SOAP messages are
fundamentally one-way transmissions from a SOAP sender to a SOAP receiver;
however, SOAP messages are often combined to implement patterns such as
request/response.
SOAP implementations
can be optimized to exploit the unique characteristics of particular network
systems. For example, the HTTP binding described in [1](SOAP in HTTP) provides a
request/response message exchange pattern that may be leveraged by SOAP
applications. provides for SOAP response messages to be
delivered as HTTP responses, using the same connection as the inbound request.
SOAP
provides a distributed processing model that assumes
that a SOAP message originates at an initial SOAP sender and is sent to an
ultimate SOAP receiver via zero or more SOAP intermediaries. This section
defines the SOAP distributed processing model. Section 5 defines
a framework for describing how additional features such as routing, reliability
and security fit into the distributed processing model.
A SOAP node can be
the initial SOAP sender, the ultimate SOAP receiver, or a SOAP intermediary, in
which case it is both a SOAP sender and a SOAP receiver. SOAP does not
provide a routing mechanism, however SOAP does recognise that a SOAP sender
originates a SOAP message which is sent to an ultimate SOAP receiver, via zero
or more SOAP intermediaries.
A SOAP node
receiving a SOAP message MUST perform processing according to the SOAP
processing model as described in this section and, if appropriate,
generate SOAP faults, SOAP responses and send additional SOAP messages, as
provided by the remainder of this specification.
In processing a SOAP
message, a SOAP node is said to act in the role of one or more SOAP actors,
each of which is identified by a URI known as the SOAP actor name. Each SOAP
node MUST act in the role of the special SOAP actor named
"http://www.w3.org/2001/12/soap-envelope/actor/next", and can
additionally assume the roles of zero or more other SOAP actors. SOAP
nodes MUST NOT act in the role of the special SOAP actor named
"http://www.w3.org/2001/12/soap-envelope/actor/none". A
SOAP node can establish itself as the ultimate SOAP receiver by acting in the
(additional) role of the anonymous SOAP actor. The roles assumed
MUST be invariant during the processing of an individual SOAP message; because
this specification deals only with the processing of individual SOAP messages,
no statement is made regarding the possibility that a given piece of software
might or might not act in varying roles when processing more than one SOAP
message.
SOAP nodes MUST NOT
act in the role of the special SOAP actor named
"http://www.w3.org/2001/12/soap-envelope/actor/none". Header
blocks targeted to this special actor are carried with the message to the
ultimate receiver, but are never formally "processed". Such blocks
MAY carry data that is required for processing of other blocks.
While the purpose of
a SOAP actor name is to identify a SOAP node, there are no routing or message
exchange semantics associated with the SOAP actor name. For example, SOAP
Actors MAY be named with a URI useable to route SOAP messages to an appropriate
SOAP node. Conversely, it is also appropriate to use SOAP actor roles with
names that are related more indirectly to message routing (e.g.
"http://example.org/banking/anyAccountMgr") or which are unrelated to
routing (e.g. a URI meant to identify "all cache management software";
such a header might be used, for example, to carry an indication to any
concerned software that the containing SOAP message is idempotent, and can
safely be cached and replayed.)
Except for
"http://www.w3.org/2001/12/soap-envelope/actor/next",
and "http://www.w3.org/2001/12/soap-envelope/actor/none"
and the anonymous actor this
specification does not prescribe the criteria by which a given node determines
the (possible empty) set of roles in which
it acts on a given message. For example, implementations can base this
determination on factors including, but not limited to: hardcoded choices in
the implementation, information provided by the transport binding (e.g. the URI
to which the message was physically delivered), configuration information made
by users during system installation, etc.
SOAP header blocks
carry optional actor attribute
information items (see 4.2.2 SOAP actor Attribute)
that are used to target them to the appropriate SOAP node(s). SOAP header
blocks with no such attribute information item are implicitly targeted
at the anonymous SOAP actor, implying that they are to be
processed by the ultimate SOAP receiver. This specification refers
to the (implicit or explicit) value of the SOAP actor attribute as the SOAP actor for the corresponding SOAP
header block.
A SOAP header block
is said to be targeted to a SOAP node if the SOAP actor (if present) on the header
block matches (see [7]) a role played by the SOAP node, or
in the case of a SOAP header block with no actor attribute information item, if the SOAP node is
acting in the role of the ultimate SOAP receiver.
Header
blocks targeted to the special actor
"http://www.w3.org/2001/12/soap-envelope/actor/none" are carried with
the message to the ultimate receiver, but are never formally
"processed". Such blocks MAY carry data that is required for
processing of other blocks.
A SOAP Node that
acts in the role of the anonymous actor with
respect to a particular SOAP message becomes the The
ultimate SOAP recipient of that a SOAP
message. Such a SOAP node is additionally
responsible for processing all parts of the
message intended for the anonymous actor, including the message
body., according to the
rules described in this section. The SOAP message
path for that message ends at the ultimate recipient. However,
the ultimate recipient may delegate all or part of its responsibility to other
entities. The ultimate recipient may happen to use distinct SOAP message exchanges
to interact with such entities. Nevertheless, responsibility for the processing
of parts of a SOAP message targetted at the anonymous actor rests with the
ultimate recipient of that message[1]
It is likely that
specifications for a wide variety of header functions will be developed over
time, and that some SOAP nodes MAY include the software necessary to implement
one or more such extensions. A SOAP header block is said to be understood by a
SOAP node if the software at that SOAP node has been written to fully conform
to and implement the semantics conveyed by the combination of local name and
namespace name of the outer-most element information item of that SOAP
header block.
SOAP header blocks
carry optional mustUnderstand attribute
information items (see 4.2.3 SOAP mustUnderstand
Attribute). When the value of such an attribute information item
is "true" or "1", the SOAP block is said to be mandatory.
For every mandatory
SOAP header block targeted to a node, that node MUST either process the block according
to the semantics conveyed by the combination of local name and namespace name
of the outer-most element information item of that block; or not
process the SOAP message at all, and instead generate a fault (see 2.6 Processing SOAP Messages and 4.4 SOAP Fault).
Mandatory blocks
MUST be presumed to somehow modify the semantics of other headers or body
elements. Tagging SOAP blocks as mandatory thus assures that such changes in
semantics will not be silently (and, presumably, erroneously) ignored
by a SOAP node
to which the header block is targetted.
The mustUnderstand attribute
information item is not intended as a mechanism for detecting errors in
routing, misidentification of nodes, failure of a node to serve in its intended
role(s), etc., any of which may result in a failure to even attempt processing,
and the subsequent removal, of a given SOAP header block from a
SOAP envelope. This specification therefore does not require any fault to be
generated based on the presence or value of this attribute on a SOAP header
block not targeted at the current processing node, for example when it is
suspected that such a block has survived erronously due to a routing or
targeting error at a preceeding intermediairy. In particular, it is not an
error for a mandatory header block targeted to a role other than the ones
assumed by the ultimate SOAP receiver to reach that node without having been
processed.
A SOAP body consists
of zero or more namespace qualified element information items, which
are the immediate children of the Body element
information item. The ultimate SOAP receiver MUST correctly process all
such body elements. However, Part 1 of this specification (this
document) mandates no particular structure or interpretation of such elements,
and provides no standard means for specifying the processing to be done.
When multiple body
elements are present, such elements MAY represent a single unit of work to be
performed, MAY represent multiple separate processing steps, possibly but not
necessarily in order, MAY represent data or metadata, MAY convey a mixture of
work units and data, etc. The ultimate SOAP recipient MAY use the local name(s)
and namespace name(s), on any or all body elements, to determine the processing
to be performed. Indeed, the SOAP RPC convention (see [1]Using SOAP
for RPC) uses just such a method. Conversely, other
information in the body and/or headers MAY be used to make such a
determination.[2]
This section sets
out the rules by which SOAP messages are processed. Unless otherwise stated,
processing must be semantically equivalent to performing the following steps
separately, and in the order given. Note however that nothing in this
specification should be taken to prevent the use of optimistic concurrency,
roll back, or other techniques that might provide increased flexibility in
processing order as long as all SOAP messages, SOAP faults and
application-level side effects are equivalent to those that would be obtained
by direct implementation of the following rules in the order shown below.
1.
Determine the set of roles in which the node is to act.
The contents of the SOAP envelope, including header blocks and the body, MAY be
inspected in making such determination.
2.
Identify all header blocks targeted at the node that are
mandatory.
3.
If one or more of the header blocks identified in the
preceding step are not understood by the node then generate a single SOAP
MustUnderstand fault (see 4.4.6 MustUnderstand Faults).
If such a fault is generated, any further processing MUST NOT be done. Faults
relating to the existence or contents of the body MUST NOT be generated in this
step.[3]
4. Process all
header blocks targeted at the node and, in the case of the ultimate SOAP
recipient, the SOAP body. A SOAP node MUST process all SOAP header blocks
targeted at it. A SOAP node MAY choose to ignore the processing implied by
non-mandatory SOAP header blocks targeted at it.
5.
In the case of a SOAP intermediary, and where
the message is to be forwarded further along the message path, remove all SOAP
header blocks targeted at the node, and possibly insert new SOAP header blocks.
In all cases where a
SOAP header block is processed, the SOAP node must understand the SOAP header
block and must do such processing in a manner fully conformant
with the specification for that block. The ultimate recipient MUST process the
SOAP body, in a manner consistent with 2.5
Structure and Interpretation of SOAP Bodies.
If processing is
unsuccessful, exactly one fault MUST be generated by the node. Header-related
faults other than mustUnderstand faults (see 4.4 SOAP
Fault) MUST be SOAP Sender or DataEncodingUnknown faults (see 4.4.5 SOAP Fault Codes) and MUST conform to the
specification for the corresponding SOAP header block. Faults relating to the
body MUST be SOAP Sender or DataEncodingUnknown faults (see 4.4.5 SOAP Fault Codes)[4].
SOAP nodes can make
reference to any information in the SOAP envelope when processing a SOAP block.
For example, a caching function can cache the entire SOAP message, if desired.
The processing of
particular SOAP header block MAY control or determine the order of processing
for other SOAP header blocks and/or the SOAP body. For example, one could
create a SOAP header block to force processing of other SOAP header blocks in
lexical order. In the absence of such a controlling block, the order of header
and body processing is at the discretion of the SOAP node; header blocks MAY be
processed in arbitrary order, and such processing MAY precede, be interleaved
with, or MAY follow processing of the body. For example, a "begin
transaction" header block would typically precede, a "commit
transaction" would likely follow, and a "logging" function might
run concurrently with body processing.
If the SOAP node is
a SOAP intermediary, the SOAP message pattern and results of processing (e.g.
no fault generated) MAY require that the SOAP message be sent further along the
SOAP message path. Such relayed SOAP messages MUST contain all SOAP header
blocks and the SOAP body from the original SOAP message, in the original order,
except that SOAP header blocks targeted at the SOAP intermediary MUST be
removed (such SOAP blocks are removed regardless of whether they were processed
or ignored). Additional SOAP header blocks MAY be inserted at any point in the
SOAP message, and such inserted SOAP header blocks MAY be indistinguishable
from one or more just removed (effectively leaving them in place, but
emphasizing the need to reinterpret at each SOAP node along the SOAP message
path.)
Note:
The above rules
apply to processing at a single node. SOAP extensions features
MAY be designed to ensure that mandatory (and other) headers are
processed in an appropriate order, as the message moves along the message path
towards the ultimate recipient. Specifically, such extensions features
might specify that a (Sender) fault is generated if some SOAP
header blocks have inadvertently survied past some intended point in the
message path. Such extensions MAY depend on the presence or value of the mustUnderstand attribute
information item in the surviving headers when determining whether an
error has occurred.