RFC3529
Network Working Group W. Harold Request for Comments: 3529 IBM Category: Experimental April 2003
Using Extensible Markup Language-Remote Procedure Calling
(XML-RPC) in Blocks Extensible Exchange Protocol (BEEP)
Status of this Memo
This memo defines an Experimental Protocol for the Internet community. It does not specify an Internet standard of any kind. Discussion and suggestions for improvement are requested. Distribution of this memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (2003). All Rights Reserved.
Abstract
XML-RPC is an Extensible Markup Language-Remote Procedure Calling protocol that works over the Internet. It defines an XML format for messages that are transfered between clients and servers using HTTP. An XML-RPC message encodes either a procedure to be invoked by the server, along with the parameters to use in the invocation, or the result of an invocation. Procedure parameters and results can be scalars, numbers, strings, dates, etc.; they can also be complex record and list structures.
This document specifies a how to use the Blocks Extensible Exchange Protocol (BEEP) to transfer messages encoded in the XML-RPC format between clients and servers.
6.4 Registration: The System (Well-Known) TCP port number
Appendix
Contents
Introduction
This memo specifies how messages encoded in the XML-RPC [1] format are transmitted using a BEEP profile [2].
Throughout this memo, the terms "request" and "response" refer to the "methodCall" and "methodResponse" elements defined by the XML-RPC specification [1]. Further the terms "peer", "client", "server", and "one-to-one" are used in the context of BEEP. In particular, Sections 2.1 and 2.1.1 of [2] discuss BEEP roles and exchange styles.
BEEP Profile Identification
The BEEP profile for XML-RPC is identified as
http://iana.org/beep/transient/xmlrpc
in the BEEP "profile" element during channel creation.
In BEEP, when the first channel is successfully created, the "serverName" attribute in the "start" element identifies the "virtual host" associated with the peer acting in the server role, e.g.,
<start number='1' serverName='stateserver.example.com'>
<profile uri='http://iana.org/beep/transient/xmlrpc' />
</start>
The "serverName" attribute is analogous to HTTP's "Host" request- header field (c.f., Section 14.23 of [3]).
There are two states in the BEEP profile for XML-RPC, "boot", the profile's initial state, and "ready":
o In the "boot" state, the peer requesting the creation of the
channel sends a "bootmsg" (either during channel initialization or in a "MSG" message).
* If the other peer sends a "bootrpy" (either during channel
initialization or in a "RPY" message), then the "ready" state
is entered
* Otherwise, the other peer sends an "error" (either during
channel initialization or in a "ERR" message), and no state
change occurs.
o In the "ready" state, the initiating peer begins an XML-RPC
message pattern by sending a "MSG" message containing a request. The other peer completes the message pattern by sending back a "RPY" message containing a response.
Profile Initialization
The boot message is used to identify the resource accessed by the channel bound to the BEEP profile for XML-RPC.
The DTD syntax for the boot message and its response are:
<!ELEMENT bootmsg EMPTY>
<!ATTLIST bootmsg
resource CDATA #REQUIRED>
<!ELEMENT bootrpy EMPTY>
The boot message contains a single mandatory attribute: "resource", which is analagous to HTTP's "abs_path" Request-URI parameter (c.f., Section 5.1.2 of [3])
If the peer acting in the server role recognizes the requested resource, it replies with a boot response. Otherwise, if the boot message is improperly formed, or if the requested resource isn't recognized, the peer acting in the server role replies with an error message (c.f., Section 7.1 of [2]).
Typically, the boot message and its response are exchanged during channel initialization (c.f., Section 2.3.1.2 of [2]).
For example, here the boot message and its response are exchanged during channel initialization:
C: <start number='1' serverName='stateserver.example.com'> C: <profile uri='http://iana.org/beep/transient/xmlrpc'> C: <![CDATA[<bootmsg resource='/NumberToName' />]]> C: </profile> C: </start>
S: <profile uri='http://iana.org/beep/transient/xmlrpc'> S: <![CDATA[<bootrpy />]]> S: </profile>
The channel bound to the BEEP profile for XML-RPC is now in the "ready" state.
Alternatively, here is an example in which the boot exchange is unsuccessful:
C: <start number='1' serverName='stateserver.example.com'> C: <profile uri='http://iana.org/beep/transient/xmlrpc'> C: <![CDATA[<bootmsg resource='/NameToCapital' />]]> C: </profile> C: </start>
S: <profile uri='http://iana.org/beep/transient/xmlrpc'> S: <![CDATA[<error code='550'>resource not S: supported</error>]]> S: </profile>
Although the channel was created successfully, it remains in the "boot" state.
XML-RPC Message Packages
The BEEP profile for XML-RPC transmits requests and responses encoded as UTF-8 using the media type "application/xml" [4], e.g.,
I: MSG 1 1 . 0 364 I: Content-Type: application/xml I: I: <?xml version="1.0"?> I: <methodCall> I: <methodName>examples.getStateName</methodName> I: <params> I: <param> I: <value><i4>41</i4></value> I: </param>
I: </params> I: </methodCall> I: END
and its associated response
L: RPY 1 1 . 201 100 L: Content-Type: application/xml L: L: <?xml version="1.0"?> L: <methodResponse> L: <params> L: <param> L: <value><string>South Dakota</string></value> L: </param> L: </params> L: </methodRespose> L: END
XML-RPC Message Exchange
A request/response exchange involves sending a request, which results in a response being returned.
The BEEP profile for XML-RPC achieves this using a one-to-one exchange, in which the client sends a "MSG" message containing an request, and the server sends back a "RPY" message containing an response.
The BEEP profile for XML-RPC does not use the "ERR" message for XML- RPC faults when performing one-to-one exchanges. Whatever response is generated by the server is always returned in the "RPY" message.
URL Schemes
This memo defines two URL schemes, "xmlrpc.beep" and "xmlrpc.beeps", which identify the use of XML-RPC over BEEP over TCP. Note that, at present, a "generic" URL scheme for XML-RPC is not defined.
The xmlrpc.beep URL Scheme
The "xmlrpc.beep" URL scheme uses the "generic URI" syntax defined in Section 3 of [5], specifically:
o the value "xmlrpc.beep" is used for the scheme component; and,
o the server-based naming authority defined in Section 3.2.2 of [5]
is used for the authority component.
o the path component maps to the "resource" component of the boot
message sent during profile initialization (if absent, it defaults to "/").
The values of both the scheme and authority components are case- insensitive.
For example, the URL
xmlrpc.beep://stateserver.example.com/NumberToName
might result in the example shown in Section 2.1.
Resolving IP/TCP Address Information
The "xmlrpc.beep" URL scheme indicates the use of the BEEP profile for XML-RPC running over TCP/IP.
If the authority component contains a domain name and a port number, e.g.,
xmlrpc.beep://stateserver.example.com:1026
then the DNS is queried for the A RRs corresponding to the domain name, and the port number is used directly.
If the authority component contains a domain name and no port number, e.g.,
xmlrpc.beep://stateserver.example.com
the SRV algorithm [6] is used with a service parameter of "xmlrpc- beep" and a protocol parameter of "tcp" to determine the IP/TCP addressing information. If no appropriate SRV RRs are found (e.g., for "_xmlrpc-beep._tcp.stateserver.example.com"), then the DNS is queried for the A RRs corresponding to the domain name and the port number used is assigned by the IANA for the registration in Section 6.4.
If the authority component contains an IP address, e.g.,
xmlrpc.beep://10.0.0.2:1026
then the DNS is not queried, and the IP address is used directly. If a port number is present, it is used directly; otherwise, the port number used is assigned by the IANA for the registration in Section 6.4.
While the use of literal IPv6 addresses in URLs is discouraged, if a literal IPv6 address is used in a "xmlrpc.beep" URL, it must conform to the syntax specified in [7].
The xmlrpc.beeps URL Scheme
The "xmlrpc.beeps" URL scheme is identical, in all ways, to the "xmlrpc.beep" URL scheme specified in Section 5.1, with the exception that prior to starting the BEEP profile for XML-RPC, the BEEP session must be tuned for privacy. In particular, note that both URL schemes use the identical algorithms and parameters for address resolution as specified in Section 5.1.1 (e.g., the same service name for SRV lookups, the same port number for TCP, and so on).
There are two ways to perform privacy tuning on a BEEP session, either:
o a transport security profile may be successfully started; or,
o a user authentication profile that supports transport security may
be successfully started.
In either case the client must present the authority component of the URL in the "serverName" attribute of the "start" element it uses to tune the session for privacy.
When TLS is used for privacy the client must verify that the authority component of the URL matches the server's identity as presented in the server's certificate. Section 2.4 of [9] describes the matching process.
For the URL:
xmlrpc.beeps://stateserver.example.com/NumberToName
the whole process might look like:
S: <wait for incoming connection @ stateserver.example.com> C: <open connection to stateserver.example.com> C: RPY 0 0 . 0 52 C: Content-Type: application/xml C: C: <greeting /> C: END S: RPY 0 0 . 0 110 S: Content-Type: application/xml S: S: <greeting>
S: <profile uri='http://iana.org/beep/TLS' /> S: <profile uri='http://iana.org/beep/SASL/DIGEST-MD5' /> S: </greeting> S: END C: MSG 0 1 . 52 158 C: Content-Type: application/xml C: C: <start number='1' serverName='stateserver.example.com'> C: <profile uri='http://iana.org/beep/TLS'> C: <![CDATA[<ready />]]> C: </profile> C: </start> C: END S: RPY 0 1 . 110 121 S: Content-Type: application/xml S: S: <profile uri='http://iana.org/beep/TLS'> S: <![CDATA[<proceed />]]> S: </profile> S: END
... TLS negotiations ...
S: RPY 0 0 . 0 88 S: Content-Type: application/xml S: S: <greeting> S: <profile uri='http://iana.org/beep/transient/xmlrpc'> S: </greeting> S: END C: RPY 0 0 . 0 52 C: Content-Type: application/xml C: C: <greeting /> C: END
... use the server's certificate to verify that it is
in fact stateserver.example.com ...
C: MSG 0 1 . 112 211 C: Content-Type: application/xml C: C: <start number='3' serverName='stateserver.example.com'> C: <profile uri='http://iana.org/beep/transient/xmlrpc'> C: <![CDATA[<bootmsg resource='/NumberToName' />]]> C: </profile> C: </start> C: END
S: RPY 0 2 . 341 402 S: Content-Type: application/xml S: S: <profile uri='http://iana.org/beep/transient/xmlrpc'> S: <![CDATA[<bootrpy />]]> S: </profile> S: END
Initial Registrations
Registration: The XML-RPC Profile
Profile Identification: http://iana.org/beep/transient/xmlrpc
Messages exchanged during Channel Creation: bootmsg, bootrpy
Messages starting one-to-one exchanges: bootmsg, methodCall
Messages in positive replies: bootrpy, methodResponse
Messages in negative replies: error
Messages in one-to-many exchanges: none
Message Syntax: methodCall, methodResponse as defined in [1]
Message Semantics: c.f., [1]
Contact Information: Ward Harold <[email protected]>
Registration: The xmlrpc.beep URL Scheme
URL scheme name: xmlrpc.beep
URL scheme syntax: c.f., Section 5.1
Character encoding considerations: c.f., the "generic URI" syntax
defined in Section 3 of [5]
Intended usage: identifies a XML-RPC resource made available using
the BEEP profile for XML-RPC
Applications using this scheme: c.f., "Intended usage", above
Interoperability considerations: n/a
Security Considerations: c.f., Section 7
Relevant Publications: c.f., [1], and [2]
Contact Information: Ward Harold <[email protected]>
Author/Change controller: the IESG
Registration: The xmlrpc.beeps URL Scheme
URL scheme name: xmlrpc.beeps
URL scheme syntax: c.f., Section 5.2
Character encoding considerations: c.f., the "generic URI" syntax
defined in Section 3 of [5]
Intended usage: identifies a XML-RPC resource made available using
the BEEP profile for XML-RPC after the BEEP session has been tuned for privacy
Applications using this scheme: c.f., "Intended usage", above
Interoperability considerations: n/a
Security Considerations: c.f., Section 7
Relevant Publications: c.f., [1], and [2]
Contact Information: Ward Harold <[email protected]>
Author/Change controller: the IESG
Registration: The System (Well-Known) TCP port number for XML-RPC
over BEEP
Protocol Number: TCP
Message Formats, Types, Opcodes, and Sequences: c.f., Section 2.1
Functions: c.f., [1]
Use of Broadcast/Multicast: none
Proposed Name: XML-RPC over BEEP
Short name: xmlrpc-beep
Contact Information: Ward Harold <[email protected]>
Security Considerations
Although service provisioning is a policy matter, at a minimum, all implementations must provide the following tuning profiles:
for authentication: http://iana.org/beep/SASL/DIGEST-MD5
for confidentiality: http://iana.org/beep/TLS (using the
TLS_RSA_WITH_3DES_EDE_CBC_SHA cipher)
for both: http://iana.org/beep/TLS (using the
TLS_RSA_WITH_3DES_EDE_CBC_SHA cipher supporting client-side certificates)
Further, implementations may choose to offer MIME-based security services providing message integrity and confidentiality, such as OpenPGP [8] or S/MIME [10].
Regardless, consult [2]'s Section 9 for a discussion of BEEP-specific security issues.
References
[1] Winer, D., "XML-RPC Specification", January 1999,
http://www.xmlrpc.com/spec
[2] Rose, M., "The Blocks Extensible Exchange Protocol Core", RFC
3080, March 2001.
[3] Fielding, R., Gettys, J., Mogul, J., Frystyk, H., Masinter, L.,
Leach, P. and T. Berners-Lee, "Hypertext Transfer Protocol --
HTTP/1.1", RFC 2616, June 1999.
[4] Murata, M., St. Laurent, S. and D. Kohn, "XML Media Types", RFC
3023, January 2001.
[5] Berners-Lee, T., Fielding, R. and L. Masinter, "Uniform Resource
Identifiers (URI): Generic Syntax", RFC 2396, August 1998.
[6] Gulbrandsen, A., Vixie, P. and L. Esibov, "A DNS RR for
specifying the location of services (DNS SRV)", RFC 2782, February 2000.
[7] Hinden, R., Carpenter, B. and L. Masinter, "Format for Literal
IPv6 Addresses in URL's", RFC 2732, December 1999.
[8] Elkins, M., Del Torto, D., Levien, R. and T. Roessler, "MIME
Security with OpenPGP", RFC 3156, August 2001.
[9] Newman, C., "Using TLS with IMAP, POP3 and ACAP", RFC 2595, June
1999.
[10] Ramsdell, B., "S/MIME Version 3 Message Specification", RFC
2633, June 1999.
[11] O'Tuathail, E. and M. Rose, "Using the Simple Object Access
Protocol (SOAP) in Blocks Extensible Exchange Protocol (BEEP)",
RFC 3288, June 2002.
Appendix A. Acknowledgements
This document is based, in part, on Using SOAP in BEEP [11] and the author gratefully acknowledges the contributions of Marshall Rose
Appendix B. IANA Considerations
The IANA has registered the profile specified in Section 6.1, and has selected an IANA-specific URI, e.g.,
http://iana.org/beep/xmlrpc
The IANA has registered "xmlrpc.beep" and "xmlrpc.beeps" as URL schemes, as specified in Section 6.2 and Section 6.3, respectively. (See: http://www.iana.org/assignments/uri-schemes)
The IANA has registered "XML-RPC over BEEP" as a TCP port number (602), as specified in Section 6.4. (See: http://www.iana.org/assignments/port-numbers)
Author's Address
Ward K Harold IBM 11400 Burnet Road Austin, Texas 78759 US
Phone: +1 512 838 3622 EMail: [email protected]
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