/*============================================================================
                         packetsocket
==============================================================================

  This is a facility for communicating socket-style, with defined
  packets like a datagram socket but with reliable delivery like a
  stream socket.  It's like a POSIX "sequential packet" socket, except
  it is built on top of a stream socket, so it is usable on the many
  systems that have stream sockets but not sequential packet sockets.

  By Bryan Henderson 2007.05.12

  Contributed to the public domain by its author.
============================================================================*/


/*============================================================================
  The protocol for carrying packets on a character stream:

  The protocol consists of the actual bytes to be transported with a bare
  minimum of framing information added:

     An ASCII Escape (<ESC> == 0x1B) character marks the start of a
     4-ASCII-character control word.  These are defined:

       <ESC>PKT : marks the beginning of a packet.
       <ESC>END : marks the end of a packet.
       <ESC>ESC : represents an <ESC> character in the packet
       <ESC>NOP : no meaning

     Any other bytes after <ESC> is a protocol error.

     A stream is all the data transmitted during a single socket
     connection.

     End of stream in the middle of a packet is a protocol error.  

     All bytes not part of a control word are literal bytes of a packet.

  You can create a packet socket from any file descriptor from which
  you can read and write a bidirectional character stream.  Typically,
  it's a TCP socket.

  One use of the NOP control word is to validate that the connection
  is still working.  You might send one periodically to detect, for
  example, an unplugged TCP/IP network cable.  It's probably better
  to use the TCP keepalive facility for that.
============================================================================*/

#include <cassert>
#include <string>
#include <queue>
#include <iostream>
#include <sstream>
#include <cstdio>
#include <cstdlib>
#include <unistd.h>
#include <errno.h>
#include <fcntl.h>
#include <poll.h>
#include <sys/types.h>

#include "c_util.h"
#include "xmlrpc-c/string_int.h"
#include "xmlrpc-c/girerr.hpp"
using girerr::throwf;

#include "xmlrpc-c/packetsocket.hpp"


#define ESC 0x1B   //  ASCII Escape character
#define ESC_STR "\x1B"

namespace xmlrpc_c {


packet::packet() :
    bytes(NULL), length(0), allocSize(0) {}
 


void
packet::initialize(const unsigned char * const data,
                   size_t                const dataLength) {

    this->bytes = reinterpret_cast<unsigned char *>(malloc(dataLength));

    if (this->bytes == NULL)
        throwf("Can't get storage for a %u-byte packet.", dataLength);

    this->allocSize = dataLength;

    memcpy(this->bytes, data, dataLength);

    this->length = dataLength;
}



packet::packet(const unsigned char * const data,
               size_t                const dataLength) {

    this->initialize(data, dataLength);
}



packet::packet(const char * const data,
               size_t       const dataLength) {

    this->initialize(reinterpret_cast<const unsigned char *>(data),
                     dataLength);
}



packet::~packet() {

    if (this->bytes)
        free(bytes);
}



void
packet::addData(const unsigned char * const data,
                size_t                const dataLength) {
/*----------------------------------------------------------------------------
   Add the 'length' bytes at 'data' to the packet.

   We allocate whatever additional memory is needed to fit the new
   data in.
-----------------------------------------------------------------------------*/
    size_t const neededSize(this->length + dataLength);

    if (this->allocSize < neededSize)
        this->bytes = reinterpret_cast<unsigned char *>(
            realloc(this->bytes, neededSize));

    if (this->bytes == NULL)
        throwf("Can't get storage for a %u-byte packet.", neededSize);

    memcpy(this->bytes + this->length, data, dataLength);

    this->length += dataLength;
}



packetPtr::packetPtr() {
    // Base class constructor will construct pointer that points to nothing
}



packetPtr::packetPtr(packet * const packetP) : autoObjectPtr(packetP) {}



packet *
packetPtr::operator->() const {

    girmem::autoObject * const p(this->objectP);
    return dynamic_cast<packet *>(p);
}



packetSocket::packetSocket(int const sockFd) {

    int dupRc;

    dupRc = dup(sockFd);
    
    if (dupRc < 0)
        throwf("dup() failed.  errno=%d (%s)", errno, strerror(errno));
    else {
        this->sockFd = dupRc;

        this->inEscapeSeq = false;
        this->inPacket    = false;

        this->escAccum.len = 0;
        
        fcntl(this->sockFd, F_SETFL, O_NONBLOCK);

        this->eof = false;
    }
}



packetSocket::~packetSocket() {

    close(this->sockFd);
}



/*----------------------------------------------------------------------------
   To complete the job, we should provide writing services analogous
   to the reading services.  That means a no-wait write method and
   the ability to interrupt with a signal without corrupting the write
   stream.

   We're a little to lazy to do that now, since we don't need it yet,
   but here's a design for that:

   The packetSocket has a send queue of packets called the write
   buffer.  It stores packetPtr pointers to packets created by the
   user.

   packetSocket::write() adds a packet to the write buffer, then calls
   packetSocket::writeToFile().  If you give it a null packetPtr,
   it just calls writeToFile().

   packetSocket::writeToFile() writes from the write buffer to the
   socket whatever the socket will take immediately.  It writes the
   start sequence, writes the packet data, then writes the end
   sequence.  The packetSocket keeps track of where it is in the
   process of writing the current send packet (including start end
   end sequences) it is.

   packetSocket::write() returns a "flushed" flag indicating that there
   is nothing left in the write buffer.

   packetSocket::writeWait() just calls packetSocket::write(), then
   packetSocket::flush() in a poll() loop.
-----------------------------------------------------------------------------*/


static void
writeFd(int                   const fd,
        const unsigned char * const data,
        size_t                const size,
        size_t *              const bytesWrittenP) {

    size_t totalBytesWritten;
    bool full;  // File image is "full" for now - won't take any more data

    full = false;
    totalBytesWritten = 0;

    while (totalBytesWritten < size && !full) {
        ssize_t rc;

        rc = write(fd, &data[totalBytesWritten], size - totalBytesWritten);

        if (rc < 0) {
            if (errno == EAGAIN)
                full = true;
            else
                throwf("write() of socket failed with errno %d (%s)",
                       errno, strerror(errno));
        } else if (rc == 0)
            throwf("Zero byte short write.");
        else {
            size_t const bytesWritten(rc);
            totalBytesWritten += bytesWritten;
        }
    }
    *bytesWrittenP = totalBytesWritten;
}



static void
writeFdWait(int                   const fd,
            const unsigned char * const data,
            size_t                const size) {
/*----------------------------------------------------------------------------
   Write the 'size' bytes at 'data' to the file image 'fd'.  Wait as long
   as it takes for the file image to be able to take all the data.
-----------------------------------------------------------------------------*/
    size_t totalBytesWritten;

    // We do the first one blind because it will probably just work
    // and we don't want to waste the poll() call and buffer arithmetic.

    writeFd(fd, data, size, &totalBytesWritten);

    while (totalBytesWritten < size) {
        struct pollfd pollfds[1];
        
        pollfds[0].fd = fd;
        pollfds[0].events = POLLOUT;
        
        poll(pollfds, ARRAY_SIZE(pollfds), -1);

        size_t bytesWritten;

        writeFd(fd, &data[totalBytesWritten], size - totalBytesWritten,
                &bytesWritten);

        totalBytesWritten += bytesWritten;
    }
}



void
packetSocket::writeWait(packetPtr const& packetP) const {

    const unsigned char * const packetStart(
        reinterpret_cast<const unsigned char *>(ESC_STR "PKT"));
    const unsigned char * const packetEnd(
        reinterpret_cast<const unsigned char *>(ESC_STR "END"));

    writeFdWait(this->sockFd, packetStart, 4);

    writeFdWait(this->sockFd, packetP->getBytes(), packetP->getLength());

    writeFdWait(this->sockFd, packetEnd, 4);
}



static ssize_t
libc_read(int    const fd,
          void * const buf,
          size_t const count) {

    return read(fd, buf, count);
}



void
packetSocket::takeSomeEscapeSeq(const unsigned char * const buffer,
                                size_t                const length,
                                size_t *              const bytesTakenP) {
/*----------------------------------------------------------------------------
   Take and process some bytes from the incoming stream 'buffer',
   which contains 'length' bytes, assuming they are within an escape
   sequence.
-----------------------------------------------------------------------------*/
    size_t bytesTaken;

    bytesTaken = 0;

    while (this->escAccum.len < 3 && bytesTaken < length)
        this->escAccum.bytes[this->escAccum.len++] = buffer[bytesTaken++];

    assert(this->escAccum.len <= 3);

    if (this->escAccum.len == 3) {
        if (0) {
        } else if (xmlrpc_memeq(this->escAccum.bytes, "NOP", 3)) {
            // Nothing to do
        } else if (xmlrpc_memeq(this->escAccum.bytes, "PKT", 3)) {
            this->packetAccumP = packetPtr(new packet);
            this->inPacket = true;
        } else if (xmlrpc_memeq(this->escAccum.bytes, "END", 3)) {
            if (this->inPacket) {
                this->readBuffer.push(this->packetAccumP);
                this->inPacket = false;
                this->packetAccumP = packetPtr();
            } else
                throwf("END control word received without preceding PKT");
        } else if (xmlrpc_memeq(this->escAccum.bytes, "ESC", 3)) {
            if (this->inPacket)
                this->packetAccumP->addData((const unsigned char *)ESC_STR, 1);
            else
                throwf("ESC control work received outside of a packet");
        } else
            throwf("Invalid escape sequence 0x%02x%02x%02x read from "
                   "stream socket under packet socket",
                   this->escAccum.bytes[0],
                   this->escAccum.bytes[1],
                   this->escAccum.bytes[2]);
        
        this->inEscapeSeq = false;
        this->escAccum.len = 0;
    }
    *bytesTakenP = bytesTaken;
}



void
packetSocket::takeSomePacket(const unsigned char * const buffer,
                             size_t                const length,
                             size_t *              const bytesTakenP) {

    assert(!this->inEscapeSeq);

    const unsigned char * const escPos(
        (const unsigned char *)memchr(buffer, ESC, length));

    if (escPos) {
        size_t const escOffset(escPos - &buffer[0]);
        // move everything before the escape sequence into the
        // packet accumulator.
        this->packetAccumP->addData(buffer, escOffset);

        // Caller can pick up from here; we don't know nothin' 'bout
        // no escape sequences.

        *bytesTakenP = escOffset;
    } else {
        // No complete packet yet and no substitution to do;
        // just throw the whole thing into the accumulator.
        this->packetAccumP->addData(buffer, length);
        *bytesTakenP = length;
    }
}



void
packetSocket::verifyNothingAccumulated() {
/*----------------------------------------------------------------------------
   Throw an error if there is a partial packet accumulated.
-----------------------------------------------------------------------------*/
    if (this->inEscapeSeq)
        throwf("Streams socket closed in the middle of an "
               "escape sequence");
    
    if (this->inPacket)
        throwf("Stream socket closed in the middle of a packet "
               "(%u bytes of packet received; no END marker to mark "
               "end of packet)", this->packetAccumP->getLength());
}



void
packetSocket::processBytesRead(const unsigned char * const buffer,
                               size_t                const bytesRead) {

    unsigned int cursor;  // Cursor into buffer[]
    cursor = 0;
    while (cursor < bytesRead) {
        size_t bytesTaken;

        if (this->inEscapeSeq)
            this->takeSomeEscapeSeq(&buffer[cursor],
                                    bytesRead - cursor,
                                    &bytesTaken);
        else if (buffer[cursor] == ESC) {
            this->inEscapeSeq = true;
            bytesTaken = 1;
        } else if (this->inPacket)
            this->takeSomePacket(&buffer[cursor],
                                 bytesRead - cursor,
                                 &bytesTaken);
        else
            throwf("Byte 0x%02x is not in a packet or escape sequence.  "
                   "Sender is probably not using packet socket protocol",
                   buffer[cursor]);
        
        cursor += bytesTaken;
    }
}



void
packetSocket::readFromFile() {
/*----------------------------------------------------------------------------
   Read some data from the underlying stream socket.  Read as much as is
   available right now, up to 4K.  Update 'this' to reflect the data read.

   E.g. if we read an entire packet, we add it to the packet buffer
   (this->readBuffer).  If we read the first part of a packet, we add
   it to the packet accumulator (*this->packetAccumP).  If we read the end
   of a packet, we add the full packet to the packet buffer and empty
   the packet accumulator.  Etc.
-----------------------------------------------------------------------------*/
    bool wouldblock;

    wouldblock = false;

    while (this->readBuffer.empty() && !this->eof && !wouldblock) {
        unsigned char buffer[4096];
        ssize_t rc;

        rc = libc_read(this->sockFd, buffer, sizeof(buffer));

        if (rc < 0) {
            if (errno == EWOULDBLOCK)
                wouldblock = true;
            else
                throwf("read() of socket failed with errno %d (%s)",
                       errno, strerror(errno));
        } else {
            size_t const bytesRead(rc);

            if (bytesRead == 0) {
                this->eof = true;
                this->verifyNothingAccumulated();
            } else
                this->processBytesRead(buffer, bytesRead);
        }
    }
}



void
packetSocket::read(bool *      const eofP,
                   bool *      const gotPacketP,
                   packetPtr * const packetPP) {
/*----------------------------------------------------------------------------
   Read one packet from the socket, through the internal packet buffer.

   If there is a packet immediately available, return it as *packetPP and
   return *gotPacketP true.  Otherwise, return *gotPacketP false.

   Iff the socket has no more data coming (it is shut down) and there
   is no complete packet in the packet buffer, return *eofP.

   This leaves one other possibility: there is no full packet immediately
   available, but there may be in the future because the socket is still
   alive.  In that case, we return *eofP == false and *gotPacketP == false.

   Any packet we return belongs to caller; Caller must delete it.
-----------------------------------------------------------------------------*/
    // Move any packets now waiting to be read in the underlying stream
    // socket into our packet buffer (this->readBuffer).

    this->readFromFile();

    if (this->readBuffer.empty()) {
        *gotPacketP = false;
        *eofP = this->eof;
    } else {
        *gotPacketP = true;
        *eofP = false;
        *packetPP = this->readBuffer.front();
        readBuffer.pop();
    }
}



void
packetSocket::readWait(volatile const int * const interruptP,
                       bool *               const eofP,
                       bool *               const gotPacketP,
                       packetPtr *          const packetPP) {

    bool gotPacket;
    bool eof;

    gotPacket = false;
    eof = false;

    while (!gotPacket && !eof && !*interruptP) {
        struct pollfd pollfds[1];

        pollfds[0].fd = this->sockFd;
        pollfds[0].events = POLLIN;

        poll(pollfds, ARRAY_SIZE(pollfds), -1);

        this->read(&eof, &gotPacket, packetPP);
    }

    *gotPacketP = gotPacket;
    *eofP = eof;
}



void
packetSocket::readWait(volatile const int * const interruptP,
                       bool *               const eofP,
                       packetPtr *          const packetPP) {

    bool gotPacket;

    this->readWait(interruptP, eofP, &gotPacket, packetPP);

    if (!gotPacket)
        throwf("Packet read was interrupted");
}



void
packetSocket::readWait(bool *      const eofP,
                       packetPtr * const packetPP) {

    int const interrupt(0);  // Never interrupt

    this->readWait(&interrupt, eofP, packetPP);
}

} // namespace