Provide new data protocol for segment messages.

apm-commons/apm-trace/src/main/java/org/skywalking/apm/trace/SegmentsMessage.java

@@ -1,13 +1,6 @@
 package org.skywalking.apm.trace;
 
 import com.google.gson.Gson;
-import com.google.gson.GsonBuilder;
-import com.google.gson.TypeAdapter;
-import com.google.gson.annotations.JsonAdapter;
-import com.google.gson.stream.JsonReader;
-import com.google.gson.stream.JsonWriter;
-
-import java.io.IOException;
 import java.util.Collections;
 import java.util.LinkedList;
 import java.util.List;
@@ -18,7 +11,6 @@
  *
  * @author wusheng
  */
-@JsonAdapter(SegmentsMessage.Serializer.class)
 public class SegmentsMessage {
     private List<TraceSegment> segments;
 
@@ -34,40 +26,23 @@ public List<TraceSegment> getSegments() {
         return Collections.unmodifiableList(segments);
     }
 
-    public static class Serializer extends TypeAdapter<SegmentsMessage> {
-
-        @Override
-        public void write(JsonWriter out, SegmentsMessage value) throws IOException {
-            Gson gson = new GsonBuilder()
-                .excludeFieldsWithoutExposeAnnotation()
-                .create();
-
-            out.beginArray();
-            try {
-                for (TraceSegment segment : value.segments) {
-                    out.jsonValue(gson.toJson(segment));
-                }
-            } finally {
-                out.endArray();
-            }
-        }
-
-        @Override
-        public SegmentsMessage read(JsonReader in) throws IOException {
-            SegmentsMessage message = new SegmentsMessage();
-            in.beginArray();
-            Gson gson = new GsonBuilder()
-                .excludeFieldsWithoutExposeAnnotation()
-                .create();
-            try {
-                while (in.hasNext()) {
-                    TraceSegment traceSegment = gson.fromJson(in, TraceSegment.class);
-                    message.append(traceSegment);
-                }
-            } finally {
-                in.endArray();
-            }
-            return message;
+    /**
+     * This serialization mechanism started from 3.1, it is similar to network package.
+     * The data protocol is
+     *
+     * segment1.json.length + ' '(one blank space) + segment1.json
+     * + segment2.json.length + ' '(one blank space) + segment2.json
+     * + etc.
+     *
+     * @param gson the serializer for {@link TraceSegment}
+     * @return the string represents the <code>SegmentMessage</code>
+     */
+    public String serialize(Gson gson) {
+        StringBuilder buffer = new StringBuilder();
+        for (TraceSegment segment : segments) {
+            String segmentJson = gson.toJson(segment);
+            buffer.append(segmentJson.length()).append(' ').append(segmentJson);
         }
+        return buffer.toString();
     }
 }

apm-commons/apm-trace/src/test/java/org/skywalking/apm/trace/TraceSegmentTestCase.java

@@ -108,15 +108,18 @@ public void testSerialize() {
 
         SegmentsMessage message = new SegmentsMessage();
         message.append(segment);
-        String json = gson.toJson(message);
 
-        message = gson.fromJson(json, SegmentsMessage.class);
+        String jsonString = message.serialize(gson);
+        int length = Integer.parseInt(jsonString.substring(0, 4));
 
-        TraceSegment newSegment = message.getSegments().get(0);
+        String segmentJson = jsonString.substring(5);
 
-        Assert.assertEquals(segment.getSpans().size(), newSegment.getSpans().size());
-        Assert.assertEquals(segment.getRefs().get(0).getTraceSegmentId(), newSegment.getRefs().get(0).getTraceSegmentId());
-        Assert.assertEquals(Tags.SPAN_LAYER.get(segment.getSpans().get(1)), Tags.SPAN_LAYER.get(newSegment.getSpans().get(1)));
-        Assert.assertEquals(segment.getSpans().get(1).getLogs().get(0).getTime(), newSegment.getSpans().get(1).getLogs().get(0).getTime());
+        Assert.assertEquals(length, segmentJson.length());
+        TraceSegment recoverySegment = gson.fromJson(segmentJson, TraceSegment.class);
+
+        Assert.assertEquals(segment.getSpans().size(), recoverySegment.getSpans().size());
+        Assert.assertEquals(segment.getRefs().get(0).getTraceSegmentId(), recoverySegment.getRefs().get(0).getTraceSegmentId());
+        Assert.assertEquals(Tags.SPAN_LAYER.get(segment.getSpans().get(1)), Tags.SPAN_LAYER.get(recoverySegment.getSpans().get(1)));
+        Assert.assertEquals(segment.getSpans().get(1).getLogs().get(0).getTime(), recoverySegment.getSpans().get(1).getLogs().get(0).getTime());
     }
 }

apm-sniffer/apm-agent-core/src/main/java/org/skywalking/apm/agent/core/client/CollectorClient.java

@@ -32,13 +32,17 @@ public class CollectorClient implements Runnable {
     private static long SLEEP_TIME_MILLIS = 500;
     private String[] serverList;
     private volatile int selectedServer = -1;
+    private Gson serializer;
 
     public CollectorClient() {
         serverList = Config.Collector.SERVERS.split(",");
         Random r = new Random();
         if (serverList.length > 0) {
             selectedServer = r.nextInt(serverList.length);
         }
+        serializer = new GsonBuilder()
+            .excludeFieldsWithoutExposeAnnotation()
+            .create();
     }
 
     @Override
@@ -84,10 +88,7 @@ private void sendToCollector(SegmentsMessage message) throws RESTResponseStatusE
         if (message == null) {
             return;
         }
-        Gson gson = new GsonBuilder()
-            .excludeFieldsWithoutExposeAnnotation()
-            .create();
-        String messageJson = gson.toJson(message);
+        String messageJson = message.serialize(serializer);
         CloseableHttpClient httpClient = HttpClients.custom().build();
         try {
             HttpPost httpPost = ready2Send(messageJson);