Avoid unnecessary copies by recv()ing data directly into the expat buffer

src/xmpp/xmpp_component.cpp

@@ -89,10 +89,20 @@ void XmppComponent::on_connection_close()
   log_info("XMPP server closed connection");
 }
 
-void XmppComponent::parse_in_buffer()
+void XmppComponent::parse_in_buffer(const size_t size)
 {
-  this->parser.feed(this->in_buf.data(), this->in_buf.size(), false);
-  this->in_buf.clear();
+  if (!this->in_buf.empty())
+    { // This may happen if the parser could not allocate enough space for
+      // us. We try to feed it the data that was read into our in_buf
+      // instead. If this fails again we are in trouble.
+      this->parser.feed(this->in_buf.data(), this->in_buf.size(), false);
+      this->in_buf.clear();
+    }
+  else
+    { // Just tell the parser to parse the data that was placed into the
+      // buffer it provided to us with GetBuffer
+      this->parser.parse(size, false);
+    }
 }
 
 void XmppComponent::shutdown()
@@ -308,6 +318,11 @@ Bridge* XmppComponent::get_user_bridge(const std::string& user_jid)
     }
 }
 
+void* XmppComponent::get_receive_buffer(const size_t size) const
+{
+  return this->parser.get_buffer(size);
+}
+
 void XmppComponent::send_message(const std::string& from, Xmpp::body&& body, const std::string& to)
 {
   XmlNode node("message");

src/xmpp/xmpp_component.hpp

@@ -23,7 +23,7 @@ public:
   void on_connection_failed(const std::string& reason) override final;
   void on_connected() override final;
   void on_connection_close() override final;
-  void parse_in_buffer() override final;
+  void parse_in_buffer(const size_t size) override final;
   /**
    * Send a "close" message to all our connected peers.  That message
    * depends on the protocol used (this may be a QUIT irc message, or a
@@ -142,7 +142,11 @@ private:
    * if none already exist.
    */
   Bridge* get_user_bridge(const std::string& user_jid);
-
+  /**
+   * Return a buffer provided by the XML parser, to read data directly into
+   * it, and avoiding some unnecessary copy.
+   */
+  void* get_receive_buffer(const size_t size) const override final;
   XmppParser parser;
   std::string stream_id;
   std::string served_hostname;

src/xmpp/xmpp_parser.cpp

@@ -1,6 +1,8 @@
 #include <xmpp/xmpp_parser.hpp>
 #include <xmpp/xmpp_stanza.hpp>
 
+#include <logger/logger.hpp>
+
 /**
  * Expat handlers. Called by the Expat library, never by ourself.
  * They just forward the call to the XmppParser corresponding methods.
@@ -45,9 +47,25 @@ XmppParser::~XmppParser()
   XML_ParserFree(this->parser);
 }
 
-void XmppParser::feed(const char* data, const int len, const bool is_final)
+int XmppParser::feed(const char* data, const int len, const bool is_final)
 {
-  XML_Parse(this->parser, data, len, is_final);
+  int res = XML_Parse(this->parser, data, len, is_final);
+  if (res == 0)
+    log_error("Xml_Parse encountered an error");
+  return res;
+}
+
+int XmppParser::parse(const int len, const bool is_final)
+{
+  int res = XML_ParseBuffer(this->parser, len, is_final);
+  if (res == 0)
+    log_error("Xml_Parsebuffer encountered an error");
+  return res;
+}
+
+void* XmppParser::get_buffer(const size_t size) const
+{
+  return XML_GetBuffer(this->parser, static_cast<int>(size));
 }
 
 void XmppParser::start_element(const XML_Char* name, const XML_Char** attribute)

src/xmpp/xmpp_parser.hpp

@@ -37,7 +37,15 @@ public:
   /**
    * Feed the parser with some XML data
    */
-  void feed(const char* data, const int len, const bool is_final);
+  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);
+  /**
+   * 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.
    */