scanning.bs

<pre class='metadata'>
Title: Web Bluetooth Scanning
Repository: WebBluetoothCG/web-bluetooth
Status: CG-DRAFT
ED: https://webbluetoothcg.github.io/web-bluetooth/scanning.html
Shortname: web-bluetooth-scanning
Level: 1
Editor: See contributors on GitHub, , https://github.com/WebBluetoothCG/web-bluetooth/graphs/contributors
Abstract: This document describes an API to scan for nearby Bluetooth Low Energy devices in real time.

Group: web-bluetooth-cg
!Participate: <a href="https://www.w3.org/community/web-bluetooth/">Join the W3C Community Group</a>
!Participate: <a href="https://github.com/WebBluetoothCG/web-bluetooth">Fix the text through GitHub</a>
!Participate: <a href="mailto:public-web-bluetooth@w3.org">public-web-bluetooth@w3.org</a> (<a href="https://lists.w3.org/Archives/Public/public-web-bluetooth/" rel="discussion">archives</a>)
!Participate: <a href="irc://irc.w3.org:6665/#web-bluetooth">IRC: #web-bluetooth on W3C's IRC</a>

Markup Shorthands: css no, markdown yes
</pre>

<pre class=biblio>
{
  "BLUETOOTH42": {
    "href": "https://www.bluetooth.org/DocMan/handlers/DownloadDoc.ashx?doc_id=286439",
    "title": "BLUETOOTH SPECIFICATION Version 4.2",
    "publisher": "Bluetooth SIG",
    "date": "2 December 2014"
  },
  "BLUETOOTH-GATT-REST": {
    "href": "https://www.bluetooth.org/docman/handlers/downloaddoc.ashx?doc_id=285910",
    "title": "GATT REST API",
    "publisher": "Bluetooth Internet WG",
    "date": "7 April 2014"
  },
  "BLUETOOTH-ASSIGNED": {
    "href": "https://www.bluetooth.org/en-us/specification/assigned-numbers",
    "title": "Assigned Numbers",
    "status": "Living Standard",
    "publisher": "Bluetooth SIG"
  },
  "BLUETOOTH-ASSIGNED-BASEBAND": {
    "href": "https://www.bluetooth.org/en-us/specification/assigned-numbers/baseband",
    "title": "Assigned Numbers for Baseband",
    "status": "Living Standard",
    "publisher": "Bluetooth SIG"
  },
  "BLUETOOTH-ASSIGNED-SERVICES": {
    "href": "https://developer.bluetooth.org/gatt/services/Pages/ServicesHome.aspx",
    "title": "Bluetooth GATT Specifications > Services",
    "status": "Living Standard",
    "publisher": "Bluetooth SIG"
  },
  "BLUETOOTH-ASSIGNED-CHARACTERISTICS": {
    "href": "https://developer.bluetooth.org/gatt/characteristics/Pages/CharacteristicsHome.aspx",
    "title": "Bluetooth GATT Specifications > Characteristics",
    "status": "Living Standard",
    "publisher": "Bluetooth SIG"
  },
  "BLUETOOTH-ASSIGNED-DESCRIPTORS": {
    "href": "https://developer.bluetooth.org/gatt/descriptors/Pages/DescriptorsHomePage.aspx",
    "title": "Bluetooth GATT Specifications > Descriptors",
    "status": "Living Standard",
    "publisher": "Bluetooth SIG"
  },
  "BLUETOOTH-SUPPLEMENT6": {
    "href": "https://www.bluetooth.org/DocMan/handlers/DownloadDoc.ashx?doc_id=302735",
    "title": "Supplement to the Bluetooth Core Specification Version 6",
    "date": "14 July 2015",
    "publisher": "Bluetooth SIG"
  }
}
</pre>

<pre class="anchors">
spec: ECMAScript; urlPrefix: https://tc39.github.io/ecma262/#
    type: method
        text: Array.prototype.map; url: sec-array.prototype.map
        text: [[OwnPropertyKeys]]; for: Object; url: sec-ordinary-object-internal-methods-and-internal-slots-ownpropertykeys
    type: interface
        text: TypeError; url: sec-native-error-types-used-in-this-standard-typeerror

spec: WebIDL; urlPrefix: https://heycam.github.io/webidl/#
    type: dfn
        text: a copy of the bytes held; url: dfn-get-buffer-source-copy

spec: web-bluetooth; urlPrefix: index.html#
    type: interface
        text: BluetoothDevice
</pre>
<pre class="link-defaults">
spec: promises-guide-1
    type: dfn
        text: resolve
spec:web-bluetooth
    type: dfn
        text: read only arraybuffer
    type:enum-value; for:PermissionName; text:"bluetooth"
</pre>

<style>
  .argument-list { display: inline-block; vertical-align: top; }
  /* Show self-links for various elements. This is incompatible with nearby floats. */
  .note, .why, .example, .issue { overflow: inherit; }
</style>

<section class="non-normative">
  <h2 id="introduction">Introduction</h2>

  <em>This section is non-normative.</em>

  <p>
    <a href="https://www.bluetooth.com/what-is-bluetooth-technology/bluetooth-technology-basics/low-energy">Bluetooth Low Energy (BLE)</a>
    allows devices to broadcast advertisements to nearby <a>observers</a>.
    These advertisements can contain small amounts of data
    of a variety of types defined in [[BLUETOOTH-SUPPLEMENT6]].
  </p>

  <p>
    For example, a beacon might announce that it's next to a particular museum exhibit
    and is advertising with 1mW of power,
    which would let nearby observers know their approximate distance to that exhibit.
  </p>

  <p>
    This specification extends [[web-bluetooth]] to allow websites to
    receive these advertisements from nearby BLE devices,
    with the user's permission.
  </p>

  <section>
    <h3 id="introduction-examples">Examples</h3>

    <div class="example" id="example-ibeacon">
      <p>
        To discover what iBeacons are nearby and measure their distance,
        a website could use code like the following:
      </p>
      <pre highlight="js">
        function recordNearbyBeacon(major, minor, pathLossVs1m) { ... }
        navigator.bluetooth.<a idl for="Bluetooth" lt="requestLEScan()">requestLEScan</a>({
          filters: [{manufacturerData: {0x004C: {dataPrefix: new Uint8Array([
            0x02, 0x15, // iBeacon identifier.
            0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15  // My beacon UUID.
          ])}}}],
          options: {
            keepRepeatedDevices: true,
          }
        }).then(() => {
          navigator.bluetooth.addEventListener('<a idl>advertisementreceived</a>', event => {
            let appleData = event.manufacturerData.get(<a
                href="https://www.bluetooth.org/en-us/specification/assigned-numbers/company-identifiers"
                title="Apple, Inc.'s Company Identifier">0x004C</a>);
            if (appleData.byteLength != 23) {
              // Isn't an iBeacon.
              return;
            }
            let major = appleData.getUint16(18, false);
            let minor = appleData.getUint16(20, false);
            let txPowerAt1m = -appleData.getInt8(22);
            let pathLossVs1m = txPowerAt1m - event.rssi;

            recordNearbyBeacon(major, minor, pathLossVs1m);
          });
        })
      </pre>
    </div>
  </section>
</section>

<section class="non-normative">
  <h2 id="privacy">Privacy considerations</h2>

  <em>This section is non-normative.</em>

  <p>
    <a lt="active scanning">Actively scanning</a> for advertisements
    broadcasts a <a>device address</a> of the scanning device.
    If the UA's Bluetooth system supports the <a>privacy feature</a>,
    this address rotates periodically,
    which prevents remote radios from tracking the user's device.
    However, if the UA's Bluetooth system does not support the <a>privacy feature</a>,
    this address is a stable unique identifier that's difficult to change.
    To mitigate this, UAs should either use <a>passive scanning</a>,
    use the <a>privacy feature in an observer</a>,
    or warn the user that nearby devices will learn the identity of their device.
  </p>

  <p>
    The ambient advertisements in a user's area are unlikely to directly include GPS coordinates,
    but are likely to contain unique identifiers
    that could be manually correlated with particular physical locations
    or with particular other people.
    Given that, the user needs to give permission
    before a website gets access to nearby advertisements.
  </p>

  <p>
    If a user has already given a site permission to know their location,
    it might be ok to implicitly grant access to BLE advertisements.
    However, BLE advertisements give away
    strictly less location information than full [[geolocation-api]] access,
    so UAs should allow users to grant that intermediate level of access.
  </p>

  <p>
    BLE advertisements are usually fully public,
    since they're broadcast unencrypted on 2.4GHz radio waves.
    However, it's possible that a user would
    have a device broadcast private information in a radio-shielded room.
    This is probably an inappropriate use for BLE advertisements,
    but might argue for requiring explicit permission to scan,
    rather than inferring it from having permission to get a geolocation.
  </p>
</section>

<section class="non-normative">
  <h2 id="security">Security considerations</h2>

  <em>This section is non-normative.</em>

  <p>
    Because this API doesn't write anything,
    there are few if any security implications.
    A device in a shielded room might broadcast security-sensitive information,
    but we don't have any actual attack scenarios for that.
  </p>
</section>

<section>
  <h2 id="scanning">Scanning for BLE advertisements</h2>

  <pre class="idl">
    dictionary BluetoothLEScanOptions {
      sequence&lt;BluetoothLEScanFilterInit> filters;
      boolean keepRepeatedDevices = false;
      boolean acceptAllAdvertisements = false;
    };

    partial interface Bluetooth {
      [SecureContext]
      Promise&lt;BluetoothLEScan> requestLEScan(optional BluetoothLEScanOptions options);
    };
  </pre>
  <div class="note" heading="{{Bluetooth/requestLEScan()}} summary">
    <p>
      <code>navigator.bluetooth.{{requestLEScan(options)}}</code>
      starts scanning for BLE advertisements,
      asking the user for permission if they haven't yet granted it.
    </p>
    <p>
      Because this could show a prompt,
      it requires a <a>secure context</a>,
      and UAs are likely to require a <a lt="triggered by user activation">user gesture</a>.
    </p>
    <p>
      Advertising events that <a for="BluetoothLEScanFilter">match</a>
      a {{BluetoothLEScanFilter}} in an active {{BluetoothLEScan}}
      cause {{advertisementreceived}} events to be dispatched
      to the sending {{BluetoothDevice}}.
      A filter matches if the advertisement includes data equal to each <a>present</a> member.
      Usually, you'll only include one member in each filter.
    </p>
    <p>
      Normally scans will discard
      the second and subsequent advertisements from a single device
      to save power.
      If you need to receive them,
      set <dfn dict-member for="BluetoothLEScanOptions">keepRepeatedDevices</dfn> to `true`.
      Note that setting {{BluetoothLEScanOptions/keepRepeatedDevices}} to `false`
      doesn't guarantee you won't get redundant events;
      it just allows the UA to save power by omitting them.
    </p>
    <p>
      In the rare case that you want to receive every advertisement without filtering them,
      use the <dfn dict-member for="BluetoothLEScanOptions">acceptAllAdvertisements</dfn> field.
    </p>
  </div>

  <div algorithm>
    <p>
      The <code><dfn method for="Bluetooth">requestLEScan(|options|)</dfn></code> method,
      when invoked, MUST return <a>a new promise</a> |promise|
      and run the following steps <a>in parallel</a>:
    </p>
    <ol class="algorithm">
      <li>
        If <code>|options|.acceptAllAdvertisements</code> is `true`,
        and <code>|options|.filters</code> is present,
        <a>reject</a> |promise| with a {{TypeError}} and abort these steps.

        Note: There's no need to include filters if all advertisements are being accepted.
      </li>
      <li>
        If <code>|options|.acceptAllAdvertisements</code> is `false`,
        and <code>|options|.filters</code> is either absent or empty,
        <a>reject</a> |promise| with a {{TypeError}} and abort these steps.

        Note: An empty set of filters wouldn't return any advertisements.
      </li>
      <li>
        Let |filters| be
        <code>|options|.filters.map(filter=>new
        {{BluetoothLEScanFilter/BluetoothLEScanFilter()|BluetoothLEScanFilter}}(filter))</code>.
        If this throws an exception,
        <a>reject</a> |promise| with that exception and abort these steps.
      </li>
      <li id="scanning-permission">
        <a>Request permission to use</a>
        <pre highlight="js">
          {
            name: <a idl>"bluetooth-le-scan"</a>,
            filters: <var>options</var>.filters,
            keepRepeatedDevices: <var>options</var>.keepRepeatedDevices,
            acceptAllAdvertisements: <var>options</var>.acceptAllAdvertisements,
          }
        </pre>

        Note: This may require that this algorithm was <a>triggered by user activation</a>.
      </li>
      <li>
        If the result is {{"denied"}},
        reject |promise| with a {{NotAllowedError}} and abort these steps.
      </li>
      <li>
        Let |scan| be a new {{BluetoothLEScan}} instance
        whose fields are initialized as in the following table:
        <table class="data">
          <thead><th>Field</th><th>Initial value</th></thead>
          <tr><td>{{BluetoothLEScan/filters}}</td><td>|filters|</td></tr>
          <tr>
            <td>{{BluetoothLEScan/keepRepeatedDevices}}</td>
            <td><code>|options|.keepRepeatedDevices</code></td>
          </tr>
          <tr>
            <td>{{BluetoothLEScan/acceptAllAdvertisements}}</td>
            <td><code>|options|.acceptAllAdvertisements</code></td>
          </tr>
          <tr><td>{{BluetoothLEScan/active}}</td><td>`true`</td></tr>
        </table>
      </li>
      <li>
        Add |scan| to <code>navigator.bluetooth.{{[[activeScans]]}}</code>.
      </li>
      <li>
        Ensure the UA is scanning for BLE advertisements
        in a mode that will receive at least
        all advertisements <a for="BluetoothLEScan">matching</a> any scan
        in any {{[[activeScans]]}} set in the whole UA.

        <p class="issue" id="issue-limit-scan-periods">
          Find wording that allows the UA to limit its scan to only certain periods of time,
          to save power.
        </p>
      </li>
      <li>
        If the UA fails to start scanning,
        remove |scan| from <code>navigator.bluetooth.{{[[activeScans]]}}</code>,
        <a>reject</a> |promise| with one of the following errors,
        and abort these steps:

        <dl class="switch">
          <dt>The UA doesn't support scanning for advertisements</dt>
          <dd>{{NotSupportedError}}</dd>

          <dt>Bluetooth is turned off</dt>
          <dd>{{InvalidStateError}}</dd>

          <dt>Other reasons</dt>
          <dd>{{UnknownError}}</dd>
        </dl>
      </li>
      <li>
        <a>Resolve</a> |promise| with |scan|.
      </li>
    </ol>
  </div>

  <section>
    <h3 id="scan-control">Controlling a BLE scan</h3>

    <pre class="idl">
      [Constructor(optional BluetoothDataFilterInit init)]
      interface BluetoothDataFilter {
        readonly attribute ArrayBuffer dataPrefix;
        readonly attribute ArrayBuffer mask;
      };

      [Constructor(optional object init)]
      interface BluetoothManufacturerDataFilter {
        readonly maplike&lt;unsigned short, BluetoothDataFilter>;
      };

      [Constructor(optional object init)]
      interface BluetoothServiceDataFilter {
        readonly maplike&lt;UUID, BluetoothDataFilter>;
      };

      [Constructor(optional BluetoothLEScanFilterInit init)]
      interface BluetoothLEScanFilter {
        readonly attribute DOMString? name;
        readonly attribute DOMString? namePrefix;
        readonly attribute FrozenArray&lt;UUID>? services;
        readonly attribute BluetoothManufacturerDataFilter manufacturerData;
        readonly attribute BluetoothServiceDataFilter serviceData;
      };

      interface BluetoothLEScan {
        readonly attribute FrozenArray&lt;BluetoothLEScanFilter> filters;
        readonly attribute boolean keepRepeatedDevices;
        readonly attribute boolean acceptAllAdvertisements;

        readonly attribute boolean active;

        void stop();
      };
    </pre>

    <div class="note" heading="{{BluetoothLEScan}} members">
      <p>
        {{BluetoothLEScan/stop()|BluetoothLEScan.stop()}}
        stops a previously-requested scan.
        Sites should do this as soon as possible to avoid wasting power.
      </p>
    </div>

    <div algorithm>
      <p>
        The <dfn constructor for="BluetoothLEScanFilter">BluetoothLEScanFilter(|init|)</dfn>
        constructor, when invoked MUST perform the following steps:
      </p>
      <ol class="algorithm">
        <li>
          Initialize all nullable fields to `null`.
        </li>
        <li>
          If no member of |init| is present, throw a {{TypeError}}.

          Note: A filter can't implicitly allow all advertisements.
          Use {{BluetoothLEScanOptions/acceptAllAdvertisements}} to explicitly do it.
        </li>
        <li>
          Initialize {{BluetoothLEScanFilter/manufacturerData}} as
          <code>new BluetoothManufacturerDataFilter(|init|.{{BluetoothLEScanFilterInit/manufacturerData}})</code>.
        </li>
        <li>
          Initialize {{BluetoothLEScanFilter/serviceData}} as
          <code>new BluetoothManufacturerDataFilter(|init|.{{BluetoothLEScanFilterInit/serviceData}})</code>.
        </li>
        <li>
          If <code>|init|.{{BluetoothLEScanFilterInit/services}}</code> is present,
          initialize <code>this.{{BluetoothLEScanFilter/services}}</code> as
          <code>{{BluetoothUUID/getService()|BluetoothUUID.getService}}(|init|.{{BluetoothLEScanFilterInit/services}}</code>.
        </li>
        <li>
          For each other <a>present</a> member in |init|,
          set `this`'s attribute with a matching identifier to the value of the member.
        </li>
        <li>
          If any of the above calls threw an exception,
          propagate that exception from this constructor.
        </li>
      </ol>
    </div>

    <div algorithm>
      <p>
        The <dfn method for="BluetoothLEScan">stop()</dfn> method, when invoked,
        MUST perform the following steps:
      </p>
      <ol class="algorithm">
        <li>Set <code>this.{{BluetoothLEScan/active}}</code> to `false`.</li>
        <li>Remove `this` from <code>navigator.bluetooth.{{[[activeScans]]}}</code>.</li>
        <li>
          The UA SHOULD reconfigure or stop its BLE scan to save power
          while still receiving any advertisements that
          <a for="BluetoothLEScan">match</a> any scan
          in any {{[[activeScans]]}} set in the whole UA.
        </li>
      </ol>
    </div>

    <div algorithm>
      <p>
        The <dfn constructor for="BluetoothManufacturerDataFilter">BluetoothManufacturerDataFilter(|init|)</dfn>
        constructor, when invoked, MUST perform the following steps:
      </p>
      <ol>
        <li>
          If |init| is not present
          or <code>|init|.{{Object/[[OwnPropertyKeys]]}}()</code> is empty,
          then `this` has no <a>map entries</a>.
          Abort these steps.
        </li>
        <li>
          Let |canonicalInit| be the `manufacturerData` field of the result of
          <a for="BluetoothLEScanFilterInit">canonicalizing</a> <code>{manufacturerData: |init|}</code>.
          If this throws an exception,
          propagate that exception from this constructor and abort these steps.
        </li>
        <li>
          `this`'s <a>map entries</a> map from each |key| in
          <code>|canonicalInit|.{{Object/[[OwnPropertyKeys]]}}()</code>,
          parsed as a base-10 integer,
          to its value of <code>new {{BluetoothDataFilter}}(|canonicalInit|[|key|])</code>.
        </li>
      </ol>
    </div>

    <div algorithm>
      <p>
        The <dfn constructor for="BluetoothServiceDataFilter">BluetoothServiceDataFilter(|init|)</dfn>
        constructor, when invoked, MUST perform the following steps:
      </p>
      <ol>
        <li>
          If |init| is not present
          or <code>|init|.{{Object/[[OwnPropertyKeys]]}}()</code> is empty,
          then `this` has no <a>map entries</a>.
          Abort these steps.
        </li>
        <li>
          Let |canonicalInit| be the `serviceData` field of the result of
          <a for="BluetoothLEScanFilterInit">canonicalizing</a> <code>{serviceData: |init|}</code>.
          If this throws an exception,
          propagate that exception from this constructor and abort these steps.
        </li>
        <li>
          `this`'s <a>map entries</a> map from each |key| in
          <code>|canonicalInit|.{{Object/[[OwnPropertyKeys]]}}()</code>,
          to its value of <code>new {{BluetoothDataFilter}}(|canonicalInit|[|key|])</code>.
        </li>
      </ol>
    </div>

    <div algorithm>
      <p>
        The <dfn constructor for="BluetoothDataFilter">BluetoothDataFilter(|init|)</dfn>
        constructor, when invoked, MUST perform the following steps:
      </p>
      <ol>
        <li>
          Let |canonicalInit| be
          the result of <a for="BluetoothDataFilterInit">canonicalizing</a> |init|.
          If this throws an exception,
          propagate that exception from this constructor and abort these steps.
        </li>
        <li>
          Initialize <code>this.{{BluetoothDataFilter/dataPrefix}}</code> as
          a <a>read only ArrayBuffer</a> whose contents are
          <a>a copy of the bytes held</a> by
          <code>|canonicalInit|.{{BluetoothDataFilterInit/dataPrefix}}</code>.
        </li>
        <li>
          Initialize <code>this.{{BluetoothDataFilter/mask}}</code> as
          a <a>read only ArrayBuffer</a> whose contents are
          <a>a copy of the bytes held</a> by
          <code>|canonicalInit|.{{BluetoothDataFilterInit/mask}}</code>.
        </li>
      </ol>
    </div>
  </section>

  <section>
    <h3 id="permission">Permission to scan</h3>

    <p>
      The <dfn enum-value for="PermissionName">"bluetooth-le-scan"</dfn>
      <a>powerful feature</a>'s
      permission-related algorithms and types
      are defined as follows:
    </p>
    <dl>
      <dt><a>permission descriptor type</a></dt>
      <dd>
        <pre class="idl">
          dictionary BluetoothLEScanPermissionDescriptor : PermissionDescriptor {
            // These match BluetoothLEScanOptions.
            sequence&lt;BluetoothLEScanFilterInit> filters;
            boolean keepRepeatedDevices = false;
            boolean acceptAllAdvertisements = false;
          };
        </pre>
      </dd>

      <dt><a>permission result type</a></dt>
      <dd>
        <pre class="idl">
          interface BluetoothLEScanPermissionResult : PermissionStatus {
            attribute FrozenArray&lt;BluetoothLEScan> scans;
          };
        </pre>
      </dd>

      <dt><a>permission query algorithm</a></dt>
      <dd algorithm="permission-query">
        <p>
          Given a {{BluetoothLEScanPermissionDescriptor}} |descriptor|
          and a {{BluetoothLEScanPermissionResult}} |result|:
        </p>
        <ol class="algorithm">
          <li>
            Update <code>|result|.{{PermissionStatus/state}}</code>
            to |descriptor|'s <a>permission state</a>.
          </li>
          <li>
            If <code>|result|.{{PermissionStatus/state}}</code> is {{"denied"}},
            set <code>|result|.scans</code> to an empty {{FrozenArray}}
            and abort these steps.
          </li>
          <li>
            Update <code>|result|.{{scans}}</code> to
            a new {{FrozenArray}} containing
            the elements of <code>navigator.bluetooth.{{[[activeScans]]}}</code>.

            <p class="issue" id="issue-should-query-filter">
              Consider filtering the result to active scans that
              match the fields of the descriptor.
            </p>
          </li>
        </ol>
      </dd>

      <dt><a>permission request algorithm</a></dt>
      <dd algorithm="permission-request">
        <p>
          Given a {{BluetoothLEScanPermissionDescriptor}} |descriptor|
          and a {{BluetoothLEScanPermissionResult}} |result|:
        </p>
        <ol class="algorithm">
          <li>
            Let |promise| be the result of
            <code>navigator.bluetooth.{{requestLEScan()|requestLEScan}}(|descriptor|)</code>.
          </li>
          <li>Wait for |promise| to settle.</li>
          <li>
            If |promise| rejected, throw the reason it rejected with,
            and abort these steps.
          </li>
          <li>
            Update <code>|result|.status</code> to
            |descriptor|'s <a>permission state</a>.
          </li>
          <li>
            Update <code>|result|.scans</code> to
            a new {{FrozenArray}} whose single element is the value in |promise|.
          </li>
        </ol>
      </dd>

      <dt>
        <a>permission revocation algorithm</a>
      </dt>
      <dd algorithm="permission-revocation">
        <ol class="algorithm">
          <li>
            For each |activeScan| in <code>navigator.bluetooth.{{[[activeScans]]}}</code>:
            <ol>
              <li>
                If the <a>permission state</a> of
                <pre highlight="js">
                  {
                    name: "bluetooth-le-scan",
                    filters: <var>activeScan</var>.filters,
                    keepRepeatedDevices: <var>activeScan</var>.keepRepeatedDevices
                  }
                </pre>
                is not {{"granted"}},
                call <code>|activeScan|.{{stop()}}</code>.
              </li>
            </ol>
          </li>
        </ol>
      </dd>
    </dl>
  </section>
</section>

<section>
  <h2 id="events">Event handling</h2>

  <section>
    <h3 id="advertising-events">Responding to advertising events</h3>

    <div algorithm="receive-advertising-event">
      <p>
        When the UA receives an <a>advertising event</a> |event|
        (consisting of an advertising packet and an optional scan response),
        it MUST run the following steps:
      </p>
      <ol class="algorithm">
        <li>
          Let <var>device</var> be the <a>Bluetooth device</a> that sent the advertising event.
        </li>
        <li>
          For each {{Bluetooth}} instance |bluetooth| in the UA,
          <a>queue a task</a> on
          |bluetooth|'s <a>relevant settings object</a>'s <a>responsible event loop</a>
          to do the following sub-steps:
          <ol>
            <li>
              Let |scans| be the set of
              {{BluetoothLEScan}}s in <code>|bluetooth|.{{[[activeScans]]}}</code>
              that <a for="BluetoothLEScan">match</a> |event|.
            </li>
            <li>If |scans| is empty, abort these sub-steps.</li>
            <li class="note">
              Note: the user's <a href="#scanning-permission">permission to scan</a>
              likely indicates that
              they intend newly-discovered devices to appear in
              {{"bluetooth"}}'s <a>extra permission data</a>,
              but possibly with {{AllowedBluetoothDevice/mayUseGATT}} set to `false`.
            </li>
            <li>
              <a>Get the `BluetoothDevice` representing</a> |device| inside |bluetooth|,
              and let |deviceObj| be the result.
            </li>
            <li>
              Add each {{BluetoothLEScan}} in |scans|
              to <code>|deviceObj|.{{[[returnedFromScans]]}}</code>.
            </li>
            <li>
              <a>Fire an `advertisementreceived` event</a>
              for |event| at |deviceObj|.
            </li>
          </ol>
        </li>
      </ol>
    </div>

    <div algorithm="bluetoothlescan-match">
      <p>
        An advertising event |event|
        <dfn for="BluetoothLEScan" lt="match">matches</dfn> a {{BluetoothLEScan}} |scan|
        if the following steps return `match`:
      </p>
      <ol class="algorithm">
        <li>
          <code>|scan|.acceptAllAdvertisements</code> is `false` and
          |event| doesn't <a for="BluetoothLEScanFilter">match</a>
          any filter in <code>|scan|.{{BluetoothLEScan/filters}}</code>,
          return `no match`.
        </li>
        <li>
          If <code>|scan|.{{BluetoothLEScan/keepRepeatedDevices}}</code> is `false`,
          there is a {{BluetoothDevice}} |device| that
          represents the <a>same Bluetooth device</a> as the one that sent |event|,
          and <code>|device|.{{[[returnedFromScans]]}}</code> includes |scan|,
          the UA MAY return `no match`.
        </li>
        <li>Return `match`.</li>
      </ol>
    </div>

    <div algorithm="bluetoothlescanfilter-match">
      <p>
        An advertising event |event|
        <dfn for="BluetoothLEScanFilter" lt="match">matches</dfn>
        a {{BluetoothLEScanFilter}} |filter|
        if all of the following conditions hold:
      </p>
      <ul>
        <li>
          If <code>|filter|.name</code> is non-<code>null</code>,
          |event| has a <a>Local Name</a> equal to <code>|filter|.name</code>.

          Note: A <a>Shortened Local Name</a>
          can match a {{BluetoothLEScanFilter/name}} filter.
        </li>
        <li>
          If <code>|filter|.namePrefix</code> is non-<code>null</code>,
          |event| has a <a>Local Name</a>,
          and <code>|filter|.namePrefix</code> is a prefix of it.
        </li>
        <li>
          If <code>|filter|.serviceUUID</code> is non-<code>null</code>,
          it is equal to a <a>Service UUID</a> in |event|.
        </li>
        <li>
          For each (|id|, |filter|) in <code>|filter|.manufacturerData</code>'s <a>map entries</a>,
          some <a>Manufacturer Specific Data</a> in |event|
          has a Company Identifier Code of |id|,
          and whose array of bytes <a for="BluetoothDataFilterInit">matches</a> |filter|.
        </li>
        <li>
          For each (|uuid|, |filter|) in
          <code>|filter|.serviceData</code>'s <a>map entries</a>,
          some <a>Service Data</a> in |event|
          has a UUID whose 128-bit representation is |uuid|,
          and whose array of bytes <a for="BluetoothDataFilterInit">matches</a> |filter|.
        </li>
      </ul>
    </div>
  </section>
</section>

<section>
  <h2 id="changes">Changes to existing interfaces</h2>

  <p>
    Instances of {{Bluetooth}} additionally have the following internal slots:
  </p>
  <table class="data" dfn-for="Bluetooth" dfn-type="attribute">
    <thead>
      <th>Internal Slot</th>
      <th>Initial Value</th>
      <th>Description (non-normative)</th>
    </thead>
    <tr>
      <td><dfn>\[[activeScans]]</dfn></td>
      <td>
        An empty set of {{BluetoothLEScan}} instances.
      </td>
      <td>
        The contents of this set will have {{BluetoothLEScan/active}} equal to `true`.
      </td>
    </tr>
  </table>

  <p>
    Instances of {{BluetoothDevice}} additionally have the following internal slots:
  </p>
  <table class="data" dfn-for="BluetoothDevice" dfn-type="attribute">
    <thead>
      <th>Internal Slot</th>
      <th>Initial Value</th>
      <th>Description (non-normative)</th>
    </thead>
    <tr>
      <td><dfn>\[[returnedFromScans]]</dfn></td>
      <td>
        An empty set of {{BluetoothLEScan}} objects.
      </td>
      <td>
        Used to implement {{BluetoothLEScanOptions/keepRepeatedDevices}}.
      </td>
    </tr>
  </table>
</section>

<section>
  <h2 id="terminology">Terminology and conventions</h2>

  <p>
    This specification uses a few conventions and several terms from other specifications.
    This section lists those and links to their primary definitions.
  </p>

  <p>
    When an algorithm in this specification uses a name defined in this or another specification,
    the name MUST resolve to its initial value,
    ignoring any changes that have been made to the name in the current execution environment.
    For example, when the {{Bluetooth/requestLEScan()}} algorithm says to call
    <code>|options|.filters.map(filter=>new
    {{BluetoothLEScanFilter/BluetoothLEScanFilter()|BluetoothLEScanFilter}}(filter))</code>,
    this MUST apply the
    {{Array.prototype.map}} algorithm defined in [[ECMAScript]]
    with <code>|options|.services</code> as its <code>this</code> parameter and
    the algorithm defined at {{BluetoothLEScanFilter/BluetoothLEScanFilter()}}
    as its <code>callbackfn</code> parameter,
    regardless of any modifications that have been made to <code>window</code>,
    <code>Array</code>, <code>Array.prototype</code>, <code>Array.prototype.map</code>,
    <code>Function</code>, <code>Function.prototype</code>,
    <code>BluetoothLEScanFilter</code>, or other objects.
  </p>

  <dl>
    <dt>[[!BLUETOOTH42]]</dt>
    <dd>
      <ol>
        <li value="1">Architecture &amp; Terminology Overview
          <ol type="A">
            <li value="1">General Description
              <ol>
                <li value="2">Overview of Bluetooth Low Energy Operation
                  (defines <dfn lt="advertising event|advertising events">advertising events</dfn>)
                </li>
              </ol>
            </li>
          </ol>
        </li>
        <li value="3">Core System Package [Host volume]
          <ol type="A">
            <li value="3">Generic Access Profile
              <ol>
                <li value="2">Profile Overview
                  <ol>
                    <li value="2">Profile Roles
                      <ol>
                        <li value="2">Roles when Operating over an LE Physical Transport
                          <ol>
                            <li value="2"><dfn>Observer</dfn> Role</li>
                          </ol>
                        </li>
                      </ol>
                    </li>
                  </ol>
                </li>
                <li value="10">Security Aspects &mdash; LE Physical Transport
                  <ol>
                    <li value="7"><dfn>Privacy Feature</dfn>
                      <ol>
                        <li value="4"><dfn>Privacy Feature in an Observer</dfn>
                      </ol>
                    </li>
                  </ol>
                </li>
              </ol>
            </li>
          </ol>
        </li>
        <li value="6">Core System Package [Low Energy Controller volume]
          <ol type="A">
            <li value="2">Link Layer Specification
              <ol>
                <li value="1">General Description
                  <ol>
                    <li value="3"><dfn>Device Address</dfn></li>
                  </ol>
                </li>
                <li value="2">Air Interface Packets
                  <ol>
                    <li value="3">Advertising Channel PDU
                      <ol>
                        <li value="1">Advertising PDUs
                          <ol>
                            <li value="1"><dfn>ADV_IND</dfn></li>
                            <li value="2"><dfn>ADV_DIRECT_IND</dfn></li>
                            <li value="3"><dfn>ADV_NONCONN_IND</dfn></li>
                            <li value="4"><dfn>ADV_SCAN_IND</dfn></li>
                          </ol>
                        </li>
                      </ol>
                    </li>
                  </ol>
                </li>
                <li value="4">Air Interface Protocol
                  <ol>
                    <li value="4">Non-Connected States
                      <ol>
                        <li value="3">Scanning State
                          <ol>
                            <li value="1"><dfn>Passive Scanning</dfn></li>
                            <li value="2"><dfn>Active Scanning</dfn></li>
                          </ol>
                        </li>
                      </ol>
                    </li>
                  </ol>
                </li>
              </ol>
            </li>
          </ol>
        </li>
      </ol>
    </dd>
    <dt>[[!BLUETOOTH-SUPPLEMENT6]]</dt>
    <dd>
      <ol type="A">
        <li value="1">Data Types Specification
          <ol>
            <li value="1">Data Types Definitions and Formats
              <ol>
                <li value="1"><dfn>Service UUID</dfn></li>
                <li value="1">
                  <dfn>Local Name</dfn>
                  also defines <dfn>Shortened Local Name</dfn>
                  and <dfn>Complete Local Name</dfn>
                </li>
                <li value="4"><dfn>Manufacturer Specific Data</dfn></li>
                <li value="11"><dfn>Service Data</dfn></li>
              </ol>
            </li>
          </ol>
        </li>
      </ol>
    </dd>
  </dl>
</section>