Zepp OS: Refactor file upload, fix notification icons > 56x56px

- File uploads are split in chunks, with the size dictated by the
  watches. There seem to be 2 protocol versions, without any noticeable
  differences
- Extract the file upload logic to a standalone class. This makes it
  easier to keep track of concurrent requests, each of which have their
  own session id
- Icons larger than 8KB will end up split in multiple chunks - we now
  handle that correctly
- Notification icons are also requested in 2 different formats, but
  the actual encoding seems to be the same, with only a different id

app/src/main/java/nodomain/freeyourgadget/gadgetbridge/devices/huami/Huami2021Service.java

@@ -23,7 +23,6 @@ public class Huami2021Service {
     public static final short CHUNKED2021_ENDPOINT_HTTP = 0x0001;
     public static final short CHUNKED2021_ENDPOINT_CALENDAR = 0x0007;
     public static final short CHUNKED2021_ENDPOINT_CONFIG = 0x000a;
-    public static final short CHUNKED2021_ENDPOINT_ICONS = 0x000d;
     public static final short CHUNKED2021_ENDPOINT_WEATHER = 0x000e;
     public static final short CHUNKED2021_ENDPOINT_ALARMS = 0x000f;
     public static final short CHUNKED2021_ENDPOINT_CANNED_MESSAGES = 0x0013;
@@ -232,16 +231,6 @@ public class Huami2021Service {
     public static final byte CONFIG_CMD_SET = 0x05;
     public static final byte CONFIG_CMD_ACK = 0x06;
 
-    /**
-     * Config, for {@link Huami2021Service#CHUNKED2021_ENDPOINT_ICONS}.
-     */
-    public static final byte ICONS_CMD_CAPABILITIES_REQUEST = 0x01;
-    public static final byte ICONS_CMD_CAPABILITIES_RESPONSE = 0x02;
-    public static final byte ICONS_CMD_SEND_REQUEST = 0x03;
-    public static final byte ICONS_CMD_SEND_RESPONSE = 0x04;
-    public static final byte ICONS_CMD_DATA_SEND = 0x10;
-    public static final byte ICONS_CMD_DATA_ACK = 0x11;
-
     /**
      * Reminders, for {@link Huami2021Service#CHUNKED2021_ENDPOINT_REMINDERS}.
      */

app/src/main/java/nodomain/freeyourgadget/gadgetbridge/service/devices/huami/Huami2021Support.java

@@ -27,7 +27,6 @@ import static nodomain.freeyourgadget.gadgetbridge.model.ActivityUser.PREF_USER_
 import static nodomain.freeyourgadget.gadgetbridge.service.btle.BLETypeConversions.fromUint16;
 import static nodomain.freeyourgadget.gadgetbridge.service.btle.BLETypeConversions.fromUint8;
 import static nodomain.freeyourgadget.gadgetbridge.service.btle.BLETypeConversions.mapTimeZone;
-import static nodomain.freeyourgadget.gadgetbridge.service.devices.huami.Huami2021Config.ConfigArg.DATE_FORMAT;
 import static nodomain.freeyourgadget.gadgetbridge.service.devices.huami.Huami2021Config.ConfigArg.FITNESS_GOAL_CALORIES;
 import static nodomain.freeyourgadget.gadgetbridge.service.devices.huami.Huami2021Config.ConfigArg.FITNESS_GOAL_FAT_BURN_TIME;
 import static nodomain.freeyourgadget.gadgetbridge.service.devices.huami.Huami2021Config.ConfigArg.FITNESS_GOAL_SLEEP;
@@ -121,9 +120,9 @@ import nodomain.freeyourgadget.gadgetbridge.service.devices.huami.operations.Fet
 import nodomain.freeyourgadget.gadgetbridge.service.devices.huami.operations.HuamiFetchDebugLogsOperation;
 import nodomain.freeyourgadget.gadgetbridge.service.devices.huami.operations.UpdateFirmwareOperation;
 import nodomain.freeyourgadget.gadgetbridge.service.devices.huami.operations.UpdateFirmwareOperation2021;
+import nodomain.freeyourgadget.gadgetbridge.service.devices.huami.zeppos.services.ZeppOsFileUploadService;
 import nodomain.freeyourgadget.gadgetbridge.util.AlarmUtils;
 import nodomain.freeyourgadget.gadgetbridge.util.BitmapUtil;
-import nodomain.freeyourgadget.gadgetbridge.util.CheckSums;
 import nodomain.freeyourgadget.gadgetbridge.util.DeviceHelper;
 import nodomain.freeyourgadget.gadgetbridge.util.GB;
 import nodomain.freeyourgadget.gadgetbridge.util.GBPrefs;
@@ -143,6 +142,9 @@ public abstract class Huami2021Support extends HuamiSupport {
     // send CONTINUE commands
     private boolean heartRateRealtimeStarted;
 
+    // Services
+    private final ZeppOsFileUploadService fileUploadService = new ZeppOsFileUploadService(this);
+
     public Huami2021Support() {
         this(LOG);
     }
@@ -1366,6 +1368,7 @@ public abstract class Huami2021Support extends HuamiSupport {
         }
 
         requestCapabilityReminders(builder);
+        fileUploadService.requestCapability(builder);
 
         for (final HuamiVibrationPatternNotificationType type : coordinator.getVibrationPatternNotificationTypes(gbDevice)) {
             // FIXME: Can we read these from the band?
@@ -1437,8 +1440,8 @@ public abstract class Huami2021Support extends HuamiSupport {
             case CHUNKED2021_ENDPOINT_CONFIG:
                 handle2021Config(payload);
                 return;
-            case CHUNKED2021_ENDPOINT_ICONS:
+            case ZeppOsFileUploadService.ENDPOINT:
-                handle2021Icons(payload);
+                fileUploadService.handlePayload(payload);
                 return;
             case CHUNKED2021_ENDPOINT_WEATHER:
                 handle2021Weather(payload);
@@ -2151,12 +2154,12 @@ public abstract class Huami2021Support extends HuamiSupport {
                     return;
                 }
                 int pos = 1 + packageName.length() + 1;
-                // payload[pos] = 0x08?
+                final byte iconFormat = payload[pos];
                 pos++;
                 int width = BLETypeConversions.toUint16(subarray(payload, pos, pos + 2));
                 pos += 2;
                 int height = BLETypeConversions.toUint16(subarray(payload, pos, pos + 2));
-                sendIconForPackage(packageName, width, height);
+                sendIconForPackage(packageName, iconFormat, width, height);
                 return;
             default:
                 LOG.warn("Unexpected notification byte {}", String.format("0x%02x", payload[0]));
@@ -2176,33 +2179,6 @@ public abstract class Huami2021Support extends HuamiSupport {
         writeToChunked2021("ack notification reply", CHUNKED2021_ENDPOINT_NOTIFICATIONS, buf.array(), true);
     }
 
-    // Package names for which icon is being sent
-    // FIXME: This only handles 1 icon at a time
-    private String queuedIconPackage;
-    // Encoded TGA565 bytes
-    private byte[] queuedIconBytes;
-    // Keep track of the last time we queued an icon, as a failsafe. If somehow we didn't get the ack
-    // after 10 seconds, we'll allow another icon to be sent
-    private long queuedIconTimeMillis = 0;
-
-    protected void handle2021Icons(final byte[] payload) {
-        switch (payload[0]) {
-            case ICONS_CMD_SEND_RESPONSE:
-                LOG.info("Band acknowledged icon send request: {}", GB.hexdump(payload));
-                // FIXME: The bytes probably mean something..
-                sendNextQueuedIconData();
-                return;
-            case ICONS_CMD_DATA_ACK:
-                LOG.info("Band acknowledged icon icon data: {}", GB.hexdump(payload));
-                // After the icon is sent to the band, we need to ACK it on the notifications
-                // FIXME: The bytes probably mean something..
-                ackNotificationAfterIconSent();
-                return;
-            default:
-                LOG.warn("Unexpected icons byte {}", String.format("0x%02x", payload[0]));
-        }
-    }
-
     protected void handle2021Weather(final byte[] payload) {
         switch (payload[0]) {
             case WEATHER_CMD_DEFAULT_LOCATION_ACK:
@@ -2213,43 +2189,7 @@ public abstract class Huami2021Support extends HuamiSupport {
         }
     }
 
-    private void sendNextQueuedIconData() {
+    private void ackNotificationAfterIconSent(final String queuedIconPackage) {
-        if (queuedIconPackage == null) {
-            LOG.error("No queued icon to send");
-            return;
-        }
-
-        if (queuedIconBytes == null) {
-            LOG.error("No icon bytes for {}", queuedIconPackage);
-            return;
-        }
-
-        LOG.info("Sending icon data for {}", queuedIconPackage);
-
-        // The band always sends a full 8192 chunk, with zeroes at the end if bytes < 8192
-        final ByteBuffer buf = ByteBuffer.allocate(10 + queuedIconBytes.length);
-        buf.order(ByteOrder.LITTLE_ENDIAN);
-        buf.put(ICONS_CMD_DATA_SEND);
-        buf.put((byte) 0x03); // ?
-        buf.put((byte) 0x00); // ?
-        buf.put((byte) 0x00); // ?
-        buf.put((byte) 0x00); // ?
-        buf.put((byte) 0x00); // ?
-        buf.put((byte) 0x00); // ?
-        buf.put((byte) 0x00); // ?
-        buf.put((byte) 0x08); // ?
-        buf.put((byte) 0x17); // ?
-        buf.put(queuedIconBytes);
-
-        writeToChunked2021("send icon data", CHUNKED2021_ENDPOINT_ICONS, buf.array(), false);
-    }
-
-    private void ackNotificationAfterIconSent() {
-        if (queuedIconPackage == null) {
-            LOG.error("No queued icon to ack");
-            return;
-        }
-
         LOG.info("Acknowledging icon send for {}", queuedIconPackage);
 
         final ByteBuffer buf = ByteBuffer.allocate(1 + queuedIconPackage.length() + 1 + 1);
@@ -2259,20 +2199,30 @@ public abstract class Huami2021Support extends HuamiSupport {
         buf.put((byte) 0x00);
         buf.put((byte) 0x01);
 
-        queuedIconPackage = null;
-        queuedIconBytes = null;
-
         writeToChunked2021("ack icon send", CHUNKED2021_ENDPOINT_NOTIFICATIONS, buf.array(), true);
     }
 
-    private void sendIconForPackage(final String packageName, final int width, final int height) {
+    private void sendIconForPackage(final String packageName, final byte iconFormat, final int width, final int height) {
         if (getMTU() < 247) {
             LOG.warn("Sending icons requires high MTU, current MTU is {}", getMTU());
             return;
         }
 
-        if (queuedIconPackage != null && System.currentTimeMillis() - queuedIconTimeMillis < 10_000L) {
+        // Without the expected tga id and format string they seem to get corrupted,
-            LOG.warn("Icon for {} already queued, not sending icon for {}", queuedIconPackage, packageName);
+        // but the encoding seems to actually be the same...?
+        final String format;
+        final String tgaId;
+        switch (iconFormat) {
+            case 0x04:
+                format = "TGA_RGB565_GCNANOLITE";
+                tgaId = "SOMHP";
+                break;
+            case 0x08:
+                format = "TGA_RGB565_DAVE2D";
+                tgaId = "SOMH6";
+                break;
+            default:
+                LOG.error("Unknown icon format {}", String.format("0x%02x", iconFormat));
                 return;
         }
 
@@ -2287,19 +2237,11 @@ public abstract class Huami2021Support extends HuamiSupport {
         final Bitmap bmp = BitmapUtil.toBitmap(icon);
 
         // The TGA needs to have this ID, or the band does not accept it
-        final byte[] tgaId = new byte[46];
+        final byte[] tgaIdBytes = new byte[46];
-        System.arraycopy("SOMH6".getBytes(StandardCharsets.UTF_8), 0, tgaId, 0, 5);
+        System.arraycopy(tgaId.getBytes(StandardCharsets.UTF_8), 0, tgaIdBytes, 0, 5);
 
-        final byte[] tga565 = BitmapUtil.convertToTgaRGB565(bmp, width, height, tgaId);
+        final byte[] tga565 = BitmapUtil.convertToTgaRGB565(bmp, width, height, tgaIdBytes);
 
-        if (tga565.length > 8192) {
-            // FIXME: Pretty sure we can't send more than 8KB in a single request,
-            // but don't know how it's supposed to be encoded
-            LOG.error("TGA output is too large: {}", tga565.length);
-            return;
-        }
-
-        final String format = "TGA_RGB565_DAVE2D";
         final String url = String.format(
                 Locale.ROOT,
                 "notification://logo?app_id=%s&width=%d&height=%d&format=%s",
@@ -2310,23 +2252,27 @@ public abstract class Huami2021Support extends HuamiSupport {
         );
         final String filename = String.format("logo_%s.tga", packageName.replace(".", "_"));
 
-        final ByteBuffer buf = ByteBuffer.allocate(2 + url.length() + 1 + filename.length() + 1 + 4 + 4);
+        fileUploadService.sendFile(
-        buf.order(ByteOrder.LITTLE_ENDIAN);
+                url,
-        buf.put(ICONS_CMD_SEND_REQUEST);
+                filename,
-        buf.put((byte) 0x00);
+                tga565,
-        buf.put(url.getBytes(StandardCharsets.UTF_8));
+                new ZeppOsFileUploadService.Callback() {
-        buf.put((byte) 0x00);
+                    @Override
-        buf.put(filename.getBytes(StandardCharsets.UTF_8));
+                    public void onFinish(final boolean success) {
-        buf.put((byte) 0x00);
+                        LOG.info("Finished sending icon, success={}", success);
-        buf.putInt(tga565.length);
+                        if (success) {
-        buf.putInt(CheckSums.getCRC32(tga565));
+                            ackNotificationAfterIconSent(packageName);
+                        }
+                    }
+
+                    @Override
+                    public void onProgress(final int progress) {
+                        LOG.trace("Icon send progress: {}", progress);
+                    }
+                }
+        );
 
         LOG.info("Queueing icon for {}", packageName);
-        queuedIconPackage = packageName;
-        queuedIconBytes = tga565;
-        queuedIconTimeMillis = System.currentTimeMillis();
-
-        writeToChunked2021("send icon send request", CHUNKED2021_ENDPOINT_ICONS, buf.array(), false);
     }
 
     protected void handle2021Reminders(final byte[] payload) {

app/src/main/java/nodomain/freeyourgadget/gadgetbridge/service/devices/huami/HuamiSupport.java

@@ -3931,19 +3931,19 @@ public abstract class HuamiSupport extends AbstractBTLEDeviceSupport implements
         }
     }
 
-    protected void writeToChunked2021(TransactionBuilder builder, short type, byte data, boolean encrypt) {
+    public void writeToChunked2021(TransactionBuilder builder, short type, byte data, boolean encrypt) {
         writeToChunked2021(builder, type, new byte[]{data}, encrypt);
     }
 
-    protected void writeToChunked2021(TransactionBuilder builder, short type, byte[] data, boolean encrypt) {
+    public void writeToChunked2021(TransactionBuilder builder, short type, byte[] data, boolean encrypt) {
         huami2021ChunkedEncoder.write(builder, type, data, force2021Protocol(), encrypt);
     }
 
-    protected void writeToChunked2021(final String taskName, short type, byte data, boolean encrypt) {
+    public void writeToChunked2021(final String taskName, short type, byte data, boolean encrypt) {
         writeToChunked2021(taskName, type, new byte[]{data}, encrypt);
     }
 
-    protected void writeToChunked2021(final String taskName, short type, byte[] data, boolean encrypt) {
+    public void writeToChunked2021(final String taskName, short type, byte[] data, boolean encrypt) {
         try {
             final TransactionBuilder builder = performInitialized(taskName);
             writeToChunked2021(builder, type, data, encrypt);

app/src/main/java/nodomain/freeyourgadget/gadgetbridge/service/devices/huami/zeppos/AbstractZeppOsService.java

@@ -0,0 +1,40 @@
+/*  Copyright (C) 2022 José Rebelo
+
+    This file is part of Gadgetbridge.
+
+    Gadgetbridge is free software: you can redistribute it and/or modify
+    it under the terms of the GNU Affero General Public License as published
+    by the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    Gadgetbridge 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 Affero General Public License for more details.
+
+    You should have received a copy of the GNU Affero General Public License
+    along with this program.  If not, see <http://www.gnu.org/licenses/>. */
+package nodomain.freeyourgadget.gadgetbridge.service.devices.huami.zeppos;
+
+import nodomain.freeyourgadget.gadgetbridge.service.btle.TransactionBuilder;
+import nodomain.freeyourgadget.gadgetbridge.service.devices.huami.Huami2021Support;
+
+public abstract class AbstractZeppOsService {
+    private final Huami2021Support mSupport;
+
+    public AbstractZeppOsService(final Huami2021Support support) {
+        this.mSupport = support;
+    }
+
+    public abstract short getEndpoint();
+    public abstract boolean isEncrypted();
+    public abstract void handlePayload(final byte[] payload);
+
+    protected void write(final String taskName, final byte[] data) {
+        this.mSupport.writeToChunked2021(taskName, getEndpoint(), data, isEncrypted());
+    }
+
+    protected void write(final TransactionBuilder builder, final byte[] data) {
+        this.mSupport.writeToChunked2021(builder, getEndpoint(), data, isEncrypted());
+    }
+}

app/src/main/java/nodomain/freeyourgadget/gadgetbridge/service/devices/huami/zeppos/services/ZeppOsFileUploadService.java

@@ -0,0 +1,278 @@
+/*  Copyright (C) 2022 José Rebelo
+
+    This file is part of Gadgetbridge.
+
+    Gadgetbridge is free software: you can redistribute it and/or modify
+    it under the terms of the GNU Affero General Public License as published
+    by the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    Gadgetbridge 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 Affero General Public License for more details.
+
+    You should have received a copy of the GNU Affero General Public License
+    along with this program.  If not, see <http://www.gnu.org/licenses/>. */
+package nodomain.freeyourgadget.gadgetbridge.service.devices.huami.zeppos.services;
+
+import org.apache.commons.lang3.ArrayUtils;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import java.nio.ByteBuffer;
+import java.nio.ByteOrder;
+import java.nio.charset.StandardCharsets;
+import java.util.HashMap;
+import java.util.Map;
+
+import nodomain.freeyourgadget.gadgetbridge.service.btle.BLETypeConversions;
+import nodomain.freeyourgadget.gadgetbridge.service.btle.TransactionBuilder;
+import nodomain.freeyourgadget.gadgetbridge.service.devices.huami.Huami2021Support;
+import nodomain.freeyourgadget.gadgetbridge.service.devices.huami.zeppos.AbstractZeppOsService;
+import nodomain.freeyourgadget.gadgetbridge.util.CheckSums;
+
+public class ZeppOsFileUploadService extends AbstractZeppOsService {
+    private static final Logger LOG = LoggerFactory.getLogger(ZeppOsFileUploadService.class);
+
+    public static final short ENDPOINT = 0x000d;
+
+    public static final byte CMD_CAPABILITIES_REQUEST = 0x01;
+    public static final byte CMD_CAPABILITIES_RESPONSE = 0x02;
+    public static final byte CMD_UPLOAD_REQUEST = 0x03;
+    public static final byte CMD_UPLOAD_RESPONSE = 0x04;
+    public static final byte CMD_DATA_SEND = 0x10;
+    public static final byte CMD_DATA_ACK = 0x11;
+
+    public static final byte FLAG_FIRST_CHUNK = 0x01;
+    public static final byte FLAG_LAST_CHUNK = 0x02;
+
+    private final Map<Byte, FileSendRequest> mSessionRequests = new HashMap<>();
+
+    private int mChunkSize = -1;
+
+    public ZeppOsFileUploadService(final Huami2021Support support) {
+        super(support);
+    }
+
+    @Override
+    public short getEndpoint() {
+        return ENDPOINT;
+    }
+
+    @Override
+    public boolean isEncrypted() {
+        return false;
+    }
+
+    @Override
+    public void handlePayload(final byte[] payload) {
+        byte session;
+        byte status;
+
+        switch (payload[0]) {
+            case CMD_CAPABILITIES_RESPONSE:
+                final int version = payload[1] & 0xff;
+                if (version != 1 && version != 2) {
+                    LOG.error("Unsupported file upload service version: {}", version);
+                    return;
+                }
+                mChunkSize = BLETypeConversions.toUint16(payload, 2);
+                LOG.info("Got file upload service: version={}, chunkSize={}", version, mChunkSize);
+                return;
+            case CMD_UPLOAD_RESPONSE:
+                session = payload[1];
+                status = payload[2];
+                final int existingProgress = BLETypeConversions.toUint32(payload, 3);
+                LOG.info("Band acknowledged file upload request: session={}, status={}, existingProgress={}", session, status, existingProgress);
+                if (status != 0) {
+                    LOG.error("Unexpected status from band for session {}, aborting", session);
+                    onFinish(session, false);
+                    return;
+                }
+                if (existingProgress != 0) {
+                    LOG.info("Updating existing progress for session {} to {}", session, existingProgress);
+                    final FileSendRequest request = mSessionRequests.get(session);
+                    if (request == null) {
+                        LOG.error("No request found for session {}", session);
+                        return;
+                    }
+                    request.setProgress(existingProgress);
+                }
+                sendNextQueuedData(session);
+                return;
+            case CMD_DATA_ACK:
+                session = payload[1];
+                status = payload[2];
+                LOG.info("Band acknowledged file upload data: session={}, status={}", session, status);
+                if (status != 0) {
+                    LOG.error("Unexpected status from band, aborting session {}", session);
+                    onFinish(session, false);
+                    return;
+                }
+                sendNextQueuedData(session);
+                return;
+            default:
+                LOG.warn("Unexpected file upload byte {}", String.format("0x%02x", payload[0]));
+        }
+    }
+
+    public void requestCapability(final TransactionBuilder builder) {
+        write(builder, new byte[]{CMD_CAPABILITIES_REQUEST});
+    }
+
+    public void sendFile(final String url, final String filename, final byte[] bytes, final Callback callback) {
+        if (mChunkSize < 0) {
+            LOG.error("Service not initialized, refusing to send {}", url);
+            callback.onFinish(false);
+            return;
+        }
+
+        LOG.info("Sending {} bytes to {}", bytes.length, url);
+
+        final FileSendRequest request = new FileSendRequest(url, filename, bytes, callback);
+
+        final byte session = (byte) mSessionRequests.size();
+
+        final ByteBuffer buf = ByteBuffer.allocate(2 + url.length() + 1 + filename.length() + 1 + 4 + 4);
+        buf.order(ByteOrder.LITTLE_ENDIAN);
+        buf.put(CMD_UPLOAD_REQUEST);
+        buf.put(session);
+        buf.put(url.getBytes(StandardCharsets.UTF_8));
+        buf.put((byte) 0x00);
+        buf.put(filename.getBytes(StandardCharsets.UTF_8));
+        buf.put((byte) 0x00);
+        buf.putInt(bytes.length);
+        buf.putInt(CheckSums.getCRC32(bytes));
+
+        write("send file upload request", buf.array());
+
+        mSessionRequests.put(session, request);
+    }
+
+    private void sendNextQueuedData(final byte session) {
+        final FileSendRequest request = mSessionRequests.get(session);
+        if (request == null) {
+            LOG.error("No request found for session {}", session);
+            return;
+        }
+
+        if (request.getProgress() >= request.getSize()) {
+            LOG.info("Sending {} finished", request.getUrl());
+            onFinish(session, true);
+            return;
+        }
+
+        LOG.debug("Sending file data for session={}, progress={}, index={}", session, request.getProgress(), request.getIndex());
+
+        final ByteBuffer buf = ByteBuffer.allocate(10 + mChunkSize);
+        buf.order(ByteOrder.LITTLE_ENDIAN);
+        buf.put(CMD_DATA_SEND);
+
+        byte flags = 0;
+        if (request.getProgress() == 0) {
+            flags |= FLAG_FIRST_CHUNK;
+        }
+        if (request.getProgress() + mChunkSize >= request.getSize()) {
+            flags |= FLAG_LAST_CHUNK;
+        }
+
+        buf.put(flags);
+        buf.put(session);
+        buf.put(request.getIndex());
+        if ((flags & FLAG_FIRST_CHUNK) > 0) {
+            buf.put((byte) 0x00); // ?
+            buf.put((byte) 0x00); // ?
+            buf.put((byte) 0x00); // ?
+            buf.put((byte) 0x00); // ?
+        }
+
+        final byte[] payload = ArrayUtils.subarray(
+                request.getBytes(),
+                request.getProgress(),
+                request.getProgress() + mChunkSize
+        );
+
+        buf.putShort((short) payload.length);
+        buf.put(payload);
+
+        request.setProgress(request.getProgress() + payload.length);
+        request.setIndex((byte) (request.getIndex() + 1));
+        request.getCallback().onProgress(request.getProgress());
+
+        write("send file data", buf.array());
+    }
+
+    private void onFinish(final byte session, final boolean success) {
+        final FileSendRequest request = mSessionRequests.get(session);
+        if (request == null) {
+            LOG.error("No request found for session {}", session);
+            return;
+        }
+
+        mSessionRequests.remove(session);
+
+        request.getCallback().onFinish(success);
+    }
+
+    /**
+     * Wrapper class to keep track of ongoing file send requests and their progress.
+     */
+    public static class FileSendRequest {
+        private final String url;
+        private final String filename;
+        private final byte[] bytes;
+        private final Callback callback;
+        private int progress = 0;
+        private byte index = 0;
+
+        public FileSendRequest(final String url, final String filename, final byte[] bytes, final Callback callback) {
+            this.url = url;
+            this.filename = filename;
+            this.bytes = bytes;
+            this.callback = callback;
+        }
+
+        public String getUrl() {
+            return url;
+        }
+
+        public String getFilename() {
+            return filename;
+        }
+
+        public byte[] getBytes() {
+            return bytes;
+        }
+
+        public int getSize() {
+            return bytes.length;
+        }
+
+        public Callback getCallback() {
+            return callback;
+        }
+
+        public int getProgress() {
+            return progress;
+        }
+
+        public void setProgress(final int progress) {
+            this.progress = progress;
+        }
+
+        public byte getIndex() {
+            return index;
+        }
+
+        public void setIndex(final byte index) {
+            this.index = index;
+        }
+    }
+
+    public interface Callback {
+        void onFinish(boolean success);
+
+        void onProgress(int progress);
+    }
+}