Commit cc508f6c authored by Stephen Morris's avatar Stephen Morris
Browse files

[2982] Updates to address review comments

parent 77c1644d
......@@ -36,22 +36,22 @@
* Regardless of your field of expertise, you are encouraged to visit
* <a href="http://bind10.isc.org/">BIND10 webpage (http://bind10.isc.org)</a>
*
* @section hookDevelopersGuide
* - @subpage hookIntroduction
* - @subpage hookLanguages
* - @subpage hookTerminology
* - @subpage hookTutorial
* - @subpage hookFrameworkFunctions
* - @subpage hookCallouts
* - @subpage hookExampleCallouts
* - @subpage hookBuild
* - @subpage hookConfiguration
* - @subpage hookAdvancedTopics
* - @subpage hookContextCreateDestroy
* - @subpage hookCalloutRegistration
* - @subpage hookMultipleLibraries
* - @subpage hookInterLibraryData
* - @subpage hookRegisterMultipleLibraries
* @section hooksdgDevelopersGuide
* - @subpage hooksdgIntroduction
* - @subpage hooksdgLanguages
* - @subpage hooksdgTerminology
* - @subpage hooksdgTutorial
* - @subpage hooksdgFrameworkFunctions
* - @subpage hooksdgCallouts
* - @subpage hooksdgExampleCallouts
* - @subpage hooksdgBuild
* - @subpage hooksdgConfiguration
* - @subpage hooksdgAdvancedTopics
* - @subpage hooksdgContextCreateDestroy
* - @subpage hooksdgCalloutRegistration
* - @subpage hooksdgMultipleLibraries
* - @subpage hooksdgInterLibraryData
* - @subpage hooksdgRegisterMultipleLibraries
*
* @section dnsMaintenanceGuide DNS Maintenance Guide
* - Authoritative DNS (todo)
......
......@@ -12,10 +12,14 @@
// OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
// PERFORMANCE OF THIS SOFTWARE.
// Note: the prefix "hooksdg" to all labels is an abbreviation for "Hooks
// Developer's Guide" and is used to prevent a clash with symbols in any
// other Doxygen file.
/**
@page hookDevelopersGuide Hook Developer's Guide
@page hooksdgDevelopersGuide Hook Developer's Guide
@section hookIntroduction Introduction
@section hooksdgIntroduction Introduction
Although the BIND 10 framework and its associated DNS and DHCP programs
provide comprehensive functionality, there will be times when it does
......@@ -31,7 +35,7 @@ understanding how it works will take a significant amount of time. In
addition, despite the fact that its object-oriented design keeps the
coupling between modules to a minimum, an inappropriate change to one
part of the program during the extension could cause another to
behave oddly or to stop working altogether, adding to development time.
behave oddly or to stop working altogether.
- The change may need to be re-applied or re-written with every new
version of BIND 10. As new functionality is added or bugs are fixed,
......@@ -39,59 +43,59 @@ the code or algorithms in the core software may change - and may change
significantly.
To overcome these problems, BIND 10 provides the "Hooks" interface -
a defined interface for third-party or user-written code (for ease of
reference in the rest of this document, such code will be referred to
as "user-written code"). At specific points in its processing ("hook
points") BIND 10 will make a call to this code. The call passes data
that the user can examine and, if required, modify. BIND 10 used the
modified code in the remainder of its processing.
In order to minimise the interaction between BIND 10 and the
a defined interface for third-party or user-written code. (For ease of
reference in the rest of this document, all such code will be referred
to as "user code".) At specific points in its processing
("hook points") BIND 10 will make a call to this code. The call passes
data that the user code can examine and, if required, modify.
BIND 10 uses the modified data in the remainder of its processing.
In order to minimise the interaction between BIND 10 and the user
code, the latter is built independently of BIND 10 in the form of
a shared library (or libraries). These are made known to BIND 10
through its configuration mechanism, and BIND 10 loads the library at
run time. Libraries can be unloaded and reloaded as needed while BIND
10 is running.
Use of a defined API and BIND 10 configuration mechanism means that as
new versions of BIND 10 are released, there is no need to modify the
user-written code. Unless there is a major change in an interface
(which will be clearly documented) all that will be required is a
rebuild of the libraries.
Use of a defined API and the BIND 10 configuration mechanism means that
as new versions of BIND 10 are released, there is no need to modify
the user code. Unless there is a major change in an interface
(which will be clearly documented), all that will be required is a rebuild
of the libraries.
@note Although the defined interface should not change, the internals
of some of the classes and structures referenced by the user-written
code may alter. These changes will need to be reflected in the compiled
version of the software, hence the need for a rebuild.
of some of the classes and structures referenced by the user code may
change between versions of BIND 10. These changes have to be reflected
in the compiled version of the software, hence the need for a rebuild.
@subsection hookLanguages Languages
@subsection hooksdgLanguages Languages
The core of BIND 10 is written in C++. While it is the intention to
provide interfaces into user code written into other languages, the
initial versions of the Hooks system requires that user code be written
in C++. All examples in this guide are in that language.
provide interfaces into user code written in other languages, the initial
versions of the Hooks system requires that user code be written in C++.
All examples in this guide are in that language.
@subsection hookTerminology Terminology
@subsection hooksdgTerminology Terminology
In the remainder of this guide, the following terminology is used:
- Hook/Hook Point - used interchageably, this is a point in the code at
which a call to user-written functions is made. Each hook has a name and
each hook can have any number (including 0) of user-written functions
which a call to user functions is made. Each hook has a name and
each hook can have any number (including 0) of user functions
attached to it.
- Callout - a user-written function called by the server at a hook
- Callout - a user function called by the server at a hook
point. This is so-named because the server "calls out" to the library
to execute a user-written function.
to execute a user function.
- Framework function - the functions that a user-written library needs to
supply in order for the hooks framework for load and unload the library.
- Framework function - the functions that a user library needs to
supply in order for the hooks framework to load and unload the library.
- User code/user library - non-BIND 10 code that is compiled into a
shared library and loaded by BIND 10 into its address space.
@section hookTutorial Tutorial
@section hooksdgTutorial Tutorial
To illustrate how to write code that integrates with BIND 10, we will
use the following (rather contrived) example:
......@@ -103,14 +107,14 @@ IPv4 addresses according to their hardware address, and want to log both
the hardware address and allocated IP address for the clients of interest.
The following sections describe how to implement these requirements.
The code presented here is not efficient and there are better ways
of doing the task. The aim is to illustrate the main features of
user-written hook code rather than provide an optimal solution.
The code presented here is not efficient and there are better ways of
doing the task. The aim however, is to illustrate the main features of
user hook code not to provide an optimal solution.
@subsection hookFrameworkFunctions Framework Functions
@subsection hooksdgFrameworkFunctions Framework Functions
Loading an initializing a library holding user-written code makes use
Loading and initializing a library holding user code makes use
of three (user-supplied) functions:
- version - defines the version of BIND 10 code with which the user-library
......@@ -118,10 +122,10 @@ is built
- load - called when the library is loaded by the server.
- unload - called when the library is unloaded by the server.
Of these, only "version" is mandatory, although our in out example, all three
Of these, only "version" is mandatory, although our in our example, all three
are used.
@subsubsection hookVersionFunction The "version" Function
@subsubsection hooksdgVersionFunction The "version" Function
"version" is used by the hooks framework to check that the libraries
it is loading are compatible with the version of BIND 10 being run.
......@@ -129,14 +133,14 @@ Although the hooks system allows BIND 10 and user code to interface
through a defined API, the relationship is somewhat tight in that the
user code will depend on the internal structures of BIND 10. If these
change - as they can between BIND 10 releases - and BIND 10 is run with
a version of user-written code built against an earlier version of BIND
a version of user code built against an earlier version of BIND
10, a program crash could result.
To guard against this, the "version" function must be provided in
every library. It returns a constant defined in the version of header
files against which it was built. The hooks framework checks this for
compatibility with the running version of BIND 10 before proceeding with
the library load.
To guard against this, the "version" function must be provided in every
library. It returns a constant defined in header files of the version
of BIND 10 against which it was built. The hooks framework checks this
for compatibility with the running version of BIND 10 before loading
the library.
In this tutorial, we'll put "version" in its own file, version.cc. The
contents are:
......@@ -155,10 +159,11 @@ int version() {
};
@endcode
The file "hooks/hooks.h" is specified relative to the BIND 10 libraries source
directory - this is covered later in the section @ref hookBuild. It defines the
symbol BIND10_HOOKS_VERSION, which has a value that changes on every release
of BIND 10: this is the value that needs to be returned to the hooks framework.
The file "hooks/hooks.h" is specified relative to the BIND 10 libraries
source directory - this is covered later in the section @ref hooksdgBuild.
It defines the symbol BIND10_HOOKS_VERSION, which has a value that changes
on every release of BIND 10: this is the value that needs to be returned
to the hooks framework.
A final point to note is that the definition of "version" is enclosed
within 'extern "C"' braces. All functions accessed by the hooks
......@@ -166,31 +171,36 @@ framework use C linkage, mainly to avoid the name mangling that
accompanies use of the C++ compiler, but also to avoid issues related
to namespaces.
@subsubsection hookLoadUnloadFunctions The "load" and "unload" Functions
@subsubsection hooksdgLoadUnloadFunctions The "load" and "unload" Functions
As the names suggest, "load" is called when a library is loaded and
"unload" called when it is unloaded. (It is always guaranteed that "load"
is called: "unload" may not be called in some circumstances, e.g. if the
system shuts down abnormally.) These functions are the places where any
library-wide resources are allocated and deallocated. "load" is also
the place where any callouts with non-standard names can be registered:
this is covered further in the section @ref hookCalloutRegistration.
"unload" called when it is unloaded. (It is always guaranteed that
"load" is called: "unload" may not be called in some circumstances,
e.g. if the system shuts down abnormally.) These functions are the
places where any library-wide resources are allocated and deallocated.
"load" is also the place where any callouts with non-standard names
(names that are not hook point names) can be registered:
this is covered further in the section @ref hooksdgCalloutRegistration.
The example does not make any use callouts with non-standard names. However,
as our design requires that the log file be open while BIND 10 is active
and the library loaded, we'll open the file in the "load" function and close
it in "unload". We create two files, one for the file handle declaration:
it in "unload".
We create two files, one for the file handle declaration:
@code
// library_common.h
#ifndef LIBRARY_COMMON_H
#define LIBRARY_COMMON_H
#include <fstream>
// "Interesting clients" log file handle declaration.
extern std::fstream interesting;
#endif
#endif // LIBRARY_COMMON_H
@endcode
... and one to hold the "load" and "unload" functions:
......@@ -227,37 +237,40 @@ Notes:
outside of any function. This means it can be accessed by any function
within the user library. For convenience, the definition is in the
load_unload.cc file.
- "load" is called with a LibraryHandle argument, used in the registration
of functions. As no functions are being called in this example,
the argument specification omits the variable name (whilst retaining the type)
to avoid an "unused variable" compiler warning. (The LibraryHandle is
discussed in the section @ref hookLibraryHandle.)
- "load" is called with a LibraryHandle argument, this being used in
the registration of functions. As no functions are being registered
in this example, the argument specification omits the variable name
(whilst retaining the type) to avoid an "unused variable" compiler
warning. (The LibraryHandle and its use is discussed in the section
@ref hooksdgLibraryHandle.)
- In the current version of the hooks framework, it is not possible to pass
any configuration information to the "load" function. The name of the log
file must therefore be hard-coded as an absolute path name, or communicated
to the user-written code by some other means.
- "load" returns 0 on success and non-zero on error. The hooks framework
file must therefore be hard-coded as an absolute path name or communicated
to the user code by some other means.
- "load" must 0 on success and non-zero on error. The hooks framework
will abandon the loading of the library if "load" returns an error status.
(In this example, "interesting" can be tested as a boolean value,
returning "true" if the file opened successfully.)
- "unload" closes the log file if it is open and is a no-op otherwise. As
with "load", a zero value is returned on success and a non-zero value
with "load", a zero value must be returned on success and a non-zero value
on an error. The hooks framework will record a non-zero status return
as an error in the current BIND 10 log but otherwise ignore it.
- As before, the function definitions are enclosed in 'extern "C"' braces.
@subsection hookCallouts Callouts
@subsection hooksdgCallouts Callouts
Having sorted out the framework, we now come to the functions that
actually do something. These functions are known as "callouts" because
the BIND 10 code "calls out" to them. Each BIND 10 server has a number
of hooks to which callouts can be attached: the purpose of the hooks
and the data passed to callouts is documented elsewhere.
the BIND 10 code "calls out" to them. Each BIND 10 server has a number of
hooks to which callouts can be attached: server-specific documentation
describes in detail the points in the server at which the hooks are
present together with the data passed to callouts attached to them.
Before we continue with the example, we'll discuss how arguments are
passed to callouts and how information can be moved between them.
passed to callouts and information is returned to the server. We will
also discuss how information can be moved between callouts.
@subsubsection hookCalloutSignature The Callout Signature
@subsubsection hooksdgCalloutSignature The Callout Signature
All callouts are declared with the signature:
@code
......@@ -279,7 +292,7 @@ log an error, specifying both the library and hook that generated it.
Effectively the return status provides a quick way for a callout to log
error information to the BIND 10 logging system.
@subsubsection hookArguments Callout Arguments
@subsubsection hooksdgArguments Callout Arguments
The CalloutHandle object provides two methods to get and set the
arguments passed to the callout. These methods are called (naturally
......@@ -296,7 +309,7 @@ following code snippets.
handle.setArgument("data_count", count);
handle.setArgument("inpacket", pktptr);
// Call the hook code...
// Call the callouts attached to the hook
...
// Retrieve the modified values
......@@ -342,15 +355,13 @@ be thrown if an attempt is made to retrieve it into a variable of type
"const char*". (However, if an argument is set as a "const int", it can
be retrieved into an "int".) The documentation of each hook point will
detail the data type of each argument.
- Although all arguments can be modified, some altered values may not
be read by the server. (These would be ones that the server considers
"read-only".) Consult the documentation of each hook to see whether an
argument can be used to transfer data back to the server.
- If a pointer to an object is passed to a callout (either a "raw"
pointer, or a boost smart pointer (as in the example above), and the
underlying object altered through that pointer, the change will be
underlying object is altered through that pointer, the change will be
reflected in the server even if no call is made to setArgument.
In all cases, consult the documentation for the particular hook to see whether
......@@ -361,10 +372,54 @@ the server.
- If you alter an argument, call CalloutHandle::setArgument to update the
value in the CalloutHandle object.
@subsubsection hookCalloutContext Per-Request Context
@subsubsection hooksdgSkipFlag The "Skip" Flag
When a to callouts attached to a hook returns, the server will usually continue
its processing. However, a callout might have done something that means that
the server should follow another path. Possible actions a server could take
include:
- Skip the next stage of processing because the callout has already
done it. For example, a hook is located just before the DHCP server
allocates an address to the client. A callout may decide to allocate
special addresses for certain clients, in which case it needs to tell
the server not to allocate an address in this case.
- Drop the packet and continue with the next request. A possible scenario
is a DNS server where a callout inspects the source address of an incoming
packet and compares it against a black list; if the address is on it,
the callout notifies the server to drop the packet.
To handle these common cases, the CalloutHandle has a "skip" flag.
This is set by a callout when it wishes the server to skip normal
processing. It is set false by the hooks framework before callouts on a
hook are called. If the flag is set on return, the server will take the
"skip" action relevant for the hook.
The methods to get and set the "skip" flag are getSkip and setSkip. Their
usage is intuitive:
@code
// Get the current setting of the skip flag.
bool skip = handle.getSkip();
// Do some processing...
:
if (lease_allocated) {
// Flag the server to skip the next step of the processing as we
// already have an address.
handle.setSkip(true);
}
return;
@endcode
Like arguments, the "skip" flag is passed to all callouts on a hook. Callouts
later in the list are able to examine (and modify) the settings of earlier ones.
@subsubsection hooksdgCalloutContext Per-Request Context
Although many of the BIND 10 modules can be characterised as handling
a single packet - e.g. the DHCPv4 server receives a DISCOVER packet,
singles packet - e.g. the DHCPv4 server receives a DISCOVER packet,
processes it and responds with an OFFER, this is not true in all cases.
The principal exception is the recursive DNS resolver: this receives a
packet from a client but that packet may itself generate multiple packets
......@@ -381,9 +436,8 @@ per-request basis.
Context only exists only for the duration of the request: when a request
is completed, the context is destroyed. A new request starts with no
context information. Context is particularly useful in servers that may
be processing multiple requests simultaneously: callouts are effectively
attaching data to a request and that data follows the request around the
system.
be processing multiple requests simultaneously: callouts can effectively
attach data to a request that follows the request around the system.
Context information is held as name/value pairs in the same way
as arguments, being accessed by the pair of methods setContext and
......@@ -391,11 +445,9 @@ getContext. They have the same restrictions as the setArgument and
getArgument methods - the type of data retrieved from context must
<B>exactly</B> match the type of the data set.
As the example in the tutorial uses per-request context, no separate
example is given here.
The example in the next section illustrates their use.
@subsection hookExampleCallouts Example Callouts
@subsection hooksdgExampleCallouts Example Callouts
Continuing with the tutorial, the requirements need us to retrieve the
hardware address of the incoming packet, classify it, and write it,
......@@ -409,14 +461,14 @@ We will do the classification here.
- v4_lease_write_post - called when the lease (an assignment of an IPv4
address to a client for a fixed period of time) has been written to the
database. It is passed two (constant) arguments, the query ("query")
database. It is passed two arguments, the query ("query")
and the response (called "reply"). This is the point at which the
example code will write the hardware and IP addresses to the log file.
The standard for naming callouts is to give them the same name as
the hook. If this is done, the callouts will be automatically found
by the Hooks system (this is discussed further in section @ref
hookCalloutRegistration). For our example, we will assume this is the
hooksdgCalloutRegistration). For our example, we will assume this is the
case, so the code for the first callout (used to classify the client's
hardware address) is:
......@@ -435,7 +487,6 @@ using namespace std;
extern "C" {
// This callout is called at the "pkt_rcvd" hook.
int pkt_rcvd(CalloutHandle& handle) {
// A pointer to the packet is passed to the callout via a "boost" smart
......@@ -485,7 +536,6 @@ using namespace std;
extern "C" {
// This callout is called at the "v4_lease_write_post" hook.
int v4_lease_write_post(CalloutHandle& handle) {
// Obtain the hardware address of the "interesting" client. We have to
......@@ -495,10 +545,10 @@ int v4_lease_write_post(CalloutHandle& handle) {
try (handle.getArgument("hwaddr", hwaddr) {
// getArgument didn't throw so the client is interesting. Get a pointer
// to the reply. This is read-only so is passed through a smart pointer
// const Pkt4 object. Note that the argument list also contains a
// pointer to the query: we don't need to access that in this example.
ConstPkt4Ptr reply;
// to the reply. Note that the argument list for this hook also
// contains a pointer to the query: we don't need to access that in this
// example.
Pkt4Ptr reply;
handle.getArgument("reply", reply);
// Get the string form of the IP address.
......@@ -523,13 +573,13 @@ int v4_lease_write_post(CalloutHandle& handle) {
};
@endcode
@subsection hookBuild Building the Library
@subsection hooksdgBuild Building the Library
Building the code requires building a shareable library. This requires
the the code be compiled as positition-independent code (using the
compiler's -fpic switch) and linked as a shared library (with the linker's
-shared switch). The build command also needs to point to the BIND 10 include
directory and link in the appropriate libraries.
compiler's "-fpic" switch) and linked as a shared library (with the
linker's "-shared" switch). The build command also needs to point to
the BIND 10 include directory and link in the appropriate libraries.
Assuming that BIND 10 has been installed in the default location, the
command line needed to create the library using the Gnu C++ compiler on a
......@@ -542,20 +592,18 @@ g++ -I /usr/include/bind10 -L /usr/lib/bind10 -fpic -shared -o example.so \
@endcode
Notes:
- the compilation command and switches required may vary depending on
- The compilation command and switches required may vary depending on
your operating system and compiler - consult the relevant documentation
for details.
- the values for the -I and -L switches depend on where you have installed
BIND 10.
- the list of libraries that need to be included in the command line
- The values for the "-I" and "-L" switches depend on where you have
installed BIND 10.
- The list of libraries that need to be included in the command line
depends on the functionality used by the hook code and the module to
which they are attached (e.g. hook code for DNS will need to link against
the libb10-dns++ library). Depending on operating system, you may also need
to explicitly list libraries on which the BIND 10 libraries depend, e.g.
in the command line above, libb10-exceptions depends on log4cplus, so it
is possible that "-llog4cplus" may need to be appended to the command line.
to explicitly list libraries on which the BIND 10 libraries depend.
@subsection hookConfiguration Configuring the Hook Library
@subsection hooksdgConfiguration Configuring the Hook Library
The final step is to make the library known to BIND 10. All BIND 10 modules to
which hooks can be added contain the "hook_library" element, and user
......@@ -565,17 +613,17 @@ To add the example library (assumed to be in /usr/local/lib) to the DHCPv4
module, the following bindctl commands must be executed:
@code
> config add Dhcp4/hook_library
> config set Dhcp4/hook_library[0]/name "/usr/local/lib/example.so"
> config add Dhcp4/hook_libraries
> config set Dhcp4/hook_libraries[0] "/usr/local/lib/example.so"
> config commit
@endcode
The DHCPv4 server will load the library and execute the callouts each time a
request is received.
@section hookAdvancedTopics Advanced Topics
@section hooksdgAdvancedTopics Advanced Topics
@subsection hookContextCreateDestroy Context Creation and Destruction
@subsection hooksdgContextCreateDestroy Context Creation and Destruction
As well as the hooks defined by the server, the hooks framework defines
two hooks of its own, "context_create" and "context_destroy". The first
......@@ -585,14 +633,14 @@ to initialize per-request context. The second is called after all
server-defined hooks have been processed, and is to allow a library to
tidy up.
As an example, the v4_lease_write
example above required that the code check for an exception being
thrown when accessing the "hwaddr" context item in case it was not set.
An alternative strategy would have been to provide a callout for the
"context_create" hook and set the context item "hwaddr" to an empty
string. Instead of needing to handle an exception, v4_lease_write would
be guaranteed to get something when looking for the hwaddr item and so
could write or not write the output depending on the value.
As an example, the v4_lease_write example above required that the code
check for an exception being thrown when accessing the "hwaddr" context
item in case it was not set. An alternative strategy would have been to
provide a callout for the "context_create" hook and set the context item
"hwaddr" to an empty string. Instead of needing to handle an exception,
v4_lease_write would be guaranteed to get something when looking for
the hwaddr item and so could write or not write the output depending on
the value.
In most cases, "context_destroy" is not needed as the Hooks system
automatically deletes context. An example where it could be required
......@@ -600,32 +648,143 @@ is where memory has been allocated by a callout during the processing
of a request and a raw pointer to it stored in the context object. On
destruction of the context, that memory will not be automatically
released. Freeing in the memory in the "context_destroy callout will solve
that problem. (Actually, when the context is destroyed, the destructor
that problem.
Actually, when the context is destroyed, the destructor
associated with any objects stored in it are run. Rather than point to
allocated memory with a raw pointer, a better idea would be to point to
it with a boost "smart" pointer and store that pointer in the context.
When the context is destroyed, the smart pointer's destructor is run,
which will automatically delete the pointed-to object.)
which will automatically delete the pointed-to object.
These approaches are illustrated in the following examples.
Here it is assumed that the hooks library is performing some form of
security checking on the packet and needs to maintain information in
a user-specified "SecurityInformation" object. (The details of this
fictitious object are of no concern here.) The object is created in
the context_create callout and used in both the pkt4_rcvd and the
v4_lease_write_post callouts.
@subsection hookCalloutRegistration Registering Callouts
@code
// Storing information in a "raw" pointer. Assume that the
As briefly mentioned in @ref hookExampleCallouts, the standard is for
callouts in the user library to have the same name as the name of the hook
to which they are being attached. This was followed in the tutorial, e.g.
the callout that needed to be attached to the "pkt_rcvd" hook was named
pkt_rcvd.
#include <hooks/hooks.h>
:
extern "C" {
The reason for this standard is that when the library is loaded, the
hook framework automatically searches the library for functions with the
same names as the server hooks. When it finds one, it attaches it to
that hook point. This simplifies the loading process and bookkeeping
required to create a library of callouts.
// context_create callout - called when the request is created.
int context_create(CalloutHandle& handle) {
// Create the security information and store it in the context
// for this packet.
SecurityInformation* si = new SecurityInformation();
handle.setContext("security_information", si);
}
// Callouts that use the context
int pktv_rcvd(CalloutHandle& handle) {
// Retrieve the pointer to the SecurityInformation object
SecurityInformation si;
handle.getContext("security_information", si);
:
:
// Set the security information
si->setSomething(...);
// The pointed-to information has been updated but the pointer has not been
// altered, so there is no need to call setContext() again.
}
int v4_lease_write_post(CalloutHandle& handle) {
// Retrieve the pointer to the SecurityInformation object
SecurityInformation si;
handle.getContext("security_information", si);
:
:
// Retrieve security information
bool active = si->getSomething(...);
:
}
// Context destruction. We need to delete the pointed-to SecurityInformation
// object because we will lose the pointer to it when the CalloutHandle is
// destroyed.
int context_destroy(CalloutHandle& handle) {
// Retrieve the pointer to the SecurityInformation object
SecurityInformation si;
handle.getContext("security_information", si);
// Delete the pointed-to memory.
delete si;
}