ServerCore/Socket.h

#ifndef __Socket_h__
#define __Socket_h__

#include "ZString.h"
#include <queue>
#include <mutex>
#include <atomic>
#include <sys/epoll.h>

namespace core {

   class EPoll;

   ///
   /// Socket
   ///
   /// The core component to managing a socket.
   ///
   /// Hooks into the EPoll through the registration and unregistration process and provides a
   /// communication socket of the specified protocol type. This object provides for all receiving
   /// data threading through use of the EPoll object and also provides buffering for output data
   /// requests to the socket.
   ///
   /// A program using a socket object can request to open a socket (network or device) and
   /// communicate through the streambuffer interface of the socket object.
   ///
   /// The socket side of the Socket accepts EPOLLIN event and will maintain the data in a buffer
   /// for the stream readers to read. A onDataReceived event is then sent with the data received in
   /// the buffer that can be read through the stream. Only sockets that send events to epoll can be
   /// used with this object.
   ///
   /// When writing to the stream the data is written into a buffer and a EPOLLOUT is scheduled. Upon
   /// receiving the EPOLLOUT event then the buffer is written to the socket output.
   ///

   class Socket {

    public:

      ///
      /// Constructor
      ///
      /// @param ePoll The EPoll socket descriptor.
      /// @param text A title for this socket.
      ///

      Socket(EPoll &ePoll, std::string text = "");

      ///
      /// Destructor
      ///

      virtual ~Socket();

      ///
      /// Use the shutdown() method to terminate the socket connection and remove resources.
      /// This method is provided to ensure that all destructors are called for all inherited
      /// objects with a virtual destructor.
      ///

      void shutdown(std::string text = "unknown");

      ///
      /// setDescriptor establishes the file descriptor for the socket and registers the socket
      /// on the EPoll controller. setDescriptor will invoke the onRegister() event.
      ///

      void setDescriptor(int descriptor); ///<Set the descriptor for the socket.

      int getDescriptor(); ///< Get the descriptor for the socket.

      ///
      /// The event received from epoll is sent through the eventReceived
      /// method which will parse the event and call the read and write
      /// callbacks on the socket.
      ///
      /// This method is called by the BMAEPoll object and should not be called
      /// from any user extended classes unless an epoll event is being
      /// simulated.
      ///
      /// The return value of false will delete the socket object causing the destructors to run.
      /// The return value of true will enable the socket on ePoll to receive more events.
      ///

      bool eventReceived(struct epoll_event event, long long eventId); ///< Parse epoll event and call specified callbacks.

      ///
      /// Write data to the socket.
      ///

      int write(std::string data);
      void write(char *buffer, int length);

      void output(std::stringstream &out);

      ///
      /// The onRegister method is called before the socket is registered with
      /// ePoll so objects extending the Socket definition can initialize the socket
      /// before receiving events. Evoked when the
      /// descriptor is set using setDescriptor for the socket.
      ///

      virtual void onRegister(); ///< Called before the socket has registered with the epoll processing.
      virtual void onRegistered(); ///< Called after the socket has been registered with epoll processing.

      virtual void onUnregister();

      ///
      /// ePoll and socket communcation events will be stopped. The default method will
      /// close the socket and clean up the connection. If this is overridden by an
      /// extended object then the object should call this method to clean the socket up.
      ///

      virtual void onUnregistered(); ///< Called when the socket has finished unregistering for the epoll processing.

      bool needsToWrite();

      bool reset = false;

      volatile bool shutDown = false;

      void enableSocket();
      void disableSocket();

    protected:

      EPoll &ePoll;           // The EPoll control object.

      void setBufferSize(int length);

      int getBufferSize();

      ///
      /// The onConnected method is called when the socket is ready to communicate. 
      /// Writing to the socket can begin on this call to initiate a contact with the
      /// remote device.
      ///

//      virtual void onConnected(); ///< Called when socket is open and ready to communicate.

      ///
      /// The connectionRequest method is called to instantiate a new session handler object
      /// and form a new connection to a listening server.
      ///
      
      virtual void connectionRequest(); 

      ///
      ///
      ///

//   virtual void onDisconnected(); ///< Called when socket is closing and no longer ready to communicate.

      ///
      /// The onDataReceived method is called when the socket has received an event from
      /// epoll and there is data ready to be read from the socket. The default handler 
      /// will pull the data and put it into the streambuf for the socket. EPOLLIN
      ///
      /// @param data the data that has been received from the socket.
      ///

      virtual void onDataReceived(std::string data); ///< Called when data is received from the socket.

      ///
      ///
      ///

      virtual void onDataReceived(coreutils::ZString &data);

      ///
      /// receiveData will read the data from the socket and place it in the socket buffer.
      /// TLS layer overrides this to be able to read from SSL.
      ///

      virtual void receiveData(coreutils::ZString &buffer);

      ///
      /// sendData writes data to the socket descriptor. TLS layer overrides this to
      /// write through SSL instead of a raw socket write.
      ///
      /// @return The number of bytes written, or -1 on error.
      ///

      virtual int sendData(const char *data, int length);

      ///
      /// Overridden by TCPSocket to report whether the last sendData()
      /// call failed specifically because the TLS layer needs a READ to
      /// make progress (SSL_ERROR_WANT_READ), as opposed to any other
      /// reason - see waitingOnReadToWrite's own doc comment for why
      /// writeSocket()/resetSocket() need to know this. Always false for
      /// a plain (non-TLS) socket, which has no such distinction.
      ///

      virtual bool sendNeedsRead() { return false; }

    private:

      std::string text;
      int descriptor = -1;
      std::mutex outlock;
      bool readHangup = false;
      // Was `volatile bool` - volatile gives no actual thread-safety
      // (no atomicity, no cross-thread visibility guarantee), and this
      // flag is now load-bearing (see Socket::write()'s own check of it)
      // rather than just feeding a diagnostic log line.
      std::atomic<bool> inHandler{false};

      //-------------------------------------------------------------------------------------
      // the writeSocket is called when epoll has received a write request for a socket.
      // Writing data to this socket is queued in the streambuf and permission is requested
      // to write to the socket. This routine handles the writing of the streambuf data
      // buffer to the socket.
      //-------------------------------------------------------------------------------------

      void writeSocket();

 //  int_type underflow();
//   int_type uflow();
//   int_type pbackfail(int_type ch);
//   streamsize showmanyc();

      char *buffer;     // This is a pointer to the managed buffer space.
      int length;       // This is the length of the buffer.

      std::queue<std::string> fifo;

      // Counts consecutive writeSocket() calls that sent zero bytes for
      // the SAME queued fifo entry (SSL_ERROR_WANT_READ from
      // TLS::sendData() is the confirmed real case - see writeSocket()'s
      // own doc comment). resetSocket() re-arms EPOLLWRNORM whenever the
      // fifo is non-empty regardless of WHY the last send failed, and an
      // already-writable TCP socket (the common case) makes EPOLLWRNORM
      // fire again essentially immediately - so a send that keeps
      // failing for a reason unrelated to socket writability (like SSL
      // needing a read first) spins this cycle as fast as the CPU can
      // run it, forever, with zero actual progress. Confirmed live: one
      // stuck connection generated a 55GB, then a 12.9GB debug log
      // before being noticed, at roughly 20 log lines per millisecond.
      // Reset to 0 on any successful send (even a partial one - real
      // progress happened); past the threshold, the connection is
      // clearly never going to un-stick itself and gets shut down.
      int consecutiveWriteStalls = 0;

      // Set by writeSocket() when the last failed send specifically
      // needed a read to proceed (sendNeedsRead() true) rather than
      // being genuinely stalled on write-readiness. resetSocket() skips
      // adding EPOLLWRNORM to the re-armed event mask while this is
      // true - re-arming it anyway just spins the CPU as fast as it can
      // loop, since an already-writable TCP socket keeps firing
      // EPOLLWRNORM immediately while the actual blocker (more bytes
      // from the peer) has nothing to do with write-readiness at all.
      // Cleared on any EPOLLIN event (see eventReceived()) so the write
      // gets a fresh attempt via that same event's own trailing
      // resetSocket() call, once there's real reason to expect progress.
      bool waitingOnReadToWrite = false;

      void resetSocket();

      std::mutex lock;

   };

}

#endif