Agent Message Transport Protocol
for HTTP Specification
FIPA Agent Message Transport Protocol for HTTP Specification
FIPA Agent Management
Date of this status
Approved for Experimental
Line numbering added
© 2000 Foundation for Intelligent Physical Agents - http://www.fipa.org/
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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]).
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:
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.
· 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.
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
· 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).
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.
The syntax used for the representation of the FIPA message envelope is that defined in [FIPA00085].
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.
[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.
[RFC822] Standard for the Format of ARPA Internet Text
Messages. Request for Comments, 1982.
[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.
[RFC2045] Multipurpose Internet Mail Extensions
(MIME) Part One: Format of Internet Message Bodies. Request for Comments, 1996.
[RFC2046] Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types. Request for Comments, 1996.
Transfer Protocol - HTTP/1.1. Request for Comments, 1999.
The agent firstname.lastname@example.org sends a message to the agent email@example.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. firstname.lastname@example.org sends a message to email@example.com:
POST http://foo.com:80/acc HTTP/1.1
Content-Type: multipart-mixed ;
This is not part of the MIME multipart encoded message.
<received-by value="http://foo.com/acc" />
<received-date value="20000508T042651481" />
<received-id value="123456789" />
Content-Type: application/text; charset=US-ASCII
:addresses (sequence http://bar.com:80/acc))
:addresses (sequence http://foo.com:80/acc )) )
2. The ACC responds with a successful notification:
HTTP/1.1 200 OK