Backout d74a924a149b (in effect relanding bug 707320) due to M-oth orange

toolkit/components/telemetry/Telemetry.cpp

@@ -38,6 +38,7 @@
  * ***** END LICENSE BLOCK ***** */
 
 #include "base/histogram.h"
+#include "base/pickle.h"
 #include "nsIComponentManager.h"
 #include "nsIServiceManager.h"
 #include "nsCOMPtr.h"
@@ -47,6 +48,8 @@
 #include "jsapi.h" 
 #include "nsStringGlue.h"
 #include "nsITelemetry.h"
+#include "nsIFile.h"
+#include "nsILocalFile.h"
 #include "Telemetry.h" 
 #include "nsTHashtable.h"
 #include "nsHashKeys.h"
@@ -54,6 +57,7 @@
 #include "nsXULAppAPI.h"
 #include "nsThreadUtils.h"
 #include "mozilla/Mutex.h"
+#include "mozilla/FileUtils.h"
 
 namespace {
 
@@ -227,11 +231,9 @@ enum reflectStatus {
 };
 
 enum reflectStatus
-ReflectHistogramSnapshot(JSContext *cx, JSObject *obj, Histogram *h)
+ReflectHistogramAndSamples(JSContext *cx, JSObject *obj, Histogram *h,
+                           const Histogram::SampleSet &ss)
 {
-  Histogram::SampleSet ss;
-  h->SnapshotSample(&ss);
-
   // We don't want to reflect corrupt histograms.
   if (h->FindCorruption(ss) != Histogram::NO_INCONSISTENCIES) {
     return REFLECT_CORRUPT;
@@ -260,6 +262,14 @@ ReflectHistogramSnapshot(JSContext *cx, JSObject *obj, Histogram *h)
   return REFLECT_OK;
 }
 
+enum reflectStatus
+ReflectHistogramSnapshot(JSContext *cx, JSObject *obj, Histogram *h)
+{
+  Histogram::SampleSet ss;
+  h->SnapshotSample(&ss);
+  return ReflectHistogramAndSamples(cx, obj, h, ss);
+}
+
 JSBool
 JSHistogram_Add(JSContext *cx, uintN argc, jsval *vp)
 {
@@ -677,6 +687,333 @@ TelemetryImpl::GetHistogramById(const nsACString &name, JSContext *cx, jsval *re
   return WrapAndReturnHistogram(h, cx, ret);
 }
 
+class TelemetrySessionData : public nsITelemetrySessionData
+{
+  NS_DECL_ISUPPORTS
+  NS_DECL_NSITELEMETRYSESSIONDATA
+
+public:
+  static nsresult LoadFromDisk(nsIFile *, TelemetrySessionData **ptr);
+  static nsresult SaveToDisk(nsIFile *, const nsACString &uuid);
+
+  TelemetrySessionData(const char *uuid);
+  ~TelemetrySessionData();
+
+private:
+  struct EnumeratorArgs {
+    JSContext *cx;
+    JSObject *snapshots;
+  };
+  typedef nsBaseHashtableET<nsUint32HashKey, Histogram::SampleSet> EntryType;
+  typedef nsTHashtable<EntryType> SessionMapType;
+  static PLDHashOperator ReflectSamples(EntryType *entry, void *arg);
+  SessionMapType mSampleSetMap;
+  nsCString mUUID;
+
+  bool DeserializeHistogramData(Pickle &pickle, void **iter);
+  static bool SerializeHistogramData(Pickle &pickle);
+
+  // The file format version.  Should be incremented whenever we change
+  // how individual SampleSets are stored in the file.
+  static const unsigned int sVersion = 1;
+};
+
+NS_IMPL_THREADSAFE_ISUPPORTS1(TelemetrySessionData, nsITelemetrySessionData)
+
+TelemetrySessionData::TelemetrySessionData(const char *uuid)
+  : mUUID(uuid)
+{
+  mSampleSetMap.Init();
+}
+
+TelemetrySessionData::~TelemetrySessionData()
+{
+  mSampleSetMap.Clear();
+}
+
+NS_IMETHODIMP
+TelemetrySessionData::GetUuid(nsACString &uuid)
+{
+  uuid = mUUID;
+  return NS_OK;
+}
+
+PLDHashOperator
+TelemetrySessionData::ReflectSamples(EntryType *entry, void *arg)
+{
+  struct EnumeratorArgs *args = static_cast<struct EnumeratorArgs *>(arg);
+  // This has the undesirable effect of creating a histogram for the
+  // current session with the given ID.  But there's no good way to
+  // compute the ranges and buckets from scratch.
+  Histogram *h = nsnull;
+  nsresult rv = GetHistogramByEnumId(Telemetry::ID(entry->GetKey()), &h);
+  if (NS_FAILED(rv)) {
+    return PL_DHASH_STOP;
+  }
+
+  // Don't reflect histograms with no data associated with them.
+  if (entry->mData.sum() == 0) {
+    return PL_DHASH_NEXT;
+  }
+
+  JSObject *snapshot = JS_NewObject(args->cx, NULL, NULL, NULL);
+  if (!(snapshot
+        && ReflectHistogramAndSamples(args->cx, snapshot, h, entry->mData)
+        && JS_DefineProperty(args->cx, args->snapshots,
+                             h->histogram_name().c_str(),
+                             OBJECT_TO_JSVAL(snapshot), NULL, NULL,
+                             JSPROP_ENUMERATE))) {
+    return PL_DHASH_STOP;
+  }
+
+  return PL_DHASH_NEXT;
+}
+
+NS_IMETHODIMP
+TelemetrySessionData::GetSnapshots(JSContext *cx, jsval *ret)
+{
+  JSObject *snapshots = JS_NewObject(cx, NULL, NULL, NULL);
+  if (!snapshots) {
+    return NS_ERROR_FAILURE;
+  }
+
+  struct EnumeratorArgs args = { cx, snapshots };
+  PRUint32 count = mSampleSetMap.EnumerateEntries(ReflectSamples,
+                                                  static_cast<void*>(&args));
+  if (count != mSampleSetMap.Count()) {
+    return NS_ERROR_FAILURE;
+  }
+
+  *ret = OBJECT_TO_JSVAL(snapshots);
+  return NS_OK;
+}
+
+bool
+TelemetrySessionData::DeserializeHistogramData(Pickle &pickle, void **iter)
+{
+  PRUint32 count = 0;
+  if (!pickle.ReadUInt32(iter, &count)) {
+    return false;
+  }
+
+  for (size_t i = 0; i < count; ++i) {
+    int stored_length;
+    const char *name;
+    if (!pickle.ReadData(iter, &name, &stored_length)) {
+      return false;
+    }
+
+    Telemetry::ID id;
+    nsresult rv = TelemetryImpl::GetHistogramEnumId(name, &id);
+    if (NS_FAILED(rv)) {
+      // We serialized a non-static histogram.  Just drop its data on
+      // the floor.  If we can't deserialize the data, though, we're in
+      // trouble.
+      Histogram::SampleSet ss;
+      if (!ss.Deserialize(iter, pickle)) {
+        return false;
+      }
+    }
+
+    EntryType *entry = mSampleSetMap.GetEntry(id);
+    if (!entry) {
+      entry = mSampleSetMap.PutEntry(id);
+      if (NS_UNLIKELY(!entry)) {
+        return false;
+      }
+      if (!entry->mData.Deserialize(iter, pickle)) {
+        return false;
+      }
+    }
+  }
+
+  return true;
+}
+
+nsresult
+TelemetrySessionData::LoadFromDisk(nsIFile *file, TelemetrySessionData **ptr)
+{
+  *ptr = nsnull;
+  nsresult rv;
+  nsCOMPtr<nsILocalFile> f(do_QueryInterface(file, &rv));
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  AutoFDClose fd;
+  rv = f->OpenNSPRFileDesc(PR_RDONLY, 0, &fd);
+  if (NS_FAILED(rv)) {
+    return NS_ERROR_FAILURE;
+  }
+
+  PRInt32 size = PR_Available(fd);
+  if (size == -1) {
+    return NS_ERROR_FAILURE;
+  }
+
+  nsAutoArrayPtr<char> data(new char[size]);
+  PRInt32 amount = PR_Read(fd, data, size);
+  if (amount != size) {
+    return NS_ERROR_FAILURE;
+  }
+
+  Pickle pickle(data, size);
+  void *iter = NULL;
+
+  unsigned int storedVersion;
+  if (!(pickle.ReadUInt32(&iter, &storedVersion)
+        && storedVersion == sVersion)) {
+    return NS_ERROR_FAILURE;
+  }
+
+  const char *uuid;
+  int uuidLength;
+  if (!pickle.ReadData(&iter, &uuid, &uuidLength)) {
+    return NS_ERROR_FAILURE;
+  }
+
+  nsAutoPtr<TelemetrySessionData> sessionData(new TelemetrySessionData(uuid));
+  if (!sessionData->DeserializeHistogramData(pickle, &iter)) {
+    return NS_ERROR_FAILURE;
+  }
+
+  *ptr = sessionData.forget();
+  return NS_OK;
+}
+
+bool
+TelemetrySessionData::SerializeHistogramData(Pickle &pickle)
+{
+  StatisticsRecorder::Histograms hs;
+  StatisticsRecorder::GetHistograms(&hs);
+
+  if (!pickle.WriteUInt32(hs.size())) {
+    return false;
+  }
+
+  for (StatisticsRecorder::Histograms::const_iterator it = hs.begin();
+       it != hs.end();
+       ++it) {
+    const Histogram *h = *it;
+    const char *name = h->histogram_name().c_str();
+
+    Histogram::SampleSet ss;
+    h->SnapshotSample(&ss);
+
+    if (!(pickle.WriteData(name, strlen(name)+1)
+          && ss.Serialize(&pickle))) {
+      return false;
+    }
+  }
+
+  return true;
+}
+
+nsresult
+TelemetrySessionData::SaveToDisk(nsIFile *file, const nsACString &uuid)
+{
+  nsresult rv;
+  nsCOMPtr<nsILocalFile> f(do_QueryInterface(file, &rv));
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  AutoFDClose fd;
+  rv = f->OpenNSPRFileDesc(PR_WRONLY | PR_CREATE_FILE | PR_TRUNCATE, 0600, &fd);
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  Pickle pickle;
+  if (!pickle.WriteUInt32(sVersion)) {
+    return NS_ERROR_FAILURE;
+  }
+
+  // Include the trailing NULL for the UUID to make reading easier.
+  const char *data;
+  size_t length = uuid.GetData(&data);
+  if (!(pickle.WriteData(data, length+1)
+        && SerializeHistogramData(pickle))) {
+    return NS_ERROR_FAILURE;
+  }
+
+  PRInt32 amount = PR_Write(fd, static_cast<const char*>(pickle.data()),
+                            pickle.size());
+  if (amount != pickle.size()) {
+    return NS_ERROR_FAILURE;
+  }
+
+  return NS_OK;
+}
+
+class SaveHistogramEvent : public nsRunnable
+{
+public:
+  SaveHistogramEvent(nsIFile *file, const nsACString &uuid,
+                     nsITelemetrySaveSessionDataCallback *callback)
+    : mFile(file), mUUID(uuid), mCallback(callback)
+  {}
+
+  NS_IMETHOD Run()
+  {
+    nsresult rv = TelemetrySessionData::SaveToDisk(mFile, mUUID);
+    mCallback->Handle(!!NS_SUCCEEDED(rv));
+    return rv;
+  }
+
+private:
+  nsCOMPtr<nsIFile> mFile;
+  nsCString mUUID;
+  nsCOMPtr<nsITelemetrySaveSessionDataCallback> mCallback;
+};
+
+NS_IMETHODIMP
+TelemetryImpl::SaveHistograms(nsIFile *file, const nsACString &uuid,
+                              nsITelemetrySaveSessionDataCallback *callback,
+                              bool isSynchronous)
+{
+  nsCOMPtr<nsIRunnable> event = new SaveHistogramEvent(file, uuid, callback);
+  if (isSynchronous) {
+    return event ? event->Run() : NS_ERROR_FAILURE;
+  } else {
+    return NS_DispatchToCurrentThread(event);
+  }
+}
+
+class LoadHistogramEvent : public nsRunnable
+{
+public:
+  LoadHistogramEvent(nsIFile *file,
+                     nsITelemetryLoadSessionDataCallback *callback)
+    : mFile(file), mCallback(callback)
+  {}
+
+  NS_IMETHOD Run()
+  {
+    TelemetrySessionData *sessionData = nsnull;
+    nsresult rv = TelemetrySessionData::LoadFromDisk(mFile, &sessionData);
+    if (NS_FAILED(rv)) {
+      mCallback->Handle(nsnull);
+    } else {
+      nsCOMPtr<nsITelemetrySessionData> data(sessionData);
+      mCallback->Handle(data);
+    }
+    return rv;
+  }
+
+private:
+  nsCOMPtr<nsIFile> mFile;
+  nsCOMPtr<nsITelemetryLoadSessionDataCallback> mCallback;
+};
+
+NS_IMETHODIMP
+TelemetryImpl::LoadHistograms(nsIFile *file,
+                              nsITelemetryLoadSessionDataCallback *callback)
+{
+  nsCOMPtr<nsIRunnable> event = new LoadHistogramEvent(file, callback);
+  return NS_DispatchToCurrentThread(event);
+}
+
 NS_IMETHODIMP
 TelemetryImpl::GetCanRecord(bool *ret) {
   *ret = mCanRecord;

toolkit/components/telemetry/TelemetryPing.js

@@ -42,6 +42,7 @@ const Cu = Components.utils;
 Cu.import("resource://gre/modules/Services.jsm");
 Cu.import("resource://gre/modules/XPCOMUtils.jsm");
 Cu.import("resource://gre/modules/LightweightThemeManager.jsm");
+Cu.import("resource://gre/modules/ctypes.jsm");
 
 // When modifying the payload in incompatible ways, please bump this version number
 const PAYLOAD_VERSION = 1;
@@ -179,6 +180,10 @@ TelemetryPing.prototype = {
   _histograms: {},
   _initialized: false,
   _prevValues: {},
+  // Generate a unique id once per session so the server can cope with
+  // duplicate submissions.
+  _uuid: generateUUID(),
+  _prevSession: null,
 
   /**
    * Returns a set of histograms that can be converted into JSON
@@ -187,8 +192,7 @@ TelemetryPing.prototype = {
    *    histogram_type: <0 for exponential, 1 for linear>, bucketX:countX, ....} ...}
    * where bucket[XY], count[XY] are positive integers.
    */
-  getHistograms: function getHistograms() {
-    let hls = Telemetry.histogramSnapshots;
+  getHistograms: function getHistograms(hls) {
     let info = Telemetry.registeredHistograms;
     let ret = {};
 
@@ -397,24 +401,48 @@ TelemetryPing.prototype = {
   send: function send(reason, server) {
     // populate histograms one last time
     this.gatherMemory();
+    let data = this.getSessionPayloadAndSlug(reason);
+
+    // Don't record a successful ping for previous session data.
+    this.doPing(server, data.slug, data.payload, !data.previous);
+    this._prevSession = null;
+
+    // We were sending off data from before; now send the actual data
+    // we've collected this session.
+    if (data.previous) {
+      data = this.getSessionPayloadAndSlug(reason);
+      this.doPing(server, data.slug, data.payload, true);
+    }
+  },
+
+  getSessionPayloadAndSlug: function getSessionPayloadAndSlug(reason) {
+    // Use a deterministic url for testing.
+    let isTestPing = (reason == "test-ping");
+    let havePreviousSession = !!this._prevSession;
+    let slug = (isTestPing
+                ? reason
+                : (havePreviousSession
+                   ? this._prevSession.uuid
+                   : this._uuid));
     let payloadObj = {
       ver: PAYLOAD_VERSION,
-      info: this.getMetadata(reason),
-      simpleMeasurements: getSimpleMeasurements(),
-      histograms: this.getHistograms(),
-      slowSQL: Telemetry.slowSQL
+      // Send a different reason string for previous session data.
+      info: this.getMetadata(havePreviousSession ? "saved-session" : reason),
     };
+    if (havePreviousSession) {
+      payloadObj.histograms = this.getHistograms(this._prevSession.snapshots);
+    }
+    else {
+      payloadObj.simpleMeasurements = getSimpleMeasurements();
+      payloadObj.histograms = this.getHistograms(Telemetry.histogramSnapshots);
+      payloadObj.slowSQL = Telemetry.slowSQL;
+    }
+    return { previous: !!havePreviousSession, slug: slug, payload: JSON.stringify(payloadObj) };
+  },
 
-    let isTestPing = (reason == "test-ping");
-    // Generate a unique id once per session so the server can cope with duplicate submissions.
-    // Use a deterministic url for testing.
-    if (!this._path)
-      this._path = "/submit/telemetry/" + (isTestPing ? reason : generateUUID());
-    
-    let hping = Telemetry.getHistogramById("TELEMETRY_PING");
-    let hsuccess = Telemetry.getHistogramById("TELEMETRY_SUCCESS");
-
-    let url = server + this._path;
+  doPing: function doPing(server, slug, payload, recordSuccess) {
+    let submitPath = "/submit/telemetry/" + slug;
+    let url = server + submitPath;
     let request = Cc["@mozilla.org/xmlextras/xmlhttprequest;1"]
                   .createInstance(Ci.nsIXMLHttpRequest);
     request.mozBackgroundRequest = true;
@@ -423,6 +451,7 @@ TelemetryPing.prototype = {
     request.setRequestHeader("Content-Type", "application/json");
 
     let startTime = new Date();
+    let file = this.savedHistogramsFile();
 
     function finishRequest(channel) {
       let success = false;
@@ -430,15 +459,23 @@ TelemetryPing.prototype = {
         success = channel.QueryInterface(Ci.nsIHttpChannel).requestSucceeded;
       } catch(e) {
       }
+      if (recordSuccess) {
+        let hping = Telemetry.getHistogramById("TELEMETRY_PING");
+        let hsuccess = Telemetry.getHistogramById("TELEMETRY_SUCCESS");
+
         hsuccess.add(success);
         hping.add(new Date() - startTime);
-      if (isTestPing)
+      }
+      if (success && file.exists()) {
+        file.remove(true);
+      }
+      if (slug == "test-ping")
         Services.obs.notifyObservers(null, "telemetry-test-xhr-complete", null);
     }
     request.addEventListener("error", function(aEvent) finishRequest(request.channel), false);
     request.addEventListener("load", function(aEvent) finishRequest(request.channel), false);
 
-    request.send(JSON.stringify(payloadObj));
+    request.send(payload);
   },
   
   attachObservers: function attachObservers() {
@@ -459,6 +496,25 @@ TelemetryPing.prototype = {
     }
   },
 
+  savedHistogramsFile: function savedHistogramsFile() {
+    let profileDirectory = Services.dirsvc.get("ProfD", Ci.nsILocalFile);
+    let profileFile = profileDirectory.clone();
+
+    // There's a bunch of binary data in the file, so we need to be
+    // sensitive to multiple machine types.  Use ctypes to get some
+    // discriminating information.
+    let size = ctypes.voidptr_t.size;
+    // Hack to figure out endianness.
+    let uint32_array_t = ctypes.uint32_t.array(1);
+    let array = uint32_array_t([0xdeadbeef]);
+    let uint8_array_t = ctypes.uint8_t.array(4);
+    let array_as_bytes = ctypes.cast(array, uint8_array_t);
+    let endian = (array_as_bytes[0] === 0xde) ? "big" : "little"
+    let name = "sessionHistograms.dat." + size + endian;
+    profileFile.append(name);
+    return profileFile;
+  },
+
   /**
    * Initializes telemetry within a timer. If there is no PREF_SERVER set, don't turn on telemetry.
    */
@@ -479,6 +535,7 @@ TelemetryPing.prototype = {
     Services.obs.addObserver(this, "private-browsing", false);
     Services.obs.addObserver(this, "profile-before-change", false);
     Services.obs.addObserver(this, "sessionstore-windows-restored", false);
+    Services.obs.addObserver(this, "quit-application-granted", false);
 
     // Delay full telemetry initialization to give the browser time to
     // run various late initializers. Otherwise our gathered memory
@@ -492,6 +549,12 @@ TelemetryPing.prototype = {
       delete self._timer
     }
     this._timer.initWithCallback(timerCallback, TELEMETRY_DELAY, Ci.nsITimer.TYPE_ONE_SHOT);
+
+    // Load data from the previous session.
+    let loadCallback = function(data) {
+      self._prevSession = data;
+    }
+    Telemetry.loadHistograms(this.savedHistogramsFile(), loadCallback);
   },
 
   /** 
@@ -502,6 +565,7 @@ TelemetryPing.prototype = {
     Services.obs.removeObserver(this, "sessionstore-windows-restored");
     Services.obs.removeObserver(this, "profile-before-change");
     Services.obs.removeObserver(this, "private-browsing");
+    Services.obs.removeObserver(this, "quit-application-granted");
   },
 
   /**
@@ -567,6 +631,11 @@ TelemetryPing.prototype = {
       }
       this.send(aTopic == "idle" ? "idle-daily" : aTopic, server);
       break;
+    case "quit-application-granted":
+      Telemetry.saveHistograms(this.savedHistogramsFile(),
+                               this._uuid, function (success) success,
+                               /*isSynchronous=*/true);
+      break;
     }
   },
 

toolkit/components/telemetry/nsITelemetry.idl

@@ -38,8 +38,39 @@
  * ***** END LICENSE BLOCK ***** */
 
 #include "nsISupports.idl"
+#include "nsIFile.idl"
 
-[scriptable, uuid(db854295-478d-4de9-8211-d73ed7d81cd0)]
+[scriptable, uuid(c177b6b0-5ef1-44f5-bc67-6bcf7d2518e5)]
+interface nsITelemetrySessionData : nsISupports
+{
+  /**
+   * The UUID of our previous session.
+   */
+  readonly attribute ACString uuid;
+
+  /**
+   * An object containing a snapshot from all registered histograms that had
+   * data recorded in the previous session.
+   * { name1: data1, name2: data2, .... }
+   * where the individual dataN are as nsITelemetry.histogramSnapshots.
+   */
+  [implicit_jscontext]
+  readonly attribute jsval snapshots;
+};
+
+[scriptable, function, uuid(aff36c9d-7e4c-41ab-a9b6-53773bbca0cd)]
+interface nsITelemetryLoadSessionDataCallback : nsISupports
+{
+  void handle(in nsITelemetrySessionData data);
+};
+
+[scriptable, function, uuid(40065f26-afd2-4417-93de-c1de9adb1548)]
+interface nsITelemetrySaveSessionDataCallback : nsISupports
+{
+  void handle(in bool success);
+};
+
+[scriptable, uuid(22fc825e-288f-457e-80d5-5bb35f06d37e)]
 interface nsITelemetry : nsISupports
 {
   /**
@@ -127,6 +158,34 @@ interface nsITelemetry : nsISupports
   [implicit_jscontext]
   jsval getHistogramById(in ACString id);
 
+  /**
+   * Save persistent histograms to the given file.
+   *
+   * @param file - filename for saving
+   * @param uuid - UUID of this session
+   * @param callback - function to be caled when file writing is complete
+   * @param isSynchronous - whether the save is done synchronously.  Defaults
+   *        to asynchronous saving.
+   */
+  void saveHistograms(in nsIFile file, in ACString uuid,
+                      in nsITelemetrySaveSessionDataCallback callback,
+                      [optional] in boolean isSynchronous);
+
+  /* Reconstruct an nsITelemetryDataSession object containing histogram
+   * information from the given file; the file must have been produced
+   * via saveHistograms.  The file is read asynchronously.
+   *
+   * This method does not modify the histogram information being
+   * collected in the current session.
+   *
+   * The reconstructed object is then passed to the given callback.
+   *
+   * @param file - the file to load histogram information from
+   * @param callback - function to process histogram information
+   */
+  void loadHistograms(in nsIFile file,
+                      in nsITelemetryLoadSessionDataCallback callback);
+
   /**
    * Set this to false to disable gathering of telemetry statistics.
    */

toolkit/components/telemetry/tests/unit/test_nsITelemetry.js

@@ -105,6 +105,45 @@ function test_privateMode() {
   do_check_neq(uneval(orig), uneval(h.snapshot()));
 }
 
+function generateUUID() {
+  let str = Cc["@mozilla.org/uuid-generator;1"].getService(Ci.nsIUUIDGenerator).generateUUID().toString();
+  // strip {}
+  return str.substring(1, str.length - 1);
+}
+
+// Check that we do sane things when saving to disk.
+function test_loadSave()
+{
+  let dirService = Cc["@mozilla.org/file/directory_service;1"]
+                    .getService(Ci.nsIProperties);
+  let tmpDir = dirService.get("TmpD", Ci.nsILocalFile);
+  let tmpFile = tmpDir.clone();
+  tmpFile.append("saved-histograms.dat");
+  if (tmpFile.exists()) {
+    tmpFile.remove(true);
+  }
+
+  let saveFinished = false;
+  let loadFinished = false;
+  let uuid = generateUUID();
+  let loadCallback = function(data) {
+    do_check_true(data != null);
+    do_check_eq(uuid, data.uuid);
+    loadFinished = true;
+    do_test_finished();
+  };
+  let saveCallback = function(success) {
+    do_check_true(success);
+    Telemetry.loadHistograms(tmpFile, loadCallback);
+    saveFinished = true;
+  };
+  do_test_pending();
+  Telemetry.saveHistograms(tmpFile, uuid, saveCallback);
+  do_register_cleanup(function () do_check_true(saveFinished));
+  do_register_cleanup(function () do_check_true(loadFinished));
+  do_register_cleanup(function () tmpFile.exists() && tmpFile.remove(true));
+}
+
 function run_test()
 {
   let kinds = [Telemetry.HISTOGRAM_EXPONENTIAL, Telemetry.HISTOGRAM_LINEAR]
@@ -121,4 +160,6 @@ function run_test()
   test_getHistogramById();
   test_getSlowSQL();
   test_privateMode();
+  test_loadSave();
+
 }