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The resolver :ref:`library <lib_index>` leverages the `processing API`_ from the libknot to separate packet processing code
Writing extensions
into layers. In order to keep the core library sane and coverable, there are only two built-in layers:
==================
the :c:func:`iterate_layer`, and the :c:func:`itercache_layer`. The resolver context however can
load shared libraries on runtime, which allows us to build and register external modules as well.
.. contents::
:depth: 2
:local:
Supported languages
Supported languages
-------------------
-------------------
Currently modules written in C are supported.
Currently modules written in C are supported.
There is also a rudimentary support for writing modules in Go |---| ⑴ the library has no native Go bindings, library is accessible using CGO_, ⑵ gc doesn't support building shared libraries, GCCGO_ is required, ⑶ no coroutines and no garbage collecting thread, as the Go code is called from C threads.
There is also a rudimentary support for writing modules in Go |---| |(1)| the library has no native Go bindings, library is accessible using CGO_, |(2)| gc doesn't support building shared libraries, GCCGO_ is required, |(3)| no coroutines and no garbage collecting thread, as the Go code is called from C threads.
There is a plan for Lua scriptables, but it's not implemented yet.
Available services
------------------
*Note* |---| This is only crash-course in the library internals, see the resolver :ref:`library <lib_index>` documentation for the complete overview of the services.
The library offers following services:
- :ref:`Cache <lib_cache>` - MVCC cache interface for retrieving/storing resource records.
- :ref:`Resolution plan <lib_rplan>` - Query resolution plan, a list of partial queries (with hierarchy) sent in order to satisfy original query. This contains information about the queries, nameserver choice, timing information, answer and its class.
- :ref:`Nameservers <lib_nameservers>` - Reputation database of nameservers, this serves as an aid for nameserver choice.
If you're going to publish a layer in your module, it's going to be called by the query resolution driver for each query,
so you're going to work with :ref:`struct kr_layer_param <lib_api_rplan>` as your per-query context. This structure contains pointers to
resolution context, resolution plan and also the final answer. You're likely to retrieve currently solved query from the query plan:
This is only passive processing of the incoming answer. If you want to change the course of resolution, say satisfy a query from a local cache before the library issues a query to the nameserver, you can use states (see the `Static hints`_ for example).
.. note:: There is a plan for Lua scriptables, but it's not implemented yet.
"``X_props()``", "``Props()``", "", "NULL-terminated list of properties"
"``X_props()``", "``Props()``", "", "NULL-terminated list of properties"
.. [#] Mandatory symbol.
.. [#] Mandatory symbol.
...
@@ -102,12 +39,10 @@ A module is a shared library defining specific functions, here's an overview of
...
@@ -102,12 +39,10 @@ A module is a shared library defining specific functions, here's an overview of
The ``X_`` corresponds to the module name, if the module name is ``hints``, then the prefix for constructor would be ``hints_init()``.
The ``X_`` corresponds to the module name, if the module name is ``hints``, then the prefix for constructor would be ``hints_init()``.
This doesn't apply for Go, as it for now always implements `main` and requires capitalized first letter in order to export its symbol.
This doesn't apply for Go, as it for now always implements `main` and requires capitalized first letter in order to export its symbol.
How does the module get loaded
.. note::
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The resolution context :c:type:`struct kr_context` holds loaded modules for current context. A module can be registered with :c:func:`kr_context_register`, which triggers module constructor *immediately* after the load. Module destructor is automatically called when the resolution context closes.
The resolution context :c:type:`struct kr_context` holds loaded modules for current context. A module can be registered with :c:func:`kr_context_register`, which triggers module constructor *immediately* after the load. Module destructor is automatically called when the resolution context closes.
If the module exports a layer implementation, it is automatically discovered by :c:func:`kr_resolver` on resolution init and plugged in. The order in which the modules are registered corresponds to the call order of layers.
If the module exports a layer implementation, it is automatically discovered by :c:func:`kr_resolver` on resolution init and plugged in. The order in which the modules are registered corresponds to the call order of layers.
Writing a module in C
Writing a module in C
---------------------
---------------------
...
@@ -123,7 +58,7 @@ As almost all the functions are optional, the minimal module looks like this:
...
@@ -123,7 +58,7 @@ As almost all the functions are optional, the minimal module looks like this:
Let's define an observer thread for the module as well. It's going to be stub for the sake of brevity,
Let's define an observer thread for the module as well. It's going to be stub for the sake of brevity,
but you can for example create a condition, and notify the thread from query processing by declaring
but you can for example create a condition, and notify the thread from query processing by declaring
module layer (see the `Available services`_).
module layer (see the :ref:`Writing layers <lib-layers>`).
.. code-block:: c
.. code-block:: c
...
@@ -244,6 +179,8 @@ Configuring modules
...
@@ -244,6 +179,8 @@ Configuring modules
There is a callback ``X_config()`` but it's NOOP for now, as the configuration is not yet implemented.
There is a callback ``X_config()`` but it's NOOP for now, as the configuration is not yet implemented.
.. _mod-properties:
Exposing module properties
Exposing module properties
--------------------------
--------------------------
...
@@ -286,7 +223,7 @@ Here's an example how a module can expose its property:
...
@@ -286,7 +223,7 @@ Here's an example how a module can expose its property:
{
{
static struct kr_prop prop_list[] = {
static struct kr_prop prop_list[] = {
/* Callback, Name, Description */
/* Callback, Name, Description */
{&get_size, "size", "Return number of records."},
{&get_size, "get_size", "Return number of records."},
{NULL, NULL, NULL}
{NULL, NULL, NULL}
};
};
return prop_list;
return prop_list;
...
@@ -302,14 +239,16 @@ Once you load the module, you can call the module property from the interactive
...
@@ -302,14 +239,16 @@ Once you load the module, you can call the module property from the interactive
...
...
[system] started in interactive mode, type 'help()'
[system] started in interactive mode, type 'help()'
> modules.load('cached')
> modules.load('cached')
> return cached.size()
> cached.get_size()
{ "size": 53 }
{ "size": 53 }
*Note* |---| this relies on function pointers, so the same ``static inline`` trick as for the ``Layer()`` is required for C/Go.
*Note* |---| this relies on function pointers, so the same ``static inline`` trick as for the ``Layer()`` is required for C/Go.
