metrics: Add an option to metrics_client to dump the logs cache.

The format of the metrics dump is rudimentary just yet. Here is an example:

  Metrics from /data/misc/metrics/uma-events

  name: hello     type: USER_ACTION
  name: world     type: USER_ACTION

This required the following changes:
* Added -d option to metrics_client
* Refactored file handling in SerializationUtils
 - Factored out file opening and log parsing into helper methods
 - Added ReadMetricsFromFile which is read-only so does not truncate the file

Change-Id: I6032d74242c79c678ec42a14e78fccc54e7af455
diff --git a/metricsd/metrics_client.cc b/metricsd/metrics_client.cc
index 57e96c2..f658b22 100644
--- a/metricsd/metrics_client.cc
+++ b/metricsd/metrics_client.cc
@@ -17,9 +17,15 @@
 #include <cstdio>
 #include <cstdlib>
 
+#include <base/memory/scoped_vector.h>
+
+#include "constants.h"
 #include "metrics/metrics_library.h"
+#include "serialization/metric_sample.h"
+#include "serialization/serialization_utils.h"
 
 enum Mode {
+    kModeDumpLogs,
     kModeSendSample,
     kModeSendEnumSample,
     kModeSendSparseSample,
@@ -36,12 +42,13 @@
           "        metrics_client -s   name sample\n"
           "        metrics_client -v   event\n"
           "        metrics_client -u action\n"
-          "        metrics_client [-cg]\n"
+          "        metrics_client [-cdg]\n"
           "\n"
           "  default: send metric with integer values \n"
           "           |min| > 0, |min| <= sample < |max|\n"
           "  -c: return exit status 0 if user consents to stats, 1 otherwise,\n"
           "      in guest mode always return 1\n"
+          "  -d: dump cached logs to the console\n"
           "  -e: send linear/enumeration histogram data\n"
           "  -g: return exit status 0 if machine in guest mode, 1 otherwise\n"
           "  -s: send a sparse histogram sample\n"
@@ -132,17 +139,57 @@
   return metrics_lib.IsGuestMode() ? 0 : 1;
 }
 
+static int DumpLogs() {
+  printf("Metrics from %s\n\n", metrics::kMetricsEventsFilePath);
+
+  ScopedVector<metrics::MetricSample> metrics;
+  metrics::SerializationUtils::ReadMetricsFromFile(
+      metrics::kMetricsEventsFilePath, &metrics);
+
+  for (ScopedVector<metrics::MetricSample>::const_iterator i = metrics.begin();
+       i != metrics.end(); ++i) {
+    const metrics::MetricSample* sample = *i;
+    printf("name: %s\t", sample->name().c_str());
+    printf("type: ");
+
+    switch (sample->type()) {
+      case metrics::MetricSample::CRASH:
+        printf("CRASH");
+        break;
+      case metrics::MetricSample::HISTOGRAM:
+        printf("HISTOGRAM");
+        break;
+      case metrics::MetricSample::LINEAR_HISTOGRAM:
+        printf("LINEAR_HISTOGRAM");
+        break;
+      case metrics::MetricSample::SPARSE_HISTOGRAM:
+        printf("SPARSE_HISTOGRAM");
+        break;
+      case metrics::MetricSample::USER_ACTION:
+        printf("USER_ACTION");
+        break;
+    }
+
+    printf("\n");
+  }
+
+  return 0;
+}
+
 int main(int argc, char** argv) {
   enum Mode mode = kModeSendSample;
   bool secs_to_msecs = false;
 
   // Parse arguments
   int flag;
-  while ((flag = getopt(argc, argv, "abcegstuv")) != -1) {
+  while ((flag = getopt(argc, argv, "abcdegstuv")) != -1) {
     switch (flag) {
       case 'c':
         mode = kModeHasConsent;
         break;
+      case 'd':
+        mode = kModeDumpLogs;
+        break;
       case 'e':
         mode = kModeSendEnumSample;
         break;
@@ -203,6 +250,8 @@
       return HasConsent();
     case kModeIsGuestMode:
       return IsGuestMode();
+    case kModeDumpLogs:
+      return DumpLogs();
     default:
       ShowUsage();
       return 0;