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+#pragma once
+
+
+#include <xmpp/xmpp_stanza.hpp>
+
+#include <functional>
+
+#include <expat.h>
+
+/**
+ * A SAX XML parser that builds XML nodes and spawns events when a complete
+ * stanza is received (an element of level 2), or when the document is
+ * opened/closed (an element of level 1)
+ *
+ * After a stanza_event has been spawned, we delete the whole stanza. This
+ * means that even with a very long document (in XMPP the document is
+ * potentially infinite), the memory is never exhausted as long as each
+ * stanza is reasonnably short.
+ *
+ * The element names generated by expat contain the namespace of the
+ * element, a colon (':') and then the actual name of the element. To get
+ * an element "x" with a namespace of "http://jabber.org/protocol/muc", you
+ * just look for an XmlNode named "http://jabber.org/protocol/muc:x"
+ *
+ * TODO: enforce the size-limit for the stanza (limit the number of childs
+ * it can contain). For example forbid the parser going further than level
+ * 20 (arbitrary number here), and each XML node to have more than 15 childs
+ * (arbitrary number again).
+ */
+class XmppParser
+{
+public:
+ explicit XmppParser();
+ ~XmppParser();
+ XmppParser(const XmppParser&) = delete;
+ XmppParser& operator=(const XmppParser&) = delete;
+ XmppParser(XmppParser&&) = delete;
+ XmppParser& operator=(XmppParser&&) = delete;
+
+public:
+ /**
+ * Feed the parser with some XML data
+ */
+ int feed(const char* data, const int len, const bool is_final);
+ /**
+ * Parse the data placed in the parser buffer
+ */
+ int parse(const int size, const bool is_final);
+ /**
+ * Reset the parser, so it can be used from scratch afterward
+ */
+ void reset();
+ /**
+ * Get a buffer provided by the xml parser.
+ */
+ void* get_buffer(const size_t size) const;
+ /**
+ * Add one callback for the various events that this parser can spawn.
+ */
+ void add_stanza_callback(std::function<void(const Stanza&)>&& callback);
+ void add_stream_open_callback(std::function<void(const XmlNode&)>&& callback);
+ void add_stream_close_callback(std::function<void(const XmlNode&)>&& callback);
+
+ /**
+ * Called when a new XML element has been opened. We instanciate a new
+ * XmlNode and set it as our current node. The parent of this new node is
+ * the previous "current" node. We have all the element's attributes in
+ * this event.
+ *
+ * We spawn a stream_event with this node if this is a level-1 element.
+ */
+ void start_element(const XML_Char* name, const XML_Char** attribute);
+ /**
+ * Called when an XML element has been closed. We close the current_node,
+ * set our current_node as the parent of the current_node, and if that was
+ * a level-2 element we spawn a stanza_event with this node.
+ *
+ * And we then delete the stanza (and everything under it, its children,
+ * attribute, etc).
+ */
+ void end_element(const XML_Char* name);
+ /**
+ * Some inner or tail data has been parsed
+ */
+ void char_data(const XML_Char* data, const size_t len);
+ /**
+ * Calls all the stanza_callbacks one by one.
+ */
+ void stanza_event(const Stanza& stanza) const;
+ /**
+ * Calls all the stream_open_callbacks one by one. Note: the passed node is not
+ * closed yet.
+ */
+ void stream_open_event(const XmlNode& node) const;
+ /**
+ * Calls all the stream_close_callbacks one by one.
+ */
+ void stream_close_event(const XmlNode& node) const;
+
+private:
+ /**
+ * Init the XML parser and install the callbacks
+ */
+ void init_xml_parser();
+
+ /**
+ * Expat structure.
+ */
+ XML_Parser parser{};
+ /**
+ * The current depth in the XML document
+ */
+ size_t level;
+ /**
+ * The deepest XML node opened but not yet closed (to which we are adding
+ * new children, inner or tail)
+ */
+ XmlNode* current_node;
+ /**
+ * The root node has no parent, so we keep it here: the XmppParser object
+ * is its owner.
+ */
+ std::unique_ptr<XmlNode> root;
+ /**
+ * A list of callbacks to be called on an *_event, receiving the
+ * concerned Stanza/XmlNode.
+ */
+ std::vector<std::function<void(const Stanza&)>> stanza_callbacks;
+ std::vector<std::function<void(const XmlNode&)>> stream_open_callbacks;
+ std::vector<std::function<void(const XmlNode&)>> stream_close_callbacks;
+};
+
+