feat(agent): implement HTTP JFR snapshot creation

src/main/java/io/cryostat/net/AgentClient.java

@@ -130,6 +130,57 @@ Future<IRecordingDescriptor> startRecording(StartRecordingRequest req) {
                 });
     }
 
+    Future<IRecordingDescriptor> startSnapshot() {
+        StartRecordingRequest snapshotReq = new StartRecordingRequest("snapshot", "", "", 0, 0, 0);
+
+        Future<HttpResponse<String>> f =
+                invoke(
+                        HttpMethod.POST,
+                        "/recordings/",
+                        Buffer.buffer(gson.toJson(snapshotReq)),
+                        BodyCodec.string());
+
+        return f.map(
+                resp -> {
+                    int statusCode = resp.statusCode();
+                    if (HttpStatusCodeIdentifier.isSuccessCode(statusCode)) {
+                        String body = resp.body();
+                        return gson.fromJson(body, SerializableRecordingDescriptor.class)
+                                .toJmcForm();
+                    } else if (statusCode == 403) {
+                        throw new UnsupportedOperationException();
+                    } else {
+                        throw new RuntimeException("Unknown failure");
+                    }
+                });
+    }
+
+    Future<Void> updateRecordingOptions(long id, IConstrainedMap<String> newSettings) {
+
+        JsonObject jsonSettings = new JsonObject();
+        for (String key : newSettings.keySet()) {
+            jsonSettings.put(key, newSettings.get(key));
+        }
+        Future<HttpResponse<Void>> f =
+                invoke(
+                        HttpMethod.PATCH,
+                        String.format("/recordings/%d", id),
+                        jsonSettings.toBuffer(),
+                        BodyCodec.none());
+
+        return f.map(
+                resp -> {
+                    int statusCode = resp.statusCode();
+                    if (HttpStatusCodeIdentifier.isSuccessCode(statusCode)) {
+                        return null;
+                    } else if (statusCode == 403) {
+                        throw new UnsupportedOperationException();
+                    } else {
+                        throw new RuntimeException("Unknown failure");
+                    }
+                });
+    }
+
     Future<Buffer> openStream(long id) {
         Future<HttpResponse<Buffer>> f =
                 invoke(HttpMethod.GET, "/recordings/" + id, BodyCodec.buffer());

src/main/java/io/cryostat/net/AgentJFRService.java

@@ -174,7 +174,11 @@ public List<String> getServerTemplates() throws FlightRecorderException {
 
     @Override
     public IRecordingDescriptor getSnapshotRecording() throws FlightRecorderException {
-        throw new UnimplementedException();
+        try {
+            return client.startSnapshot().toCompletionStage().toCompletableFuture().get();
+        } catch (ExecutionException | InterruptedException e) {
+            throw new FlightRecorderException("Failed to create snapshot recording", e);
+        }
     }
 
     @Override
@@ -245,9 +249,18 @@ public void updateEventOptions(IRecordingDescriptor arg0, IConstrainedMap<EventO
     }
 
     @Override
-    public void updateRecordingOptions(IRecordingDescriptor arg0, IConstrainedMap<String> arg1)
+    public void updateRecordingOptions(
+            IRecordingDescriptor recordingDescriptor, IConstrainedMap<String> newSettings)
             throws FlightRecorderException {
-        throw new UnimplementedException();
+        try {
+            long recordingId = recordingDescriptor.getId();
+            client.updateRecordingOptions(recordingId, newSettings)
+                    .toCompletionStage()
+                    .toCompletableFuture()
+                    .get();
+        } catch (ExecutionException | InterruptedException e) {
+            throw new FlightRecorderException("Failed to update recording options", e);
+        }
     }
 
     @Override