FOUNDATION FOR INTELLIGENT PHYSICAL AGENTS

 

 

FIPA Agent Message Transport Protocol
for HTTP Specification

 

 

 

 

 

 

 

 

 

 

© 2000 Foundation for Intelligent Physical Agents - http://www.fipa.org/

Geneva, Switzerland

Notice

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.

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 Procedures for Technical Work. A complete overview of the FIPA specifications and their current status may be found in the FIPA List of Specifications. A list of terms and abbreviations used in the FIPA specifications may be found in the FIPA Glossary.

FIPA is a non-profit association registered in Geneva, Switzerland. As of January 2000, the 56 members of FIPA represented 17countries worldwide. Further information about FIPA as an organization, membership information, FIPA specifications and upcoming meetings may be found at http://www.fipa.org/.

Contents

1     Scope. 3

2     Message Transport Protocol for HTTP. 3

2.1      Component Name. 3

2.2      Interface Definition. 3

2.2.1      Request3

2.2.2      Response. 3

2.2.3      Notes. 3

2.3      Envelope Syntax. 3

2.4      Notes for Developers. 3

2.5      References. 3

3     Informative Annex A — Example. 3

1         Scope

This document is part of the FIPA specifications and deals with message transportation between inter-operating agents. This document also forms part of the FIPA Agent Management Specification [FIPA00023] and contains specifications for:

 

·         The transportation of messages between agents using the Hypertext Transfer Protocol (HTTP - see [RFC2616]).

 

2         Message Transport Protocol for HTTP

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.

 

2.1        Component Name

The name assigned to this component is:

 

fipa.mts.mtp.http.std

 

2.2        Interface Definition

2.2.1          Request

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 [RFC822] – hence parsers must be able to handle this type of encoding.

 

-          The mandatory parameter Host: thatmust 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: thatmust have the value 1.0.

 

-          The optional parameter Content-Length: thatcontains 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 ContentType 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 ContentType header. This charset parameter value must have the same value as the value of the envelope payload-encoding field.

 

The parts encoded in the multipart message body are enclosed between boundary delimiters. The boundary delimiter is formed from the boundary value specified as parameter for the ContentType header. The boundary value must be a sequence of maximum 70 ASCII chars. Each MIME part is to be considered enclosed between two occurrences of the sequence "CRLF--boundary value". The last boundary delimiter must be a boundary delimiter ending line and is formed from the usual boundary delimiter followed by the sequence "--", that is, "CRLF--boundary value--".

 

The envelope body encoding must therefore have the following structure:

 

-          MIME headers  (at least a MIME-Version header and a ContentType 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 ContentType header line that must have the value appropriate for the envelope representation (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 ContentType header line that must have the value appropriate for the FIPA Message representation.

 

-          A boundary delimiter line that defines the end of the FIPA Message. This boundary line MAY be a boundary delimiter ending line.

 

2.2.2          Response

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 (i.e. it should not be relied upon for message transfer).

 

2.2.3          Notes

The default connection behaviour on HTTP version 1.1 is to have persistent connections 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 [RFC822]. 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.

 

2.3       Envelope Syntax

The syntax used for the representation of the FIPA message envelope is that defined in [FIPA00085].

 

2.4       Notes for Developers

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 ContentType 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.

2.5        References

[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/

[FIPA00085]      FIPA Agent Message Transport Envelope Representation in XML. Foundation for Intelligent Physical Agents, 2000.
http://www.fipa.org/specs/fipa00085/

[RFC822]          Standard for the Format of ARPA Internet Text Messages. Request for Comments, 1982.
http://www.ietf.org/rfc/rfc0822.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

 

3         Informative Annex A — Example

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/xml

 

<?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>

 

    <encrypted>no encryption</encrypted>

 

    <received >

      <received-by value="http://foo.com/acc" />

      <received-date value="20000508T042651481" />

      <received-id value="123456789" />

    </received>

  </params>

</envelope>[4]

 

--251D738450A171593A1583EB

Content-Type: application/text; 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]