Open Pluggable Edge Services A. Beck
Internet-Draft Lucent Technologies
Expires: April 26, 2004 A. Rousskov
The Measurement Factory
October 27, 2003
P: Message Processing Language
draft-ietf-opes-rules-p-02
Status of this Memo
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Copyright Notice
Copyright (C) The Internet Society (2003). All Rights Reserved.
Abstract
P is a simple configuration language designed for specification of
message processing instructions at application proxies. P can be used
to instruct an intermediary how to manipulate the application message
being proxied. Such instructions are needed in an Open Pluggable Edge
Services (OPES) context.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Language elements . . . . . . . . . . . . . . . . . . . . . . 7
3.1 Objects . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
3.2 Type conversion . . . . . . . . . . . . . . . . . . . . . . . 8
3.3 Operators . . . . . . . . . . . . . . . . . . . . . . . . . . 8
3.4 Expressions . . . . . . . . . . . . . . . . . . . . . . . . . 11
3.5 Statements . . . . . . . . . . . . . . . . . . . . . . . . . . 11
3.6 Assignments . . . . . . . . . . . . . . . . . . . . . . . . . 12
4. Modules . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
4.1 Interpreter-module interface . . . . . . . . . . . . . . . . . 15
4.2 Modules and namespace . . . . . . . . . . . . . . . . . . . . 15
5. OPES Services . . . . . . . . . . . . . . . . . . . . . . . . 17
6. Failures . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
7. Security Considerations . . . . . . . . . . . . . . . . . . . 20
8. Compliance . . . . . . . . . . . . . . . . . . . . . . . . . . 21
A. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
B. To-do . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
C. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 25
D. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . . 26
Normative References . . . . . . . . . . . . . . . . . . . . . 28
Informative References . . . . . . . . . . . . . . . . . . . . 29
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 29
Intellectual Property and Copyright Statements . . . . . . . . 30
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1. Introduction
The Open Pluggable Edge Services (OPES) architecture
[I-D.ietf-opes-architecture], enables cooperative application
services (OPES services) between a data provider, a data consumer,
and zero or more OPES processors. The application services under
consideration analyze and possibly transform application-level
messages exchanged between the data provider and the data consumer.
OPES processors need to be told what services are to be applied to
what application messages. P language can be used for this
configuration task.
In other words, P language primary objective is to express statements
similar to:
if message meets criteria C,
then apply service S;
Figure 1
Thus, P programs mostly deal with formulating message-dependent
conditions and executing services.
P design attempts to satisfy several conflicting goals:
flexibility: Application intermediaries deal with a wide range of
applications and protocols (SMTP, HTTP, RTSP, IM, etc.). The
language must be able to accommodate virtually all known tasks in
selecting a desired adaptation service for a message of a known
application protocol (and conceivable future applications).
efficiency: Language interpretation must be efficient enough to be
comparable with other message processing overheads at a typical
application proxy (e.g., interpreting HTTP headers to determine
response cachability).
simplicity: Typical configurations must be easy to write and
understand for a typical OPES system administrator.
correctness: Many message handling configurations are written without
direct access to intermediaries that will use those
configurations. The extent of off-line (compile-time) correctness
checks should catch all syntax errors and many common semantic
errors such as undefined values and type conflicts.
compactness: It is possible that some processing instructions will be
piggybacked as headers/metadata to messages they refer to, placing
stringent size requirements on language code.
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security: It should be difficult if not impossible to write malicious
code that would result in security vulnerability of compliant
language interpreter.
While P addresses OPES needs, its design is meant to be applicable
for a variety of similar intermediary configuration tasks such as
access control list (ACL) specification and message routing in proxy
meshes or load-balancing environments.
P design is based on a minimal useful subset of features from several
programming languages such as R (S), Smalltalk, and C++. Technically
speaking, P is a single-assignment, lazy evaluation, strongly typed
functional programming language.
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2. Syntax
P syntax is defined by the following Augmented Backus-Naur Form
(ABNF) [RFC2234]:
code = *statement
statement =
expression-statement /
assignment-statement /
compound-statement /
if-statement /
comment /
";"
if-statement = if-head *if-alt [if-tail]
if-head = "if" "(" expression ")" "{" code "}"
if-alt = "elsif" "(" expression ")" "{" code "}"
if-tail = "else" "{" code "}"
compound-statement = "{" code "}"
assignment = identifier ":=" expression ";"
expression-statement = expression ";"
expression =
constant-expression /
name /
function-call /
"(" expression ")" /
"{" code "}" /
unary-op expression /
expression binary-op expression
constant-expression = boolean / number / string
name = identifier *( "." identifier)
function-call = name "(" [call-parameters] ")"
call-parameters = expression *( "," expression)
identifier = (ALPHA / "_") *(ALPHA / DIGIT / "_")
unary-op =
"+" / "-" /
identifier
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binary-op =
"==" / "!=" /
"<" / ">" / ">=" / "<=" /
"+" / "-" / "*" / "/" / "%" /
identifier
comment = "/*" OCTET "*/" ; no nesting allowed
boolean = "true" / "false"
number = 1*DIGIT ; no leading zeros
string = DQUOTE *string-char DQUOTE
string-char =
%x00-21 / %x23-5B / %x5D-FF / ; any but quote and backslash
escape-sequence ; C++ or XML escape sequence? XXX
Figure 2
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3. Language elements
3.1 Objects
P is centered around the concept of an "object" that is similar to
objects from other object-oriented languages. An object is,
essentially, a piece of data or information. The value of an object
is indistinguishable from the object itself. Object type is defined
by the semantics of applicable operations and manipulations. Almost
everything in P is an object, even a piece of code. Here are a few P
objects, listed one per line:
0
"http://www.ietf.org/"
Core
{ a := 1/0; }
Many objects contain other objects, often called members. Members
are accessible by their name, using the member access operator (".").
Member access operator has a single parameter: the name of the member
to access. All P objects support "." operator, but not all objects
have members. Here are a few examples:
Http.message.headers
Core.interpreter.stop
"string".nosuchmember
Many objects support operators other than member access. For example,
member objects that support function call "()" operator are often
call methods.
Http.message.headers.have(header)
Core.interpreter.stop()
1 / 0
"string" + "string"
P operators are described in Section 3.3. below.
P does not have built-in facilities for describing object types. When
writing a P program, only objects known to interpreter (e.g., Core)
and objects generated by known objects (e.g., Http.message.headers)
can be used. P supports loadable modules that can be used to add
objects to support new application protocols. In fact, P core
supports no application protocols directly. Instead, modules like
"HTTP" can be used to process messages depending on application
protocol being proxied.
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3.2 Type conversion
Interpreters MUST NOT silently convert (cast) object types. When
explicit conversion (casting) is needed objects should provide
polymorphic methods (methods with the same name but different formal
parameter types).
3.3 Operators
Operators are used in P to denote common operations on built-in
object types and language constructs. No operators are defined for
objects provided by modules. P operators do not modify their
operands. Note that all operators may result a failure.
Unary Operators
+--------------+-------------+-------------+------------------------+
| operator | operand | result type | semantics |
| | type | | |
+--------------+-------------+-------------+------------------------+
| + | number | number | returns operand |
| | | | |
| - | number | number | returns zero minus |
| | | | operand |
| | | | |
| import | string | module | imports module members |
| | | | into global namespace |
| | | | and returns a module |
| | | | object that can be |
| | | | used to access this |
| | | | module members |
| | | | explicitly; operand is |
| | | | module identifier, a |
| | | | URI; fails on any |
| | | | error |
| | | | |
| not | boolean | boolean | logical negation |
| | | | |
| try | code | boolean | interpret operand and |
| | | | return true or fail; |
| | | | try is the only |
| | | | operator defined for |
| | | | code; try never |
| | | | returns false |
+--------------+-------------+-------------+------------------------+
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Binary Operators
+-------------+-----------+----------+------------------------------+
| operator | operands | result | semantics |
| | type | type | |
+-------------+-----------+----------+------------------------------+
| == | boolean | boolean | simple value equality |
| | or | | |
| | integer | | |
| | | | |
| != | boolean | boolean | simple value inequality |
| | or number | | |
| | | | |
| < | number | boolean | less than; ">", "<=" and |
| | | | ">=" are defined similarly |
| | | | |
| equal | string | boolean | left string equals right |
| | | | string |
| | | | |
| contains | string | boolean | left contains right |
| | | | |
| begins_with | string | boolean | left string begins with the |
| | | | right string |
| | | | |
| ends_with | string | boolean | left string ends with the |
| | | | right string |
| | | | |
| and | boolean | boolean | short-circuited logical |
| | | | conjunction: the right |
| | | | expression is evaluated only |
| | | | if the left expression is |
| | | | true |
| | | | |
| or | boolean | boolean | short-circuited logical |
| | | | disjunction: the right |
| | | | expression is evaluated only |
| | | | if the left expression is |
| | | | false |
| | | | |
| xor | boolean | boolean | exclusive logical |
| | | | conjunction; cannot be |
| | | | short-circuited: both |
| | | | operands are evaluated |
| | | | |
| otherwise | statement | any | short-circuited failure |
| | | | detection: the right |
| | | | expression is evaluated only |
| | | | if the left expression |
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| | | | fails; returns the value of |
| | | | the last expression |
| | | | evaluated |
| | | | |
| - | number | number | arithmetic difference |
| | | | |
| + | number | number | arithmetic sum |
| | | | |
| + | string | string | concatenation |
| | | | |
| * | number | number | arithmetic product |
| | | | |
| / | number | number | arithmetic ratio; rounded to |
| | | | the closest integer (XXX?) |
| | | | |
| % | number | number | arithmetic modulo |
| | | | |
| . | name | object | object member access; fails |
| | | member | if the object produced by |
| | | | expression on the right does |
| | | | not have the member named by |
| | | | the expression on the left. |
+-------------+-----------+----------+------------------------------+
A function call is an n-ary operator. Besides the function name, it
takes zero or more actual parameters as operands.
All string operators described above are case-sensitive and come with
the corresponding case-insensitive operators: EqualS, ContainS,
Begins_witH, and Ends_witH (XXX: bad idea to name using case?) (XXX:
should we force programmers to pick the right variant instead of
providing efficient, but usually wrong default: contains_s and
contains_i?)
Operator precedence defines natural evaluation order used in
mathematics and many programming languages. In the following list,
operators are ordered based on their precedence. Operators with
smaller precedence index are evaluated first. Operators with the same
precedence index are evaluated in the left-to-right order of
occurrence in an expression.
1. .
2. ()
3. not
4. * /
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5. + -
6. all binary operators on string: equals, contains, ...
7. import
8. == != < <= > >=
9. and
10. or
11. xor (XXX: misplaced?)
12. try (XXX: misplaced?)
13. otherwise
3.4 Expressions
P expressions are used in if-statements to specify the condition for
the if-statement body to be interpreted.
if (Http.request.method == "GET" and time.current() > time.noon) {
...
}
Figure 6
Evaluation of an expression stops when the value of an expression is
known and cannot be changed by further evaluation. This
short-circuiting optimization technique is common to many programming
languages. In the following example, the value of A will never be
interpreted when C is interpreted, regardless of the context where C
is used:
C := false and A;
if (C) { ... };
if (!C) { ... };
...
Figure 7
3.5 Statements
Objects are manipulated using if-statements and function-calls.
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if (Http.request.method == "GET") {
Services.applyOne(serviceFoo);
}
Figure 8
3.6 Assignments
Most procedural programming languages use variables to store
intermediate processing results. In such languages, a variable is
essentially a named piece of memory that can be assigned a value and
can be updated with new values as needed. P does not have such
variables. Instead, P uses a "single assignment" approach: an
expression can be tagged with a name and that name can be reused many
times in the program. On the surface, this is equivalent to having
all "traditional" variables declared as "constant". The following two
if-statements are semantically equivalent in P:
if (Http.request.headers.have(Http.makeHeader("Client-IP"))) {...}
h := Http.makeHeader("Client-IP");
hs := Http.request.headers();
if (hs.have(h)) {...}
Figure 9
If the expression changes, a new name must be used to tag the new
expression. After an assignment statement, the value of the name is
not the value of the expression, but the expression itself. Thus,
the following two code fragments are equivalent and make no sense in
P (the first fragment would make sense in languages such as C++):
h := Http.makeHeader("Client-IP");
h := Http.makeHeader("Server-IP");
h := Http.makeHeader("Client-IP");
Http.makeHeader("Client-IP") := Http.makeHeader("Server-IP");
Figure 10
The interpreter can but does not have to evaluate the expression
named in the assignment statement until the name is actually used in
an expression that requires evaluation (e.g., as a parameter of a
function call statement). This allows for optional performance
optimizations where only used expressions are evaluated.
P does not have user-defined functions. However, some code reuse is
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possible because P code is a valid expression and, hence, can be
named and reused:
code := { ... complicated service action ... };
if (condition1) { code; };
...
if (condition2) { code; };
Figure 11
XXX: document whether expression has to be evaluated in the
assignment context or use context.
Names introduced using assignments have global scope. Global scope
makes it possible to select among alternative values without
user-defined functions or true variables:
if (condition) {
/* no "service" name exists at this point */
service := Services.findOne(uri1);
} else {
/* no "service" name exists at this point */
service := Services.findOne(uri2);
service.authorization(myAuth);
}
Services.applyOne(service); /* service name is still visible */
Figure 12
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4. Modules
Application-specific support is available in P via modules. Module is
an object. Interpreters MUST supply two modules named Core and
Services. The Core module contains members for manipulating built-in
P object types such as integers and strings. The Services module
manages OPES services. Application specific modules can be loaded
into the namespace of a P program via the import operator (see
Section 3.3). For example, the following P code imports an HTTP
module, names the result (the module itself) "Http", and checks for
the presence of a certain HTTP message header:
Http := import "http://ietf.org/opes/rules/p/HTTP";
if (Http.message.headers.have("Accept")) { ... }
Figure 13
It is not possible to import a Core or Services module explicitly.
Instead, interpreters MUST provide access to Core and Services
members as if those modules were imported just before the program
text.
Modules are identified by their URIs [RFC2396]. A module
specification SHOULD contain a globally unique URI for that module.
Module URIs are usually not used to fetch module implementation
remotely, but to identify a suitable local copy of a module; they are
identifiers, not locators. Interpreters maintain a directory of
known-to-them module URIs. When a module needs to be imported, the
interpreter checks internal metadata and loads the requested module
using module-specific interface. If the module is not known or
loading fails, the import operator fails and the failure is
propagated using standard failure propagation rules (see Section 6).
The following example attempts to import one of the SMTP modules.
/* load one of the available SMTP modules */
Smtp := import "http://ietf.org/opes/rules/p/SMTP" otherwise
import "http://examle.org/opes/optimized/SMTPv3";
Figure 14
Import operation has program scope. It is not possible to "unload" an
imported module.
{
M := import "http://ietf.org/opes/rules/p/HTTP";
...
}
/* M and M members are still visible here */
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if (M.connection.is_persistent()) { ... }
Figure 15
4.1 Interpreter-module interface
Most modules are not written in P since the language lacks native
mechanisms for defining module or function interface. Most modules
are tightly integrated with OPES processors because application
adaptation requires access to processor's internal state. For
example, an HTTP intermediary implemented in C++ can use modules
written in C++ and may require that implementors inherit their
modules from a given C++ class. Such modules may be loaded using,
for example, a "dynamically loadable module" mechanism supported by
most modern operating systems. Similarly, a Java OPES processor may
require that all modules implement a given Java interface and use
Java importing mechanism. This specification does not document any
specific interface between an interpreter and third-party modules.
Nevertheless, an interpreter MAY support loading of modules written
in P (similar to C++ #include directives). The interface for
distinguishing URIs of P programs from integrated modules is
implementation-dependent and is not described here. For example, an
interpreter may assume that all unknown module URIs correspond to raw
P programs and attempt to include such a program if the URI scheme is
known to the interpreter:
MyLibrary := import "file://usr/local/lib/globalrules.p";
Figure 16
4.2 Modules and namespace
Members of imported modules belong to the global namespace and are
directly accessible (visible) without the module name prefix. This
simple rule may lead to conflicts when two imported modules contain a
member with the same name. Interpreters MUST fail if any name
resolution is ambiguous. Interpreters MUST NOT use heuristics to
guess programmer's intent. Programmers have to use fully qualified
names to resolve ambiguities.
For example, all of the import statements below pollute global name
space, but the first two provide a way for a programmer to resolve
conflicts, if any:
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/* import HTTP module */
Http := import "http://ietf.org/opes/rules/p/HTTP";
/* import SMTP module */
Smtp := import "http://ietf.org/opes/rules/p/SMTP";
/* import a local file without naming it */
import "file:///usr/local/globalrules.p";
Figure 17
In the following example, both the Http and Smtp modules have the
same member named "message", and the code leads to an ambiguity, even
though Smtp module's message does not have a "method" member:
Smtp := import "http://ietf.org/opes/rules/p/SMTP";
Http := import "http://ietf.org/opes/rules/p/HTTP";
method1 := message.method; /* error: HTTP or SMTP "message"? */
method2 := Http.message.method; /* OK: HTTP "message" */
Figure 18
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5. OPES Services
Services module contains basic attributes and methods for searching
and executing OPES services:
Services.findOne(URI): returns a service object that corresponds to
the specified URI. Fails if no corresponding object exists.
Services.applyOne(service, ...): applies the specified service to the
current application message and optionally supplies
service-specific application parameters. XXX: should parameters
include the part of the message to be modified or just services
metadata?
Here is a service application example for a German to French
translation service:
Http := import("Http");
if (Http.response.language_is("german")) {
service := Services.findOne("opes://svs/tran/german/french");
service.toDialect("southern");
Services.applyOne(service, Http.request.headers);
}
Figure 19
XXX: explain how failures are propagated and can be handled
XXX: add Core.interpreter.stop and Core.interpreter.restart methods.
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6. Failures
Virtually any P statement may fail: expression denominator may be
zero, named members may not exist, functions may not support supplied
parameters, service execution may fail, interpreter may ran out of
resources during an assignment, etc. A failure immediately stops
interpretation of the expression that caused it.
Failure is propagated up the expression and statement stack until the
stack is empty or an "otherwise" alternative is reached (see Section
3.3). If the stack is empty, the entire P program interpretation
terminates with a failure. If an "otherwise" alternative is
encountered, the failure is forgotten and interpretation resumes with
that alternative.
Failure propagation rules allow to catch failures, similar to an
exception mechanisms in languages like C++ or Java, except that P
exceptions are not objects (they carry no information). For example,
here is a simple way to introduce a backup/failover service:
{
...
Services.applyOne(unsafeService);
} otherwise {
...
Services.applyOne(failoverService);
};
Figure 20
The "otherwise" operator makes it simple to select among
failure-prone alternatives:
service := findOne(uri1) otherwise findOne(uri2);
Figure 21
The following example illustrates how a failure-prone service can be
retried twice if needed:
code := {
/* code executing the service */
};
try code otherwise try code otherwise try code;
Figure 22
It is possible to force the interpreter to fail using the
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"Core.interpreter.fail(reason)" call. This is handy when there is a
logical failure that the interpreter cannot detect on its own:
{
/* large piece of code executing several services,
each manipulating the current HTTP message ... */
/* checkpoint */
if (!Http.message.headers.have("Content-Length")) {
Core.interpreter.fail("services did not set CL");
}
/* OK, continue message manipulation ... */
} otherwise {
/* recover from failure ... */
}
Figure 23
This specification has no failure reporting requirements. The extent
and form of failure reporting depends on the environment: Developer
environments would benefit from extensive and detailed reporting of
failures. Stand-alone intermediaries processing P instructions may
benefit from some reporting, appropriately implemented not to bring
down the proxy due to high volume of failures. User environments,
especially mobile and similarly resource-constraint applications
should probably conserve scarce resources and produce no reports by
default.
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7. Security Considerations
XXX: document non-obvious vulnerabilities: too many names, too deep
nesting, invalid math, too much error logging; execution of
unauthorized services, unauthorized exposure of sensitive information
to authorized services.
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8. Compliance
XXX: define what a compliant interpreter is.
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Appendix A. Examples
This appendix contains half-baked examples to illustrate P usage in
common OPES environments. Example themes are taken from
[I-D.beck-opes-irml] to ease the comparison with IRML.
Here is a data provider example:
interpreter.languageVersion("1.0"); // fails if incompatible
Http := import("Http");
lookup(Http);
// Is the requested web document our home page?
isHome := request.uri.looksLikeHome();
// Does the user send us a specific cookie?
cookie := makeHeader("Cookie", "sew=23");
haveCookie := request.headers.have(cookie);
if (isHome and haveCookie) {
Services := import("Services");
service := Services.findOne("opes://local.net/add-lcl-content");
service.clientIp(request.clientIp);
Services.applyOne(service);
}
Figure 24
Here is a data consumer example:
Services := import("Services");
service := Services.findOne("opes://privacy.net/priv-serv");
service.action("remove-referer");
Services.applyOne(service);
Figure 25
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Appendix B. To-do
i18n: What are IETF and real-world internationalization requirements
for languages? Can we say that everything is Unicode UTF-8 and be
done with it? Does UTF have a notion of space characters like
ASCII does? If not, how can we separate grammar tokens without
requiring them to be ASCII?
namespaces: Module lookup facility leads to potential conflicts among
identical names from different modules. What is the best way to
resolve these conflicts? How other languages do it?
security: Write Security Considerations section. A lot can be moved
from the IRML security section. Some can be borrowed from OCP
Core.
module URI: Is there an IETF document that tells us how to assign/
manage URIs for new "things" like modules? For example, do we use
http://ietf.org/opes/http for HTTP module? Or do we use iana.org
domain name instead? Is http:// a good choice for the scheme or
should we use opes:// or even p://?!. Do we use de-facto file://
for local filenames from where raw P code can be included
directly? Note that modules like HTTP are not written in P!
examples: Add more simple but realistic and illustrative examples:
HTTP header anonymization, OPES/HTTP trace entry management (e.g.,
removing trace entries of a given OPES service), removing a virus
attachment from an SMTP message. Ask filtering/ICAP people to
supply use cases.
interpreter API: Document that we do not document interpreter API --
how, for example, an implemented HTTP module is actually "loaded".
Mention that the solution would depend on the interpreter
implementation and the same HTTP module is unlikely to be
compatible with different interpreters.
define interpreter: Add terminology section. Define interpreter to
mean compiler, or run-time interpreter, or bytecode generator, or
anything of that kind.
op keywords: Document that operator names (via identifier BNF entry)
are not keywords: object members can use identifiers that clash
with operator names since there can be no ambiguity.
statement value: Document values of all statements (e.g.,
compound-statement value is the value of the last statement in a
compound)?
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RE: Decide whether we should support regular expression matching
natively.
if-else-if: Make if-else-if syntax compact.
str ==: Remove "==" for strings in examples. There is no such
operator for strings anymore.
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Appendix C. Acknowledgments
The authors gratefully acknowledge contributions of: Anwar M. Haneef
(Motorola) and Geetha Manjunath (Hewlett Packard).
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Appendix D. Change Log
Internal WG revision control IDs: $RCSfile: rules-lang.xml,v $
$Revision: 1.23 $.
2003/10/08
* Added (expression) expression to BNF.
2003/09/22
* Added missing concatenation operator for strings.
2003/09/21
* Explained undocumented relationship between interpreters and
third-party modules.
2003/09/19
* Simplified module importing and lookup facilities. Import is
now a built-in operator and not a Core method. Explicit lookup
control is gone in favor of always-lookup default.
2003/09/18
* Completed syntax BNF except for escape sequences.
* Distinguish interpretation failure from boolean false: use
"otherwise" and "or" operators respectively. With just "or" it
was impossible to say whether, say, "h.has(foo)" failed or "h"
just does not have "foo".
* Use Perl semantics for "otherwise" -- return the value of last
evaluated expression, not true/false.
* Nearly completed a set of supported operators, including
operators for strings.
* Operators should only be supported for built-in objects because
it is difficult to define how "5 + object" is interpreted
without running into problems with "object + object" ("object +
5" is easy but we need symmetry). It is unlikely that we are
losing much with this limitation anyway -- protocol objects
would rarely have good semantics for operators.
* Defined scope rules for new names introduced by assignments.
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* Added Acknowledgments section.
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Normative References
[RFC2234] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", RFC 2234, November 1997.
[RFC2396] Berners-Lee, T., Fielding, R. and L. Masinter, "Uniform
Resource Identifiers (URI): Generic Syntax", RFC 2396,
August 1998.
[I-D.ietf-opes-architecture]
Barbir, A., "An Architecture for Open Pluggable Edge
Services (OPES)", draft-ietf-opes-architecture-04 (work in
progress), December 2002.
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Informative References
[RFC2616] Fielding, R., Gettys, J., Mogul, J., Nielsen, H.,
Masinter, L., Leach, P. and T. Berners-Lee, "Hypertext
Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.
[I-D.beck-opes-irml]
Beck, A. and M. Hofmann, "IRML: A Rule Specification
Language for Intermediary Services",
draft-beck-opes-irml-03 (work in progress), June 2003.
Authors' Addresses
Andre Beck
Lucent Technologies
101 Crawfords Corner Rd.
Holmdel, NJ
US
Phone: +1 732 332-5983
EMail: abeck@bell-labs.com
Alex Rousskov
The Measurement Factory
EMail: rousskov@measurement-factory.com
URI: http://www.measurement-factory.com/
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