+ /* According to the XML 1.0 specifications, when there is an XML declaration
+ * at the beginning of an XML document, it is invalid to have
+ * white spaces before that declaration (reminder: a XML declaration looks like:
+ * <?xml version="1.0" encoding="UTF-8"?>). In contrast, when there is no XML declaration,
+ * it is valid to have white spaces at the beginning of the document.
+ *
+ * When they send a NETCONF message, several NETCONF servers start with a new line (either
+ * LF or CRLF), presumably to improve readability in interactive sessions with a human being.
+ * Some NETCONF servers send an XML declaration, some others do not.
+ *
+ * If a server starts a NETCONF message with white spaces and follows with an XML
+ * declaration, XmlUtil.readXmlToDocument() will fail because this is invalid XML.
+ * But in the spirit of the "NETCONF over SSH" RFC 4742 and to improve interoperability, we want
+ * to accept those messages.
+ *
+ * To do this, the following code strips the leading bytes before the start of the XML messages.
+ */
+
+ // Skip all leading whitespaces by moving the reader index to the first non whitespace character
+ while (in.isReadable()) {
+ if (!isWhitespace(in.readByte())) {
+ // return reader index to the first non whitespace character
+ in.readerIndex(in.readerIndex() - 1);
+ break;
+ }
+ }
+
+ // Warn about leading whitespaces
+ if (in.readerIndex() != 0 && LOG.isWarnEnabled()) {
+ final byte[] strippedBytes = new byte[in.readerIndex()];
+ in.getBytes(0, strippedBytes, 0, in.readerIndex());
+ LOG.warn("XML message with unwanted leading bytes detected. Discarded the {} leading byte(s): '{}'",
+ in.readerIndex(), ByteBufUtil.hexDump(Unpooled.wrappedBuffer(strippedBytes)));
+ }
+ }
+ if (in.isReadable()) {