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<pre class="metadata">
Title: WebUSB API
Status: w3c/CG-DRAFT
ED: https://wicg.github.io/webusb
Shortname: webusb
Level: 1
Editor: Reilly Grant 83788, Google LLC https://www.google.com, [email protected]
Editor: Ken Rockot 87080, Google LLC https://www.google.com, [email protected]
Editor: Ovidio Ruiz-Henríquez 106543, Google LLC https://www.google.com, [email protected]
Abstract: This document describes an API for securely providing access to Universal Serial Bus devices from web pages.
Group: wicg
Repository: https://github.com/WICG/webusb/
!Participate: <a href="https://www.w3.org/community/wicg/">Join the W3C Community Group</a>
!Participate: <a href="irc://irc.w3.org:6665/#webusb">IRC: #webusb on W3C's IRC</a> (Stay around for an answer, it make take a while)
!Participate: <a href="http://stackoverflow.com/questions/tagged/webusb">Ask questions on StackOverflow</a>
</pre>
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# Introduction # {#introduction}
<em>This section is non-normative</em>.
The Universal Serial Bus (USB) is the de-facto standard for wired peripherals.
Most USB devices implement one of roughly a dozen standard "device classes"
which specify a way for the device to advertise the features it supports and
commands and data formats for using those features. Standard device classes
include keyboard, mice, audio, video and storage devices. Operating systems
support such devices using the "class driver" provided by the OS vendor. There
is however a long tail of devices that do not fit into one of the standardized
device classes. These devices require hardware vendors to write native drivers
and SDKs in order for developers to take advantage of them and this native code
prevents these devices from being used by the web.
The WebUSB API provides a way to safely expose USB device services to the web.
It provides an API familiar to developers who have used existing native USB
libraries and exposes the device interfaces defined by existing specifications.
With this API hardware manufacturers will have the ability to build
cross-platform JavaScript SDKs for their devices. This will be good for the web
because, instead of waiting for a new kind of device to be popular enough for
browsers to provide a specific API, new and innovative hardware can be built
for the web from day one.
For more information about USB see [[#appendix-intro]].
# Motivating Applications # {#motivating-applications}
<em>This section is non-normative</em>.
## Educational Devices ## {#app-edu-devices}
The software delivery model of the web is a key enabler for educational
applications because they can be quickly loaded on any computer without
questions of platform compatibility or administrative credentials. Science
classes are incorporating computerized measurement and data logging into their
lessons. These tools require bundled software that may be difficult to install
on managed computers as every new native application adds overhead to an already
stressed IT department. Web-based hardware APIs allow support for these devices
to be built directly into existing online course materials, providing a
completely seamless experience.
Students learning to code with one of the many microcontroller development kits
can take advantage of online developer tools to write and upload their code.
These tools already exist however they require a native component to interface
between the browser and the hardware. These native extensions add a barrier to
entry and may expose the user to security vulnerabilities in a way that that
code running in the sandboxed web environment does not.
## Web Drivers ## {#app-drivers}
The composablity of the web allows a new ecosystem of hardware support to be
built entirely from web technology. Taking 3D printers an example, imagine that
a site hosting 3D object designs wants to integrate printing directly into their
page. The web supports 2D printing but there is no API for the 3D variety. If
manufacturers host embeddable pages that use the WebUSB API to send data to
their printers, sites can use these pages to integrate support for the hardware
in the same way that features such as embedded maps are added to many existing
sites.
## Devices Updates and Diagnostics ## {#app-updates-and-diagnostics}
While wireless protocols such as Bluetooth are often the more convenient choice
for consumer devices USB ports continue to proliferate because they are an easy
solution for power delivery and can serve as the connection of last resort when
the device isn't working. By integrating update and diagnostic tools into their
support site a hardware manufacturer can provide tools for customers on any
platform and collect better diagnostic data when a customer reaches out for
support through their website. The <a>landing page</a> provides a way for the
device manufacturer to direct the user to the right part of their website for
help with their device.
# Security and Privacy Considerations # {#security-and-privacy}
<em>This section is non-normative</em>.
The WebUSB API is a powerful feature and has the possibility to expose users to
a number of new privacy and security risks. These risks can be broadly divided
into three categories that will be described in the sections below.
## Abusing Access to a Device ## {#abusing-a-device}
Peripheral devices can serve a number of purposes. They may store data, as a
flash drive does. They may collect information about the outside world as a
camera or microphone does. They may manipulate objects in the outside world as
a printer does. Each of the examples above have high-level APIs in the web
platform with security features that aim to prevent their abuse by a malicious
website. Storing data to or from an external drive requires the user to select
the file manually. Turning on the microphone or camera requires permission from
the user and may activate an indicator to let the user know data collection is
in progress. Printing a document requires explicit action as well. This API
provides a generic mechanism to connect to devices not covered by these
existing high-level APIs and so it requires a similarly generic mechanism for
preventing a malicious page from abusing a device.
The first of these protections is the {{USB/requestDevice()}} function. The UA
may display a permission prompt when this function is called. Even for a
non-malicious page this action also preserves user privacy by preventing a site
from connecting to a device before the user is aware that such a connection is
possible. The UA may also display an indicator when a device connection is
active.
Secondly, this specification requires that only secure contexts as described
in [[powerful-features]] can access USB devices. This ensures both the
authenticity of the code executing on behalf of the origin and that data read
from the device may not be intercepted in transit.
Lastly, since USB devices are unable to distinguish requests from multiple
sources, operating systems only allow a USB interface to have a single owning
user-space or kernel-space driver. The UA acts as a user-space driver, therefore
allowing only a single execution context to claim a USB interface at a time. The
{{USBDevice/claimInterface()}} function will fail if multiple execution contexts
attempt to claim an interface.
## Attacking a Device ## {#attacking-a-device}
Historically, unless they were created for high security applications, USB
devices have been designed to trust the host they are connected to and so the
host is the traditional guardian of access to the capabilities a device
provides. In the development of this specification two possibilities were
considered. First, the UA could notify the device of the origin from which a
request originated. This would be similar to the <code>Referrer</code> header
included in HTTP request. The difficulty of this approach is that it places
the burden of access control on the device. Devices often have very limited
processing and storage capabilities and so an effort was made to limit the
amount of work necessary on the part of the device.
The approach initially chosen during drafting of this specification was to
instead require that the UA control access though a mechanism similiar to
[[CORS]]. The device could provide the UA with a set of static data structures
defining a set of origins that are allowed to connect to it. To support a
transition period for existing devices it was proposed that information about
allowed origins could also be provided out of band through some kind of public
registry.
A downside of this approach was two-fold. First, it required vendors to build
new devices with WebUSB in mind or rely on a public registry system that proved
difficult to specify. Product development cycles are long and as only an
Editor's Draft this specification does not have the clout necessary to influence
product planning. Second, it provided no mechanism for third-party developers to
use this API with a device. This limited innovation and the number of developers
who could take advantage of this new capability.
After considering these options the authors have decided that the permission
prompt encouraged by the {{USB/requestDevice()}} method and the integration with
[[#permissions-policy]] provide adequate protection against unwanted access to a
device.
## Attacking the Host ## {#attacking-the-host}
If a device is compromised then in addition to abusing its own capabilities
the attacker may also use it to in turn attack the host to which it is connected
or if the exploit is persistent any host it is connected to later. The methods
above are the ways in which this specification attempts to mitigate this attack
vector for once the device is under the control of an attacker (for example, by
uploading a malicious firmware image) there is nothing that can be done by the
UA to prevent further damage.
This specification recommends device manufacturers practice defense in depth by
designing their devices to only accept signed firmware updates and/or require
physical access to the device in order to apply some configuration changes.
# WebUSB Descriptors and Requests # {#webusb-descriptors-and-requests}
This specification defines descriptors and commands the UA MAY use to gather
information about the device specific to implementing this API.
<h3 dfn>WebUSB Platform Capability Descriptor</h3>
A device announces support for the WebUSB command set by including the
following <a>Platform Descriptor</a> in its <a>Binary Object
Store</a>:
<table>
<tr>
<th>Offset</th>
<th>Field</th>
<th>Size</th>
<th>Value</th>
<th>Description</th>
</tr>
<tr>
<td>0</td>
<td>bLength</td>
<td>1</td>
<td>Number</td>
<td>Size of this descriptor. Must be set to 24.</td>
</tr>
<tr>
<td>1</td>
<td>bDescriptorType</td>
<td>1</td>
<td>Constant</td>
<td>DEVICE CAPABILITY descriptor type ([[!USB31]] Table 9-6).</td>
</tr>
<tr>
<td>2</td>
<td>bDevCapabilityType</td>
<td>1</td>
<td>Constant</td>
<td>PLATFORM capability type ([[!USB31]] Table 9-14).</td>
</tr>
<tr>
<td>3</td>
<td>bReserved</td>
<td>1</td>
<td>Number</td>
<td>This field is reserved and shall be set to zero.</td>
</tr>
<tr>
<td>4</td>
<td>PlatformCapabilityUUID</td>
<td>16</td>
<td>UUID</td>
<td>Must be set to {3408b638-09a9-47a0-8bfd-a0768815b665}.</td>
</tr>
<tr>
<td>20</td>
<td>bcdVersion</td>
<td>2</td>
<td>BCD</td>
<td>Protocol version supported. Must be set to 0x0100.</td>
</tr>
<tr>
<td>22</td>
<td>bVendorCode</td>
<td>1</td>
<td>Number</td>
<td>bRequest value used for issuing WebUSB requests.</td>
</tr>
<tr>
<td>23</td>
<td>iLandingPage</td>
<td>1</td>
<td>Number</td>
<td>URL descriptor index of the device's <a>landing page</a>.</td>
</tr>
</table>
The <code>iLandingPage</code> field, when non-zero, indicates a
<dfn>landing page</dfn> which the device manufacturer would like the user to
visit in order to control their device. The UA MAY suggest the user navigate
to this URL when the device is connected.
Note: The USB is a little-endian bus and so according to [[RFC4122]] the UUID
above MUST be sent over the wire as the byte sequence <code>{0x38, 0xB6, 0x08,
0x34, 0xA9, 0x09, 0xA0, 0x47, 0x8B, 0xFD, 0xA0, 0x76, 0x88, 0x15, 0xB6,
0x65}</code>.
## WebUSB Device Requests ## {#device-requests}
All <a>control transfers</a> defined by this specification are considered to
be vendor-specific requests. The <code>bVendorCode</code> value found
in the <a>WebUSB Platform Capability Descriptor</a> provides the UA
with the <code>bRequest</code> the device expects the host to use when
issuing <a>control transfers</a> these requests. The request type is then
specified in the <code>wIndex</code> field.
<table>
<caption>WebUSB Request Codes</caption>
<tr>
<th>Constant</th>
<th>Value</th>
</tr>
<tr>
<td>(Reserved)</td>
<td>1</td>
</tr>
<tr>
<td>GET_URL</td>
<td>2</td>
</tr>
</table>
<h4 dfn>Get URL</h4>
This request fetches the URL descriptor with the given index.
The device MUST respond with the <a>URL Descriptor</a> at the given
index or stall the transfer if the index is invalid.
<table>
<tr>
<th>bmRequestType</td>
<th>bRequest</th>
<th>wValue</th>
<th>wIndex</th>
<th>wLength</th>
<th>Data</th>
</tr>
<tr>
<td>11000000B</td>
<td><code>bVendorCode</code></td>
<td>Descriptor Index</td>
<td>GET_URL</td>
<td>Descriptor Length</td>
<td>Descriptor</td>
</tr>
</table>
## WebUSB Descriptors ## {#webusb-descriptors}
These descriptor types are returned by requests defined in this
specification.
<table>
<caption>WebUSB Descriptor Types</caption>
<tr>
<th>Constant</th>
<th>Value</th>
</tr>
<tr>
<td>(Reserved)</td>
<td>0-2</td>
</tr>
<tr>
<td>WEBUSB_URL</td>
<td>3</td>
</tr>
</table>
<h4 dfn>URL Descriptor</h4>
This descriptor contains a single URL and is returned by the <a>Get URL</a>
request.
<table>
<tr>
<th>Offset</th>
<th>Field</th>
<th>Size</th>
<th>Value</th>
<th>Description</th>
</tr>
<tr>
<td>0</td>
<td>bLength</td>
<td>1</td>
<td>Number</td>
<td>Size of this descriptor.</td>
</tr>
<tr>
<td>1</td>
<td>bDescriptorType</td>
<td>1</td>
<td>Constant</td>
<td>WEBUSB_URL.</td>
</tr>
<tr>
<td>2</td>
<td>bScheme</td>
<td>1</td>
<td>Number</td>
<td>URL scheme prefix.</td>
</tr>
<tr>
<td>3</td>
<td>URL</td>
<td>Variable</td>
<td>String</td>
<td>UTF-8 encoded URL (excluding the scheme prefix).</td>
</tr>
</table>
The <code>bScheme</code> field MUST be one of these values:
<table>
<caption>URL Prefixes</caption>
<tr>
<th>Value</th>
<th>Prefix</th>
</tr>
<tr>
<td>0</td>
<td>"http://"</td>
</tr>
<tr>
<td>1</td>
<td>"https://"</td>
</tr>
<tr>
<td>255</td>
<td>""</td>
</tr>
</table>
The special value <code>255</code> indicates that the entire URL, including
scheme, is encoded in the <code>URL</code> field.
# Device Enumeration # {#enumeration}
<xmp class="idl">
dictionary USBDeviceFilter {
unsigned short vendorId;
unsigned short productId;
octet classCode;
octet subclassCode;
octet protocolCode;
DOMString serialNumber;
};
dictionary USBDeviceRequestOptions {
required sequence<USBDeviceFilter> filters;
};
[Exposed=(DedicatedWorker,SharedWorker,Window), SecureContext]
interface USB : EventTarget {
attribute EventHandler onconnect;
attribute EventHandler ondisconnect;
Promise<sequence<USBDevice>> getDevices();
[Exposed=Window] Promise<USBDevice> requestDevice(USBDeviceRequestOptions options);
};
[Exposed=Window, SecureContext]
partial interface Navigator {
[SameObject] readonly attribute USB usb;
};
[Exposed=(DedicatedWorker,SharedWorker), SecureContext]
partial interface WorkerNavigator {
[SameObject] readonly attribute USB usb;
};
</xmp>
<div class="example">
In this example, we retrieve some devices to include in a UI. When the page is
first loaded, it should check if it already has permission to access any
connected devices by calling {{USB/getDevices()}},
<pre highlight="js">
document.addEventListener('DOMContentLoaded', async () => {
let devices = await navigator.usb.getDevices();
devices.forEach(device => {
// Add |device| to the UI.
});
});
</pre>
After the page is loaded the user may <a>connect</a> or <a>disconnect</a> a
device from their system so script should also register for these events in
order to keep the interface up-to-date,
<pre highlight="js">
navigator.usb.addEventListener('connect', event => {
// Add |event.device| to the UI.
});
navigator.usb.addEventListener('disconnect', event => {
// Remove |event.device| from the UI.
});
</pre>
If this is the first time the user has visited the page then it won't have
permission to access any devices so the page must first call
{{USB/requestDevice()}} while the [=relevant global object=] has a
<a>transient activation</a>. In this case the page supports devices from vendor
<code>0xABCD</code> that carry the vendor-specific subclass <code>0x01</code>,
<pre highlight="js">
let button = document.getElementById('request-device');
button.addEventListener('click', async () => {
let device;
try {
device = await navigator.usb.requestDevice({ filters: [{
vendorId: 0xABCD,
classCode: 0xFF, // vendor-specific
protocolCode: 0x01
}]});
} catch (err) {
// No device was selected.
}
if (device !== undefined) {
// Add |device| to the UI.
}
});
</pre>
</div>
A USB device |device| <dfn data-lt="match a device filter">matches a device
filter</dfn> |filter| if the following steps return <code>match</code>:
1. Let |deviceDesc| be |device|'s <a>device descriptor</a>.
1. If <code>|filter|.{{USBDeviceFilter/vendorId}}</code> is present and
<code>|deviceDesc|.idVendor</code> does not equal
<code>|filter|.{{USBDeviceFilter/vendorId}}</code>, return
<code>mismatch</code>.
1. If <code>|filter|.{{USBDeviceFilter/productId}}</code> is present and
<code>|deviceDesc|.idProduct</code> does not equal
<code>|filter|.{{USBDeviceFilter/productId}}</code>, return
<code>mismatch</code>.
1. If <code>|filter|.{{USBDeviceFilter/serialNumber}}</code> is present then,
let |serialNumber| be the <a>string descriptor</a> with index
<code>|deviceDesc|.iSerialNumber</code>. If |device| returns an error when
requesting |serialNumber| or |serialNumber| is not equal to
<code>|filter|.{{USBDeviceFilter/serialNumber}}</code>, return
<code>mismatch</code>.
1. If <code>|filter|.{{USBDeviceFilter/classCode}}</code> is present and,
for any of |device|'s interface's |interface|, |interface| <a>matches
the interface filter</a> |filter|, return <code>match</code>.
1. If <code>|filter|.{{USBDeviceFilter/classCode}}</code> is present and
<code>|deviceDesc|.bDeviceClass</code> is not equal to
<code>|filter|.{{USBDeviceFilter/classCode}}</code>, return
<code>mismatch</code>.
1. If <code>|filter|.{{USBDeviceFilter/subclassCode}}</code> is present and
<code>|deviceDesc|.bDeviceSubClass</code> is not equal to
<code>|filter|.{{USBDeviceFilter/subclassCode}}</code>, return
<code>mismatch</code>.
1. If <code>|filter|.{{USBDeviceFilter/protocolCode}}</code> is present and
<code>|deviceDesc|.bDeviceProtocol</code> is not equal to
<code>|filter|.{{USBDeviceFilter/protocolCode}}</code>, return
<code>mismatch</code>.
1. Return <code>match</code>.
Note: The steps above treat the <code>bDeviceClass</code>,
<code>bDeviceSubClass</code> and <code>bDeviceProtocol</code> fields of the
<a>device descriptor</a> as though they were part of an <a>interface
descriptor</a> which is also compared against the provided filter.
A USB interface |interface| <dfn data-lt="matches the interface filter">matches
an interface filter</dfn> |filter| if the following steps return
<code>match</code>:
1. Let |desc| be |interface|'s <a>interface descriptor</a>.
1. If <code>|filter|.{{USBDeviceFilter/classCode}}</code> is present and
<code>|desc|.bInterfaceClass</code> is not equal to
<code>|filter|.{{USBDeviceFilter/classCode}}</code>, return
<code>mismatch</code>.
1. If <code>|filter|.{{USBDeviceFilter/subclassCode}}</code> is present and
<code>|desc|.bInterfaceSubClass</code> is not equal to
<code>|filter|.{{USBDeviceFilter/subclassCode}}</code>, return
<code>mismatch</code>.
1. If <code>|filter|.{{USBDeviceFilter/protocolCode}}</code> is present and
<code>|desc|.bInterfaceProtocol</code> is not equal to
<code>|filter|.{{USBDeviceFilter/protocolCode}}</code>, return
<code>mismatch</code>.
1. Return <code>match</code>.
A {{USBDeviceFilter}} |filter|
<dfn data-lt="is not a valid filter">is valid</dfn> if the following steps
return <code>valid</code>:
1. If <code>|filter|.{{USBDeviceFilter/productId}}</code> is present and
<code>|filter|.{{USBDeviceFilter/vendorId}}</code> is not present,
return <code>invalid</code>.
1. If <code>|filter|.{{USBDeviceFilter/subclassCode}}</code> is present and
<code>|filter|.{{USBDeviceFilter/classCode}}</code> is not present,
return <code>invalid</code>.
1. If <code>|filter|.{{USBDeviceFilter/protocolCode}}</code> is present and
<code>|filter|.{{USBDeviceFilter/subclassCode}}</code> is not present,
return <code>invalid</code>.
1. Return <code>valid</code>.
The UA MUST be able to <dfn>enumerate all devices attached to the system</dfn>.
It is, however NOT required to perform this work each time an algorithm
requests an enumeration. The UA MAY cache the result of the first enumeration
it performs and then begin monitoring for device connection and disconnection
events, adding connected devices to its cached enumeration and removing
disconnected devices. This mode of operation is preferred as it reduces the
number of operating system calls made and amount of bus traffic generated by
the {{USB/getDevices()}} and {{USB/requestDevice()}} methods.
The {{USB/onconnect}} attribute is an Event handler IDL attribute for the
<a>connect</a> event type.
The {{USB/ondisconnect}} attribute is an Event handler IDL attribute for the
<a>disconnect</a> event type.
The {{USB/getDevices()}} method, when invoked, MUST return a new {{Promise}} and
run the following steps <a>in parallel</a>:
1. <a>Enumerate all devices attached to the system</a>. Let this result be
|enumerationResult|.
2. Let |devices| be a new empty {{Array}}.
3. For each |device| in |enumerationResult|:
1. If this is the first call to this method, <a>check permissions for
|device|</a>.
2. Search for an element |allowedDevice| in
<code>|storage|.{{USBPermissionStorage/allowedDevices}}</code> where
|device| is in |allowedDevice|@{{[[devices]]}}. If no such element
exists, continue to the next |device|.
3. Add the {{USBDevice}} object representing |device| to |devices|.
4. <a>Resolve</a> |promise| with |devices|.
The {{USB/requestDevice()}} method, when invoked, MUST run the following steps:
1. <a>Request permission to use</a> the following descriptor,
<pre highlight="js">
{
name: "usb"
filters: <var>options</var>.<a idl for="USBDeviceRequestOptions">filters</a>
}
</pre>
Let |permissionResult| be the resulting {{Promise}}.
2. <a>Upon fulfillment</a> of |permissionResult| with |result| run the
following steps:
1. If <code>|result|.{{USBPermissionResult/devices}}</code> is empty,
throw a {{NotFoundError}} and abort these steps.
2. Return <code>|result|.{{USBPermissionResult/devices}}[0]</code>.
To <dfn>request the "usb" permission</dfn>, given a {{USBPermissionStorage}}
|storage|, a {{USBPermissionDescriptor}} |options| and a {{USBPermissionResult}}
|status|, the UA MUST return a new {{Promise}} |promise| and run the following
steps <a>in parallel</a>:
1. For each |filter| in
<code>|options|.{{USBPermissionDescriptor/filters}}</code> if |filter|
<a>is not a valid filter</a> <a>reject</a> |promise| with a {{TypeError}}
and abort these steps.
2. Check that the algorithm was triggered while the [=relevant global object=]
had a <a>transient activation</a>. Otherwise, <a>reject</a> |promise| with
a {{SecurityError}} and abort these steps.
3. Set <code>|status|.{{PermissionStatus/state}}</code> to <code>"ask"</code>.
4. <a>Enumerate all devices attached to the system</a>. Let this result be
|enumerationResult|.
5. Remove devices from |enumerationResult| if they do not <a>match a device
filter</a> in <code>|options|.{{USBPermissionDescriptor/filters}}</code>.
6. Display a prompt to the user requesting they select a device from
|enumerationResult|. The UA SHOULD show a human-readable name for each
device.
7. Wait for the user to have selected a |device| or cancelled the
prompt.
8. If the user cancels the prompt, set
<code>|status|.{{USBPermissionResult/devices}}</code> to an empty
{{FrozenArray}}, <a>resolve</a> |promise| with <code>undefined</code>,
and abort these steps.
9. <a>Add |device| to |storage|</a>.
10. Let |deviceObj| be the {{USBDevice}} object representing |device|.
11. Set <code>|status|.{{USBPermissionResult/devices}}</code> to a new
{{FrozenArray}} containing |deviceObj| as its only element.
12. <a>Resolve</a> |promise| with <code>undefined</code>.
To <dfn data-lt="add device to storage">add an allowed <a>USB device</a></dfn>
|device| to {{USBPermissionStorage}} |storage|, the UA MUST run the following
steps:
1. Search for an element |allowedDevice| in
<code>|storage|.{{USBPermissionStorage/allowedDevices}}</code> where
|device| is in |allowedDevice|@{{[[devices]]}}. If one is found, abort
these steps.
2. Let |vendorId| and |productId| be |device|'s <a>vendor ID</a> and
<a>product ID</a>.
3. Let |serialNumber| be |device|'s <a>serial number</a> if it has one,
otherwise <code>undefined</code>.
6. Append <code>{ vendorId: |vendorId|, productId: |productId|, serialNumber: |serialNumber| }</code>,
with a {{[[devices]]}} internal slot containing a single entry |device| to
<code>|storage|.{{USBPermissionStorage/allowedDevices}}</code>.
To <dfn data-lt="check permissions for device">check permissions for a new
<a>USB device</a></dfn> |device|, given a {{USBPermissionStorage}} |storage|,
the UA MUST run the following steps:
1. Let |vendorId| and |productId| be |device|'s <a>vendor ID</a> and
<a>product ID</a>.
2. Let |serialNumber| be |device|'s if it has one, otherwise
<code>undefined</code>.
3. Search for an element |allowedDevice| in
<code>|storage|.{{USBPermissionStorage/allowedDevices}}</code> where:
* <code>|allowedDevice|.{{AllowedUSBDevice/vendorId}}</code> equals
|vendorId|.
* <code>|allowedDevice|.{{AllowedUSBDevice/productId}}</code> equals
|productId|.
* <code>|allowedDevice|.{{AllowedUSBDevice/serialNumber}}</code> equals
|serialNumber|.
4. If no such element exists, return <code>null</code>.
5. Add |device| to |allowedDevice|@{{[[devices]]}}.
6. Return |allowedDevice|.
To <dfn data-lt="remove device from storage">remove an allowed <a>USB
device</a></dfn> |device|, given a {{USBPermissionStorage}} |storage|,
the UA MUST run the following steps:
1. Search for an element |allowedDevice| in
<code>|storage|.{{USBPermissionStorage/allowedDevices}}</code> where
|device| is in |allowedDevice|@{{[[devices]]}}, if no such element exists,
abort these steps.
2. Remove |allowedDevice| from
<code>|storage|.{{USBPermissionStorage/allowedDevices}}</code>.
## Events ## {#events}
<xmp class="idl">
dictionary USBConnectionEventInit : EventInit {
required USBDevice device;
};
[
Exposed=(DedicatedWorker,SharedWorker,Window),
SecureContext
]
interface USBConnectionEvent : Event {
constructor(DOMString type, USBConnectionEventInit eventInitDict);
[SameObject] readonly attribute USBDevice device;
};
</xmp>
When the UA detects a new <a>USB device</a> |device| connected to the host it
MUST perform the following steps for each script execution environment:
1. Let |storage| be the {{USBPermissionStorage}} object in the current
script execution environment.
2. <a>Check permissions for |device|</a> with |storage| and let
|allowedDevice| be the result.
3. If |allowedDevice| is <code>null</code>, abort these steps.
4. Let |deviceObj| be the {{USBDevice}} object representing |device|.
5. Let |event| be a new {{USBConnectionEvent}}, with the <code>device</code>
attribute set to |deviceObj|.
6. Fire an event named <dfn>connect</dfn> on {{Navigator/usb}}, using |event|
as the event object.
When the UA detects a <a>USB device</a> |device| has been disconnected from the
host it MUST perform the following steps for each script execution environment:
1. Let |storage| be the {{USBPermissionStorage}} object in the current
script execution environment.
2. Search for an element |allowedDevice| in
<code>|storage|.{{USBPermissionStorage/allowedDevices}}</code> where
|device| is in |allowedDevice|@{{[[devices]]}}, if no such element exists,
abort these steps.
3. Remove |device| from |allowedDevice|@{{[[devices]]}}.
4. If <code>|allowedDevice|.{{AllowedUSBDevice/serialNumber}}</code> is
<code>undefined</code> and |allowedDevice|@{{[[devices]]}} is empty remove
|allowedDevice| from
<code>|storage|.{{USBPermissionStorage/allowedDevices}}</code>.
5. Let |device| be the {{USBDevice}} object representing |device|.
6. Let |event| be a new {{USBConnectionEvent}}, with the <code>device</code>
attribute set to |device|.
7. Fire an event named <dfn>disconnect</dfn> on {{Navigator/usb}}, using
|event| as the event object.
# Device Usage # {#device-usage}
<div class="example">
In this example we imagine a data logging device supporting up to 8 16-bit data
channels. It has a single configuration (<code>bConfigurationValue 1</code>)
with a single interface (<code>bInterfaceNumber 1</code>) with a single
bulk endpoint (<code>bEndpointAddress 0x81</code> which means that it is
endpoint 1 and an IN endpoint). When data is sampled it is available on this
endpoint. The maximum packet size on this endpoint is 16 bytes to support all 8
channels being activated at the same time. To save bus bandwidth, however, any
combination of channels can be activated and deactivated. The packet will only
be the length necessary to transmit the data collected.
To get started we open the device, select the first configuration (it only has
one but the operating system may not have already done this during enumeration)
and claim the data logging interface,
<pre highlight="js">
await device.<a idl for="USBDevice" data-lt="open()">open</a>();
if (device.<a idl for="USBDevice">configuration</a> === null)
await device.<a idl for="USBDevice" data-lt="selectConfiguration()">selectConfiguration</a>(1);
await device.<a idl for="USBDevice" data-lt="claimInterface()">claimInterface</a>(1);
</pre>
For this particular application we care about reading from channels 1, 2 and 5
so we issue a <a>control transfer</a> to activate these channels,
<pre highlight="js">
await device.<a idl for="USBDevice" data-lt="controlTransferOut()">controlTransferOut</a>({
<a idl for="USBControlTransferParameters">requestType</a>: '<a idl for="USBRequestType">vendor</a>',
<a idl for="USBControlTransferParameters">recipient</a>: '<a idl for="USBRecipient">interface</a>',
<a idl for="USBControlTransferParameters">request</a>: 0x01, // vendor-specific request: enable channels
<a idl for="USBControlTransferParameters">value</a>: 0x0013, // 0b00010011 (channels 1, 2 and 5)
<a idl for="USBControlTransferParameters">index</a>: 0x0001 // Interface 1 is the recipient
});
</pre>
The application may now start polling the device for data. As we only expect
data from 3 channels we request a 6 byte buffer. As long as we receive a
complete buffer the captured values (transmitted in big endian) are printed to
the console log. If the device has encountered an error and signals this by
stalling the endpoint then the error is cleared before continuing,
<pre highlight="js">
while (true) {
let result = await device.<a idl for="USBDevice" data-lt="transferIn()">transferIn</a>(1, 6);
if (result.<a idl for="USBInTransferResult">data</a> && result.data.byteLength === 6) {
console.log('Channel 1: ' + result.data.getUint16(0));
console.log('Channel 2: ' + result.data.getUint16(2));
console.log('Channel 5: ' + result.data.getUint16(4));
}
if (result.<a idl for="USBInTransferResult">status</a> === 'stall') {
console.warn('Endpoint stalled. Clearing.');
await device.<a idl for="USBDevice" data-lt="clearHalt()">clearHalt</a>(1);
}
}
</pre>
</div>
## The USBDevice Interface ## {#usbdevice-interface}
<xmp class="idl">
enum USBTransferStatus {
"ok",
"stall",
"babble"
};
[
Exposed=(DedicatedWorker,SharedWorker,Window),
SecureContext
]
interface USBInTransferResult {
constructor(USBTransferStatus status, optional DataView? data);
readonly attribute DataView? data;
readonly attribute USBTransferStatus status;
};
[
Exposed=(DedicatedWorker,SharedWorker,Window),
SecureContext
]
interface USBOutTransferResult {
constructor(USBTransferStatus status, optional unsigned long bytesWritten = 0);
readonly attribute unsigned long bytesWritten;
readonly attribute USBTransferStatus status;
};
[
Exposed=(DedicatedWorker,SharedWorker,Window),
SecureContext
]
interface USBIsochronousInTransferPacket {
constructor(USBTransferStatus status, optional DataView? data);
readonly attribute DataView? data;
readonly attribute USBTransferStatus status;
};
[
Exposed=(DedicatedWorker,SharedWorker,Window),
SecureContext
]
interface USBIsochronousInTransferResult {
constructor(sequence<USBIsochronousInTransferPacket> packets, optional DataView? data);
readonly attribute DataView? data;
readonly attribute FrozenArray<USBIsochronousInTransferPacket> packets;
};
[
Exposed=(DedicatedWorker,SharedWorker,Window),
SecureContext
]
interface USBIsochronousOutTransferPacket {
constructor(USBTransferStatus status, optional unsigned long bytesWritten = 0);
readonly attribute unsigned long bytesWritten;
readonly attribute USBTransferStatus status;
};
[
Exposed=(DedicatedWorker,SharedWorker,Window),
SecureContext
]
interface USBIsochronousOutTransferResult {
constructor(sequence<USBIsochronousOutTransferPacket> packets);
readonly attribute FrozenArray<USBIsochronousOutTransferPacket> packets;
};
[Exposed=(DedicatedWorker,SharedWorker,Window), SecureContext]
interface USBDevice {
readonly attribute octet usbVersionMajor;
readonly attribute octet usbVersionMinor;
readonly attribute octet usbVersionSubminor;
readonly attribute octet deviceClass;
readonly attribute octet deviceSubclass;
readonly attribute octet deviceProtocol;
readonly attribute unsigned short vendorId;
readonly attribute unsigned short productId;
readonly attribute octet deviceVersionMajor;
readonly attribute octet deviceVersionMinor;
readonly attribute octet deviceVersionSubminor;
readonly attribute DOMString? manufacturerName;
readonly attribute DOMString? productName;
readonly attribute DOMString? serialNumber;
readonly attribute USBConfiguration? configuration;
readonly attribute FrozenArray<USBConfiguration> configurations;
readonly attribute boolean opened;
Promise<undefined> open();
Promise<undefined> close();
Promise<undefined> forget();
Promise<undefined> selectConfiguration(octet configurationValue);
Promise<undefined> claimInterface(octet interfaceNumber);
Promise<undefined> releaseInterface(octet interfaceNumber);
Promise<undefined> selectAlternateInterface(octet interfaceNumber, octet alternateSetting);
Promise<USBInTransferResult> controlTransferIn(USBControlTransferParameters setup, unsigned short length);
Promise<USBOutTransferResult> controlTransferOut(USBControlTransferParameters setup, optional BufferSource data);
Promise<undefined> clearHalt(USBDirection direction, octet endpointNumber);
Promise<USBInTransferResult> transferIn(octet endpointNumber, unsigned long length);
Promise<USBOutTransferResult> transferOut(octet endpointNumber, BufferSource data);
Promise<USBIsochronousInTransferResult> isochronousTransferIn(octet endpointNumber, sequence<unsigned long> packetLengths);
Promise<USBIsochronousOutTransferResult> isochronousTransferOut(octet endpointNumber, BufferSource data, sequence<unsigned long> packetLengths);
Promise<undefined> reset();
};
</xmp>
Instances of {{USBDevice}} are created with the <a>internal
slots</a> described in the following table:
<table class="data" dfn-for="USBDevice" dfn-type="attribute">
<tr>
<th><a>Internal Slot</a></th>
<th>Initial Value</th>
<th>Description (non-normative)</th>
</tr>
<tr>
<td><dfn>\[[configurations]]</dfn></td>
<td>An empty <a>sequence</a> of {{USBConfiguration}}</code></td>
<td>
All configurations supported by this device.
</td>
</tr>
<tr>
<td><dfn>\[[configurationValue]]</dfn></td>
<td><always set in prose></td>
<td>
The current configuration value of the device.
</td>
</tr>
<tr>
<td><dfn>\[[selectedAlternateSetting]]</dfn></td>
<td>An <a>empty</a> list of <a>integer</a></td>
<td>
The current alternate setting for each interface on the current configuration.
</td>
</tr>
<tr>
<td><dfn>\[[claimedInterface]]</dfn></td>
<td>An <a>empty</a> list of <a>boolean</a></td>
<td>
The claimed status for each interface on the current configuration.
</td>
</tr>
</table>
<div algorithm="find the device descriptor for the connected USB device">
To <dfn>find the device descriptor for the connected USB device</dfn>,
perform the following steps:
1. Let |deviceDescriptor| be the <a>device descriptor</a> of the connected
device by performing <a>Get Descriptor</a> with
<code>DescriptorType</code> set to <code>DEVICE</code>.
1. Return |deviceDescriptor|.
</div>
<div algorithm="find a list of configuration descriptors for the connected USB device">
To <dfn>find a list of configuration descriptors for the connected USB device</dfn>,
perform the following steps:
1. Let |deviceDescriptor| be the result of
<a>finding the device descriptor for the connected USB device</a>.