| Abstract: | This specification defines an XMPP protocol extension that enables any two entities to establish a one-to-one bytestream between themselves, where the data is broken down into smaller chunks and transported in-band over XMPP. |
| Authors: | Justin Karneges, Peter Saint-Andre |
| Copyright: | © 1999 - 2010 XMPP Standards Foundation. SEE LEGAL NOTICES. |
| Status: | Draft |
| Type: | Standards Track |
| Version: | 1.2 |
| Last Updated: | 2009-03-17 |
NOTICE: The protocol defined herein is a Draft Standard of the XMPP Standards Foundation. Implementations are encouraged and the protocol is appropriate for deployment in production systems, but some changes to the protocol are possible before it becomes a Final Standard.
1. Introduction
2. Protocol
2.1. Creating a Bytestream
2.2. Sending Data
2.3. Closing the Bytestream
3. Bidirectionality
4. Use of Message Stanzas
5. Usage Guidelines
6. Security Considerations
7. IANA Considerations
8. XMPP Registrar Considerations
8.1. Protocol Namespaces
9. XML Schema
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
This document describes In-Band Bytestreams (IBB), a simple XMPP protocol extension that enables two entities to establish a virtual bytestream over which they can exchange Base64-encoded chunks of data over XMPP itself. Because IBB provides a generic bytestream, its usage is open-ended. To date it has been used as a fallback method for sending files when out-of-band methods such as SOCKS5 Bytestreams [1] are not available. However, IBB could also be useful for any kind of relatively low-bandwidth activity, such as games, shell sessions, or encrypted communication.
IBB as specified in this document defines two protocol aspects:
Other methods can be used for setup and teardown, such as Jingle [2] as specified in Jingle In-Band Bytestreams Transport Method [3].
In order to set up an in-band bytestream, the initiator sends an IQ stanza of type "set" containing an <open/> element qualified by the 'http://jabber.org/protocol/ibb' namespace. This element possesses three attributes:
Example 1. Initiator requests session
<iq from='romeo@montague.net/orchard'
id='jn3h8g65'
to='juliet@capulet.com/balcony'
type='set'>
<open xmlns='http://jabber.org/protocol/ibb'
block-size='4096'
sid='i781hf64'
stanza='iq'/>
</iq>
If the responder wishes to proceed with the IBB session, it returns an IQ-result to the initiator.
Example 2. Responder accepts session
<iq from='juliet@capulet.com/balcony'
id='jn3h8g65'
to='romeo@montague.net/orchard'
type='result'/>
If the responder does not support IBB, it returns a <service-unavailable/> or <feature-not-implemented/> error.
Example 3. Responder does not support IBB
<iq from='juliet@capulet.com/balcony'
id='jn3h8g65'
to='romeo@montague.net/orchard'
type='error'/>
<error type='cancel'>
<service-unavailable xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
</error>
</iq>
If the responder supports IBB but would prefer a smaller block-size, it returns a <resource-constraint/> error.
Example 4. Responder prefers smaller chunks
<iq from='juliet@capulet.com/balcony'
id='jn3h8g65'
to='romeo@montague.net/orchard'
type='error'/>
<error type='modify'>
<resource-constraint xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
</error>
</iq>
If the responder supports IBB but does not wish to proceed with the session, it returns a <not-acceptable/> error.
Example 5. Responder does not wish to proceed
<iq from='juliet@capulet.com/balcony'
id='jn3h8g65'
to='romeo@montague.net/orchard'
type='error'/>
<error type='cancel'>
<not-acceptable xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
</error>
</iq>
If the responder informs the initiator that it wishes to proceed with the session, the initiator can begin to send data over the bytestream (in addition, because the bytestream is bidirectional, the responder can also send data; see the Bidirectionality section of this document for details).
Each chunk of data is contained in a <data/> element qualified by the 'http://jabber.org/protocol/ibb' namespace. The data element SHOULD be sent in an IQ stanza to enable proper tracking and throttling, but MAY be sent in a message stanza. The data to be sent, prior to any wrapping in the <data/> element and IQ or message stanza, MUST NOT be larger than the 'block-size' determined in the bytestream negotiation.
Example 6. Sending data in an IQ stanza
<iq from='romeo@montague.net/orchard'
id='kr91n475'
to='juliet@capulet.com/balcony'
type='set'>
<data xmlns='http://jabber.org/protocol/ibb' seq='0' sid='i781hf64'>
qANQR1DBwU4DX7jmYZnncmUQB/9KuKBddzQH+tZ1ZywKK0yHKnq57kWq+RFtQdCJ
WpdWpR0uQsuJe7+vh3NWn59/gTc5MDlX8dS9p0ovStmNcyLhxVgmqS8ZKhsblVeu
IpQ0JgavABqibJolc3BKrVtVV1igKiX/N7Pi8RtY1K18toaMDhdEfhBRzO/XB0+P
AQhYlRjNacGcslkhXqNjK5Va4tuOAPy2n1Q8UUrHbUd0g+xJ9Bm0G0LZXyvCWyKH
kuNEHFQiLuCY6Iv0myq6iX6tjuHehZlFSh80b5BVV9tNLwNR5Eqz1klxMhoghJOA
</data>
</iq>
Each chunk of data is included as the XML character data of the <data/> element after being encoded as Base64 as specified in Section 4 of RFC 4648 [4].
The <data/> element MUST possess a 'seq' attribute; this is a 16-bit unsigned integer that acts as a counter for data chunks sent within this session. The 'seq' value starts at 0 (zero) and MUST be incremented for each packet sent. Thus, the second chunk sent has a 'seq' value of 1, the third chunk has a 'seq' value of 2, and so on. The counter loops at maximum, so that after value 65535 the 'seq' MUST start again at 0.
The <data/> element MUST also possess a 'sid' attribute that ties the data chunk to this particular IBB session.
In the case of IQ stanzas, if the packet can be processed then the recipient MUST reply with an IQ stanza of type "result".
Example 7. Acknowledging data using IQ
<iq from='juliet@capulet.com/balcony'
id='kr91n475'
to='romeo@montague.net/orchard'
type='result'/>
The sender need not wait for these acknowledgements before sending further stanzas. However, it is RECOMMENDED that the sender does wait in order to minimize possible rate-limiting penalties.
It is possible that delivery of the stanza might fail, e.g. because the recipient has gone offline or because a server-to-server link has gone down). In this case the entity that detects the error shall return an appropriate XMPP stanza eror, such as <recipient-unavailable/> or <remote-server-timeout/>. Upon receiving notice that delivery of a data packet has failed, the sender MUST consider the bytestream to be closed and invalid.
It is also possible that the recipient might detect an error with the data packet, e.g. because the session ID is unknown, because the sequence number has already been used, or because the data is not formatted in accordance with Section 4 of RFC 4648. In this case the recipient shall return an appropriate XMPP stanza error, such as <item-not-found/>, <unexpected-request/> or <bad-request/>. Upon receiving notice that a data packet cannot be processed by the recipient, the sender SHOULD close the bytestream as described under Closing the Bytestream but MAY attempt to correct the error and re-send the offending data packet using the same sequence number (the recipient MUST NOT consider a sequence number to have been used until the data packet has been successfully processed).
Data packets MUST be processed in the order they are received. If an out-of-sequence packet is received for a particular bytestream (determined by checking the 'seq' attribute), then this indicates that a packet has been lost. The recipient MUST NOT process the data of such an out-of-sequence packet, nor any that follow it within the same bytestream; instead, the recipient MUST close the bytestream as described in the next section.
To close the bytestream, either party sends an IQ-set containing a <close/> element.
Example 8. Closing the bytestream
<iq from='romeo@montague.net/orchard'
id='us71g45j'
to='juliet@capulet.com/balcony'
type='set'>
<close xmlns='http://jabber.org/protocol/ibb' sid='i781hf64'/>
</iq>
The receiving party then acknowledges that the bytestream has been closed by returning an IQ-result.
<iq from='juliet@capulet.com/balcony'
id='us71g45j'
to='romeo@montague.net/orchard'
type='result'/>
It is possible that the recipient of the close notification does not know about the bytestream, in which case it would return an <item-not-found/> error.
Example 10. Recipient does not know about the IBB session
<iq type='error'
from='juliet@capulet.com/balcony'
to='romeo@montague.net/orchard'
id='us71g45j'>
<error type='cancel'>
<item-not-found xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
</error>
</iq>
In either case, the sender MUST consider the bytestream to be closed and invalid.
An in-band bytestream is bidirectional. Therefore, either party to the bytestream is allowed to send data. Each sender MUST initialize the 'seq' attribute to zero and increment the 'seq' value by one with each chunk of data it sends. Each recipient MUST track chunks based on the 'seq' values it receives. The 'seq' values in each direction are independent of the values in the other direction. Thus there are two data sequences for each SessionID.
It is RECOMMENDED to use IQ stanzas when sending data packets. However, an application MAY use message stanzas instead. If message stanzas are used when sending data packets, the sender SHOULD also use Advanced Message Processing [5] or some other stanza flow-control method. For proper tracking of delivery and processing errors related to data packets, the 'id' attribute SHOULD be used with message stanzas.
Example 11. Sending data in a message stanza
<message from='romeo@montague.net/orchard'
id='dsw71gj3'
to='juliet@capulet.com/balcony'>
<data xmlns='http://jabber.org/protocol/ibb' seq='0' sid='i781hf64'>
qANQR1DBwU4DX7jmYZnncmUQB/9KuKBddzQH+tZ1ZywKK0yHKnq57kWq+RFtQdCJ
WpdWpR0uQsuJe7+vh3NWn59/gTc5MDlX8dS9p0ovStmNcyLhxVgmqS8ZKhsblVeu
IpQ0JgavABqibJolc3BKrVtVV1igKiX/N7Pi8RtY1K18toaMDhdEfhBRzO/XB0+P
AQhYlRjNacGcslkhXqNjK5Va4tuOAPy2n1Q8UUrHbUd0g+xJ9Bm0G0LZXyvCWyKH
kuNEHFQiLuCY6Iv0myq6iX6tjuHehZlFSh80b5BVV9tNLwNR5Eqz1klxMhoghJOA
</data>
</message>
The In-Band Bytestreams protocol is as secure as the underlying XMPP transport. The application that uses IBB could have its own security layer, but this is outside of the scope of IBB.
An entity MUST verify any Base64 data received. An implementation MUST reject (not ignore) any characters that are not explicitly allowed by the Base64 alphabet; this helps to guard against creation of a covert channel that could be used to "leak" information. An implementation MUST NOT break on invalid input and MUST reject any sequence of Base64 characters containing the pad ('=') character if that character is included as something other than the last character of the data (e.g., "=AAA" or "BBBB=CCC"); this helps to guard against buffer overflow attacks and other attacks on the implementation. Base encoding visually hides otherwise easily recognized information, such as passwords, but does not provide any computational confidentiality. Base64 encoding MUST follow the definition in Section 4 of RFC 4648.
This document requires no interaction with the Internet Assigned Numbers Authority (IANA) [6].
The XMPP Registrar [7] includes 'http://jabber.org/protocol/ibb' in its registry of XML namespaces at <http://xmpp.org/registrar/namespaces.html>.
<?xml version='1.0' encoding='UTF-8'?>
<xs:schema
xmlns:xs='http://www.w3.org/2001/XMLSchema'
targetNamespace='http://jabber.org/protocol/ibb'
xmlns='http://jabber.org/protocol/ibb'
elementFormDefault='qualified'>
<xs:annotation>
<xs:documentation>
The protocol documented by this schema is defined in
XEP-0047: http://www.xmpp.org/extensions/xep-0047.html
</xs:documentation>
</xs:annotation>
<xs:element name='open'>
<xs:complexType>
<xs:simpleContent>
<xs:extension base='empty'>
<xs:attribute name='block-size' type='xs:unsignedShort' use='required'/>
<xs:attribute name='sid' type='xs:NMTOKEN' use='required'/>
<xs:attribute name='stanza' use='optional' default='iq'>
<xs:simpleType>
<xs:restriction base='xs:NCName'>
<xs:enumeration value='iq'>
<xs:enumeration value='message'/>
</xs:restriction>
</xs:simpleType>
</xs:attribute>
</xs:extension>
</xs:simpleContent>
</xs:complexType>
</xs:element>
<xs:element name='close'>
<xs:complexType>
<xs:simpleContent>
<xs:extension base='empty'>
<xs:attribute name='sid' type='xs:NMTOKEN' use='required'/>
</xs:extension>
</xs:simpleContent>
</xs:complexType>
</xs:element>
<xs:element name='data'>
<xs:complexType>
<xs:simpleContent>
<xs:extension base='xs:string'>
<xs:attribute name='seq' type='xs:unsignedShort' use='required'/>
<xs:attribute name='sid' type='xs:NMTOKEN' use='required'/>
</xs:extension>
</xs:simpleContent>
</xs:complexType>
</xs:element>
<xs:simpleType name='empty'>
<xs:restriction base='xs:string'>
<xs:enumeration value=''/>
</xs:restriction>
</xs:simpleType>
</xs:schema>
Series: XEP
Number: 0047
Publisher: XMPP Standards Foundation
Status:
Draft
Type:
Standards Track
Version: 1.2
Last Updated: 2009-03-17
Approving Body: XMPP Council
Dependencies: XMPP Core
Supersedes: None
Superseded By: None
Short Name: ibb
Schema: <http://www.xmpp.org/schemas/ibb.xsd>
Source Control:
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This document in other formats:
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Email:
justin@affinix.com
JabberID:
justin@andbit.net
Email:
stpeter@jabber.org
JabberID:
stpeter@jabber.org
URI:
https://stpeter.im/
The Extensible Messaging and Presence Protocol (XMPP) is defined in the XMPP Core (RFC 3920) and XMPP IM (RFC 3921) specifications contributed by the XMPP Standards Foundation to the Internet Standards Process, which is managed by the Internet Engineering Task Force in accordance with RFC 2026. Any protocol defined in this document has been developed outside the Internet Standards Process and is to be understood as an extension to XMPP rather than as an evolution, development, or modification of XMPP itself.
The primary venue for discussion of XMPP Extension Protocols is the <standards@xmpp.org> discussion list.
Discussion on other xmpp.org discussion lists might also be appropriate; see <http://xmpp.org/about/discuss.shtml> for a complete list.
Errata can be sent to <editor@xmpp.org>.
The following requirements keywords as used in this document are to be interpreted as described in RFC 2119: "MUST", "SHALL", "REQUIRED"; "MUST NOT", "SHALL NOT"; "SHOULD", "RECOMMENDED"; "SHOULD NOT", "NOT RECOMMENDED"; "MAY", "OPTIONAL".
1. XEP-0065: SOCKS5 Bytestreams <http://xmpp.org/extensions/xep-0065.html>.
2. XEP-0166: Jingle <http://xmpp.org/extensions/xep-0166.html>.
3. XEP-0261: Jingle In-Band Bytestreams Transport Method <http://xmpp.org/extensions/xep-0261.html>.
4. RFC 4648: The Base16, Base32, and Base64 Data Encodings <http://tools.ietf.org/html/rfc4648>.
5. XEP-0079: Advanced Message Processing <http://xmpp.org/extensions/xep-0079.html>.
6. 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/>.
7. 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 <http://xmpp.org/registrar/>.
Note: Older versions of this specification might be available at http://xmpp.org/extensions/attic/
END