GCS_MAVLink: Initial FTP support

libraries/GCS_MAVLink/GCS.h

@@ -15,6 +15,7 @@
 #include <AP_Common/Bitmask.h>
 #include <AP_Devo_Telem/AP_Devo_Telem.h>
 #include <RC_Channel/RC_Channel.h>
+#include <AP_Filesystem/AP_Filesystem_Available.h>
 
 #include "MissionItemProtocol_Waypoints.h"
 #include "MissionItemProtocol_Rally.h"
@@ -612,6 +613,83 @@ private:
 
     uint8_t send_parameter_async_replies();
 
+#if HAVE_FILESYSTEM_SUPPORT
+
+    enum class FTP_OP : uint8_t {
+        None = 0,
+        TerminateSession = 1,
+        ResetSessions = 2,
+        ListDirectory = 3,
+        OpenFileRO = 4,
+        ReadFile = 5,
+        CreateFile = 6,
+        WriteFile = 7,
+        RemoveFile = 8,
+        CreateDirectory = 9,
+        RemoveDirectory = 10,
+        OpenFileWO = 11,
+        TruncateFile = 12,
+        Rename = 13,
+        CalcFileCRC32 = 14,
+        BurstReadFile = 15,
+        Ack = 128,
+        Nack = 129,
+    };
+
+    enum class FTP_ERROR : uint8_t {
+        None = 0,
+        Fail = 1,
+        FailErrno = 2,
+        InvalidDataSize = 3,
+        InvalidSession = 4,
+        NoSessionsAvailable = 5,
+        EndOfFile = 6,
+        UnknownCommand = 7,
+        FileExists = 8,
+        FileProtected = 9,
+        FileNotFound = 10,
+    };
+
+    struct pending_ftp {
+        uint32_t offset;
+        mavlink_channel_t chan;        
+        uint16_t seq_number;
+        FTP_OP opcode;
+        FTP_OP req_opcode;
+        bool  burst_complete;
+        uint8_t size;
+        uint8_t session;
+        uint8_t sysid;
+        uint8_t compid;
+        uint8_t data[239];
+    };
+
+    enum class FTP_FILE_MODE {
+        Read,
+        Write,
+    };
+
+    struct ftp_state {
+        ObjectBuffer<pending_ftp> *requests;
+        ObjectBuffer<pending_ftp> *replies;
+
+        // session specific info, currently only support a single session over all links
+        int fd = -1;
+        FTP_FILE_MODE mode; // work around AP_Filesystem not supporting file modes
+        int16_t current_session;
+    };
+    static struct ftp_state ftp;
+
+    static void ftp_error(struct pending_ftp &response, FTP_ERROR error); // FTP helper method for packing a NAK
+    static int emit_dir_entry(char *dest, size_t space, const char * path, const struct dirent * entry); // FTP helper for emitting a dir response
+    static void ftp_list_dir(struct pending_ftp &request, struct pending_ftp &response);
+
+    bool ftp_init(void);
+    void handle_file_transfer_protocol(const mavlink_message_t &msg);
+    void send_ftp_replies(void);
+    void ftp_worker(void);
+#endif // HAVE_FILESYSTEM_SUPPORT
+
     void send_distance_sensor(const class AP_RangeFinder_Backend *sensor, const uint8_t instance) const;
 
     virtual bool handle_guided_request(AP_Mission::Mission_Command &cmd) = 0;

libraries/GCS_MAVLink/GCS_Common.cpp

@@ -1017,6 +1017,10 @@ void GCS_MAVLINK::update_send()
         AP::logger().handle_log_send();
     }
 
+#if HAVE_FILESYSTEM_SUPPORT
+    send_ftp_replies();
+#endif // HAVE_FILESYSTEM_SUPPORT
+
     if (!deferred_messages_initialised) {
         initialise_message_intervals_from_streamrates();
         deferred_messages_initialised = true;
@@ -3037,6 +3041,11 @@ void GCS_MAVLINK::handle_common_message(const mavlink_message_t &msg)
         AP::logger().handle_mavlink_msg(*this, msg);
         break;
 
+    case MAVLINK_MSG_ID_FILE_TRANSFER_PROTOCOL:
+#if HAVE_FILESYSTEM_SUPPORT
+        handle_file_transfer_protocol(msg);
+#endif // HAVE_FILESYSTEM_SUPPORT
+        break;
 
     case MAVLINK_MSG_ID_DIGICAM_CONTROL:
         {
@@ -4692,10 +4701,16 @@ uint64_t GCS_MAVLINK::capabilities() const
     if (AP::rally()) {
         ret |= MAV_PROTOCOL_CAPABILITY_MISSION_RALLY;
     }
+
     if (AP::fence()) {
         // FIXME: plane also supports this...
         ret |= MAV_PROTOCOL_CAPABILITY_MISSION_FENCE;
     }
+
+#if HAVE_FILESYSTEM_SUPPORT
+    ret |= MAV_PROTOCOL_CAPABILITY_FTP;
+#endif // HAVE_FILESYSTEM_SUPPORT
+
     return ret;
 }
 

libraries/GCS_MAVLink/GCS_FTP.cpp

@@ -0,0 +1,602 @@
+/*
+   GCS MAVLink functions related to FTP
+
+   This program is free software: you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation, either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+#include <AP_HAL/AP_HAL.h>
+
+#include "GCS.h"
+
+#include <AP_Filesystem/AP_Filesystem.h>
+
+#if HAVE_FILESYSTEM_SUPPORT
+
+extern const AP_HAL::HAL& hal;
+
+struct GCS_MAVLINK::ftp_state GCS_MAVLINK::ftp;
+
+bool GCS_MAVLINK::ftp_init(void) {
+    // we can simply check if we allocated everything we need
+    if (ftp.requests != nullptr) {
+        return true;
+    }
+
+    ftp.requests = new ObjectBuffer<pending_ftp>(5);
+    if (ftp.requests == nullptr) {
+        goto failed;
+    }
+    ftp.replies = new ObjectBuffer<pending_ftp>(30);
+    if (ftp.replies == nullptr) {
+        goto failed;
+    }
+
+    if (!hal.scheduler->thread_create(FUNCTOR_BIND_MEMBER(&GCS_MAVLINK::ftp_worker, void),
+                                      "FTP", 1024, AP_HAL::Scheduler::PRIORITY_IO, 0)) {
+        goto failed;
+    }
+
+    return true;
+
+failed:
+    delete ftp.requests;
+    ftp.requests = nullptr;
+    delete ftp.replies;
+    ftp.replies = nullptr;
+
+    return false;
+}
+
+void GCS_MAVLINK::handle_file_transfer_protocol(const mavlink_message_t &msg) {
+    if (ftp_init()) {
+        mavlink_file_transfer_protocol_t packet;
+        mavlink_msg_file_transfer_protocol_decode(&msg, &packet);
+
+        struct pending_ftp request;
+
+        request.chan = chan;
+        request.seq_number = *(uint16_t *)packet.payload;
+
+        request.session = packet.payload[2];
+        request.opcode = static_cast<FTP_OP>(packet.payload[3]);
+        request.size = packet.payload[4];
+        request.req_opcode = static_cast<FTP_OP>(packet.payload[5]);
+        request.burst_complete = packet.payload[6];
+        request.offset = *(uint32_t *)(&packet.payload[8]);
+        request.sysid = msg.sysid;
+        request.compid = msg.compid;
+        memcpy(request.data, &packet.payload[12], sizeof(packet.payload) - 12);
+
+        if (!ftp.requests->push(request)) {
+            // dropping the message, no buffer space to queue it in
+            // we could NACK it, but that can lead to GCS confusion, so we're treating it like lost data
+        }
+    }
+}
+
+void GCS_MAVLINK::send_ftp_replies(void) {
+    if (ftp.replies == nullptr) {
+        return;
+    }
+
+    for (uint8_t i = 0; i < 20; i++) {
+        if (!HAVE_PAYLOAD_SPACE(chan, FILE_TRANSFER_PROTOCOL)) {
+            return;
+        }
+        if ((i > 0) && comm_get_txspace(chan) < (2 * (packet_overhead() + MAVLINK_MSG_ID_FILE_TRANSFER_PROTOCOL_LEN))) {
+            // if this isn't the first packet we have to leave deadspace for the next message
+            return;
+        }
+
+        struct pending_ftp reply;
+        uint8_t payload[251] = {};
+        if (ftp.replies->peek(reply) && (reply.chan == chan)) {
+                ((uint16_t *)payload)[0] = reply.seq_number;
+                payload[2] = reply.session;
+                payload[3] = static_cast<uint8_t>(reply.opcode);
+                payload[4] = reply.size;
+                payload[5] = static_cast<uint8_t>(reply.req_opcode);
+                payload[6] = reply.burst_complete ? 1 : 0;
+                *(uint32_t *)(&payload[8]) = reply.offset;
+                memcpy(&payload[12], reply.data, sizeof(reply.data));
+                mavlink_msg_file_transfer_protocol_send(
+                    reply.chan,
+                    0, reply.sysid, reply.compid,
+                    payload);
+                ftp.replies->pop(reply);
+        } else {
+            return;
+        }
+    }
+}
+
+void GCS_MAVLINK::ftp_error(struct pending_ftp &response, FTP_ERROR error) {
+    response.opcode = FTP_OP::Nack;
+    response.data[0] = static_cast<uint8_t>(error);
+    response.size = 1;
+
+    // FIXME: errno's are not thread-local as they should be on ChibiOS
+    if (error == FTP_ERROR::FailErrno) {
+        // translate the errno's that we have useful messages for
+        switch (errno) {
+            case EEXIST:
+                response.data[0] = static_cast<uint8_t>(FTP_ERROR::FileExists);
+                break;
+            case ENOENT:
+                response.data[0] = static_cast<uint8_t>(FTP_ERROR::FileNotFound);
+                break;
+            default:
+                response.data[1] = static_cast<uint8_t>(errno);
+                response.size = 2;
+                break;
+        }
+    }
+}
+
+void GCS_MAVLINK::ftp_worker(void) {
+    pending_ftp request;
+    pending_ftp reply = {};
+    reply.session = -1; // flag the reply as invalid for any reuse
+
+    while (true) {
+        while (!ftp.requests->pop(request)) {
+            // nothing to handle, delay ourselves a bit then check again. Ideally we'd use conditional waits here
+            hal.scheduler->delay(10);
+        }
+
+        // if it's a rerequest and we still have the last response then send it
+        if ((request.sysid == reply.sysid) && (request.compid = reply.compid) &&
+            (request.session == reply.session) && (request.seq_number + 1 == reply.seq_number)) {
+            while (!ftp.replies->push(reply)) {
+                hal.scheduler->delay(10);
+            }
+            continue;
+        }
+
+        // setup the response
+        memset(&reply, 0, sizeof(reply));
+        reply.req_opcode = request.opcode;
+        reply.session = request.session;
+        reply.seq_number = request.seq_number + 1;
+        reply.chan = request.chan;
+        reply.sysid = request.sysid;
+        reply.compid = request.compid;
+
+        // sanity check the request size
+        if (request.size > sizeof(request.data)) {
+            ftp_error(reply, FTP_ERROR::InvalidDataSize);
+            while (!ftp.replies->push(reply)) {
+                hal.scheduler->delay(10);
+            }
+            continue;
+        }
+
+        // reject anything not belonging to our current session, unless we are terminating a session, then just kill it and move on
+        if (((ftp.current_session >= 0) && (request.session != ftp.current_session))
+            && ((request.opcode == FTP_OP::TerminateSession) || (request.opcode == FTP_OP::ResetSessions))) {
+            reply.opcode = FTP_OP::Ack;
+        } else {
+            // dispatch the command as needed
+            switch (request.opcode) {
+                case FTP_OP::None:
+                    reply.opcode = FTP_OP::Ack;
+                    break;
+                case FTP_OP::TerminateSession:
+                case FTP_OP::ResetSessions:
+                    // we already handled this, just listed for completeness
+                    if (ftp.fd != -1) {
+                        AP::FS().close(ftp.fd);
+                        ftp.fd = -1;
+                    }
+                    ftp.current_session = -1;
+                    reply.opcode = FTP_OP::Ack;
+                    break;
+                case FTP_OP::ListDirectory:
+                    ftp_list_dir(request, reply);
+                    break;
+                case FTP_OP::OpenFileRO:
+                    {
+                        // only allow one file to be open per session
+                        if (ftp.fd != -1) {
+                            ftp_error(reply, FTP_ERROR::Fail);
+                            break;
+                        }
+
+                        // sanity check that our the request looks well formed
+                        const size_t file_name_len = strnlen((char *)request.data, sizeof(request.data));
+                        if ((file_name_len != request.size) || (request.size == 0)) {
+                            ftp_error(reply, FTP_ERROR::InvalidDataSize);
+                            break;
+                        }
+
+                        request.data[sizeof(request.data) - 1] = 0; // ensure the path is null terminated
+
+                        // get the file size
+                        struct stat st;
+                        if (AP::FS().stat((char *)request.data, &st)) {
+                            ftp_error(reply, FTP_ERROR::FailErrno);
+                            break;
+                        }
+                        const size_t file_size = st.st_size;
+
+                        // actually open the file
+                        ftp.fd = AP::FS().open((char *)request.data, 0);
+                        if (ftp.fd == -1) {
+                            ftp_error(reply, FTP_ERROR::FailErrno);
+                            break;
+                        }
+                        ftp.mode = FTP_FILE_MODE::Read;
+
+                        reply.opcode = FTP_OP::Ack;
+                        reply.size = sizeof(uint32_t);
+                        *((int32_t *)reply.data) = (int32_t)file_size;
+                        break;
+                    }
+                case FTP_OP::ReadFile:
+                    {
+                        // must actually be working on a file
+                        if (ftp.fd == -1) {
+                            ftp_error(reply, FTP_ERROR::FileNotFound);
+                            break;
+                        }
+
+                        // must have the file in read mode
+                        if ((ftp.mode != FTP_FILE_MODE::Read)) {
+                            ftp_error(reply, FTP_ERROR::Fail);
+                            break;
+                        }
+
+                        // seek to requested offset
+                        if (AP::FS().lseek(ftp.fd, request.offset, SEEK_SET) == -1) {
+                            ftp_error(reply, FTP_ERROR::FailErrno);
+                            break;
+                        }
+
+                        // fill the buffer
+                        const ssize_t read_bytes = AP::FS().read(ftp.fd, reply.data, request.size);
+                        if (read_bytes == -1) {
+                            ftp_error(reply, FTP_ERROR::FailErrno);
+                            break;
+                        }
+                        if (read_bytes == 0) {
+                            ftp_error(reply, FTP_ERROR::EndOfFile);
+                            break;
+                        }
+
+                        reply.opcode = FTP_OP::Ack;
+                        reply.offset = request.offset;
+                        reply.size = (uint8_t)read_bytes;
+                        break;
+                    }
+                case FTP_OP::Ack:
+                case FTP_OP::Nack:
+                    // eat these, we just didn't expect them
+                    continue;
+                    break;
+                case FTP_OP::OpenFileWO:
+                case FTP_OP::CreateFile:
+                    {
+                        // only allow one file to be open per session
+                        if (ftp.fd != -1) {
+                            ftp_error(reply, FTP_ERROR::Fail);
+                            break;
+                        }
+
+                        // sanity check that our the request looks well formed
+                        const size_t file_name_len = strnlen((char *)request.data, sizeof(request.data));
+                        if ((file_name_len != request.size) || (request.size == 0)) {
+                            ftp_error(reply, FTP_ERROR::InvalidDataSize);
+                            break;
+                        }
+
+                        request.data[sizeof(request.data) - 1] = 0; // ensure the path is null terminated
+
+                        // actually open the file
+                        ftp.fd = AP::FS().open((char *)request.data,
+                                               (request.opcode == FTP_OP::CreateFile) ? O_WRONLY|O_CREAT|O_TRUNC : O_CREAT|O_WRONLY|O_TRUNC);
+                        if (ftp.fd == -1) {
+                            ftp_error(reply, FTP_ERROR::FailErrno);
+                            break;
+                        }
+                        ftp.mode = FTP_FILE_MODE::Write;
+
+                        reply.opcode = FTP_OP::Ack;
+                        break;
+                    }
+                case FTP_OP::WriteFile:
+                    {
+                        // must actually be working on a file
+                        if (ftp.fd == -1) {
+                            ftp_error(reply, FTP_ERROR::FileNotFound);
+                            break;
+                        }
+
+                        // must have the file in write mode
+                        if ((ftp.mode != FTP_FILE_MODE::Write)) {
+                            ftp_error(reply, FTP_ERROR::Fail);
+                            break;
+                        }
+
+                        // seek to requested offset
+                        if (AP::FS().lseek(ftp.fd, request.offset, SEEK_SET) == -1) {
+                            ftp_error(reply, FTP_ERROR::FailErrno);
+                            break;
+                        }
+
+                        // fill the buffer
+                        const ssize_t write_bytes = AP::FS().write(ftp.fd, request.data, request.size);
+                        if (write_bytes == -1) {
+                            ftp_error(reply, FTP_ERROR::FailErrno);
+                            break;
+                        }
+
+                        reply.opcode = FTP_OP::Ack;
+                        reply.offset = request.offset;
+                        break;
+                    }
+                case FTP_OP::CreateDirectory:
+                    {
+                        // sanity check that our the request looks well formed
+                        const size_t file_name_len = strnlen((char *)request.data, sizeof(request.data));
+                        if ((file_name_len != request.size) || (request.size == 0)) {
+                            ftp_error(reply, FTP_ERROR::InvalidDataSize);
+                            break;
+                        }
+
+                        request.data[sizeof(request.data) - 1] = 0; // ensure the path is null terminated
+
+                        // actually make the directory
+                        if (AP::FS().mkdir((char *)request.data) == -1) {
+                            ftp_error(reply, FTP_ERROR::FailErrno);
+                            break;
+                        }
+
+                        reply.opcode = FTP_OP::Ack;
+                        break;
+                    }
+                case FTP_OP::RemoveDirectory:
+                case FTP_OP::RemoveFile:
+                    {
+                        // sanity check that our the request looks well formed
+                        const size_t file_name_len = strnlen((char *)request.data, sizeof(request.data));
+                        if ((file_name_len != request.size) || (request.size == 0)) {
+                            ftp_error(reply, FTP_ERROR::InvalidDataSize);
+                            break;
+                        }
+
+                        request.data[sizeof(request.data) - 1] = 0; // ensure the path is null terminated
+
+                        // actually open the file
+                        if (AP::FS().unlink((char *)request.data) == -1) {
+                            ftp_error(reply, FTP_ERROR::FailErrno);
+                            break;
+                        }
+
+                        reply.opcode = FTP_OP::Ack;
+                        break;
+                    }
+                case FTP_OP::CalcFileCRC32:
+                    {
+                        // sanity check that our the request looks well formed
+                        const size_t file_name_len = strnlen((char *)request.data, sizeof(request.data));
+                        if ((file_name_len != request.size) || (request.size == 0)) {
+                            ftp_error(reply, FTP_ERROR::InvalidDataSize);
+                            break;
+                        }
+
+                        request.data[sizeof(request.data) - 1] = 0; // ensure the path is null terminated
+
+                        // actually open the file
+                        int fd = AP::FS().open((char *)request.data, O_RDONLY);
+                        if (fd == -1) {
+                            ftp_error(reply, FTP_ERROR::FailErrno);
+                            break;
+                        }
+
+                        uint32_t checksum = 0;
+                        ssize_t read_size;
+                        do {
+                            read_size = AP::FS().read(fd, reply.data, sizeof(reply.data));
+                            if (read_size == -1) {
+                                ftp_error(reply, FTP_ERROR::FailErrno);
+                                AP::FS().close(fd);
+                                break;
+                            }
+                            checksum = crc_crc32(checksum, reply.data, MIN((size_t)read_size, sizeof(reply.data)));
+                        } while (read_size > 0);
+
+                        AP::FS().close(fd);
+
+                        // reset our scratch area so we don't leak data, and can leverage trimming
+                        memset(reply.data, 0, sizeof(reply.data));
+                        reply.size = sizeof(uint32_t);
+                        ((uint32_t *)reply.data)[0] = checksum;
+                        reply.opcode = FTP_OP::Ack;
+                        break;
+                    }
+                case FTP_OP::BurstReadFile:
+                    {
+                        // must actually be working on a file
+                        if (ftp.fd == -1) {
+                            ftp_error(reply, FTP_ERROR::FileNotFound);
+                            break;
+                        }
+
+                        // must have the file in read mode
+                        if ((ftp.mode != FTP_FILE_MODE::Read)) {
+                            ftp_error(reply, FTP_ERROR::Fail);
+                            break;
+                        }
+
+                        // seek to requested offset
+                        if (AP::FS().lseek(ftp.fd, request.offset, SEEK_SET) == -1) {
+                            ftp_error(reply, FTP_ERROR::FailErrno);
+                            break;
+                        }
+
+                        bool more_pending = true;
+                        const uint32_t transfer_size = 100;
+                        for (uint32_t i = 0; (i < transfer_size) && more_pending; i++) {
+                            // fill the buffer
+                            const ssize_t read_bytes = AP::FS().read(ftp.fd, reply.data, sizeof(reply.data));
+                            if (read_bytes == -1) {
+                                ftp_error(reply, FTP_ERROR::FailErrno);
+                                more_pending = false;
+                                break;
+                            }
+
+                            if (read_bytes != sizeof(reply.data)) {
+                                // don't send any old data
+                                memset(reply.data + read_bytes, 0, sizeof(reply.data) - read_bytes);
+                            }
+
+                            if (read_bytes == 0) {
+                                ftp_error(reply, FTP_ERROR::EndOfFile);
+                                more_pending = false;
+                                break;
+                            }
+
+                            reply.opcode = FTP_OP::Ack;
+                            reply.offset = request.offset + i * sizeof(reply.data);
+                            reply.burst_complete = (i == (transfer_size - 1));
+                            reply.size = (uint8_t)read_bytes;
+
+                            while (!ftp.replies->push(reply)) { // we must fit the response, keep shoving it in
+                                hal.scheduler->delay(10);
+                            }
+
+                            // prep the reply to be used again
+                            reply.seq_number++;
+                        }
+
+                        break;
+                    }
+                case FTP_OP::TruncateFile:
+                case FTP_OP::Rename:
+                default:
+                    // this was bad data, just nack it
+                    gcs().send_text(MAV_SEVERITY_DEBUG, "Unsupported FTP: %d", static_cast<int>(request.opcode));
+                    ftp_error(reply, FTP_ERROR::Fail);
+                    break;
+            }
+        }
+
+        // send our response back out to the system
+        while (!ftp.replies->push(reply)) { // we must fit the response, keep shoving it in
+            hal.scheduler->delay(10);
+        }
+        continue;
+    }
+}
+
+// calculates how much string length is needed to fit this in a list response
+int GCS_MAVLINK::emit_dir_entry(char *dest, size_t space, const char *path, const struct dirent * entry) {
+    const bool is_file = entry->d_type == DT_REG;
+
+    if (!is_file && entry->d_type != DT_DIR) {
+        return -1; // this just forces it so we can't send this back, it's easier then sending skips to a GCS
+    }
+
+    if (is_file) {
+        const size_t full_path_len = strlen(path) + strnlen(entry->d_name, 256); // FIXME: Really should do better then just hardcoding 256
+        char full_path[full_path_len + 2];
+        hal.util->snprintf(full_path, sizeof(full_path), "%s/%s", path, entry->d_name);
+        struct stat st;
+        if (AP::FS().stat(full_path, &st)) {
+            return -1;
+        }
+        return hal.util->snprintf(dest, space, "F%s\t%d\0", entry->d_name, (int)st.st_size);
+    } else {
+        return hal.util->snprintf(dest, space, "D%s\0", entry->d_name);
+    }
+}
+
+// list the contents of a directory, skip the offset number of entries before providing data
+void GCS_MAVLINK::ftp_list_dir(struct pending_ftp &request, struct pending_ftp &response) {
+    response.offset = request.offset; // this should be set for any failure condition for debugging
+
+    const size_t directory_name_size = strnlen((char *)request.data, sizeof(request.data));
+    // sanity check that our the request looks well formed
+    if ((directory_name_size != request.size) || (request.size == 0)) {
+        ftp_error(response, FTP_ERROR::InvalidDataSize);
+        return;
+    }
+
+    request.data[sizeof(request.data) - 1] = 0; // ensure the path is null terminated
+
+    // open the dir
+    DIR *dir = AP::FS().opendir((char *)request.data);
+    if (dir == nullptr) {
+        ftp_error(response, FTP_ERROR::FailErrno);
+        AP::FS().closedir(dir);
+        return;
+    }
+
+    // burn the entries we don't care about
+    while (request.offset > 0) {
+        const struct dirent *entry = AP::FS().readdir(dir);
+        if(entry == nullptr) {
+            ftp_error(response, FTP_ERROR::EndOfFile);
+            AP::FS().closedir(dir);
+            return;
+        }
+
+        // check how much space would be needed to emit the listing
+        const int needed_space = emit_dir_entry((char *)response.data, sizeof(request.data), (char *)request.data, entry);
+
+        if (needed_space < 0 || needed_space > (int)sizeof(request.data)) {
+            continue;
+        }
+
+        request.offset--;
+    }
+
+    // start packing in entries that fit
+    uint8_t index = 0;
+    struct dirent *entry;
+    while ((entry = AP::FS().readdir(dir))) {
+        // figure out if we can fit the file
+        const int required_space = emit_dir_entry((char *)(response.data + index), sizeof(response.data) - index, (char *)request.data, entry);
+
+        // couldn't ever send this so drop it
+        if (required_space < 0) {
+            continue;
+        }
+
+        // can't fit it in this one, leave it for the next list to send
+        if ((required_space + index) >= (int)sizeof(request.data)) {
+            break;
+        }
+
+        // step the index forward and keep going
+        index += required_space + 1;
+    }
+
+    if (index == 0) {
+        ftp_error(response, FTP_ERROR::EndOfFile);
+        AP::FS().closedir(dir);
+        return;
+    }
+    
+    // strip any bad temp data from our response as it can confuse a GCS, and defeats 0 trimming
+    if (index < sizeof(response.data)) {
+        memset(response.data + index, 0, MAX(0, (int)(sizeof(response.data)) - index));
+    }
+
+    response.opcode = FTP_OP::Ack;
+    response.size = index;
+
+    AP::FS().closedir(dir);
+}
+
+#endif // HAVE_FILESYSTEM_SUPPORT