add a client data version stamp (bug 348746), r=marria

extensions/metrics/src/nsMetricsService.cpp

@@ -122,6 +122,7 @@ static const char kEventCountPref[] = "metrics.event-count";
 static const char kEnablePref[] = "metrics.upload.enable";
 
 const PRUint32 nsMetricsService::kMaxRetries = 3;
+const PRUint32 nsMetricsService::kMetricsVersion = 1;
 
 //-----------------------------------------------------------------------------
 
@@ -1280,7 +1281,6 @@ nsMetricsService::UploadData()
     return NS_ERROR_ABORT;
   }
  
-  PRBool enable = PR_FALSE;
   nsCString spec;
   nsCOMPtr<nsIPrefBranch> prefs = do_GetService(NS_PREFSERVICE_CONTRACTID);
   if (prefs) {
@@ -1436,7 +1436,8 @@ nsMetricsService::OpenCompleteXMLStream(nsILocalFile *dataFile,
 
   static const char METRICS_XML_HEAD[] =
       "<?xml version=\"1.0\"?>\n"
-      "<log xmlns=\"" NS_METRICS_NAMESPACE "\" clientid=\"%s\">\n";
+      "<log xmlns=\"" NS_METRICS_NAMESPACE "\" "
+           "version=\"%d\" clientid=\"%s\">\n";
   static const char METRICS_XML_TAIL[] = "</log>";
 
   nsCOMPtr<nsIFileInputStream> fileStream =
@@ -1454,7 +1455,7 @@ nsMetricsService::OpenCompleteXMLStream(nsILocalFile *dataFile,
       do_CreateInstance("@mozilla.org/io/string-input-stream;1");
   NS_ENSURE_STATE(stringStream);
 
-  char *head = PR_smprintf(METRICS_XML_HEAD, clientID.get());
+  char *head = PR_smprintf(METRICS_XML_HEAD, kMetricsVersion, clientID.get());
   rv = stringStream->SetData(head, -1);
   PR_smprintf_free(head);
   NS_ENSURE_SUCCESS(rv, rv);

extensions/metrics/src/nsMetricsService.h

@@ -279,6 +279,14 @@ private:
   // for several hours.
   static const PRUint32 kMaxRetries;
 
+  // This is the logging format version that is sent with each upload.
+  // The version should be incremented whenver a change is made that
+  // affects the log output, including but not limited to:
+  //  - adding or removing a collector
+  //  - adding or removing a property
+  //  - changing the meaning or interpretation of a property value
+  static const PRUint32 kMetricsVersion;
+
   PRInt32 mEventCount;
   PRInt32 mSuspendCount;
   PRBool mUploading;