2 files changed, 85 insertions, 11 deletions

diff --git a/src/main/java/org/traccar/WebDataHandler.java b/src/main/java/org/traccar/WebDataHandler.java
index 64396de03..193efd230 100644
--- a/src/main/java/org/traccar/WebDataHandler.java
+++ b/src/main/java/org/traccar/WebDataHandler.java
@@ -27,9 +27,11 @@ import org.traccar.model.Position;
 import org.traccar.model.Group;
 
 import javax.inject.Inject;
+import javax.ws.rs.core.Response;
 import javax.ws.rs.client.Client;
 import javax.ws.rs.client.Entity;
 import javax.ws.rs.client.Invocation;
+import javax.ws.rs.client.InvocationCallback;
 import java.util.HashMap;
 import java.util.Map;
 import java.io.UnsupportedEncodingException;
@@ -39,6 +41,14 @@ import java.util.Calendar;
 import java.util.Formatter;
 import java.util.Locale;
 import java.util.TimeZone;
+import java.util.concurrent.atomic.AtomicBoolean;
+
+import org.apache.commons.collections.Buffer;
+import org.apache.commons.collections.BufferUtils;
+import org.apache.commons.collections.buffer.CircularFifoBuffer;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
 
 @ChannelHandler.Sharable
 public class WebDataHandler extends BaseDataHandler {
@@ -46,6 +56,8 @@ public class WebDataHandler extends BaseDataHandler {
     private static final String KEY_POSITION = "position";
     private static final String KEY_DEVICE = "device";
 
+    private static final Logger LOGGER = LoggerFactory.getLogger(WebDataHandler.class);
+
     private final IdentityManager identityManager;
     private final ObjectMapper objectMapper;
     private final Client client;
@@ -54,6 +66,13 @@ public class WebDataHandler extends BaseDataHandler {
     private final String header;
     private final boolean json;
 
+    private final Integer queueSize;
+
+    private Buffer positionsQueue = null;
+    private AtomicBoolean sendInProgress;
+
+    private Invocation.Builder requestBuilder;
+
     @Inject
     public WebDataHandler(
             Config config, IdentityManager identityManager, ObjectMapper objectMapper, Client client) {
@@ -63,6 +82,12 @@ public class WebDataHandler extends BaseDataHandler {
         this.url = config.getString(Keys.FORWARD_URL);
         this.header = config.getString(Keys.FORWARD_HEADER);
         this.json = config.getBoolean(Keys.FORWARD_JSON);
+        Integer queueSize = (config.getInteger(Keys.FORWARD_QUEUE_SIZE, 0));
+        this.queueSize = (queueSize > 0) ? queueSize : 0;
+        if (this.queueSize > 0) {
+            this.positionsQueue = BufferUtils.synchronizedBuffer(new CircularFifoBuffer(this.queueSize));
+        }
+        this.sendInProgress = new AtomicBoolean(false);
     }
 
     private static String formatSentence(Position position) {
@@ -152,9 +177,7 @@ public class WebDataHandler extends BaseDataHandler {
         return request;
     }
 
-    @Override
-    protected Position handlePosition(Position position) {
-
+    protected void sendPosition(Position position) {
         String url;
         if (json) {
             url = this.url;
@@ -166,19 +189,63 @@ public class WebDataHandler extends BaseDataHandler {
             }
         }
 
-        Invocation.Builder requestBuilder = client.target(url).request();
-
-        if (header != null && !header.isEmpty()) {
-            for (String line: header.split("\\r?\\n")) {
-                String[] values = line.split(":", 2);
-                requestBuilder.header(values[0].trim(), values[1].trim());
+        if (!json || requestBuilder == null) {
+            requestBuilder = client.target(url).request();
+            if (header != null && !header.isEmpty()) {
+                for (String line: header.split("\\r?\\n")) {
+                     String[] values = line.split(":", 2);
+                     requestBuilder.header(values[0].trim(), values[1].trim());
+                }
             }
         }
 
+        InvocationCallback<Response> callback = new InvocationCallback<Response>() {
+            public void completed(Response response) {
+                if (positionsQueue != null) {
+                    if (response.getStatus() == 200) {
+                        positionsQueue.remove();
+                    }
+                    logQueueStatus();
+                    sendInProgress.set(false);
+                    sendQueuedPositions();
+                }
+            }
+            public void failed(Throwable throwable) {
+                if (positionsQueue != null) {
+                    logQueueStatus();
+                    sendInProgress.set(false);
+                    sendQueuedPositions();
+                }
+            }
+        };
+
         if (json) {
-            requestBuilder.async().post(Entity.json(prepareJsonPayload(position)));
+            requestBuilder.async().post(Entity.json(prepareJsonPayload(position)), callback);
+        } else {
+            requestBuilder.async().get(callback);
+        }
+    }
+
+    protected void logQueueStatus() {
+        LOGGER.info(String.format("Position forwarding queue: %d/%d",
+            positionsQueue.size(), queueSize));
+    }
+
+    protected void sendQueuedPositions() {
+        if (!positionsQueue.isEmpty() && !sendInProgress.get()) {
+            sendInProgress.set(true);
+            sendPosition((Position) positionsQueue.get());
+        }
+    }
+
+    @Override
+    protected Position handlePosition(Position position) {
+
+        if (positionsQueue == null) {
+            sendPosition(position);
         } else {
-            requestBuilder.async().get();
+            positionsQueue.add(position);
+            sendQueuedPositions();
         }
 
         return position;
diff --git a/src/main/java/org/traccar/config/Keys.java b/src/main/java/org/traccar/config/Keys.java
index 2c5dcefd5..10eda01e2 100644
--- a/src/main/java/org/traccar/config/Keys.java
+++ b/src/main/java/org/traccar/config/Keys.java
@@ -101,6 +101,13 @@ public final class Keys {
             "forward.json", Boolean.class);
 
     /**
+     * Position forwarding queue size. A ring buffer of the specified size is used to queue positions.
+     * If negative, zero, or not specified, queueing is disabled. (Legacy behaviour)
+     */
+    public static final ConfigKey FORWARD_QUEUE_SIZE = new ConfigKey(
+            "forward.queue.size", Integer.class);
+
+    /**
      * Boolean flag to enable or disable position filtering.
      */
     public static final ConfigKey FILTER_ENABLE = new ConfigKey(