Customizable error page buffer size (#11654)

Customizable error page buffer size

---------

Co-authored-by: Greg Wilkins <gregw@webtide.com>

jetty-core/jetty-server/src/main/java/org/eclipse/jetty/server/handler/ErrorHandler.java

@@ -75,6 +75,7 @@ public class ErrorHandler implements Request.Handler
     boolean _showStacks = false;
     boolean _showCauses = false;
     boolean _showMessageInTitle = true;
+    int _bufferSize = -1;
     String _defaultResponseMimeType = Type.TEXT_HTML.asString();
     HttpField _cacheControl = new PreEncodedHttpField(HttpHeader.CACHE_CONTROL, "must-revalidate,no-cache,no-store");
 
@@ -198,8 +199,7 @@ else if (charsets.contains(StandardCharsets.ISO_8859_1))
                 return false;
         }
 
-        int bufferSize = request.getConnectionMetaData().getHttpConfiguration().getOutputBufferSize();
-        bufferSize = Math.min(8192, bufferSize); // TODO ?
+        int bufferSize = getBufferSize() <= 0 ? computeBufferSize(request) : getBufferSize();
         ByteBufferPool byteBufferPool = request.getComponents().getByteBufferPool();
         RetainableByteBuffer buffer = byteBufferPool.acquire(bufferSize, false);
 
@@ -266,6 +266,13 @@ else if (charsets.contains(StandardCharsets.ISO_8859_1))
         }
     }
 
+    protected int computeBufferSize(Request request)
+    {
+        int bufferSize = request.getConnectionMetaData().getHttpConfiguration().getOutputBufferSize();
+        bufferSize = Math.min(8192, bufferSize);
+        return bufferSize;
+    }
+
     protected void writeErrorHtml(Request request, Writer writer, Charset charset, int code, String message, Throwable cause, boolean showStacks) throws IOException
     {
         if (message == null)
@@ -530,6 +537,25 @@ public static Request.Handler getErrorHandler(Server server, ContextHandler cont
         return errorHandler;
     }
 
+    /**
+     * @return Buffer size for entire error response. If error page is bigger than buffer size, it will be truncated.
+     * With a -1 meaning that a heuristic will be used (e.g. min(8K, httpConfig.bufferSize))
+     */
+    @ManagedAttribute("Buffer size for entire error response")
+    public int getBufferSize()
+    {
+        return _bufferSize;
+    }
+
+    /**
+     * @param bufferSize Buffer size for entire error response. If error page is bigger than buffer size, it will be truncated.
+     * With a -1 meaning that a heuristic will be used (e.g. min(8K, httpConfig.bufferSize))
+     */
+    public void setBufferSize(int bufferSize)
+    {
+        this._bufferSize = bufferSize;
+    }
+
     public static class ErrorRequest extends Request.AttributesWrapper
     {
         private static final Set<String> ATTRIBUTES = Set.of(ERROR_MESSAGE, ERROR_EXCEPTION, ERROR_STATUS);