Fix bug in timestamp and add last successful timestamp as upload

client/client.cc

@@ -62,16 +62,15 @@ void AutopowerClient::putResponseToServer(uint32_t statuscode, std::string messa
 
 std::string AutopowerClient::getReadableTimestamp(std::time_t rtme) {
   struct tm *msmtStartTime;
-  time(&rtme);
   msmtStartTime = gmtime(&rtme);
-  char tbuffer[1000];
-  strftime(tbuffer, sizeof tbuffer, "%FT%T", msmtStartTime);
+  char tbuffer[std::size("yyyy-mm-ddThh:mm:ssZ")];
+  strftime(tbuffer, sizeof tbuffer, "%FT%TZ", msmtStartTime);
   return std::string(tbuffer);
 }
 std::string AutopowerClient::getCurrentReadableTimestamp() {
   // Get UTC timestamp. Unfortunately std::chrono is more complicated. Hence
   // use time_t.
-  std::time_t rtme;
+  std::time_t rtme = std::time(nullptr);
   return getReadableTimestamp(rtme);
 }
 
@@ -303,6 +302,7 @@ void AutopowerClient::getAndSavePpData() {
             txn.exec_prepared("addMsmtPoint", getInternalMsmtId(), msmtPoint.measurement, msmtPoint.rawTimestamp);
             txn.commit();
             setHasWrittenOnce(true); // specify success of writing at least once to DB
+            setLastSampleTimestamp(msmtPoint.timestamp);
           } catch (std::exception &e) {
             std::string exprContent = e.what();
             std::string errorMsg = "Error while writing measurement to database: " + exprContent;
@@ -733,6 +733,7 @@ void AutopowerClient::manageMsmt() {
         statusObject["measurementSettings"]["uploadInterval"] = periodicUploadMinutes;
         statusObject["measurementSettings"]["sharedMsmtId"] = getSharedMsmtId();
         statusObject["ppIsRunning"] = false;
+        statusObject["lastSampleTimestamp"] = getReadableTimestamp(getLastSampleTimestamp());
         if (measuring() && getHasWrittenOnce() && !getHasExited()) {
           // we assume that pinpoint should now be running. Check with kill() via getPpIsCurrentlyRunning()
           statusObject["ppIsRunning"] = getPpIsCurrentlyRunning();

client/client.h

@@ -42,6 +42,20 @@ class AutopowerClient {
   bool thisMeasurementHasWrittenOnce = false;
   uint32_t periodicUploadMinutes = 5; // time to periodically upload the data in minutes. If this is 0 we never upload the content and rely on manually uploading the files
 
+
+  std::time_t lastSampleTimestamp; // the last timestamp in raw string form written to the DB
+  std::shared_mutex lastSampleMtx; // sample mutex
+
+  void setLastSampleTimestamp(std::time_t lastSampleTimestamp) {
+    std::unique_lock<std::shared_mutex>wl(lastSampleMtx);
+    this->lastSampleTimestamp = lastSampleTimestamp;
+  }
+
+  std::time_t getLastSampleTimestamp() {
+    std::shared_lock<std::shared_mutex>rl(lastSampleMtx);
+    return this->lastSampleTimestamp;
+  }
+
   std::unique_ptr<autopapi::CMeasurementApi::Stub> stub; // stub for connecting to GRPC server
   bool measuring() {
     // read measuring