FOUNDATION FOR INTELLIGENT PHYSICAL AGENTS
FIPA Agent Message Transport Protocol
for HTTP Specification
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Document title |
FIPA Agent Message Transport Protocol for HTTP Specification |
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Document number |
XC00084E |
Document source |
FIPA TC Agent Management |
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Document status |
Experimental |
Date of this status |
2002/11/01 |
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Supersedes |
None |
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Contact |
fab@fipa.org |
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Change history |
See Informative Annex C — ChangeLog |
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© 1996-2002
Foundation for Intelligent Physical Agents
http://www.fipa.org/
Geneva, Switzerland
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Notice |
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Use of the technologies described in this specification may infringe patents, copyrights or other intellectual property rights of FIPA Members and non-members. Nothing in this specification should be construed as granting permission to use any of the technologies described. Anyone planning to make use of technology covered by the intellectual property rights of others should first obtain permission from the holder(s) of the rights. FIPA strongly encourages anyone implementing any part of this specification to determine first whether part(s) sought to be implemented are covered by the intellectual property of others, and, if so, to obtain appropriate licenses or other permission from the holder(s) of such intellectual property prior to implementation. This specification is subject to change without notice. Neither FIPA nor any of its Members accept any responsibility whatsoever for damages or liability, direct or consequential, which may result from the use of this specification. |
Foreword
The Foundation for Intelligent Physical Agents (FIPA) is an international organization that is dedicated to promoting the industry of intelligent agents by openly developing specifications supporting interoperability among agents and agent-based applications. This occurs through open collaboration among its member organizations, which are companies and universities that are active in the field of agents. FIPA makes the results of its activities available to all interested parties and intends to contribute its results to the appropriate formal standards bodies where appropriate.
The members of FIPA are individually and collectively committed to open competition in the development of agent-based applications, services and equipment. Membership in FIPA is open to any corporation and individual firm, partnership, governmental body or international organization without restriction. In particular, members are not bound to implement or use specific agent-based standards, recommendations and FIPA specifications by virtue of their participation in FIPA.
The FIPA specifications are developed through direct involvement of the FIPA membership. The status of a specification can be either Preliminary, Experimental, Standard, Deprecated or Obsolete. More detail about the process of specification may be found in the FIPA Document Policy [f-out-00000] and the FIPA Specifications Policy [f-out-00003]. A complete overview of the FIPA specifications and their current status may be found on the FIPA Web site.
FIPA is a non-profit association registered in Geneva, Switzerland. As of June 2002, the 56 members of FIPA represented many countries worldwide. Further information about FIPA as an organization, membership information, FIPA specifications and upcoming meetings may be found on the FIPA Web site at http://www.fipa.org/.
Contents
2 Message Transport Protocol for HTTP
4 Informative Annex A — Example
5 Informative Annex B — Notes for Developers
This document deals with message transportation between inter-operating agents and also forms part of the FIPA Agent Management Specification [FIPA00023]. It contains specifications for:
· The transport of messages between agents using the Hypertext Transfer Protocol (HTTP - see [RFC2616]).
This MTP is based on the transfer of data representing the entire agent message including the message envelope in a HTTP request. The HTTP data transfer is a two-step process: the sender makes a HTTP request and after receiving the data the receiver sends a HTTP response. The receiver then parses the message envelope and the message is handled according to the instructions and information given in the message envelope.
The name assigned to this component is:
fipa.mts.mtp.http.std
A HTTP request comprises:
· Request Line
- The request method type that must be POST.
- The request resource identification that must be a full URI (see [RFC1630]).
- The request version that must be HTTP/1.1.
· Request Headers
- The mandatory parameter Content-Type: that must be multipart/mixed and must have a boundary parameter enclosed by double quotes. It should be anticipated that the boundary parameter may be “folded” as described in [RFC2822] – hence parsers must be able to handle this type of encoding.
- The mandatory parameter Host: that must be in the form hostname or hostname:portnumber.
- The mandatory parameter Cache-Control: that must have the value no-cache.
- The mandatory parameter MIME-Version: that must have the value 1.0.
- The optional parameter Content-Length: that contains the size of the request body[1].
· Request Body
The request body contains the agent message. The agent message has two components (separated as defined in [RFC2046] for multipart/mixed MIME content): a FIPA message envelope and a FIPA message body (the payload).
The encoded body must therefore contain at least two parts, the first part containing the FIPA message envelope, the second part containing the FIPA message being sent. Each of the two parts must specify an encoding-level Content-Type field which may be any MIME type (Implementations must assume that some parts of the multipart encoded content may contain raw binary data). Each of the two parts may contain other headers such as, for example, Content-Transfer-Encoding but the processing of these fields is not mandatory.
The charset used in headers and the boundary delimiter of the multipart encoding must be plain ASCII.
Where applicable the charset encoding of the FIPA message must be specified as a charset parameter of the Content-Type header. This charset parameter value must have the same value as the value of the envelope payload-encoding field.
The envelope body encoding must therefore have the following structure:
- MIME headers (at least a MIME-Version header and a Content-Type header that contains the boundary value).
- An empty line delimiting the MIME headers from the MIME body.
- A boundary delimiter line that delimits the beginning of the envelope part.
- A Content-Type header line that must have the value appropriate for the envelope representation: "application" "/" <string>, where the string is the component name given in each envelope specification.
- An empty line (CRLF CRLF).
- The FIPA message envelope.
- A boundary delimiter line that delimits the FIPA envelope from the FIPA message.
- A Content-Type header line that must have the value appropriate for the FIPA message: "application" "/" <string>, where the string is the component name given in each message encoding specification.
- A boundary delimiter line that defines the end of the FIPA message. This boundary line may be a boundary delimiter ending line.
A HTTP response comprises:
· Response Line
The response version must be HTTP/1.1. The response status code must either be the success code or a suitable error code as defined in [RFC2616]. The success code only means that the receiving agent has succeeded in extracting the message content from the HTTP request. More detailed information about non-HTTP related issues such as envelope parsing and message handling should be sent back to the sender agent as a separate message. If a sending MTP receives an error code then the expected behaviour would be to try sending the message using another combination of target resource address and content type or give up. The reason phrase in any error response may be any string and is used only for informational purposes.
· Response Headers
- The mandatory parameter Content-Type: can be any MIME type (see [RFC2045])
- The mandatory parameter Cache-Control: must have the value no-cache, and
- The optional parameter Content-Length: specifies the size of the response body[2].
· Response Body
The response body may contain a message reply and depending on the content type can be text, binary or multipart. The sender is not obliged to read or make use of such content (that is, it should not be relied upon for message transfer).
The default connection behaviour on HTTP version 1.1 is to have a persistent connection which means that after a request-response cycle, the connection is kept open and other requests can be made. However, because this would require a more complex implementation, connection persistence is not mandatory. In the case of a simple MTP implementation that would not support persistence, the Connection: parameter with the value close must be sent in the request headers if the MTP is acting as a sender or in the response headers if the MTP is acting as a receiver.
It should be anticipated that some of the header field values (especially the boundary parameter of the Content-Type request field) are “folded” as described in [RFC2822]. So parsers must be able to handle this type of encoding.
Compliance to the MTP described in this document does not require HTTP 1.1 features that are not explicitly mentioned here.
[FIPA00023] FIPA Agent Management Specification. Foundation for Intelligent Physical Agents, 2000. http://www.fipa.org/specs/fipa00023/
[FIPA00067] FIPA Agent Message Transport Service Specification. Foundation for Intelligent Physical Agents, 2000. http://www.fipa.org/specs/fipa00067/
[RFC2822] Standard
for the Format of ARPA Internet Text Messages. Request for Comments, 2001.
http://www.ietf.org/rfc/rfc2822.txt
[RFC1630] Universal
Resource Identifiers in WWW: A Unifying Syntax for the Expression of Names and
Addresses of Objects on the Network as used in the World Wide Web. Request for
Comments, 1994.
http://www.ietf.org/rfc/rfc1630.txt
[RFC2045] Multipurpose
Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies.
Request for Comments, 1996.
http://www.ietf.org/rfc/rfc2045.txt
[RFC2046] Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types. Request for Comments, 1996.
http://www.ietf.org/rfc/rfc2045.txt
[RFC2616] Hypertext Transfer Protocol - HTTP/1.1.
Request for Comments, 1999.
http://www.ietf.org/rfc/rfc2616.txt
The agent sender@bar.com sends a message to the agent receiver@foo.com which is resident on an AP that has an ACC with an external HTTP interface. Both agents are simple implementations that do not use connection persistence and the message encoding (see [FIPA00085]) that they use is text.
1. sender@bar.com sends a message to receiver@foo.com:
POST http://foo.com:80/acc HTTP/1.1
Cache-Control: no-cache
Host: foo.com:80
Mime-Version: 1.0
Content-Type: multipart-mixed ;
boundary="251D738450A171593A1583EB"
Content-Length: 1518
Connection: close[3]
This is not part of the MIME multipart encoded message.
--251D738450A171593A1583EB
Content-Type: application/fipa.mts.env.rep.xml.std
<?xml version="1.0"?>
<envelope>
<params index="1">
<to>
<agent-identifier>
<name>receiver@foo.com</name>
<addresses>
<url>http://foo.com/acc</url>
</addresses>
</agent-identifier>
</to>
<from>
<agent-identifier>
<name>sender@bar.com</name>
<addresses>
<url>http://bar.com/acc</url>
</addresses>
</agent-identifier>
</from>
<acl-representation>fipa.acl.rep.string.std</acl-representation>
<payload-encoding>US-ASCII</payload-encoding>
<date>20000508T042651481</date>
<received >
<received-by value="http://foo.com/acc"/>
<received-date value="20000508T042651481"/>
<received-id value="123456789"/>
</received>
</params>
</envelope>[4]
--251D738450A171593A1583EB
Content-Type: application/fipa.acl.rep.string.std; charset=US-ASCII
(inform
:sender
(agent-identifier
:name sender@bar.com
:addresses (sequence http://bar.com:80/acc))
:receiver
(agent-identifier
:name receiver@foo.com
:addresses (sequence http://foo.com:80/acc )) )
:content-length 14
:reply-with task1-003
:language fipa-sl0
:ontology planning-ontology-1
:content
"((done task1)))"
--251D738450A171593A1583EB--
2. The ACC responds with a successful notification:
HTTP/1.1 200 OK
Content-Type: text/plain
Cache-Control: no-cache
Connection: close[5]
1. The boundary field is usually “folded” on a new line. So the underlying system should be able to fold/unfold encoded MIME headers and values.
2. In the MIME body before each boundary delimiter there must be a new line separator that is considered to be part of the boundary delimiter. So sections are delimited by the sequence “CRLF--boundary value” (where CRLF are two octets with values of 13 and 10 representing the ASCII characters CR and LF, boundary value is the sequence specified in the Content-Type value as parameter, and -- are two ASCII minus characters).
3. Good implementations will generate random boundary values and will check that none of the encoded parts contains the boundary delimiter sequence.
4. It is possible to have some text before the first boundary delimiter line and after the ending boundary delimiter line, namely a prologue and an epilogue. This text is to be ignored and should be there only to emphasise the boundary delimiters.
5. [RFC2616]: “In the interest of robustness, servers SHOULD ignore any empty line(s) received where a Request-Line is expected. In other words, if the server is reading the protocol stream at the beginning of a message and receives a CRLF first, it should ignore the CRLF.
Certain buggy HTTP/1.0 client implementations generate extra CRLF’s after a POST request. To restate what is explicitly forbidden by the BNF, an HTTP/1.1 client MUST NOT preface or follow a request with an extra CRLF.”
6. In order to facilitate the dynamic discovery of remote platforms, it is recommended, but not strictly mandated, to launch the HTTP MTP server at the following URL (that is, using port 80 and fipa.mts as target):
http://<host name>:80/fipa.mts
Entire document: Changed ContentType header field to Content-Type
Page 3, lines 109-114: Removed paragraph related to MIME boundaries
Page 3, line 118: Changed the envelope part Content-Type to enable use of any FIPA specified envelope encoding
Page 3, line 134: Clarification of the message part of the Content-Type definition
Page 4, lines 176-177: Removed Section 2.3 about envelope encoding
Page 4, lines 179-193: Moved Section 2.4 to Informative Appendix B
Page 4, line 194: Added section from RFC2616 on robustness of processing empty lines
Page 4, line 194: Added note on recommended URL for HTTP MTP
Page 5, lines 199-201: Removed unused reference to FIPA00085
Page 6, line 261: Removed encrypted envelope header field from example
Page 6, line 233: Corrected the Content-Type header field value
Page 6, line 272: Corrected the Content-Type header field value
Page 7, line 288: Added quotes to ACL content