XEP-0153: vCard-Based Avatars

1. Introduction
2. Requirements
3. Use Cases
    3.1. User Publishes Avatar
    3.2. Contact Retrieves Avatar
4. Business Rules
    4.1. Inclusion of Update Data in Presence
    4.2. Downloading and Uploading the vCard
    4.3. Multiple Resources
    4.4. Resetting the Image Hash
    4.5. XML Syntax
    4.6. Image Restrictions
5. Implementation Notes
6. Security Considerations
7. IANA Considerations
8. XMPP Registrar Considerations
    8.1. Protocol Namespaces
9. XML Schema
10. Acknowledgements

Appendices
    A: Document Information
    B: Author Information
    C: Legal Notices
    D: Relation to XMPP
    E: Discussion Venue
    F: Requirements Conformance
    G: Notes
    H: Revision History

3.1 User Publishes Avatar

Before informing contacts of the user's avatar, the user's client first publishes the avatar data to the user's public vCard using the protocol defined in vcard-temp (XEP-0054) [3].

Example 1. User's Client Publishes Avatar Data to vCard

<iq from='juliet@capulet.com'
    type='set'
    id='vc1'>
  <vCard xmlns='vcard-temp'>
    <BDAY>1476-06-09</BDAY>
    <ADR>
      <CTRY>Italy</CTRY>
      <LOCALITY>Verona</LOCALITY>
      <HOME/>
    </ADR>
    <NICKNAME/>
    <N><GIVEN>Juliet</GIVEN><FAMILY>Capulet</FAMILY></N>
    <EMAIL>jcapulet@shakespeare.lit</EMAIL>
    <PHOTO>
      <TYPE>image/jpeg</TYPE>
      <BINVAL>
        Base64-encoded-avatar-file-here!
      </BINVAL>
    </PHOTO>
  </vCard>
</iq>

Example 2. User's Server Acknowledges Publish

<iq to='juliet@capulet.com' type='result' id='vc1'/>

Next, the user's client computes the SHA1 hash of the avatar image data itself (not the base64-encoded version) in accordance with RFC 3174 [4]. This hash is then included in the user's presence information. This is done by putting the hash encoded as hexadecimal digits as the XML character data of the <photo/> child of an <x/> element qualified by the 'vcard-temp:x:update' namespace, as shown in the following example:

Example 3. User's Client Includes Avatar Hash in Presence Broadcast

<presence from='juliet@capulet.com/balcony'>
  <x xmlns='vcard-temp:x:update'>
    <photo>01b87fcd030b72895ff8e88db57ec525450f000d</photo>
  </x>
</presence>

Note that while XML Schema defines the canonical representation of hexadecimal values to be upper-case, the historical use throughout the XMPP ecosystem has established lower-case use. Entities need to be able to process both and may prefer to emit lower-case for compatibility.

The user's server then broadcasts that presence information to all contacts who are subscribed to the user's presence information.

3.2 Contact Retrieves Avatar

When the recipient's client receives the hash of the avatar image, it SHOULD check the hash to determine if it already has a cached copy of that avatar image. If not, it retrieves the sender's full vCard in accordance with the protocol flow described in XEP-0054 (note that this request is sent to the user's bare JID, not full JID):

Example 4. Contact's Client Requests User's vCard

<iq from='romeo@montague.net/orchard'
    to='juliet@capulet.com'
    type='get'
    id='vc2'>
  <vCard xmlns='vcard-temp'/>
</iq>

Example 5. Server Returns vCard on Behalf of User

<iq from='juliet@capulet.com'
    to='romeo@montague.net/orchard'
    type='result'
    id='vc2'>
  <vCard xmlns='vcard-temp'>
    <BDAY>1476-06-09</BDAY>
    <ADR>
      <CTRY>Italy</CTRY>
      <LOCALITY>Verona</LOCALITY>
      <HOME/>
    </ADR>
    <NICKNAME/>
    <N><GIVEN>Juliet</GIVEN><FAMILY>Capulet</FAMILY></N>
    <EMAIL>jcapulet@shakespeare.lit</EMAIL>
    <PHOTO>
      <TYPE>image/jpeg</TYPE>
      <BINVAL>
        Base64-encoded-avatar-file-here!
      </BINVAL>
    </PHOTO>
  </vCard>
</iq>

4.1 Inclusion of Update Data in Presence

The following rules apply to inclusion of the update child element (<x xmlns='vcard-temp:x:update'/>) in presence broadcasts:

1. If a client supports the protocol defined herein, it MUST include the update child element in every presence broadcast it sends and SHOULD also include the update child in directed presence stanzas (e.g., directed presence sent when joining Multi-User Chat (XEP-0045) [5] rooms).

2. If a client is not yet ready to advertise an image, it MUST send an empty update child element, i.e.:

   Example 6. User Is Not Ready to Advertise an Image

   <presence>
     <x xmlns='vcard-temp:x:update'/>
   </presence>
   

3. If there is no avatar image to be advertised, the photo element MUST be empty, i.e.:

   Example 7. No Image to be Advertised

   <presence>
     <x xmlns='vcard-temp:x:update'>
       <photo/>
     </x>
   </presence>
   

   If the client subsequently obtains an avatar image (e.g., by updating or retrieving the vCard), it SHOULD then publish a new <presence/> stanza with character data in the <photo/> element.

   Note: This enables recipients to distinguish between the absence of an image (empty photo element) and mere support for the protocol (empty update child).

4.2 Downloading and Uploading the vCard

The following rules apply to downloading and uploading the vCard:

1. A client MUST NOT advertise an avatar image without first downloading the current vCard. Once it has done this, it MAY advertise an image. However, a client MUST advertise an image if it has just uploaded the vCard with a new avatar image. In this case, the client MAY choose not to redownload the vCard to verify its contents.

2. Within a given session, a client MUST NOT attempt to upload a given avatar image more than once. The client MAY upload the avatar image to the vCard on login and after that MUST NOT upload the vCard again unless the user actively changes the avatar image.

3. The client MUST NOT poll for new versions of the user's vCard in order to determine whether to update the avatar image hash.

4.3 Multiple Resources

Jabber/XMPP allows multiple resources to authenticate for the same JID simultaneously. This introduces the potential of conflict between the resources regarding the user's avatar image. The following rules apply when a client receives a presence broadcast from another resource of its own JID:

1. If the presence stanza received from the other resource does not contain the update child element, then the other resource does not support vCard-based avatars. That resource could modify the contents of the vCard (including the photo element); because polling for vCard updates is not allowed, the client MUST stop advertising the avatar image hash. However, the client MAY reset its hash if all instances of non-conforming resources have gone offline.

2. If the presence stanza received from the other resource contains the update child element, then the other resource conforms to the protocol for vCard-based avatars. There are three possible scenarios:

   • If the update child element is empty, then the other resource supports the protocol but does not have its own avatar image. Therefore the client can ignore the other resource and continue to broadcast the existing image hash.

   • If the update child element contains an empty photo element, then the other resource has updated the vCard with an empty BINVAL. Therefore the client MUST retrieve the vCard. If the retrieved vCard contains a photo element with an empty BINVAL, then the client MUST stop advertising the old image.

   • If the update child element contains a non-empty photo element, then the client MUST compare the image hashes. If the hashes are identical, then the client can ignore the other resource and continue to broadcast the existing image hash. If the hashes are different, then the client MUST NOT attempt to resolve the conflict by uploading its avatar image again. Instead, it MUST defer to the content of the retrieved vCard by resetting its image hash (see below) and providing that hash in future presence broadcasts.

4.4 Resetting the Image Hash

Resetting the image hash consists of the following steps:

1. Immediately send out a presence element with an empty update child element (containing no photo element).

2. Download the vCard from the server.

3. If the BINVAL is empty or missing, advertise an empty photo element in future presence broadcasts.

4. If the BINVAL contains image data, calculate the hash of image and advertise that hash in future presence broadcasts.

4.5 XML Syntax

The following rules apply to the XML syntax:

1. The <PHOTO/> element SHOULD contain a <BINVAL/> child whose XML character data is Base64-encoded data for the avatar image.

2. The <PHOTO/> element SHOULD NOT contain an <EXTVAL/> that points to a URI for the image file.

3. The <PHOTO/> element MUST NOT contain the avatar image itself.

4. The <PHOTO/> element SHOULD contain a <TYPE/> child whose XML character data specifies the content-type of the image data. The XML character data SHOULD be "image/gif", "image/jpeg", or "image/png".

5. The <PHOTO/> element MUST NOT possess a 'mime-type' attribute.

4.6 Image Restrictions

The following rules apply to images:

1. The image SHOULD use less than eight kilobytes (8k) of data; this restriction is to be enforced by the publishing client.

2. The image height and width SHOULD be between thirty-two (32) and ninety-six (96) pixels; the recommended size is sixty-four (64) pixels high and sixty-four (64) pixels wide.

3. The image SHOULD be square.

4. The image content type [6] SHOULD be image/gif, image/jpeg, or image/png; support for the "image/png" content type is REQUIRED, support for the "image/gif" and "image/jpeg" content types is RECOMMENDED, and support for any other content type is OPTIONAL.

5. The image data MUST conform to the base64Binary datatype [7] and thus be encoded in accordance with Section 6.8 of RFC 2045 [8], which recommends that base64 data should have lines limited to at most 76 characters in length. However, any whitespace characters (e.g., '\r' and '\n') MUST be ignored.

8.1 Protocol Namespaces

The XMPP Registrar [12] includes 'vcard-temp:x:update' in its registry of protocol namespaces (see <https://xmpp.org/registrar/namespaces.html>).

<?xml version='1.0' encoding='UTF-8'?>

<xs:schema
    xmlns:xs='http://www.w3.org/2001/XMLSchema'
    targetNamespace='vcard-temp:x:update'
    xmlns='vcard-temp:x:update'
    elementFormDefault='qualified'>

  <xs:annotation>
    <xs:documentation>
      The protocol documented by this schema is defined in
      XEP-0153: http://www.xmpp.org/extensions/xep-0153.html
    </xs:documentation>
  </xs:annotation>

  <xs:element name='x'>
    <xs:complexType>
      <xs:sequence>
        <xs:element name='photo' minOccurs='0' type='xs:hexBinary'/>
      </xs:sequence>
    </xs:complexType>
  </xs:element>

</xs:schema>

Peter Saint-Andre

Email: xsf@stpeter.im
JabberID: peter@jabber.org
URI: http://stpeter.im/

Copyright

Permissions

Disclaimer of Warranty

Limitation of Liability

IPR Conformance

1. XEP-0008: IQ-Based Avatars <https://xmpp.org/extensions/xep-0008.html>.

2. XEP-0084: User Avatar <https://xmpp.org/extensions/xep-0084.html>.

3. XEP-0054: vcard-temp <https://xmpp.org/extensions/xep-0054.html>.

4. RFC 3174: US Secure Hash Algorithm 1 (SHA1) <http://tools.ietf.org/html/rfc3174>.

5. XEP-0045: Multi-User Chat <https://xmpp.org/extensions/xep-0045.html>.

6. The IANA registry of content types is located at <http://www.iana.org/assignments/media-types/>.

7. See <http://www.w3.org/TR/xmlschema-2/#base64Binary>.

8. RFC 2045: Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies <http://tools.ietf.org/html/rfc2045>.

9. RFC 6120: Extensible Messaging and Presence Protocol (XMPP): Core <http://tools.ietf.org/html/rfc6120>.

10. RFC 6121: Extensible Messaging and Presence Protocol (XMPP): Instant Messaging and Presence <http://tools.ietf.org/html/rfc6121>.

11. The Internet Assigned Numbers Authority (IANA) is the central coordinator for the assignment of unique parameter values for Internet protocols, such as port numbers and URI schemes. For further information, see <http://www.iana.org/>.

12. The XMPP Registrar maintains a list of reserved protocol namespaces as well as registries of parameters used in the context of XMPP extension protocols approved by the XMPP Standards Foundation. For further information, see <https://xmpp.org/registrar/>.

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