feat(mavlink): support FTP ListDirectoryWithTime (#27542)

Add support for the MAVLink FTP ListDirectoryWithTime command (opcode 16),
which returns directory listings with each file's last-modification time
appended as decimal seconds since the UNIX epoch (0 if unknown).

This lets a GCS retrieve file timestamps without downloading the files,
which is useful for log download. The plain ListDirectory output is
unchanged, and clients fall back to it when the server NAKs with
UnknownCommand.

Signed-off-by: Julian Oes <julian@oes.ch>

src/modules/mavlink/mavlink_ftp.cpp

@@ -171,6 +171,10 @@ MavlinkFTP::_process_request(
 		errorCode = _workList(payload);
 		break;
 
+	case kCmdListDirectoryWithTime:
+		errorCode = _workList(payload, true);
+		break;
+
 	case kCmdOpenFileRO:
 		errorCode = _workOpen(payload, O_RDONLY);
 		break;
@@ -322,7 +326,7 @@ void MavlinkFTP::_constructPath(char *dst, int dst_len, const char *path) const
 
 /// @brief Responds to a List command
 MavlinkFTP::ErrorCode
-MavlinkFTP::_workList(PayloadHeader *payload)
+MavlinkFTP::_workList(PayloadHeader *payload, bool include_time)
 {
 	_constructPath(_work_buffer1, _work_buffer1_len, _data_as_cstring(payload));
 
@@ -380,6 +384,7 @@ MavlinkFTP::_workList(PayloadHeader *payload)
 		}
 
 		uint32_t fileSize = 0;
+		uint32_t fileTime = 0;	// seconds since the UNIX epoch, 0 if unknown
 		char direntType;
 
 		// Determine the directory entry type
@@ -401,6 +406,7 @@ MavlinkFTP::_workList(PayloadHeader *payload)
 
 					if (stat(_work_buffer2, &st) == 0) {
 						fileSize = st.st_size;
+						fileTime = st.st_mtime;
 					}
 				}
 
@@ -433,8 +439,16 @@ MavlinkFTP::_workList(PayloadHeader *payload)
 			_work_buffer2[0] = '\0';
 
 		} else if (direntType == kDirentFile) {
-			// Files send filename and file length
-			int ret = snprintf(_work_buffer2, _work_buffer2_len, "%s\t%" PRIu32, result->d_name, fileSize);
+			// Files send filename and file length, optionally followed by the modification time
+			int ret;
+
+			if (include_time) {
+				ret = snprintf(_work_buffer2, _work_buffer2_len, "%s\t%" PRIu32 "\t%" PRIu32, result->d_name, fileSize, fileTime);
+
+			} else {
+				ret = snprintf(_work_buffer2, _work_buffer2_len, "%s\t%" PRIu32, result->d_name, fileSize);
+			}
+
 			bool buf_is_ok = ((ret > 0) && (ret < _work_buffer2_len));
 
 			if (!buf_is_ok) {

src/modules/mavlink/mavlink_ftp.h

@@ -96,6 +96,7 @@ public:
 		kCmdRename,		///< Rename <path1> to <path2>
 		kCmdCalcFileCRC32,	///< Calculate CRC32 for file at <path>
 		kCmdBurstReadFile,	///< Burst download session file
+		kCmdListDirectoryWithTime,	///< List files in <path> from <offset>, including last-modification time
 
 		kRspAck = 128,		///< Ack response
 		kRspNak			///< Nak response
@@ -125,7 +126,7 @@ private:
 	void		_reply(mavlink_file_transfer_protocol_t *ftp_req);
 	int		_copy_file(const char *src_path, const char *dst_path, size_t length);
 
-	ErrorCode	_workList(PayloadHeader *payload);
+	ErrorCode	_workList(PayloadHeader *payload, bool include_time = false);
 	ErrorCode	_workOpen(PayloadHeader *payload, int oflag);
 	ErrorCode	_workRead(PayloadHeader *payload);
 	ErrorCode	_workBurst(PayloadHeader *payload, uint8_t target_system_id, uint8_t target_component_id);