Managed Namespaces

Summary

Introduction

Managed namespaces are used in the Weave SDK to provide both Weave SDK developers and integrators alike with advertised guidance and subtext on the designation of particular API sets within the SDK such that they can plan and predict their migration path across Weave SDK releases and, potentially, manage multiple, concurrent Weave APIs for a given module.

Designation

Managed namespaces may be managed as one of four designations:

Development

Any namespace managed with the Development designation is an indication to developers and integrators that the APIs contained within are under active development, may be subject to change, and are not officially supported. Integrators are generally discouraged from using these APIs unless they are specifically directed to do so.

Next

Any namespace managed with the Next designation is an indication to developers and integrators that the APIs contained within, while they have largely completed active development, may still be subject to change and are supported for early evaluation purposes. APIs so designated represent the next evoluationary front in a Weave SDK API and will become the current, default APIs at a major releaes cycle in the immediate to near future.

Backward compatibility, both from an API and over-the-wire protocol perspective, may exist but is not guaranteed in APIs so designated.

The Next managed namespace designation effectively provides developers and integrators with a view to where the Weave SDK is headed by hinting what will become the current, default API in a future release.

The Next managed namespace designation is optional such that a managed namespace may transition through a lifecycle without using it (see Managed Namespace Lifecycle).

Current

Any namespace managed with the Current designation or any unmanaged namespace (i.e. lacking a managed namespace designation) represents the current, default, official supported API for that portion or module of the Weave SDK. While there still may be ongoing enhancements to such APIs, changes will largely be incremental and backward compatibility, both API and over-the-wire, should be maintained.

The Current managed namespace designation is optional such that a managed namespace may transition through a lifecycle without using it (see Managed Namespace Lifecycle). In fact, any unmanaged namespace is implicitly Current.

Legacy

Any namespace managed with the Legacy designation is an indication to developers and integrators that the APIs contained within have been deprecated and are supplanted with a new, current API. These APIs represent what was formerly the current API.

APIs so designated will disappear altogether at the next major Weave SDK release; consequently, developers and integrators should establish plans for migration away from these APIs if they intend to stay with the leading edge of Weave SDK releases.

Managed Namespace Lifecycle

The following figure illustrates the lifecycle of a managed namespace as it transitions from Development and, potentially, to Legacy:

.-------------.      .- - - .      .- - - - -.      .--------.
| Development | -.->   Next   -.->   Current   ---> | Legacy |
'-------------'  |   '- - - '  |   ' - - - - '      '--------'
                 |             |
                 '-------------'

If it is employed, the managed namespace lifecycle begins with the Development designation.

When development is complete and the code is ready for evaluation and integration, the designation migrates to either Next or Current. Alternatively, the designation may be dropped altogether and managed namespace no longer employed, effectively making the designation implicitly Current.

If the code is to live alongside and not yet supplant current code, then the designation should migrate to Next. If the code is to supplant current code, then the designation should migrate to Current.

Using the Next designation, after the code has undergone the desired number of release and evaluation cycles, the designation migrates to Current or, again, the Designation may be dropped altogether.

Using the Current designation, if the code is to be supplanted by new code but still needs to be maintained for a number of release cycles, the designation migrates to Legacy.

From the Legacy designation, the code is eventually removed from the Weave SDK altogether.

Using Managed Namespaces

Weave SDK users may interact with managed namespaces either as developer, extending and maintaining existing code, or as an integrator, integrating Weave into their own application, platform, and system code. The follow two sections detail recommendations for dealing with Weave managed namespaces from those two perspectives.

Using Managed Namespaces as a Developer

A key focus of the Weave SDK developer is enhancing and developing new Weave SDK APIs and functionality while, in many cases, at the same time supporting existing API and functionality deployments.

Where it is not possible to satisfy both of these focus areas in backward-compatible way within the same API, managed namespaces provide a mechanism to manage these APIs in parallel, in a way that does not disrupt existing API and functionality deployments.

As a working example, assume a Weave profile, Mercury, that currently exists under the following, unmanaged, namespace hierarchy:

namespace nl {
namespace Weave {
namespace Profiles {
namespace Mercury {

// ...

}; // namespace Mercury
}; // namespace Profiles
}; // namespace Weave
}; // namespace nl

and the following public headers:

  • Weave/Profiles/Mercury/Mercury.hpp
  • Weave/Profiles/Mercury/Bar.hpp
  • Weave/Profiles/Mercury/Foo.hpp
  • Weave/Profiles/Mercury/Foobar.hpp

where Mercury.hpp is the module "umbrella" header. Most integrators simply include the module "umbrella" header as shown:

#include

However, developent of Mercury has now reached a point in which there is a need to develop a next-generation of the APIs and, potentially, the over-the-wire protocol that are not backward-compatible to existing deployments. Using managed namespaces can help accomplish this without breaking these existing deployments.

Move Existing Namespace to Current

With a goal of continuing to support the current release of the API and functionality for existing deployed integrations, the first task is to move the current code:

% cd src/lib/profiles/mercury
% mkdir Current
% mv Mercury.hpp Bar.hpp Foo.hpp Foobar.hpp *.cpp Current/

Note, in addition to moving the files, the header include guards for the moved files should also be renamed, potentially decorating them with '_CURRENT', since new, like-named files will be created their place below.

With the code moved, the next step is to manage the namespace with the appropriate designation, here 'Current'. First, create a header that defines the managed namespace, as 'Current/MercuryManagedNamespace.hpp'. Creating such a header is preferrable to repeating and duplicating this content in each header file when there are multiple header files.

% cat << EOF > Current/MercuryManagedNamespace.hpp
#ifndef _WEAVE_MERCURY_MANAGEDNAMESPACE_CURRENT_HPP
#define _WEAVE_MERCURY_MANAGEDNAMESPACE_CURRENT_HPP

#include <Weave/Support/ManagedNamespace.hpp>

#if defined(WEAVE_CONFIG_MERCURY_NAMESPACE) && WEAVE_CONFIG_MERCURY_NAMESPACE != kWeaveManagedNamespace_Current
#error Compiling Weave Mercury current-designation managed namespace file with WEAVE_CONFIG_MERCURY_NAMESPACE defined != kWeaveManagedNamespace_Current
#endif

#ifndef WEAVE_CONFIG_MERCURY_NAMESPACE
#define WEAVE_CONFIG_MERCURY_NAMESPACE kWeaveManagedNamespace_Current
#endif

namespace nl {
namespace Weave {
namespace Profiles {

namespace WeaveMakeManagedNamespaceIdentifier(Mercury, kWeaveManagedNamespaceDesignation_Current) { };

namespace Mercury = WeaveMakeManagedNamespaceIdentifier(Mercury, kWeaveManagedNamespaceDesignation_Current);

}; // namespace Profiles
}; // namespace Weave
}; // namespace nl

#endif // _WEAVE_MERCURY_MANAGEDNAMESPACE_CURRENT_HPP
EOF

Next, include this header prior to other module-specific include directives in the existing headers. For example:

#include 

#include

Create Compatibility Headers

Moving the existing headers to a new location and managing their namespace alone, however, is not enough to ensure that existing deployments will work without change since they are all using include directives that specified the headers just moved above.

To address this, compatibility wrapper headers with names matching those just moved must be created.

% touch Mercury.hpp Bar.hpp Foo.hpp Foobar.hpp

If only a Current-designated managed namespace is being created without creating a Development- or Next-designated managed namespace to accompany it, the contents of these files can simply consist of a header include guard and an include directive specifying the newly-moved header of the same name:

#ifndef _WEAVE_MERCURY_BAR_HPP
#define _WEAVE_MERCURY_BAR_HPP

#include 

#endif // _WEAVE_MERCURY_BAR_HPP

However, if a Development- or Next-designated managed namespace is being created as well to accomodate new, incompatible development, something slightly more complex needs to be done.

As before, a header for the managed namespace configuration is created, here as MercuryManagedNamespace.hpp. Again, this is preferrable to repeating and duplicating this content in each header file when there are multiple header files..

% cat << EOF > MercuryManagedNamespace.hpp
#ifndef _WEAVE_MERCURY_MANAGEDNAMESPACE_HPP
#define _WEAVE_MERCURY_MANAGEDNAMESPACE_HPP

#include <Weave/Support/ManagedNamespace.hpp>

#if defined(WEAVE_CONFIG_MERCURY_NAMESPACE)                             \
  && (WEAVE_CONFIG_MERCURY_NAMESPACE != kWeaveManagedNamespace_Current) \
  && (WEAVE_CONFIG_MERCURY_NAMESPACE != kWeaveManagedNamespace_Development)
#error "WEAVE_CONFIG_MERCURY_NAMESPACE defined, but not as namespace kWeaveManagedNamespace_Current or kWeaveManagedNamespace_Development"
#endif

#if !defined(WEAVE_CONFIG_MERCURY_NAMESPACE)
#define WEAVE_CONFIG_MERCURY_NAMESPACE kWeaveManagedNamespace_Current
#endif

#endif // _WEAVE_MERCURY_MANAGEDNAMESPACE_HPP
EOF

Note that this defaults, as desired, the managed namespace designation to 'Current' if no configuration has been defined.

With this header in place, the compatibility wrapper headers can now be edited to contain:

#include 

#if WEAVE_CONFIG_MERCURY_NAMESPACE == kWeaveManagedNamespace_Development
#include 
#else
#include 
#endif // WEAVE_CONFIG_MERCURY_NAMESPACE == kWeaveManagedNamespace_Development

or whatever is appropriate for the namespace management use case at hand.

Create Development Content

At this point, the infrastructure is now in place to start building out new functionality and APIs alongside the existing ones.

% mkdir Development
% touch Development/Mercury.hpp Development/Bar.hpp Development/Foo.hpp Development/Foobar.hpp
% cat << EOF > Development/MercuryManagedNamespace.hpp
#ifndef _WEAVE_MERCURY_MANAGEDNAMESPACE_DEVELOPMENT_HPP
#define _WEAVE_MERCURY_MANAGEDNAMESPACE_DEVELOPMENT_HPP

#include <Weave/Support/ManagedNamespace.hpp>

#if defined(WEAVE_CONFIG_MERCURY_NAMESPACE) && WEAVE_CONFIG_MERCURY_NAMESPACE != kWeaveManagedNamespace_Development
#error Compiling Weave Mercury development-designated managed namespace file with WEAVE_CONFIG_MERCURY_NAMESPACE defined != kWeaveManagedNamespace_Development
#endif

#ifndef WEAVE_CONFIG_MERCURY_NAMESPACE
#define WEAVE_CONFIG_MERCURY_NAMESPACE kWeaveManagedNamespace_Development
#endif

namespace nl {
namespace Weave {
namespace Profiles {

namespace WeaveMakeManagedNamespaceIdentifier(Mercury, kWeaveManagedNamespaceDesignation_Development) { };

namespace Mercury = WeaveMakeManagedNamespaceIdentifier(Mercury, kWeaveManagedNamespaceDesignation_Development);

}; // namespace Profiles
}; // namespace Weave
}; // namespace nl

#endif // _WEAVE_MERCURY_MANAGEDNAMESPACE_DEVELOPMENT_HPP
EOF

Of course, if a module is far simpler than the example presented here and does not have many classes, source, files, or headers, this could all be accomplished in the same header file without moving files around and creating multiple standalone configuration and compatibility headers. However, with this complex example, it should inspire managed namespace solutions along a spectrum from complex to simple.

Using Managed Namespaces as an Integrator

A key focus of the Weave SDK integrator is including the appropriate Weave SDK public API headers and integrating and developing applications against them.

As a working example, again assume a Weave profile, Mercury, that has Next-, Current-, and Legacy-designated managed namespaces, whose public headers are structured as follows:

  • Weave/Profiles/Mercury/Mercury.hpp
  • Weave/Profiles/Mercury/Bar.hpp
  • Weave/Profiles/Mercury/Foo.hpp
  • Weave/Profiles/Mercury/Foobar.hpp
  • Weave/Profiles/Mercury/Next/Mercury.hpp
  • Weave/Profiles/Mercury/Next/Bar.hpp
  • Weave/Profiles/Mercury/Next/Foo.hpp
  • Weave/Profiles/Mercury/Next/Foobar.hpp
  • Weave/Profiles/Mercury/Current/Mercury.hpp
  • Weave/Profiles/Mercury/Current/Bar.hpp
  • Weave/Profiles/Mercury/Current/Foo.hpp
  • Weave/Profiles/Mercury/Current/Foobar.hpp
  • Weave/Profiles/Mercury/Legacy/Mercury.hpp
  • Weave/Profiles/Mercury/Legacy/Bar.hpp
  • Weave/Profiles/Mercury/Legacy/Foo.hpp
  • Weave/Profiles/Mercury/Legacy/Foobar.hpp

where Mercury.hpp is the module "umbrella" header.

Unless the use case at hand motivates including a namespace managed module within Weave explicitly, for example:

#include

it is best to reference Weave module public headers by their unmanaged, default paths (e.g. Weave/Profiles/Mercury/Mercury.hpp). Doing so allows following a progression of API development without continually changing a project's include directives as those APIs flow through the managed lifecycle.

Following this strategy, deployments can then retarget their code at a different managed namespace designation, the Current designation for example, by specifying the desired configuration in the C/C++ preprocessor. This may be done on the command line, in the source code, or in a configuration or prefix header:

#define WEAVE_CONFIG_MERCURY_NAMESPACE kWeaveManagedNamespace_Current

and use the unmanaged / unqualified include path:

#include

When, and if, the managed namespace designation changes for the targeted APIs, for example from Current to Legacy, simply retarget by adjusting the preprocessor definition:

#define WEAVE_CONFIG_MERCURY_NAMESPACE kWeaveManagedNamespace_Legacy