bug 1319026 - Put an arbitrary upper-limit on TelemetryLog r=gfritzsche

To protect against pathalogically-bad cases of log abuse, limit TelemetryLog
to the first 1000 entries.

MozReview-Commit-ID: yoTFVS1VdQ

--HG--
extra : rebase_source : 04fae88fe619bb635b20f84549698348481825ea

toolkit/components/telemetry/TelemetryLog.jsm

@@ -8,10 +8,16 @@ const Cc = Components.classes;
 const Ci = Components.interfaces;
 
 const Telemetry = Cc["@mozilla.org/base/telemetry;1"].getService(Ci.nsITelemetry);
+
+const LOG_ENTRY_MAX_COUNT = 1000;
+
 var gLogEntries = [];
 
 this.TelemetryLog = Object.freeze({
   log(id, data) {
+    if (gLogEntries.length >= LOG_ENTRY_MAX_COUNT) {
+      return;
+    }
     id = String(id);
     var ts;
     try {

toolkit/components/telemetry/docs/collection/index.rst

@@ -16,7 +16,7 @@ The current data collection possibilities include:
 * :doc:`histograms` can efficiently record multiple data points
 * ``environment`` data records information about the system and settings a session occurs in
 * :doc:`events` can record richer data on individual occurences of specific actions
-* ``TelemetryLog`` allows collecting ordered event entries (note: this does not have supporting analysis tools)
+* ``TelemetryLog`` allows collecting ordered event entries up to a limit of 1000 entries (note: this does not have supporting analysis tools)
 * :doc:`measuring elapsed time <measuring-time>`
 * :doc:`custom pings <custom-pings>`
 * :doc:`stack capture <stack-capture>` allow recording application call stacks

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

@@ -7,6 +7,8 @@ Cu.import("resource://gre/modules/TelemetrySession.jsm", this);
 const TEST_PREFIX = "TEST-";
 const TEST_REGEX = new RegExp("^" + TEST_PREFIX);
 
+const LOG_ENTRY_MAX_COUNT = 1000;
+
 function check_event(event, id, data) {
   do_print("Checking message " + id);
   do_check_eq(event[0], id);
@@ -45,5 +47,14 @@ add_task(function* () {
   do_check_true(log[0][1] <= log[1][1]);
   do_check_true(log[1][1] <= log[2][1]);
 
+  // Test that we limit the overall length of the log, and that pushing
+  // it over the limit keeps the older events.
+  for (let i = 0; i < LOG_ENTRY_MAX_COUNT + 1; i++) {
+    TelemetryLog.log(TEST_PREFIX + "to_tha_limit");
+  }
+  log = TelemetrySession.getPayload().log;
+  do_check_eq(log.length, LOG_ENTRY_MAX_COUNT);
+  check_event(log[0], TEST_PREFIX + "1", ["val", "123", "undefined"]);
+
   yield TelemetryController.testShutdown();
 });