefix.
             buffer.put((byte)(0x40 | allowIntermediary | staticBit));
@@ -76,6 +75,7 @@ class EncodableEntry
             NBitInteger.encode(buffer, 4, relativeIndex);
 
             // Encode the value.
+            String value = getValue();
             if (_huffman)
             {
                 buffer.put((byte)0x80);
@@ -92,8 +92,8 @@ class EncodableEntry
         else
         {
             byte allowIntermediary = 0x00; // TODO: this is 0x10 bit, when should this be set?
-            String name = Objects.requireNonNull(_field).getName();
+            String name = getName();
-            String value = (_field.getValue() == null) ? "" : _field.getValue();
+            String value = getValue();
 
             // Encode the prefix code and the name.
             if (_huffman)
@@ -118,6 +118,42 @@ class EncodableEntry
         }
     }
 
+    public int getRequiredSize(int base)
+    {
+        if (_referencedEntry != null)
+        {
+            int relativeIndex =  _referencedEntry.getIndex() - base;
+            return 1 + NBitInteger.octectsNeeded(6, relativeIndex);
+        }
+        else if (_referencedName != null)
+        {
+            String value = getValue();
+            int relativeIndex =  _referencedName.getIndex() - base;
+            int valueLength = _huffman ? Huffman.octetsNeeded(value) : value.length();
+            return 1 + NBitInteger.octectsNeeded(4, relativeIndex) + 1 + NBitInteger.octectsNeeded(7, valueLength) + valueLength;
+        }
+        else
+        {
+            String name = getName();
+            String value = getValue();
+            int nameLength = _huffman ? Huffman.octetsNeeded(name) : name.length();
+            int valueLength = _huffman ? Huffman.octetsNeeded(value) : value.length();
+            return 2 + NBitInteger.octectsNeeded(3, nameLength) + nameLength + NBitInteger.octectsNeeded(7, valueLength) + valueLength;
+        }
+    }
+
+    private String getName()
+    {
+        String name = Objects.requireNonNull(_field).getName();
+        return (name == null) ? "" : name;
+    }
+
+    private String getValue()
+    {
+        String value = Objects.requireNonNull(_field).getValue();
+        return (value == null) ? "" : value;
+    }
+
     public int getRequiredInsertCount()
     {
         if (_referencedEntry != null && !_referencedEntry.isStatic())

jetty-http3/http3-qpack/src/main/java/org/eclipse/jetty/http3/qpack/QpackFieldPreEncoder.java

@@ -15,70 +15,61 @@ package org.eclipse.jetty.http3.qpack;
 
 import java.nio.ByteBuffer;
 
+import org.eclipse.jetty.http.HttpField;
 import org.eclipse.jetty.http.HttpFieldPreEncoder;
 import org.eclipse.jetty.http.HttpHeader;
 import org.eclipse.jetty.http.HttpVersion;
 import org.eclipse.jetty.http3.qpack.table.Entry;
+import org.eclipse.jetty.http3.qpack.table.StaticTable;
 import org.eclipse.jetty.util.BufferUtil;
 
-/**
- *  TODO: implement QpackEncoder with PreEncodedFields.
- */
 public class QpackFieldPreEncoder implements HttpFieldPreEncoder
 {
-
     @Override
     public HttpVersion getHttpVersion()
     {
-        return HttpVersion.HTTP_2;
+        return HttpVersion.HTTP_3;
     }
 
     @Override
     public byte[] getEncodedField(HttpHeader header, String name, String value)
     {
+        StaticTable staticTable = QpackContext.getStaticTable();
+        HttpField httpField = new HttpField(header, name, value);
+
+        EncodableEntry encodableEntry;
         boolean notIndexed = QpackEncoder.DO_NOT_INDEX.contains(header);
-
+        boolean huffman = !QpackEncoder.DO_NOT_HUFFMAN.contains(header);
-        ByteBuffer buffer = BufferUtil.allocate(name.length() + value.length() + 10);
-        BufferUtil.clearToFill(buffer);
-        boolean huffman;
-        int bits;
-
         if (notIndexed)
         {
-            // Non indexed field
+            encodableEntry = new EncodableEntry(httpField, huffman);
-            boolean neverIndex = QpackEncoder.NEVER_INDEX.contains(header);
-            huffman = !QpackEncoder.DO_NOT_HUFFMAN.contains(header);
-            buffer.put(neverIndex ? (byte)0x10 : (byte)0x00);
-            bits = 4;
-        }
-        else if (header == HttpHeader.CONTENT_LENGTH && value.length() > 1)
-        {
-            // Non indexed content length for 2 digits or more
-            buffer.put((byte)0x00);
-            huffman = true;
-            bits = 4;
         }
         else
         {
-            // indexed
+            Entry entry = staticTable.get(httpField);
-            buffer.put((byte)0x40);
+            if (entry != null)
-            huffman = !QpackEncoder.DO_NOT_HUFFMAN.contains(header);
+            {
-            bits = 6;
+                encodableEntry = new EncodableEntry(entry);
+            }
+            else
+            {
+                Entry nameEntry = staticTable.get(name);
+                if (nameEntry != null)
+                {
+                    encodableEntry = new EncodableEntry(nameEntry, httpField, huffman);
+                }
+                else
+                {
+                    encodableEntry = new EncodableEntry(httpField, huffman);
+                }
+            }
         }
 
-        Entry entry = QpackContext.getStaticTable().get(header);
+        // Use a base of zero as we only reference the static table.
-        if (entry != null)
+        int base = 0;
-            NBitInteger.encode(buffer, bits, entry.getIndex());
+        ByteBuffer buffer = BufferUtil.allocate(encodableEntry.getRequiredSize(base));
-        else
+        BufferUtil.clearToFill(buffer);
-        {
+        encodableEntry.encode(buffer, base);
-            buffer.put((byte)0x80);
-            NBitInteger.encode(buffer, 7, Huffman.octetsNeededLC(name));
-            Huffman.encodeLC(buffer, name);
-        }
-
-        // TODO: I think we can only encode referencing the static table or with literal representations.
-        // QpackEncoder.encodeValue(buffer, huffman, value);
-
         BufferUtil.flipToFlush(buffer, 0);
         return BufferUtil.toArray(buffer);
     }