Ability to query isLive() on OSHSystem objects.

src/main/java/org/sensorhub/oshconnect/OSHSystem.java

@@ -15,6 +15,8 @@
 import org.sensorhub.oshconnect.util.DataStreamsQueryBuilder;
 import org.sensorhub.oshconnect.util.Utilities;
 
+import java.time.Duration;
+import java.time.Instant;
 import java.util.*;
 import java.util.concurrent.ExecutionException;
 
@@ -99,6 +101,14 @@ public List<OSHDataStream> discoverDataStreams(String query) throws ExecutionExc
         return result;
     }
 
+    public boolean isLive(Duration window) throws ExecutionException, InterruptedException {
+        var cutoff = Instant.now().minus(window);
+        return getConnectedSystemsApiClientExtras()
+                .getLastObservationTimes(getId(), "").get()
+                .values().stream()
+                .anyMatch(t -> t != null && t.isAfter(cutoff));
+    }
+
     /**
      * Add or update a data stream in the list of data streams and notify listeners.
      *

src/main/java/org/sensorhub/oshconnect/net/ConSysApiClientExtras.java

@@ -24,12 +24,17 @@
 
 import java.io.*;
 import java.net.*;
+import java.nio.charset.StandardCharsets;
 import java.util.ArrayList;
 import java.util.Collections;
 import java.util.List;
 import java.util.concurrent.CompletableFuture;
 import java.util.concurrent.CompletionException;
 import java.util.function.Function;
+import java.time.Instant;
+import java.time.format.DateTimeParseException;
+import java.util.LinkedHashMap;
+import java.util.Map;
 
 public class ConSysApiClientExtras {
     static final String JSON_ARRAY_ITEMS = "items";
@@ -136,6 +141,45 @@ public CompletableFuture<List<String>> getDataStreamIds(String systemID, String
         });
     }
 
+    public CompletableFuture<Map<String, Instant>> getLastObservationTimes(String systemID, String queryString) {
+        if (queryString == null)
+            queryString = "";
+
+        return sendGetRequest(endpoint.resolve(SYSTEMS_COLLECTION + "/" + systemID + "/" + DATASTREAMS_COLLECTION + queryString), ResourceFormat.JSON, body -> {
+            try {
+                var ctx = new RequestContext(body);
+                JsonObject bodyJson = JsonParser.parseReader(new InputStreamReader(ctx.getInputStream())).getAsJsonObject();
+                JsonArray features = bodyJson.getAsJsonArray(JSON_ARRAY_ITEMS);
+
+                Map<String, Instant> times = new LinkedHashMap<>();
+                for (var feature : features) {
+                    var obj = feature.getAsJsonObject();
+                    if (!obj.has("id"))
+                        throw new IOException("No id found in feature");
+                    times.put(obj.get("id").getAsString(), parseExtentEnd(obj.getAsJsonArray("phenomenonTime")));
+                }
+                return times;
+            } catch (IOException e) {
+                throw new CompletionException(e);
+            }
+        });
+    }
+
+    private static Instant parseExtentEnd(JsonArray extent) {
+        if (extent == null || extent.size() < 2)
+            return null;
+        var end = extent.get(1).getAsString();
+        if ("0".equals(end))          // no observations yet
+            return null;
+        if ("now".equals(end))        // defensive: your node uses this on validTime, not phenomenonTime
+            return Instant.now();
+        try {
+            return Instant.parse(end);
+        } catch (DateTimeParseException e) {
+            return null;
+        }
+    }
+
     /**
      * Update a data stream.
      *
@@ -290,7 +334,7 @@ public CompletableFuture<List<ObservationData>> getObservations(String dataStrea
                 }
 
                 return observations;
-            } catch (IOException e) {
+            } catch (Exception e) {
                 throw new CompletionException(e);
             }
         });

src/main/java/org/sensorhub/oshconnect/net/websocket/WebSocketConnection.java

@@ -78,6 +78,8 @@ public void checkServerTrusted(X509Certificate[] chain, String authType) {}
                 sslContextFactory.getSslContext().getClientSessionContext().setSessionCacheSize(0);
 
                 client = new WebSocketClient(sslContextFactory);
+                client.getPolicy().setMaxBinaryMessageSize(4 * 1024 * 1024);   // Jetty 9.x
+//                client.setMaxBinaryMessageSize(4 * 1024 * 1024);               // Jetty 10/11+
 
                 client.start();
                 client.connect(this, new URI(urlString), clientUpgradeRequest);