Do not output empty metric reports.

Test: statsd unit test passed.

Change-Id: I296edbe621eaea72ad2e1dfe656698302614c0f3
diff --git a/cmds/statsd/src/metrics/CountMetricProducer.cpp b/cmds/statsd/src/metrics/CountMetricProducer.cpp
index ef27210..0455f6a 100644
--- a/cmds/statsd/src/metrics/CountMetricProducer.cpp
+++ b/cmds/statsd/src/metrics/CountMetricProducer.cpp
@@ -112,6 +112,9 @@
 void CountMetricProducer::onDumpReportLocked(const uint64_t dumpTimeNs,
                                              ProtoOutputStream* protoOutput) {
     flushIfNeededLocked(dumpTimeNs);
+    if (mPastBuckets.empty()) {
+        return;
+    }
 
     protoOutput->write(FIELD_TYPE_INT64 | FIELD_ID_ID, (long long)mMetricId);
     protoOutput->write(FIELD_TYPE_INT64 | FIELD_ID_START_REPORT_NANOS, (long long)mStartTimeNs);
diff --git a/cmds/statsd/src/metrics/DurationMetricProducer.cpp b/cmds/statsd/src/metrics/DurationMetricProducer.cpp
index 58dd464..e26fe56 100644
--- a/cmds/statsd/src/metrics/DurationMetricProducer.cpp
+++ b/cmds/statsd/src/metrics/DurationMetricProducer.cpp
@@ -168,6 +168,9 @@
 void DurationMetricProducer::onDumpReportLocked(const uint64_t dumpTimeNs,
                                                 ProtoOutputStream* protoOutput) {
     flushIfNeededLocked(dumpTimeNs);
+    if (mPastBuckets.empty()) {
+        return;
+    }
 
     protoOutput->write(FIELD_TYPE_INT64 | FIELD_ID_ID, (long long)mMetricId);
     protoOutput->write(FIELD_TYPE_INT64 | FIELD_ID_START_REPORT_NANOS, (long long)mStartTimeNs);
diff --git a/cmds/statsd/src/metrics/EventMetricProducer.cpp b/cmds/statsd/src/metrics/EventMetricProducer.cpp
index 821d8ea4..25c86d0 100644
--- a/cmds/statsd/src/metrics/EventMetricProducer.cpp
+++ b/cmds/statsd/src/metrics/EventMetricProducer.cpp
@@ -102,6 +102,9 @@
 
 void EventMetricProducer::onDumpReportLocked(const uint64_t dumpTimeNs,
                                              ProtoOutputStream* protoOutput) {
+    if (mProto->size() <= 0) {
+        return;
+    }
     protoOutput->write(FIELD_TYPE_INT64 | FIELD_ID_ID, (long long)mMetricId);
     protoOutput->write(FIELD_TYPE_INT64 | FIELD_ID_START_REPORT_NANOS, (long long)mStartTimeNs);
     protoOutput->write(FIELD_TYPE_INT64 | FIELD_ID_END_REPORT_NANOS, (long long)dumpTimeNs);
diff --git a/cmds/statsd/src/metrics/GaugeMetricProducer.cpp b/cmds/statsd/src/metrics/GaugeMetricProducer.cpp
index 17305e3..24dc5b0 100644
--- a/cmds/statsd/src/metrics/GaugeMetricProducer.cpp
+++ b/cmds/statsd/src/metrics/GaugeMetricProducer.cpp
@@ -125,6 +125,9 @@
     VLOG("gauge metric %lld report now...", (long long)mMetricId);
 
     flushIfNeededLocked(dumpTimeNs);
+    if (mPastBuckets.empty()) {
+        return;
+    }
 
     protoOutput->write(FIELD_TYPE_INT64 | FIELD_ID_ID, (long long)mMetricId);
     protoOutput->write(FIELD_TYPE_INT64 | FIELD_ID_START_REPORT_NANOS, (long long)mStartTimeNs);
diff --git a/cmds/statsd/src/metrics/ValueMetricProducer.cpp b/cmds/statsd/src/metrics/ValueMetricProducer.cpp
index e985873..ae0c673 100644
--- a/cmds/statsd/src/metrics/ValueMetricProducer.cpp
+++ b/cmds/statsd/src/metrics/ValueMetricProducer.cpp
@@ -138,6 +138,9 @@
                                              ProtoOutputStream* protoOutput) {
     VLOG("metric %lld dump report now...", (long long)mMetricId);
     flushIfNeededLocked(dumpTimeNs);
+    if (mPastBuckets.empty()) {
+        return;
+    }
     protoOutput->write(FIELD_TYPE_INT64 | FIELD_ID_ID, (long long)mMetricId);
     protoOutput->write(FIELD_TYPE_INT64 | FIELD_ID_START_REPORT_NANOS, (long long)mStartTimeNs);
     long long protoToken = protoOutput->start(FIELD_TYPE_MESSAGE | FIELD_ID_VALUE_METRICS);