Additional FTP command support plus unit test

- Restructured to a flatter class implementation
- Added support for create/remove directory, remove file
- Refactored error codes and command opcodes
- Added unit test support
- Fixed bugs found by unit test

2 files changed, 427 insertions, 311 deletions

diff --git a/src/modules/mavlink/mavlink_ftp.cpp b/src/modules/mavlink/mavlink_ftp.cpp
index 5b65dc369..72ede8797 100644
--- a/src/modules/mavlink/mavlink_ftp.cpp
+++ b/src/modules/mavlink/mavlink_ftp.cpp
@@ -31,38 +31,39 @@
  *
  ****************************************************************************/
 
+/// @file mavlink_ftp.cpp
+///	@author px4dev, Don Gagne <don@thegagnes.com>
+
 #include <crc32.h>
 #include <unistd.h>
 #include <stdio.h>
 #include <fcntl.h>
 #include <sys/stat.h>
+#include <errno.h>
 
 #include "mavlink_ftp.h"
+#include "mavlink_tests/mavlink_ftp_test.h"
 
 // Uncomment the line below to get better debug output. Never commit with this left on.
 //#define MAVLINK_FTP_DEBUG
 
-MavlinkFTP *MavlinkFTP::_server;
-
 MavlinkFTP *
-MavlinkFTP::getServer()
+MavlinkFTP::get_server(void)
 {
-	// XXX this really cries out for some locking...
-	if (_server == nullptr) {
-		_server = new MavlinkFTP;
-	}
-	return _server;
+	static MavlinkFTP server;
+        return &server;
 }
 
 MavlinkFTP::MavlinkFTP() :
-	_session_fds{},
-	_workBufs{},
-	_workFree{},
-	_lock{}
+	_request_bufs{},
+	_request_queue{},
+	_request_queue_sem{},
+	_utRcvMsgFunc{},
+	_ftp_test{}
 {
 	// initialise the request freelist
-	dq_init(&_workFree);
-	sem_init(&_lock, 0, 1);
+	dq_init(&_request_queue);
+	sem_init(&_request_queue_sem, 0, 1);
 
 	// initialize session list
 	for (size_t i=0; i<kMaxSession; i++) {
@@ -71,167 +72,247 @@ MavlinkFTP::MavlinkFTP() :
 
 	// drop work entries onto the free list
 	for (unsigned i = 0; i < kRequestQueueSize; i++) {
-		_qFree(&_workBufs[i]);
+		_return_request(&_request_bufs[i]);
 	}
 
 }
 
+#ifdef MAVLINK_FTP_UNIT_TEST
+void
+MavlinkFTP::set_unittest_worker(ReceiveMessageFunc_t rcvMsgFunc, MavlinkFtpTest *ftp_test)
+{
+	_utRcvMsgFunc = rcvMsgFunc;
+	_ftp_test = ftp_test;
+}
+#endif
+
 void
 MavlinkFTP::handle_message(Mavlink* mavlink, mavlink_message_t *msg)
 {
 	// get a free request
-	auto req = _dqFree();
+	struct Request* req = _get_request();
 
 	// if we couldn't get a request slot, just drop it
-	if (req != nullptr) {
-
-		// decode the request
-		if (req->decode(mavlink, msg)) {
+	if (req == nullptr) {
+		warnx("Dropping FTP request: queue full\n");
+		return;
+	}
 
-			// and queue it for the worker
-			work_queue(LPWORK, &req->work, &MavlinkFTP::_workerTrampoline, req, 0);
-		} else {
-			_qFree(req);
+	if (msg->msgid == MAVLINK_MSG_ID_FILE_TRANSFER_PROTOCOL) {
+		mavlink_msg_file_transfer_protocol_decode(msg, &req->message);
+		
+#ifdef MAVLINK_FTP_UNIT_TEST
+		if (!_utRcvMsgFunc) {
+			warnx("Incorrectly written unit test\n");
+			return;
+		}
+		// We use fake ids when unit testing
+		req->serverSystemId = MavlinkFtpTest::serverSystemId;
+		req->serverComponentId = MavlinkFtpTest::serverComponentId;
+		req->serverChannel = MavlinkFtpTest::serverChannel;
+#else
+		// Not unit testing, use the real thing
+		req->serverSystemId = mavlink->get_system_id();
+		req->serverComponentId = mavlink->get_component_id();
+		req->serverChannel = mavlink->get_channel();
+#endif
+		
+		// This is the system id we want to target when sending
+		req->targetSystemId = msg->sysid;
+			
+		if (req->message.target_system == req->serverSystemId) {
+			req->mavlink = mavlink;
+#ifdef MAVLINK_FTP_UNIT_TEST
+			// We are running in Unit Test mode. Don't queue, just call _worket directly.
+			_process_request(req);
+#else
+			// We are running in normal mode. Queue the request to the worker
+			work_queue(LPWORK, &req->work, &MavlinkFTP::_worker_trampoline, req, 0);
+#endif
+            return;
 		}
 	}
+
+	_return_request(req);
 }
 
+/// @brief Queued static work queue routine to handle mavlink messages
 void
-MavlinkFTP::_workerTrampoline(void *arg)
+MavlinkFTP::_worker_trampoline(void *arg)
 {
-	auto req = reinterpret_cast<Request *>(arg);
-	auto server = MavlinkFTP::getServer();
+	Request* req = reinterpret_cast<Request *>(arg);
+	MavlinkFTP* server = MavlinkFTP::get_server();
 
 	// call the server worker with the work item
-	server->_worker(req);
+	server->_process_request(req);
 }
 
+/// @brief Processes an FTP message
 void
-MavlinkFTP::_worker(Request *req)
+MavlinkFTP::_process_request(Request *req)
 {
-	auto hdr = req->header();
+	PayloadHeader *payload = reinterpret_cast<PayloadHeader *>(&req->message.payload[0]);
+
 	ErrorCode errorCode = kErrNone;
-	uint32_t messageCRC;
 
 	// basic sanity checks; must validate length before use
-	if (hdr->size > kMaxDataLength) {
-		errorCode = kErrNoRequest;
+	if (payload->size > kMaxDataLength) {
+		errorCode = kErrInvalidDataSize;
 		goto out;
 	}
 
 	// check request CRC to make sure this is one of ours
-	messageCRC = hdr->crc32;
-	hdr->crc32 = 0;
-	hdr->padding[0] = 0;
-	hdr->padding[1] = 0;
-	hdr->padding[2] = 0;
-	if (crc32(req->rawData(), req->dataSize()) != messageCRC) {
-		errorCode = kErrNoRequest;
+	if (_payload_crc32(payload) != payload->crc32) {
+		errorCode = kErrCrc;
 		goto out;
 		warnx("ftp: bad crc");
 	}
 
 #ifdef MAVLINK_FTP_DEBUG
-	printf("ftp: channel %u opc %u size %u offset %u\n", req->channel(), hdr->opcode, hdr->size, hdr->offset);
+	printf("ftp: channel %u opc %u size %u offset %u\n", req->serverChannel, payload->opcode, payload->size, payload->offset);
 #endif
 
-	switch (hdr->opcode) {
+	switch (payload->opcode) {
 	case kCmdNone:
 		break;
 
-	case kCmdTerminate:
-		errorCode = _workTerminate(req);
+	case kCmdTerminateSession:
+		errorCode = _workTerminate(payload);
 		break;
 
-	case kCmdReset:
-		errorCode = _workReset();
+	case kCmdResetSessions:
+		errorCode = _workReset(payload);
 		break;
 
-	case kCmdList:
-		errorCode = _workList(req);
+	case kCmdListDirectory:
+		errorCode = _workList(payload);
 		break;
 
-	case kCmdOpen:
-		errorCode = _workOpen(req, false);
+	case kCmdOpenFile:
+		errorCode = _workOpen(payload, false);
 		break;
 
-	case kCmdCreate:
-		errorCode = _workOpen(req, true);
+	case kCmdCreateFile:
+		errorCode = _workOpen(payload, true);
 		break;
 
-	case kCmdRead:
-		errorCode = _workRead(req);
+	case kCmdReadFile:
+		errorCode = _workRead(payload);
 		break;
 
-	case kCmdWrite:
-		errorCode = _workWrite(req);
+	case kCmdWriteFile:
+		errorCode = _workWrite(payload);
 		break;
 
-	case kCmdRemove:
-		errorCode = _workRemove(req);
+	case kCmdRemoveFile:
+		errorCode = _workRemoveFile(payload);
 		break;
 
+	case kCmdCreateDirectory:
+		errorCode = _workCreateDirectory(payload);
+		break;
+			
+	case kCmdRemoveDirectory:
+		errorCode = _workRemoveDirectory(payload);
+		break;
+			
 	default:
-		errorCode = kErrNoRequest;
+		errorCode = kErrUnknownCommand;
 		break;	
 	}
 
 out:
 	// handle success vs. error
 	if (errorCode == kErrNone) {
-		hdr->opcode = kRspAck;
+		payload->opcode = kRspAck;
 #ifdef MAVLINK_FTP_DEBUG
 		warnx("FTP: ack\n");
 #endif
 	} else {
 		warnx("FTP: nak %u", errorCode);
-		hdr->opcode = kRspNak;
-		hdr->size = 1;
-		hdr->data[0] = errorCode;
+		payload->opcode = kRspNak;
+		payload->size = 1;
+		payload->data[0] = errorCode;
+		if (errorCode == kErrFailErrno) {
+			payload->size = 2;
+			payload->data[1] = errno;
+		}
 	}
 
+	
 	// respond to the request
 	_reply(req);
 
-	// free the request buffer back to the freelist
-	_qFree(req);
+	_return_request(req);
 }
 
+/// @brief Sends the specified FTP reponse message out through mavlink
 void
 MavlinkFTP::_reply(Request *req)
 {
-	auto hdr = req->header();
+	PayloadHeader *payload = reinterpret_cast<PayloadHeader *>(&req->message.payload[0]);
 	
-	hdr->seqNumber = req->header()->seqNumber + 1;
+	payload->seqNumber = payload->seqNumber + 1;
 
-	// message is assumed to be already constructed in the request buffer, so generate the CRC
-	hdr->crc32 = 0;
-	hdr->padding[0] = 0;
-	hdr->padding[1] = 0;
-	hdr->padding[2] = 0;
-	hdr->crc32 = crc32(req->rawData(), req->dataSize());
+	payload->crc32 = _payload_crc32(payload);
 
-	// then pack and send the reply back to the request source
-	req->reply();
+	mavlink_message_t msg;
+	msg.checksum = 0;
+#ifndef MAVLINK_FTP_UNIT_TEST
+	uint16_t len =
+#endif
+	mavlink_msg_file_transfer_protocol_pack_chan(req->serverSystemId,	// Sender system id
+								    req->serverComponentId,	// Sender component id
+								    req->serverChannel,		// Channel to send on
+								    &msg,			// Message to pack payload into
+								    0,				// Target network
+								    req->targetSystemId,	// Target system id
+								    0,				// Target component id
+								    (const uint8_t*)payload);	// Payload to pack into message
+	
+	bool success = true;
+#ifdef MAVLINK_FTP_UNIT_TEST
+	// Unit test hook is set, call that instead
+	_utRcvMsgFunc(&msg, _ftp_test);
+#else
+	Mavlink	*mavlink = req->mavlink;
+	
+	mavlink->lockMessageBufferMutex();
+	success = mavlink->message_buffer_write(&msg, len);
+	mavlink->unlockMessageBufferMutex();
+		
+#endif
+
+	if (!success) {
+		warnx("FTP TX ERR");
+	}
+#ifdef MAVLINK_FTP_DEBUG
+	else {
+		warnx("wrote: sys: %d, comp: %d, chan: %d, checksum: %d",
+		      req->serverSystemId,
+		      req->serverComponentId,
+		      req->serverChannel,
+		      msg.checksum);
+	}
+#endif
 }
 
+/// @brief Responds to a List command
 MavlinkFTP::ErrorCode
-MavlinkFTP::_workList(Request *req)
+MavlinkFTP::_workList(PayloadHeader* payload)
 {
-	auto hdr = req->header();
-    
     char dirPath[kMaxDataLength];
-    strncpy(dirPath, req->dataAsCString(), kMaxDataLength);
+    strncpy(dirPath, _data_as_cstring(payload), kMaxDataLength);
     
 	DIR *dp = opendir(dirPath);
 
 	if (dp == nullptr) {
 		warnx("FTP: can't open path '%s'", dirPath);
-		return kErrNotDir;
+		return kErrFailErrno;
 	}
     
 #ifdef MAVLINK_FTP_DEBUG
-	warnx("FTP: list %s offset %d", dirPath, hdr->offset);
+	warnx("FTP: list %s offset %d", dirPath, payload->offset);
 #endif
 
 	ErrorCode errorCode = kErrNone;
@@ -239,19 +320,19 @@ MavlinkFTP::_workList(Request *req)
 	unsigned offset = 0;
 
 	// move to the requested offset
-	seekdir(dp, hdr->offset);
+	seekdir(dp, payload->offset);
 
 	for (;;) {
 		// read the directory entry
 		if (readdir_r(dp, &entry, &result)) {
 			warnx("FTP: list %s readdir_r failure\n", dirPath);
-			errorCode = kErrIO;
+			errorCode = kErrFailErrno;
 			break;
 		}
 
 		// no more entries?
 		if (result == nullptr) {
-			if (hdr->offset != 0 && offset == 0) {
+			if (payload->offset != 0 && offset == 0) {
 				// User is requesting subsequent dir entries but there were none. This means the user asked
 				// to seek past EOF.
 				errorCode = kErrEOF;
@@ -299,94 +380,95 @@ MavlinkFTP::_workList(Request *req)
 		}
 		
 		// Move the data into the buffer
-		hdr->data[offset++] = direntType;
-		strcpy((char *)&hdr->data[offset], buf);
+		payload->data[offset++] = direntType;
+		strcpy((char *)&payload->data[offset], buf);
 #ifdef MAVLINK_FTP_DEBUG
-		printf("FTP: list %s %s\n", dirPath, (char *)&hdr->data[offset-1]);
+		printf("FTP: list %s %s\n", dirPath, (char *)&payload->data[offset-1]);
 #endif
 		offset += nameLen + 1;
 	}
 
 	closedir(dp);
-	hdr->size = offset;
+	payload->size = offset;
 
 	return errorCode;
 }
 
+/// @brief Responds to an Open command
 MavlinkFTP::ErrorCode
-MavlinkFTP::_workOpen(Request *req, bool create)
+MavlinkFTP::_workOpen(PayloadHeader* payload, bool create)
 {
-	auto hdr = req->header();
-    
-	int session_index = _findUnusedSession();
+	int session_index = _find_unused_session();
 	if (session_index < 0) {
-		return kErrNoSession;
+		warnx("FTP: Open failed - out of sessions\n");
+		return kErrNoSessionsAvailable;
 	}
-
+	
+	char *filename = _data_as_cstring(payload);
 	
 	uint32_t fileSize = 0;
 	if (!create) {
 		struct stat st;
-		if (stat(req->dataAsCString(), &st) != 0) {
-			return kErrNotFile;
+		if (stat(filename, &st) != 0) {
+			return kErrFailErrno;
 		}
 		fileSize = st.st_size;
 	}
 
 	int oflag = create ? (O_CREAT | O_EXCL | O_APPEND) : O_RDONLY;
     
-	int fd = ::open(req->dataAsCString(), oflag);
+	int fd = ::open(filename, oflag);
 	if (fd < 0) {
-		return create ? kErrPerm : kErrNotFile;
+		return kErrFailErrno;
 	}
 	_session_fds[session_index] = fd;
 
-	hdr->session = session_index;
+	payload->session = session_index;
 	if (create) {
-		hdr->size = 0;
+		payload->size = 0;
 	} else {
-		hdr->size = sizeof(uint32_t);
-		*((uint32_t*)hdr->data) = fileSize;
+		payload->size = sizeof(uint32_t);
+		*((uint32_t*)payload->data) = fileSize;
 	}
 
 	return kErrNone;
 }
 
+/// @brief Responds to a Read command
 MavlinkFTP::ErrorCode
-MavlinkFTP::_workRead(Request *req)
+MavlinkFTP::_workRead(PayloadHeader* payload)
 {
-	auto hdr = req->header();
+	int session_index = payload->session;
 
-	int session_index = hdr->session;
-
-	if (!_validSession(session_index)) {
-		return kErrNoSession;
+	if (!_valid_session(session_index)) {
+		return kErrInvalidSession;
 	}
 
 	// Seek to the specified position
 #ifdef MAVLINK_FTP_DEBUG
-	warnx("seek %d", hdr->offset);
+	warnx("seek %d", payload->offset);
 #endif
-	if (lseek(_session_fds[session_index], hdr->offset, SEEK_SET) < 0) {
+	if (lseek(_session_fds[session_index], payload->offset, SEEK_SET) < 0) {
 		// Unable to see to the specified location
 		warnx("seek fail");
 		return kErrEOF;
 	}
 
-	int bytes_read = ::read(_session_fds[session_index], &hdr->data[0], kMaxDataLength);
+	int bytes_read = ::read(_session_fds[session_index], &payload->data[0], kMaxDataLength);
 	if (bytes_read < 0) {
 		// Negative return indicates error other than eof
 		warnx("read fail %d", bytes_read);
-		return kErrIO;
+		return kErrFailErrno;
 	}
 
-	hdr->size = bytes_read;
+	payload->size = bytes_read;
 
 	return kErrNone;
 }
 
+/// @brief Responds to a Write command
 MavlinkFTP::ErrorCode
-MavlinkFTP::_workWrite(Request *req)
+MavlinkFTP::_workWrite(PayloadHeader* payload)
 {
 #if 0
     // NYI: Coming soon
@@ -409,35 +491,44 @@ MavlinkFTP::_workWrite(Request *req)
 	hdr->size = result;
 	return kErrNone;
 #else
-	return kErrPerm;
+	return kErrUnknownCommand;
 #endif
 }
 
+/// @brief Responds to a RemoveFile command
 MavlinkFTP::ErrorCode
-MavlinkFTP::_workRemove(Request *req)
+MavlinkFTP::_workRemoveFile(PayloadHeader* payload)
 {
-	//auto hdr = req->header();
-
-	// for now, send error reply
-	return kErrPerm;
+	char file[kMaxDataLength];
+	strncpy(file, _data_as_cstring(payload), kMaxDataLength);
+	
+	if (unlink(file) == 0) {
+		payload->size = 0;
+		return kErrNone;
+	} else {
+		return kErrFailErrno;
+	}
 }
 
+/// @brief Responds to a Terminate command
 MavlinkFTP::ErrorCode
-MavlinkFTP::_workTerminate(Request *req)
+MavlinkFTP::_workTerminate(PayloadHeader* payload)
 {
-	auto hdr = req->header();
-    
-	if (!_validSession(hdr->session)) {
-		return kErrNoSession;
+	if (!_valid_session(payload->session)) {
+		return kErrInvalidSession;
 	}
     
-	::close(_session_fds[hdr->session]);
+	::close(_session_fds[payload->session]);
+	_session_fds[payload->session] = -1;
+	
+	payload->size = 0;
 
 	return kErrNone;
 }
 
+/// @brief Responds to a Reset command
 MavlinkFTP::ErrorCode
-MavlinkFTP::_workReset(void)
+MavlinkFTP::_workReset(PayloadHeader* payload)
 {
 	for (size_t i=0; i<kMaxSession; i++) {
 		if (_session_fds[i] != -1) {
@@ -446,11 +537,44 @@ MavlinkFTP::_workReset(void)
 		}
 	}
 
+	payload->size = 0;
+	
 	return kErrNone;
 }
 
+/// @brief Responds to a RemoveDirectory command
+MavlinkFTP::ErrorCode
+MavlinkFTP::_workRemoveDirectory(PayloadHeader* payload)
+{
+	char dir[kMaxDataLength];
+	strncpy(dir, _data_as_cstring(payload), kMaxDataLength);
+	
+	if (rmdir(dir) == 0) {
+		payload->size = 0;
+		return kErrNone;
+	} else {
+		return kErrFailErrno;
+	}
+}
+
+/// @brief Responds to a CreateDirectory command
+MavlinkFTP::ErrorCode
+MavlinkFTP::_workCreateDirectory(PayloadHeader* payload)
+{
+	char dir[kMaxDataLength];
+	strncpy(dir, _data_as_cstring(payload), kMaxDataLength);
+	
+	if (mkdir(dir, S_IRWXU | S_IRWXG | S_IRWXO) == 0) {
+		payload->size = 0;
+		return kErrNone;
+	} else {
+		return kErrFailErrno;
+	}
+}
+
+/// @brief Returns true if the specified session is a valid open session
 bool
-MavlinkFTP::_validSession(unsigned index)
+MavlinkFTP::_valid_session(unsigned index)
 {
 	if ((index >= kMaxSession) || (_session_fds[index] < 0)) {
 		return false;
@@ -458,8 +582,9 @@ MavlinkFTP::_validSession(unsigned index)
 	return true;
 }
 
+/// @brief Returns an unused session index
 int
-MavlinkFTP::_findUnusedSession(void)
+MavlinkFTP::_find_unused_session(void)
 {
 	for (size_t i=0; i<kMaxSession; i++) {
 		if (_session_fds[i] == -1) {
@@ -470,16 +595,68 @@ MavlinkFTP::_findUnusedSession(void)
 	return -1;
 }
 
+/// @brief Guarantees that the payload data is null terminated.
+///     @return Returns a pointer to the payload data as a char *
 char *
-MavlinkFTP::Request::dataAsCString()
+MavlinkFTP::_data_as_cstring(PayloadHeader* payload)
 {
 	// guarantee nul termination
-	if (header()->size < kMaxDataLength) {
-		requestData()[header()->size] = '\0';
+	if (payload->size < kMaxDataLength) {
+		payload->data[payload->size] = '\0';
 	} else {
-		requestData()[kMaxDataLength - 1] = '\0';
+		payload->data[kMaxDataLength - 1] = '\0';
 	}
 
 	// and return data
-	return (char *)&(header()->data[0]);
+	return (char *)&(payload->data[0]);
+}
+
+/// @brief Returns a unused Request entry. NULL if none available.
+MavlinkFTP::Request *
+MavlinkFTP::_get_request(void)
+{
+	_lock_request_queue();
+	Request* req = reinterpret_cast<Request *>(dq_remfirst(&_request_queue));
+	_unlock_request_queue();
+	return req;
+}
+
+/// @brief Locks a semaphore to provide exclusive access to the request queue
+void
+MavlinkFTP::_lock_request_queue(void)
+{
+	do {}
+	while (sem_wait(&_request_queue_sem) != 0);
+}
+
+/// @brief Unlocks the semaphore providing exclusive access to the request queue
+void
+MavlinkFTP::_unlock_request_queue(void)
+{
+	sem_post(&_request_queue_sem);
+}
+
+/// @brief Returns a no longer needed request to the queue
+void
+MavlinkFTP::_return_request(Request *req)
+{
+	_lock_request_queue();
+	dq_addlast(&req->work.dq, &_request_queue);
+	_unlock_request_queue();
+}
+
+/// @brief Returns the 32 bit CRC for the payload, crc32 and padding members are set to 0 for calculation.
+uint32_t
+MavlinkFTP::_payload_crc32(PayloadHeader *payload)
+{
+	// We calculate CRC with crc and padding set to 0.
+	uint32_t saveCRC = payload->crc32;
+	payload->crc32 = 0;
+	payload->padding[0] = 0;
+	payload->padding[1] = 0;
+	payload->padding[2] = 0;
+	uint32_t retCRC = crc32((const uint8_t*)payload, payload->size + sizeof(PayloadHeader));
+	payload->crc32 = saveCRC;
+		
+	return retCRC;
 }
diff --git a/src/modules/mavlink/mavlink_ftp.h b/src/modules/mavlink/mavlink_ftp.h
index 1dd8f102e..b4cc154d1 100644
--- a/src/modules/mavlink/mavlink_ftp.h
+++ b/src/modules/mavlink/mavlink_ftp.h
@@ -33,17 +33,8 @@
 
 #pragma once
 
-/**
- * @file mavlink_ftp.h
- *
- * MAVLink remote file server.
- *
- * A limited number of requests (currently 2) may be outstanding at a time.
- * Additional messages will be discarded.
- *
- * Messages consist of a fixed header, followed by a data area.
- *
- */
+/// @file mavlink_ftp.h
+///     @author px4dev, Don Gagne <don@thegagnes.com>
  
 #include <dirent.h>
 #include <queue.h>
@@ -54,183 +45,131 @@
 #include "mavlink_messages.h"
 #include "mavlink_main.h"
 
+class MavlinkFtpTest;
+
+/// @brief MAVLink remote file server. Support FTP like commands using MAVLINK_MSG_ID_FILE_TRANSFER_PROTOCOL message.
+/// A limited number of requests (kRequestQueueSize) may be outstanding at a time. Additional messages will be discarded.
 class MavlinkFTP
 {
 public:
+	/// @brief Returns the one Mavlink FTP server in the system.
+	static MavlinkFTP* get_server(void);
+    
+	/// @brief Contructor is only public so unit test code can new objects.
 	MavlinkFTP();
-
-	static MavlinkFTP	*getServer();
-
-	// static interface
-	void			handle_message(Mavlink* mavlink,
-					mavlink_message_t *msg);
-
-private:
-
-	static const unsigned	kRequestQueueSize = 2;
-
-	static MavlinkFTP	*_server;
-
-	/// @brief Trying to pack structures across differing compilers is questionable for Clients, so we pad the
-	/// structure ourselves to 32 bit alignment which should get us what we want.
-	struct RequestHeader
+	
+	/// @brief Adds the specified message to the work queue.
+	void handle_message(Mavlink* mavlink, mavlink_message_t *msg);
+    
+	typedef void (*ReceiveMessageFunc_t)(const mavlink_message_t *msg, MavlinkFtpTest* ftpTest);
+	
+	/// @brief Sets up the server to run in unit test mode.
+	///	@param rcvmsgFunc Function which will be called to handle outgoing mavlink messages.
+	///	@param ftp_test MavlinkFtpTest object which the function is associated with
+	void set_unittest_worker(ReceiveMessageFunc_t rcvMsgFunc, MavlinkFtpTest *ftp_test);
+
+	/// @brief This is the payload which is in mavlink_file_transfer_protocol_t.payload. We pad the structure ourselves to
+	/// 32 bit alignment to avoid usage of any pack pragmas.
+	struct PayloadHeader
         {
-		uint16_t	seqNumber;  ///< sequence number for message
-		uint8_t		session;    ///< Session id for read and write commands
-		uint8_t		opcode;     ///< Command opcode
-		uint8_t		size;       ///< Size of data
-		uint8_t		padding[3];
-		uint32_t	crc32;      ///< CRC for entire Request structure, with crc32 and padding set to 0
-		uint32_t	offset;     ///< Offsets for List and Read commands
-		uint8_t		data[];
+		uint16_t	seqNumber;	///< sequence number for message
+		uint8_t		session;	///< Session id for read and write commands
+		uint8_t		opcode;		///< Command opcode
+		uint8_t		size;		///< Size of data
+		uint8_t		padding[3];	///< 32 bit aligment padding
+		uint32_t	crc32;		///< CRC for entire Request structure, with crc32 and padding set to 0
+		uint32_t	offset;		///< Offsets for List and Read commands
+		uint8_t		data[];		///< command data, varies by Opcode
         };
-
+	
+	/// @brief Command opcodes
 	enum Opcode : uint8_t
 	{
-		kCmdNone,	// ignored, always acked
-		kCmdTerminate,	// releases sessionID, closes file
-		kCmdReset,	// terminates all sessions
-		kCmdList,	// list files in <path> from <offset>
-		kCmdOpen,	// opens <path> for reading, returns <session>
-		kCmdRead,	// reads <size> bytes from <offset> in <session>
-		kCmdCreate,	// creates <path> for writing, returns <session>
-		kCmdWrite,	// appends <size> bytes at <offset> in <session>
-		kCmdRemove,	// remove file (only if created by server?)
-
-		kRspAck,
-		kRspNak
+		kCmdNone,		///< ignored, always acked
+		kCmdTerminateSession,	///< Terminates open Read session
+		kCmdResetSessions,	///< Terminates all open Read sessions
+		kCmdListDirectory,	///< List files in <path> from <offset>
+		kCmdOpenFile,		///< Opens file at <path> for reading, returns <session>
+		kCmdReadFile,		///< Reads <size> bytes from <offset> in <session>
+		kCmdCreateFile,		///< Creates file at <path> for writing, returns <session>
+		kCmdWriteFile,		///< Appends <size> bytes to file in <session>
+		kCmdRemoveFile,		///< Remove file at <path>
+		kCmdCreateDirectory,	///< Creates directory at <path>
+		kCmdRemoveDirectory,	///< Removes Directory at <path>, must be empty
+		
+		kRspAck,		///< Ack response
+		kRspNak			///< Nak response
 	};
-
+	
+	/// @brief Error codes returned in Nak response PayloadHeader.data[0].
 	enum ErrorCode : uint8_t
-	{
+        {
 		kErrNone,
-		kErrNoRequest,
-		kErrNoSession,
-		kErrSequence,
-		kErrNotDir,
-		kErrNotFile,
-		kErrEOF,
-		kErrNotAppend,
-		kErrTooBig,
-		kErrIO,
-		kErrPerm
-	};
-
-    int _findUnusedSession(void);
-    bool _validSession(unsigned index);
-
-    static const unsigned kMaxSession = 2;
-    int	_session_fds[kMaxSession];
-
-	class Request
+		kErrFail,			///< Unknown failure
+		kErrFailErrno,			///< Command failed, errno sent back in PayloadHeader.data[1]
+		kErrInvalidDataSize,		///< PayloadHeader.size is invalid
+		kErrInvalidSession,		///< Session is not currently open
+		kErrNoSessionsAvailable,	///< All available Sessions in use
+		kErrEOF,			///< Offset past end of file for List and Read commands
+		kErrUnknownCommand,		///< Unknown command opcode
+		kErrCrc				///< CRC on Payload is incorrect
+        };
+	
+private:
+	/// @brief Unit of work which is queued to work_queue
+	struct Request
 	{
-	public:
-		union {
-			dq_entry_t	entry;
-			work_s		work;
-		};
-
-		bool		decode(Mavlink *mavlink, mavlink_message_t *fromMessage) {
-			if (fromMessage->msgid == MAVLINK_MSG_ID_FILE_TRANSFER_PROTOCOL) {
-				_systemId = fromMessage->sysid;
-				_mavlink = mavlink;
-				mavlink_msg_file_transfer_protocol_decode(fromMessage, &_message);
-				return _message.target_system == _mavlink->get_system_id();
-			}
-			return false;
-		}
-
-		void		reply() {
-
-			// XXX the proper way would be an IOCTL / uORB call, rather than exploiting the
-			// flat memory architecture, as we're operating between threads here.
-			mavlink_message_t msg;
-			msg.checksum = 0;
-			unsigned len = mavlink_msg_file_transfer_protocol_pack_chan(_mavlink->get_system_id(),		// Sender system id
-										    _mavlink->get_component_id(),	// Sender component id
-										    _mavlink->get_channel(),		// Channel to send on
-										    &msg,				// Message to pack payload into
-										    0,					// Target network
-										    _systemId,				// Target system id
-										    0,					// Target component id
-										    rawData());				// Payload to pack into message
-
-			_mavlink->lockMessageBufferMutex();
-			bool success = _mavlink->message_buffer_write(&msg, len);
-			_mavlink->unlockMessageBufferMutex();
-
-			if (!success) {
-				warnx("FTP TX ERR");
-			}
-#ifdef MAVLINK_FTP_DEBUG
-			else {
-				warnx("wrote: sys: %d, comp: %d, chan: %d, len: %d, checksum: %d",
-				      _mavlink->get_system_id(),
-				      _mavlink->get_component_id(),
-				      _mavlink->get_channel(),
-				      len,
-				      msg.checksum);
-			}
-#endif
-		}
-
-		uint8_t		*rawData() { return &_message.payload[0]; }
-		RequestHeader 	*header()  { return reinterpret_cast<RequestHeader *>(&_message.payload[0]); }
-		uint8_t         *requestData() { return &(header()->data[0]); }
-		unsigned	dataSize() { return header()->size + sizeof(RequestHeader); }
-		mavlink_channel_t channel() { return _mavlink->get_channel(); }
-
-		char		*dataAsCString();
-
-	private:
-		Mavlink			*_mavlink;
-		mavlink_file_transfer_protocol_t _message;
-		uint8_t _systemId;
-
+		work_s	work;			///< work queue entry
+		Mavlink	*mavlink;		///< Mavlink to reply to
+		uint8_t serverSystemId;		///< System ID to send from
+		uint8_t serverComponentId;	///< Component ID to send from
+		uint8_t serverChannel;		///< Channel to send to
+		uint8_t targetSystemId;		///< System ID to target reply to
+
+		mavlink_file_transfer_protocol_t message;	///< Protocol message
 	};
-
-	static const char	kDirentFile = 'F';
-	static const char	kDirentDir = 'D';
-	static const char	kDirentUnknown = 'U';
-	static const uint8_t	kMaxDataLength = MAVLINK_MSG_FILE_TRANSFER_PROTOCOL_FIELD_PAYLOAD_LEN - sizeof(RequestHeader);
-
-	/// Request worker; runs on the low-priority work queue to service
-	/// remote requests.
-	///
-	static void		_workerTrampoline(void *arg);
-	void			_worker(Request *req);
-
-	/// Reply to a request (XXX should be a Request method)
-	///
-	void			_reply(Request *req);
-
-	ErrorCode		_workList(Request *req);
-	ErrorCode		_workOpen(Request *req, bool create);
-	ErrorCode		_workRead(Request *req);
-	ErrorCode		_workWrite(Request *req);
-	ErrorCode		_workRemove(Request *req);
-	ErrorCode		_workTerminate(Request *req);
-	ErrorCode		_workReset();
-
-	// work freelist
-	Request			_workBufs[kRequestQueueSize];
-	dq_queue_t		_workFree;
-	sem_t			_lock;
-
-	void			_qLock() { do {} while (sem_wait(&_lock) != 0); }
-	void			_qUnlock() { sem_post(&_lock); }
-
-	void			_qFree(Request *req) {
-		_qLock();
-		dq_addlast(&req->entry, &_workFree);
-		_qUnlock();
-	}
-
-	Request			*_dqFree() {
-		_qLock();
-		auto req = reinterpret_cast<Request *>(dq_remfirst(&_workFree));
-		_qUnlock();
-		return req;
-	}
-    
+	
+	Request		*_get_request(void);
+	void		_return_request(Request *req);
+	void		_lock_request_queue(void);
+	void		_unlock_request_queue(void);
+	
+	uint32_t	_payload_crc32(PayloadHeader *hdr);
+	
+	char		*_data_as_cstring(PayloadHeader* payload);
+	
+	static void	_worker_trampoline(void *arg);
+	void		_process_request(Request *req);
+	void		_reply(Request *req);
+
+	ErrorCode	_workList(PayloadHeader *payload);
+	ErrorCode	_workOpen(PayloadHeader *payload, bool create);
+	ErrorCode	_workRead(PayloadHeader *payload);
+	ErrorCode	_workWrite(PayloadHeader *payload);
+	ErrorCode	_workTerminate(PayloadHeader *payload);
+	ErrorCode	_workReset(PayloadHeader* payload);
+	ErrorCode	_workRemoveDirectory(PayloadHeader *payload);
+	ErrorCode	_workCreateDirectory(PayloadHeader *payload);
+	ErrorCode	_workRemoveFile(PayloadHeader *payload);
+
+	static const unsigned	kRequestQueueSize = 2;			///< Max number of queued requests
+	Request			_request_bufs[kRequestQueueSize];	///< Request buffers which hold work
+	dq_queue_t		_request_queue;				///< Queue of available Request buffers
+	sem_t			_request_queue_sem;			///< Semaphore for locking access to _request_queue
+	
+	int _find_unused_session(void);
+	bool _valid_session(unsigned index);
+	
+	static const char	kDirentFile = 'F';	///< Identifies File returned from List command
+	static const char	kDirentDir = 'D';	///< Identifies Directory returned from List command
+	static const char	kDirentUnknown = 'U';	///< Identifies Unknown entry returned from List command
+	
+	/// @brief Maximum data size in RequestHeader::data
+	static const uint8_t	kMaxDataLength = MAVLINK_MSG_FILE_TRANSFER_PROTOCOL_FIELD_PAYLOAD_LEN - sizeof(PayloadHeader);
+	
+	static const unsigned kMaxSession = 2;	///< Max number of active sessions
+	int	_session_fds[kMaxSession];	///< Session file descriptors, 0 for empty slot
+	
+	ReceiveMessageFunc_t _utRcvMsgFunc;	///< Unit test override for mavlink message sending
+	MavlinkFtpTest *_ftp_test;		///< Additional parameter to _utRcvMsgFunc;
 };