/*============================================================================
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.
============================================================================*/
#define _BSD_SOURCE // gets uint defined
#include <cassert>
#include <string>
#include <queue>
#include <iostream>
#include <sstream>
#include <cstdio>
#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);
}
static void
writeFd(int const fd,
const unsigned char * const data,
size_t const size) {
size_t totalBytesWritten;
totalBytesWritten = 0;
while (totalBytesWritten < size) {
ssize_t rc;
rc = write(fd, data, size);
if (rc < 0)
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;
}
}
}
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"));
writeFd(this->sockFd, packetStart, 4);
writeFd(this->sockFd, packetP->getBytes(), packetP->getLength());
writeFd(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) {
uint 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(bool * const eofP,
packetPtr * const packetPP) {
bool gotPacket;
bool eof;
gotPacket = false;
eof = false;
while (!gotPacket && !eof) {
struct pollfd pollfds[1];
pollfds[0].fd = this->sockFd;
pollfds[0].events = POLLIN;
poll(pollfds, ARRAY_SIZE(pollfds), -1);
this->read(&eof, &gotPacket, packetPP);
}
*eofP = eof;
}
} // namespace
