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AbstractThis document is meant to be an illustration of the SOAP 1.2 Protocol Binding Framework applied to a well known internet transport mechanism, Email, specifically rfc2822.
Status of this documentThis document is a NOTE made available by the W3C for discussion only. Publication of this Note by W3C indicates no endorsement of its content by W3C, nor that W3C has, is, or will be allocating any resources to the issues addressed by the Note. This document is a work in progress and may be updated, replaced, or rendered obsolete by other documents at any time.
This document was written by members of the Transport Binding Task Force (TBTF)-- a part of the XML Protocol WG-- on behalf of the XML Protocol WG. The XML Protocol WG agreed to the publication of this document. The XML Protocol WG has no plans for further work on this document.
This version has been published to clarify the status section of the previously published version.
A list of current W3C technical documents can be found at the Technical Reports page.
MotivationThe motivation for this document is to illustrate the SOAP 1.2 Protocol Binding Framework and the creation of an alternative protocol binding specification to the Default HTTP binding. This second binding is meant to validate the Protocol Binding Framework for completeness and usability. Please note that this document is a non-normative description of an Email Binding.
It is not the responsibility of this SOAP binding to mandate a specific email infrastructure, therefore specific email infrastructure protocol commands (such as SMTP, POP3, etc) are not covered in this binding document. The underlying email infrastructure and the associated commands of specific email clients and servers along the message path are outside the scope of this email binding.
Notational ConventionsThe keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALLNOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC2119 [KEYWORDS].
Namespace URIs of the general form "some-URI" represent some application-dependent or context-dependent URI as defined in RFC2396 [URI]. The namespace prefixes "SOAP-ENV" and "ds" used in this document are associated with the namespaces "http://schemas.xmlsoap.org/soap/envelope/" and "http://www.w3.org/2000/09/xmldsig#", respectively.
1 IntroductionThis SOAP binding specification adheres to the SOAP Protocol Binding Framework (see SOAP Protocol Binding Framework), and as such uses abstract properties as a descriptive tool for defining the functionality of certain features.
Properties are named with XML qualified names (QNames). Property values are determined by the Schema type of the property, as defined in the specification which introduces the property. The following tables lists the standard prefix mappings which we assume to hold throughout this specification:
Table 1: Standard prefix mappings Prefix Namespace context http://www.example.org/2001/12/soap/bindingFramework/ExchangeContext/ mep http://www.example.org/2001/12/soap/mep/ fail http://www.example.org/2001/12/soap/mep/FailureReasons/ reqresp http://www.example.org/2001/12/soap/mep/request-response/Email applications MUST use the media type "application/soap+xml" according to [soap-media-type] when including SOAP 1.2 messages in Email exchanges. See [soap-media-type] for parameters defined by this media type and their recommended use.
2 Binding NameThe binding described here is identified with the URI:
http://www.example.org/2002/02/soap/bindings/Email/
This binding is provided as an example binding when using Email and the standard Internet Message Format described in rfc2822. Unlike HTTP, Email does not inherently provide a request/response Message Exchange Operation. An Email message meant to be a response to the original request will be sent back to the original sender. A means of correlating the original request to the resulting response will be descibed as a binding feature.
3 Supported Message Exchange PatternsAn instance of a binding to Email[RFC2822] conforming to this binding specification MUST support the following message exchange pattern:
http://www.example.org/2001/12/soap/mep/request-response/ (see SOAP 1.2, Part 2, 6.2 Request-Response MEP)
Note that although this message exchange pattern permits temporal overlap between a SOAP Request Message and a SOAP Response Message, the store-and-forward nature of Email is such that this circumstance does not arise. This binding specification treats the transmission and reception of SOAP messages as discrete events.
4 Request-Response Message Exchange OperationThe "http://www.w3.org/2002/06/soap/mep/request-response/" message pattern is described in SOAP 1.2, Part 2, 6.2 Request-Response MEP.
For binding instances conforming to this specification:
A SOAP Node instantiated at an email protocol interface (sending and receiving) may take on the role (i.e. the property reqresp:Role) of RequestingSOAPNode.
A SOAP Node instantiated at an email protocol interface (sending and receiving) may take on the role (ie. the property reqresp:Role) of RespondingSOAPNode.
The remainder of this section consists of descriptions of the MEP state machine, and its particular relation to RFC 2822. In the state tables below, the states are defined as values for the property reqresp:State (see SOAP 1.2, Part 2, 6.2 Request-Response MEP), and are of type reqresp:StateType (an enumeration over xsd:string).
Failure reasons as specified in the tables represent values of the property context:FailureReason - their values are QNames. If an implementation enters the "Fail" state, the context:FailureReason property will contain the value specified for the particular transition.
The overall flow of the behaviour of a Requesting SOAP Node follows the outline state machine description contained in SOAP 1.2, Part 2, 6.2 Request-Response MEP. The following subsections describe each state in more detail.
4.1.1 Init Table 2: State Description: Init Statename Init Description Formulate and Send Request Message Preconditons See SOAP 1.2, Part 2, 6.2.3 Request-Response Formal Description Action on Entry Formulate and send Email Request (see Table 3:Email Fields) Post Conditions None Transitions Event/Condition NextState Failure Reason Request Successfully Sent Requesting N/A Failure to send Request Failfail:TransmissionFailure Table 3: Email Fields Field Descriptions Originator and Destination Fields "From:" sender-node-uri CRLF
reqresp:ImmediateSender property of the message exchange context. Request URI The value of the URI carried in the reqresp:ImmediateDestination property of the transport message exchange context. Correlation Request Message ID The Request email msg-id value is automatically generated at the requesting node's email interface. The correlation feature correlation:requestMessageID is described in Section 5.1. Content-Type (MIME) header "application/soap+xml" (see Introduction) Email message body XML 1.0 serialisation of the SOAP message XML Infoset carried in the reqresp:OutboundMessage property of the transport message exchange context. 4.1.2 Sending Table 4:State Description: Sending Statename Sending Description Waiting for correlated Email response(Request Message completely sent on exit from Init state) Preconditons None Post Conditions
Instantiate or replace the property reqresp:ImmediateSender with a URI value that denotes the sender of the Email response (if known)
In all cases, any Email fields that are significant to features expressed outside the SOAP envelope are processed in accordance with the relevant feature specification.
fail:ReceptionFailure 4.1.3 Sending + Receiving
Table 5: State Description: Sending + Receiving State Statename Receiving Description Receive Correlated Email response entity body, which is assumed to contain a SOAP envelope serialized according the XML 1.0 + Namespaces spec. Preconditons None Post Conditions On transitions to Success, instantiate or replace the property reqresp:InboundMessage with an infoset representation of the serialized envelope in the response body. Transitions Event/Condition NextState Failure Reason Well formed Response Message Received Success Reception Failure (broken connections etc.) Fail fail:ReceptionFailure Packaging Failure (inc. mismatched Content-Type) Fail fail:PackagingFailure Malformed Response Message, eg malformed XML, message contained a DTD, an invalid SOAP Envelope Fail fail:BadResponseMessage
4.1.4 Success and Fail
These are the terminal states of for a given instance of a request-response transport message exchange. Control over the transport message exchange context returns to the local SOAP node.
4.2 Behaviour of Responding SOAP NodeThe overall flow of the behaviour of a Requesting SOAP Node follows the outline state machine description contained in SOAP 1.2, Part 2, 6.2 Request-Response MEP.
4.2.1 Init Table 6: State Description: Init Statename Init Description Receive and validate the inbound Request Message Preconditons Delivery of an Email message containing a SOAP envelope serialized according the XML 1.0. Post Conditions None Transitions Event/Condition NextState Action Receive Email message containing well formed Request Message. ReceivingInstantiate or replace the property reqresp:ImmediateSender with a URI value that denotes the sender of the Email message request
Instantiate or replace the property reqresp:InboundMessage with a value that represents an infoset representation of the received Request Message.
Any Email headers that are significant to features expressed outside the SOAP envelope (eg correlation via msg-id) are processed in accordance with the relevant feature specification.
This change of state represents a transfer of control of the inbound transport message exchange context to the local SOAP node.
Receive Email message containing malformed Request Message FailThe message is deemed to have been intended for the local SOAP node, but is deemed badly formed: ill-formed XML, contains a serialized DTD and/or does contain a valid SOAP envelope. The local SOAP node generates SOAP Fault message in accordance with the table below which it sends in the corresponding Email response message.
The transport message exchange context may be destroyed or considered not to have been created.
4.2.2 Receiving Table 7: State Description: Receiving Statename Receiving Description Waiting for Response Message to become available in Message Exchange Context as a result of processing the Request Message (note Request Message fully received on exit from Init state). Preconditons None Post Conditions See Below Transitions Event/Condition NextState Action or Failure Reason A Response Message becomes available in reqresp:OutBoundMessage indicating that the local SOAP node has generated a Response Message. Receiving + Sending reqresp:OutboundMessage MAY contain a SOAP fault.Formulate and send the Response Message (see Table 9: Email Fields)
4.2.3 Receiving + Sending Table 8: State Description: Receiving + Sending Statename Receiving + Sending Description Completing Request Message reception and Response Message transmission. (Response Message sent on exit from Receiving State). Preconditons None Post Conditions See Below Transitions Event/Condition NextState Action or Failure Reason Response Message Successfully sent Success NA Failure to send Response Message Failfail:TransmissionFailure
reqresp:ImmediateSender property of the transport message exchange context. Request URI The value of the URI carried in the reqresp:ImmediateDestination property of the transport message exchange context. Correlation Request Message ID The Request email msg-id carried in the correlation property correlation:requestMessageID is described in Section 5.1. Content-Type (MIME) header "application/soap+xml" (see Introduction) Email message body XML 1.0 serialisation of the SOAP message XML Infoset carried in the reqresp:OutBoundMessage property of the transport message exchange context. 4.2.4 Success and Fail
These are the terminal states of for a given instance of a request-response transport message exchange. From the point-of-view of the local node this message exchange has completed.
5. Features Expressed External to the Message EnvelopeThis transport binding specification defines a binding specific expression for the following features:
http://www.example.org/2001/12/soap/bindings/Email/correlation/
Other features that are compatible with the message exchange patterns listed above are supported using their generic in-envelope expression defined in the relevant feature specification.
5.1 Message Correlation using msg-idThis sub-section defines a binding specific optional feature named:
http://www.example.org/2001/12/soap/binding/Email/correlation/
In the text to follow, the prefix "correlation" is mapped to the URI "http://www.example.org/2001/12/soap/binding/Email/correlation/"
SOAP Requesters using this binding will need a mechanism to correlate response messages to their original, corresponding request message. This binding uses an externalised expression of the correlation feature (email msg-id) to supply this information.
Feature Properties Property Name Descriptioncorrelation:requestMessageID Used to hold the original request email message id, which is automatically generated by the requesting nodes email infrastructure.
The type of this property is String in the namespace http://www.w3.org/2001/XMLSchema-datatypes.
The correlation:requestMessageID property is represented using Email fields. The following table shows the points at which the property value and the Email fields are exchanged.
correlation:requestMessageID The automatically generated correlation:requestMessageID property is sent as the value of the Email field Message-ID. N/A Feature Operation (Server side) Server Property Name Request Response correlation:requestMessageID N/A The original requesting Message-ID correlation:requestMessageID will be returned to the requesting node via the Email field In-Reply-To. 6. SOAP Email Examples
See
SOAP 1.2 Primer, 3.2 SOAP over Email 7. ReferencesRetroSearch is an open source project built by @garambo | Open a GitHub Issue
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