INTERNET DRAFT James Kempf
Category: Informational Sun Microsystems, Inc.
Title: draft-kempf-2614bis-00.txt Erik Guttman
Date: December 2000 Sun Microsystems, Inc.
Modifications to the SLP API (RFC 2614)
Status of this Memo
This document is an individual contribution for consideration by the
Service Location Working Group of the Internet Engineering Task
Force.
Distribution of this memo is unlimited.
This document is an Internet-Draft and is in full conformance with
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Copyright (C) The Internet Society 2000. All Rights Reserved.
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Abstract
The SLP API been implemented on a few different platforms. Based on
the experience of implementors, some minor changes are necessary to
improve usability. This draft documents those changes.
Table of Contents
1.0 Introduction
2.0 Proposed Changes
3.0 References
4.0 Acknowledgements
5.0 Authors' Addresses
6.0 Full Copyright Statement
1.0 Introduction
The SLP API has been implemented on a few different platforms, and in
the process of implementation, a few problem areas have been
discovered. These are not major changes in function but rather simple
changes that improve usability. The following section documents
changes to RFC 2614 [1].
2.0 Proposed Changes
2.1 Number of SLPAttrCallback() Calls.
If a client calls SLPGetAttrs() to obtain the attributes of a URL,
the current specification leaves it ambiguous how many times the
callback will be called.
In the case of a SrvRqst by URL, only one reply message is necessary;
therefore, SLPAttrCallback() will be called only once with an
attribute list (or none if no list was returned). As with all
callbacks, however, a second call will occur with the errorCode
parameter set to SLP_LAST_CALL, indicating that the callback is
finished.
2.2 SLPFreeURL() Should Be SLPFree()
The description of SLPParseURL() mentions that the memory should be
freed with SLPFreeURL(). The function should be SLPFree().
2.3 SLPGetProperty() Could Cause Memory Leaks
The current definition of SLPGetProperty() requires the client to not
deallocate the returned memory. The assumption here is that the
library holds a pointer to constant memory. However, if the client
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modifies the property with SLPSetProperty() subsequent to obtaining a
pointer, the memory cannot be freed by the library either, because
the client is potentially holding a pointer. This could cause memory
leaks.
As a result, the SLPGetProperty() API changes to:
SLPError SLPGetProperty(const char* propertyName,
char** propertyValue);
Upon return, the propertyValue parameter is set to a pointer to
the property value string, or NULL if the propertyName does not
name a valid SLP property. The application is responsible for
calling SLPFree() on the property to free the memory.
Error codes that are returned: SLP_OK, SLP_MEMORY_ALLOC_FAILED,
SLP_NOT_IMPLEMENTED, or SLP_PARAMETER_BAD. The latter is returned
if the propertyName parameter does not name a valid SLP property.
2.4. Addition of SLPParseAttrs() Function
Parsing of returned attribute list is a function that every API
library client requires and therefore the library should provide some
lightweight support for attribute list parsing. The function
described in the following sections is proposed.
2.4.1. Synopsis
SLPError SLPParseAttrs(const char* pcAttrList,
const char *pcAttrId,
char** ppcAttrVal);
2.4.1. Description
Parses an attribute list to obtain the attribute value of a specified
attribute ID. The attribute value string returned in ppcAttrVal must
be freed with SLPFree(). SLP_PARSE_ERROR is returned if a value for
pcAttrId can not be found.
2.4.2. Parameters
pcAttrList
A character buffer containing a comma separated, null
terminated list of attribute id/value assignments, in SLP wire
format; i.e. "(attr-id=attr-value-list),..." [2].
pcAttrId
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The string indicating which attribute value to return, which
must not be NULL or the empty string ("").
ppcAttrVal
A pointer to a pointer to the buffer to receive attribute
attribute value, returned by the function. The returned memory
should be freed by a call to SLPFree() when no longer needed.
2.4.3. Returns
If no error occurs, the return value is SLP_OK. Otherwise, the
appropriate error code is returned. If this function is not
implemented, the library should return SLP_NOT_IMPLEMENTED. If a
parse error occurs, the library should return SLP_PARSE_ERROR.
2.5 URL Format
RFC 2614 is not explicit about the need for supplying strings having
URL format for all functions that accept service URLs. Text needs to
be added to the appropriate API function definitions making this
explicit. The format is not restricted to the service: URL format,
however the strings must be properly formatted URLs. Otherwise, the
function must return SLP_PARSE_ERROR.
2.6 Configured v.s. Discovered Scope List
Currently, the API has no way for a UA client to distinguish between
configured v.s. discovered scopes. The SLPFindScopes() function
returns all scopes, both configured and discovered. The
net.slp.useScopes property is not well defined. The current text is
ambiguous about whether it contains configured and discovered, or
just configured; and if just configured, then whether DCHP configured
scopes are included as well.
The text in Section 2.1.2 defining net.slp.useScopes should be
rewritten to clarify that net.slp.useScopes contains a list of all
configured scopes, both static and DHCP. The text in Section 4.6.2
and Section 5.5 should be rewritten to clarify that SLPFindScopes()
and ServiceLocationManger.findScopes() return both configured and
discovered scopes.
2.7 Sensible Scope Defaulting Mechanism Required
The current draft requires a programmer to call SLPFindScopes() or
ServiceLocationManager.findScopes() to discover scopes, or retrieve
the net.slp.useScopes property. If the programmer simply wants to
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default to the current set of administrator-configured scopes, there
is no need for the additional function call.
All functions and methods that take a scope string (C) or vector of
scope names (Java) should accept the empty string ("") or empty
vector as meaning "take the default configured scopes from
net.slp.useScopes".
3.0 References
[1] Kempf, J. and Guttman, E., "An API for Service Location", RFC
2614, April, 1999.
[2] Guttman, E., Perkins, C., Veizades, J., and Day, M., "Service
Location Protocol, Version 2", RFC 2608, January, 1999.
4.0 Acknowledgements
Matthew Peterson, of the OpenSLP project at Caldera Systems, provided
the definition for SLPParseAttrs() and suggested cleaning up URL
format and scope handling.
5.0 Authors' Addresses
James Kempf
Sun Labs California
Sun Microsystems, Inc.
901 San Antonio Rd., UMPK15-214
Palo Alto, CA, 94303
USA
Phone: +1 650 786 5890
Fax: +1 650 786 6445
EMail: james.kempf@sun.com
Erik Guttman
Sun Microsystems, Inc.
Eichhoelzelstr. 7
74915 Waibstadt
Germany
Phone: +49 172 865 5497
Fax: +49 7263 911 701
Email: erik.guttman@sun.com
6.0 Full Copyright Statement
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