bizhang_-obav/src/modules/mavlink/mavlink_ftp.cpp

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#include <crc32.h>
#include <unistd.h>
#include <fcntl.h>

#include "mavlink_ftp.h"

MavlinkFTP *MavlinkFTP::_server;

MavlinkFTP *
MavlinkFTP::getServer()
{
	// XXX this really cries out for some locking...
	if (_server == nullptr) {
		_server = new MavlinkFTP;
	}
	return _server;
}

MavlinkFTP::MavlinkFTP()
{
	// initialise the request freelist
	dq_init(&_workFree);
	sem_init(&_lock, 0, 1);

	// drop work entries onto the free list
	for (unsigned i = 0; i < kRequestQueueSize; i++) {
		_qFree(&_workBufs[i]);
	}

}

void
MavlinkFTP::handle_message(mavlink_message_t *msg, mavlink_channel_t channel)
{
	// get a free request
	auto req = _dqFree();

	// if we couldn't get a request slot, just drop it
	if (req != nullptr) {

		// decode the request
		req->decode(channel, msg);

		// and queue it for the worker
		work_queue(LPWORK, &req->work, &MavlinkFTP::_workerTrampoline, req, 0);
	}
}

void
MavlinkFTP::_workerTrampoline(void *arg)
{
	auto req = reinterpret_cast<Request *>(arg);
	auto server = MavlinkFTP::getServer();

	// call the server worker with the work item
	server->_worker(req);
}

void
MavlinkFTP::_worker(Request *req)
{
	auto hdr = req->header();
	ErrorCode errorCode = kErrNone;
	uint32_t messageCRC;

	// basic sanity checks; must validate length before use
	if ((hdr->magic != kProtocolMagic) || (hdr->size > kMaxDataLength)) {
		errorCode = kErrNoRequest;
		goto out;
	}

	// check request CRC to make sure this is one of ours
	messageCRC = hdr->crc32;
	hdr->crc32 = 0;
	if (crc32(req->data(), req->dataSize()) != messageCRC) {
		errorCode = kErrNoRequest;
		goto out;
	}

	switch (hdr->opcode) {
	case kCmdNone:
		break;

	case kCmdTerminate:
		if (!Session::terminate(hdr->session)) {
			errorCode = kErrNoRequest;
		}
		break;

	case kCmdReset:
		Session::reset();
		break;

	case kCmdList:
		errorCode = _workList(req);
		break;

	case kCmdOpen:
		errorCode = _workOpen(req, false);
		break;

	case kCmdCreate:
		errorCode = _workOpen(req, true);
		break;

	case kCmdRead:
		errorCode = _workRead(req);
		break;

	case kCmdWrite:
		errorCode = _workWrite(req);
		break;

	case kCmdRemove:
		errorCode = _workRemove(req);
		break;

	default:
		errorCode = kErrNoRequest;
		break;	
	}

out:
	// handle success vs. error
	if (errorCode == kErrNone) {
		hdr->opcode = kRspAck;
	} else {
		hdr->opcode = kRspNak;
		hdr->size = 1;
		hdr->data[0] = errorCode;
	}

	// respond to the request
	_reply(req);

	// free the request buffer back to the freelist
	_qFree(req);
}

void
MavlinkFTP::_reply(Request *req)
{
	auto hdr = req->header();

	// message is assumed to be already constructed in the request buffer, so generate the CRC
	hdr->crc32 = 0;
	hdr->crc32 = crc32(req->data(), req->dataSize());

	// then pack and send the reply back to the request source
	mavlink_msg_encapsulated_data_send(req->channel, req->sequence(), req->data());
}

MavlinkFTP::ErrorCode
MavlinkFTP::_workList(Request *req)
{
	auto hdr = req->header();

	// open directory

	// seek in directory

	// read entries until buffer is full

	// send reply

	return kErrNone;
}

MavlinkFTP::ErrorCode
MavlinkFTP::_workOpen(Request *req, bool create)
{
	auto hdr = req->header();

	// allocate session ID
	int session = Session::allocate();
	if (session < 0) {
		return kErrNoSession;
	}

	// get the session to open the file
	if (!Session::get(session)->open(req->dataAsCString(), create)) {
		return create ? kErrPerm : kErrNotFile;
	}

	// save the session ID in the reply
	hdr->session = session;
	hdr->size = 0;

	return kErrNone;
}

MavlinkFTP::ErrorCode
MavlinkFTP::_workRead(Request *req)
{
	auto hdr = req->header();

	// look up session
	auto session = Session::get(hdr->session);
	if (session == nullptr) {
		return kErrNoSession;
	}

	// read from file
	int result = session->read(hdr->offset, &hdr->data[0], hdr->size);

	if (result < 0) {
		return kErrIO;
	}
	hdr->size = result;
	return kErrNone;
}

MavlinkFTP::ErrorCode
MavlinkFTP::_workWrite(Request *req)
{
	auto hdr = req->header();

	// look up session
	auto session = Session::get(hdr->session);
	if (session == nullptr) {
		return kErrNoSession;
	}

	// append to file
	int result = session->append(hdr->offset, &hdr->data[0], hdr->size);

	if (result < 0) {
		// XXX might also be no space, I/O, etc.
		return kErrNotAppend;
	}

	hdr->size = result;
	return kErrNone;
}

MavlinkFTP::ErrorCode
MavlinkFTP::_workRemove(Request *req)
{
	auto hdr = req->header();

	// for now, send error reply
	return kErrPerm;
}

MavlinkFTP::Session MavlinkFTP::Session::_sessions[MavlinkFTP::Session::kMaxSession];

int
MavlinkFTP::Session::allocate()
{
	for (unsigned i = 0; i < kMaxSession; i++) {
		if (_sessions[i]._fd < 0) {
			return i;
		}
	}
	return -1;
}

MavlinkFTP::Session *
MavlinkFTP::Session::get(unsigned index)
{
	if ((index >= kMaxSession) || (_sessions[index]._fd < 0)) {
		return nullptr;
	}
	return &_sessions[index];
}

void
MavlinkFTP::Session::terminate()
{
	// clean up aborted transfers?
	if (_fd >= 0) {
		close(_fd);
		_fd = -1;
	}
}

bool
MavlinkFTP::Session::terminate(unsigned index)
 {
	Session *session = get(index);

	if (session == nullptr) {
		return false;
	}

	session->terminate();
	return true;
}

void
MavlinkFTP::Session::reset()
{
	for (unsigned i = 0; i < kMaxSession; i++) {
		terminate(i);
	}
}

bool
MavlinkFTP::Session::open(const char *path, bool create)
{
	int oflag = create ? (O_CREAT | O_EXCL | O_APPEND) : O_RDONLY;

	_fd = open(path, oflag);
	if (_fd < 0) {
		return false;
	}
	return true;
}

int
MavlinkFTP::Session::read(off_t offset, uint8_t *buf, uint8_t count)
{
	// can we seek to the location?
	if (lseek(_fd, offset, SEEK_SET) < 0) {
		return -1;
	}

	return read(_fd, buf, count);
}

int
MavlinkFTP::Session::append(off_t offset, uint8_t *buf, uint8_t count)
{
	// make sure that the requested offset matches our current position
	off_t pos = lseek(_fd, 0, SEEK_CUR);
	if (pos != offset) {
		return -1;
	}
	return write(_fd, buf, count);
}

char *
MavlinkFTP::Request::dataAsCString()
{
	// guarantee nul termination
	if (header()->size < kMaxDataLength) {
		data()[header()->size] = '\0';
	} else {
		data()[kMaxDataLength - 1] = '\0';
	}

	// and return data
	return (char *)data();
}