diff --git a/index.bs b/index.bs index 2afeeae..9f084d7 100644 --- a/index.bs +++ b/index.bs @@ -466,14 +466,15 @@ etc.

Limit maximum sampling frequency

-User agents may mitigate certain threats by -limiting the maximum [=sampling frequency=]. +User agents and [=extension specifications=] may mitigate certain threats by defining a [=sensor +type=]'s [=sensor type/maximum sampling frequency=]. + What upper limit to choose depends on the [=sensor type=], the kind of threats the user agent is trying to protect against, the expected resources of the attacker, etc. -Limiting the maximum [=sampling frequency=] prevents use cases -which rely on low latency or high data density. +Limiting the [=sensor type/maximum sampling frequency=] prevents use cases which rely on low +latency or high data density.

Stop the sensor altogether

@@ -489,9 +490,9 @@ or in a different application. An alternative to [=limit maximum sampling frequency|limiting the maximum sampling frequency=] is to limit the number of [=sensor readings=] delivered to Web application developer, -regardless of what frequency the sensor is polled at. +regardless of the [=sampling frequency=]. This allows use cases which have low latency requirement -to increase [=sampling frequency=] +to increase the [=sampling frequency=] without increasing the amount of data provided. Discarding intermediary readings prevents certain use cases, @@ -721,33 +722,57 @@ define ways to uniquely identify each one. ## Sampling Frequency and Reporting Frequency ## {#concepts-sampling-and-reporting-frequencies} -For the purpose of this specification, sampling frequency for a [=platform sensor=] is -defined as a frequency at which the user agent obtains [=sensor readings=] from the underlying -platform. +For the purpose of this specification, a [=platform sensor=]'s sampling frequency is +defined as a frequency at which a [=platform sensor=] obtains [=sensor readings=] from the +underlying [=device sensor=]. The way such [=sensor readings=] are obtained is +[=implementation-defined=]. + +The [=platform sensor=]'s [=sampling frequency=] may not correspond to the [=device sensor=]'s +actual sampling rate, which, for the purpose of this specification, is opaque. + +Note: System-level APIs for [=sensor readings=] and the underlying hardware interface to the sensors +themselves may be built for polling or events. For a polling-based [=device sensor=], the [=platform +sensor=]'s [=sampling frequency=] would be the rate at which a new reading is requested from the +system or hardware. For an event-based [=device sensor=], a [=platform sensor=] provides a requested +sampling frequency to the system or hardware, and events are generated at that frequency or below. +Events may not be generated if the sensor reading has not changed. + +A [=device sensor=] may provide bounds for the sampling frequency value it can accept from a +[=platform sensor=] in the form of a minimum sampling frequency and a +maximum sampling frequency. A [=platform sensor=]'s [=sampling +frequency=] must not be less than the [=device sensor=]'s [=device sensor/minimum sampling +frequency=] or greater than its [=device sensor/maximum sampling frequency=]. + +A [=platform sensor=]'s [=sampling frequency=] is determined based on the provided +{{Sensor/[[frequency]]}} of the [=set/items=] in its [=ordered set|set=] of [=activated sensor +objects=]. The calculation is [=implementation-defined=], but the outcome value must lie within the +bounds set by the [=platform sensor=]'s [=sensor type=]'s [=sensor type/minimum sampling +frequency|minimum=] and [=sensor type/maximum sampling frequency|maximum=] sampling frequencies and +its [=device sensor=]'s [=device sensor/minimum sampling frequency|minimum=] and [=device +sensor/maximum sampling frequency|maximum=] sampling frequencies. + +Note: For example, the user agent may estimate the [=sampling frequency=] as a Least Common +Denominator (LCD) for a set of provided {{Sensor/[[frequency]]}} capped by [=sampling frequency=] +bounds defined by the underlying platform. -The user agent can request the underlying platform to deliver [=sensor readings|readings=] at a certain -rate which is called requested sampling frequency. +The reporting frequency for a concrete {{Sensor}} object is defined as a frequency at which +the "reading" event is [=fire an event|fired=] at this object. -The [=sampling frequency=] is equal to the [=requested sampling frequency=] if the underlying platform -can support it. +A {{Sensor}} object cannot access new [=sensor readings|readings=] at a higher rate than the +user agent obtains them from the underlying platform, therefore the [=reporting frequency=] can +never exceed a [=platform sensor=]'s [=sampling frequency=], which in turn can never exceed a +[=device sensor=]'s [=device sensor/maximum sampling frequency=] (when specified). -The [=sampling frequency=] differs from the [=requested sampling frequency=] in the following cases: - - the [=requested sampling frequency=] exceeds upper or lower [=sampling frequency=] bounds - supported by the underlying platform. +The [=reporting frequency=] differs from the {{Sensor}}'s {{Sensor/[[frequency]]}} in cases such as: + - the requested {{Sensor/[[frequency]]}} lies outside the bounds returned by invoking [=get a + platform sensor's sampling bounds=] with {{Sensor}}'s associated [=platform sensor=]. - the operating system and/or the [=device sensor=] automatically discard readings that do not differ enough (in absolute or relative terms) from the previously reported ones via a hardware or operating system filter. - - the [=platform sensor=]'s associated [=sensor type=]'s [=threshold check + - the {{Sensor}} instance's associated [=sensor type=]'s [=threshold check algorithm=] fails and the [=platform sensor=]'s [=latest readings=] are not updated. -The reporting frequency for a concrete {{Sensor}} object is defined as a frequency at which -the "reading" event is [=fire an event|fired=] at this object. - -A {{Sensor}} object cannot access new [=sensor readings|readings=] at a higher rate than the -user agent obtains them from the underlying platform, therefore the [=reporting frequency=] can -never exceed the [=sampling frequency=] for the given [=sensor type=]. - ## Conditions to expose sensor readings ## {#concepts-can-expose-sensor-readings} The user agent can expose sensor readings to a given |document| if and only if @@ -781,6 +806,15 @@ A sensor type must have the following associated data: - A [=set/is empty|non-empty=] [=ordered set=] of associated [=policy-controlled feature=] tokens referred to as sensor feature names. - A [=permission revocation algorithm=]. +- A minimum sampling frequency, a positive number. It is either + [=implementation-defined=] or defined by an [=extension specification=]. If both are set, the + largest value is used. +- A maximum sampling frequency, a positive number. It is either + [=implementation-defined=] or defined by an [=extension specification=]. If both are set, the + smallest value is used. + +The [=sensor type/minimum sampling frequency=] must not be greater than the [=sensor type/maximum +sampling frequency=]. A [=sensor type=] may have the following associated data: - A [=default sensor=]. @@ -839,17 +873,19 @@ Note: There are additional privacy concerns when using cached [=sensor readings| which predate either [=navigating=] to resources in the current [=origin=], or being granted permission to access the [=platform sensor=]. --> -A [=platform sensor=] has an associated [=requested sampling frequency=] which is initially null. - -For a non-[=set/is empty|empty=] [=ordered set|set=] of [=activated sensor objects=] the -[=requested sampling frequency=] is equal to the optimal sampling frequency, which is estimated -by the user agent by taking into account the {{[[frequency]]|provided frequencies}} -of [=activated sensor objects|activated=] {{Sensor|Sensors}} and the [=sampling frequency=] bounds -defined by the underlying platform. - -Note: For example, the user agent may estimate [=optimal sampling frequency=] as a Least Common -Denominator (LCD) for a set of {{[[frequency]]|provided frequencies}} capped -by [=sampling frequency=] bounds defined by the underlying platform. +
+To get a platform sensor's sampling bounds given a [=platform sensor=] +|platformSensor|: + 1. Let |minimumFrequency| be |platformSensor|'s [=sensor type=]'s [=sensor type/minimum sampling + frequency=]. + 1. If |platformSensor|'s connected [=device sensor=] has a [=device sensor/minimum sampling + frequency=], set |minimumFrequency| to the maximum of |minimumFrequency| and this value. + 1. Let |maximumFrequency| be |platformSensor|'s [=sensor type=]'s [=sensor type/maximum sampling + frequency=]. + 1. If |platformSensor|'s connected [=device sensor=] has a [=device sensor/maximum sampling + frequency=], set |maximumFrequency| to the minimum of |maximumFrequency| and this value. + 1. Return a [=tuple=] (|minimumFrequency|, |maximumFrequency|). +
@@ -866,7 +902,7 @@ The {{Sensor}} object in "idle" [[#sensor-lifecycle|state]] is not among the [=p In this example there is a [=platform sensor=] instance per [=browsing context=]. The [=latest reading=] [=ordered map|map=] is shared between {{Sensor}} objects from the -same [=browsing context|context=] and is updated at a rate equal to the [=requested sampling frequency=] +same [=browsing context|context=] and is updated at a rate equal to the requested [=sampling frequency=] of the corresponding [=platform sensor=].
@@ -1063,12 +1099,10 @@ with the internal slots described in the following table: \[[frequency]] A double representing frequency in Hz that is used to calculate - the [=requested sampling frequency=] for the associated [=platform sensor=] + the [=sampling frequency=] for the associated [=platform sensor=] and to define the upper bound of the [=reporting frequency=] for this - {{Sensor}} object. - - This slot holds the provided {{SensorOptions}}.{{frequency!!dict-member}} value. - It is initially unset. + {{Sensor}} object. It is initially null. + \[[lastEventFiredAt]] @@ -1256,8 +1290,8 @@ to {{SensorErrorEventInit}}. 1. Set |sensor_instance|.{{[[frequency]]}} to |options|["{{frequency!!dict-member}}"]. Note: There is no guarantee that the requested |options|["{{frequency!!dict-member}}"] - can be respected. The actual [=sampling frequency=] can be calculated using - {{Sensor}} {{Sensor/timestamp!!attribute}} attributes. + can be respected. See [[#concepts-sampling-and-reporting-frequencies]] for constraints that + may be applied.

Check sensor policy-controlled features

@@ -1283,24 +1317,30 @@ to {{SensorErrorEventInit}}.
: input - :: |sensor_instance|, a {{Sensor}} object. + :: |sensor|, a {{Sensor}} object. : output - :: True if sensor instance was associated with a [=platform sensor=], + :: True if |sensor| was associated with a [=platform sensor=], false otherwise. - 1. Let |type| be the [=sensor type=] of |sensor_instance|. + 1. Let |platformSensor| be null. + 1. Let |type| be |sensor|'s associated [=sensor type=]. 1. If the device has a single [=device sensor=] which can provide [=sensor readings|readings=] for |type|, then - 1. Associate |sensor_instance| with a [=platform sensor=] corresponding + 1. Set |platformSensor| to a [=platform sensor=] corresponding to this [=device sensor=]. - 1. Return true. 1. If the device has multiple [=device sensors=] which can provide [=sensor readings|readings=] for |type|, then 1. If |type| has an associated [=default sensor=], then - 1. Associate |sensor_instance| with a [=platform sensor=] corresponding - to [=default sensor=]. - 1. Return true. - 1. Return false. + 1. Set |platformSensor| to a [=platform sensor=] corresponding + to this [=default sensor|default device sensor=]. + 1. If |platformSensor| is null, return false. + 1. Let |bounds| be the result of invoking [=get a platform sensor's sampling bounds=] with + |platformSensor|. + 1. If |sensor|.{{Sensor/[[frequency]]}} is null, set it to an [=implementation-defined=] value + dependent on |type|. + 1. If |sensor|.{{Sensor/[[frequency]]}} is less than |bounds|[0], set it to |bounds|[0]. + 1. If |sensor|.{{Sensor/[[frequency]]}} is greater than |bounds|[1], set it to |bounds|[1]. + 1. Return true.

Activate a sensor object

@@ -1362,18 +1402,24 @@ to {{SensorErrorEventInit}}.
: input - :: |sensor|, a [=platform sensor=]. + :: |platformSensor|, a [=platform sensor=]. : output :: None - 1. If |sensor|'s set of [=activated sensor objects=] [=set/is empty=], - 1. Set [=requested sampling frequency=] to null. - 1. [=map/For each=] |key| → value of [=latest reading=]. - 1. [=map/Set=] [=latest reading=][|key|] to null. - 1. Update the user-agent-specific way in which [=sensor readings=] are obtained from |sensor| - to no longer provide [=sensor readings|readings=]. + 1. If |platformSensor|'s set of [=activated sensor objects=] [=set/is empty=], + 1. Set |platformSensor|'s [=sampling frequency=] to null. + 1. [=map/For each=] |key| → value of |platformSensor|'s [=latest reading=]. + 1. [=map/Set=] |platformSensor|'s [=latest reading=][|key|] to null. + 1. Update the [=implementation-defined=] way in which [=sensor readings=] are obtained + from |platformSensor| to no longer provide [=sensor readings|readings=]. 1. Return. - 1. Set [=requested sampling frequency=] to [=optimal sampling frequency=]. + 1. Set |platformSensor|'s [=sampling frequency=] to an [=implementation-defined=] value based + on the {{Sensor/[[frequency]]}} values of the items in its [=activated sensor objects=] + [=ordered set|set=]. + 1. Let |bounds| be the result of invoking [=get a platform sensor's sampling bounds=] with + |platformSensor|. + 1. [=Assert=]: |platformSensor|'s [=sampling frequency=] is greater than or equal to + |bounds|[0] and less than or equal to |bounds|[1].

Update latest reading

@@ -1401,25 +1447,6 @@ to {{SensorErrorEventInit}}. 1. Invoke [=report latest reading updated=] with |s| as an argument. -

Find the reporting frequency of a sensor object

- -
- - : input - :: |sensor_instance|, a {{Sensor}} object. - : output - :: [=reporting frequency=] in Hz. - - 1. Let |frequency| be null. - 1. Let |f| be |sensor_instance|.{{[[frequency]]}}. - 1. if |f| is set, - 1. set |frequency| to |f| capped by the upper and lower [=sampling frequency=] - bounds for the associated [=platform sensor=]. - 1. Otherwise, - 1. user agent can assign |frequency| to an appropriate value. - 1. return |frequency|. -
-

Report latest reading updated

@@ -1436,11 +1463,9 @@ to {{SensorErrorEventInit}}. 1. If |lastReportedTimestamp| is not set 1. Queue a task to run [=notify new reading=] with |sensor_instance| as an argument. 1. Return. - 1. Let |reportingFrequency| be result of invoking [=Find the reporting frequency of a sensor object=]. - 1. If |reportingFrequency| is null - 1. Queue a task to run [=notify new reading=] with |sensor_instance| as an argument. - 1. Return. - 1. Let |reportingInterval| be the result of 1 / |reportingFrequency|. + 1. [=Assert=]: |sensor_instance|.{{Sensor/[[frequency]]}} is not null. + 1. [=Assert=]: |sensor_instance|.{{Sensor/[[frequency]]}} is greater than 0. + 1. Let |reportingInterval| be the result of 1 / |sensor_instance|.{{Sensor/[[frequency]]}}. 1. Let |timestampDelta| be the result of [=latest reading=]["timestamp"] - |lastReportedTimestamp|. 1. If |timestampDelta| is greater than or equal to |reportingInterval| 1. Queue a task to run [=notify new reading=] with |sensor_instance| as an argument. @@ -1567,13 +1592,10 @@ and whose initial [=map/values=] are implementation-dependent. Note: The user agent must provide the [=mock sensor reading=] that are initially exposed to the {{Sensor}} objects. -A [=mock sensor=] has an associated [=requested sampling frequency=]. Its default value is implementation-dependent -but must be set within a [=mock sensor=]'s associated [=sampling frequency=] bounds. - A [=mock sensor=] has an associated [=sampling frequency=] with supported bounds. The default values of supported bounds are implementation-dependent. -A [=mock sensor=] must report the [=mock sensor reading=] at the rate of its [=requested sampling frequency=] +A [=mock sensor=] must report the [=mock sensor reading=] at the rate of its [=sampling frequency=] if the user agent [=can expose sensor readings=] to the [=current browsing context=]'s [=active document=]. Note: The [=mock sensor=] defined in this specification is not intended be used by non-testing-related web content. @@ -1625,7 +1647,7 @@ The {{MockSensor}} dictionary provides information about a [=mock sensor=]. :: A double representing frequency in Hz that indicates the minimum supported [=sampling frequency=] of the associated [=mock sensor=]. : {{MockSensor/requestedSamplingFrequency}} member -:: A double representing frequency in Hz that indicates the [=requested sampling frequency=] of the associated [=mock sensor=]. +:: A double representing frequency in Hz that indicates the [=sampling frequency=] of the associated [=mock sensor=]. A serialized mock sensor is a JSON [=Object=] where a [=mock sensor=]'s fields listed in the {{MockSensor}} dictionary are mapped using the JSON Key and the associated field's value from the available [=mock sensor=] in [=current browsing context=]. @@ -2003,7 +2025,7 @@ creating multiple instances of the same [=sensor type=] and using simple {{Senso handler. Conversely, multiple {{Sensor|Sensors}} of the same [=sensor type=] can be created when they -are intended to be used with different settings, such as: [=requested sampling frequency=], +are intended to be used with different settings, such as: {{SensorOptions/frequency}}, accuracy or other settings defined in [=extension specifications=].

Definition Requirements