mantaraya36's blog

Brain dump

Schema properties

OK, so here are my ideas to enhance the server config properties system. This is my initial proposal which will surely have changes after a round of feedback.

Current state

Currently properties are stored in a GTree structure in the file config.c, in a global variable from the following struct:

00085 struct xmms_config_St {
00086     xmms_object_t obj;
00087
00088     const gchar *filename;
00089     GTree *properties;
00090
00091     /* Lock on globals are great! */
00092     GMutex *mutex;
00093
00094     /* parsing */
00095     gboolean is_parsing;
00096     GQueue *states;
00097     GQueue *sections;
00098     gchar *value_name;
00099     guint version;
00100 };

The properties themselves are very simple, and basically contain a name and a string value:

00105 struct xmms_config_property_St {
00106     xmms_object_t obj;
00107
00108     /** Name of the config directive */
00109     const gchar *name;
00110     /** The data */
00111     gchar *value;
00112 };

Important considerations

  1. The new system must support (at least initially) the current one, to avoid breaking plugins. It’s likely that once the new system is in place, a simple script could be run to modify all code to use the new system, and the old methods removed or left with compiler deprecated warnings.
  2. The new system must support reading the xml config file, and from it produce the config tree for the new system. I’m thinking of breaking backwards compatibility of the xml file, so once you run a version with the new system, the properties will be written with a few additional elements which are not understood by the old parser.

Proposal

The new system will store the properties in a tree structure made up of linked nodes. I decided against using GNode or GVariant chains as they offer more functionality than needed which would make it easier to introduce bugs if you use the wrong way to put data in. Nodes will have :

struct xmms_config_node_St {
    xmms_object_t obj;
    const gchar *name;
    node_type_t type;
    node_data_t *data;

    struct xmms_config_node_St *parent_node;
}

The data for each node can be of type: CONFIG_LIST, CONFIG_ARRAY, CONFIG_INT, CONFIG_FLOAT, or CONFIG_STRING. The last three will be final nodes in the chain, where actual values are stored. These three types hold values directly in the data pointer as gint, gfloat or gchar*.

CONFIG_LIST nodes hold a GList whose elements are nodes. This should cover hierarchical properties, starting from the root node, like:

alsa.device = default
alsa.mixer = PCM
alsa.mixer_dev = default
alsa.mixer_index = 0

where the node called “alsa” has data of type CONFIG_LIST, and it holds a list with four nodes of type string,string, string and int. It is important to note that no to nodes in a list can have the same name.

The root node is of type CONFIG_LIST, and all config options are appended as new nodes to that list. The name of the root node is ignored.

CONFIG_ARRAY is similar to CONFIG_LIST, but it is designed to handle numbered properties, as in:

effect.order.0
effect.order.1

So the nodes that comprise CONFIG_ARRAYS, do not have names, as they take the name according to their order in the GList. Counting starts from 0. The main limitation this introduces is that numbered lists will not allow named elements, for example this would not be allowed:

effect.order.0
effect.order.1
effect.order.type

as the “order” node contains a numbered list, so “type” is not a valid name in this case.

Naturally, lists can be nested within lists or arrays and viceversa.

Interface

The interface to the new system will look like:

xmms_config_node_t *xmms_config_node_lookup (const gchar *path);
xmms_config_node_t *xmms_config_node_new (node_type_t type, const gchar *name = "");

/* frees a node and its children recursively */
void xmms_config_node_free (xmms_config_node_t *);

gboolean xmms_config_node_is_list (xmms_config_node_t *node);
gboolean xmms_config_node_is_array (xmms_config_node_t *node);

gboolean xmms_config_node_is_value (xmms_config_node_t *node);
gboolean xmms_config_node_is_int (xmms_config_node_t *node);
gboolean xmms_config_node_is_float (xmms_config_node_t *node);
gboolean xmms_config_node_is_string (xmms_config_node_t *node);

void xmms_config_node_get_path (xmms_config_node_t *node, gchar *path);

const gchar* xmms_config_node_get_name (xmms_config_node_t *node);
void xmms_config_node_set_name (xmms_config_node_t *node, const gchar *name);
/* callbacks can only be set for value nodes */
void xmms_config_node_callback_set (xmms_config_property_t *prop, xmms_object_handler_t cb, gpointer userdata);
void xmms_config_node_callback_remove (xmms_config_property_t *prop, xmms_object_handler_t cb, gpointer userdata);

/* value node operations. Will return the first element if node is a list or array*/
gint xmms_config_node_get_int (xmms_config_node_t *node, gboolean *ok = NULL);
gfloat xmms_config_node_get_float (xmms_config_node_t *node, gboolean *ok = NULL);
const gchar *xmms_config_node_get_string (xmms_config_node_t *node, gboolean *ok = NULL);

/* will set the vaue for the first element if node is a list or array */
void xmms_config_node_set_int (xmms_config_node_t *node, gint value, gboolean *ok = NULL);
void xmms_config_node_set_float (xmms_config_node_t *node, gfloat value, gboolean *ok = NULL);
void xmms_config_node_set_string (xmms_config_node_t *node, const gchar *value, gboolean *ok = NULL);

/* array and list node operations */
void xmms_config_node_resize (xmms_config_node_t *node, gint size, gboolean *ok = NULL);
void xmms_config_node_append (xmms_config_node_t *parent_node, xmms_config_node_t *node, gboolean *ok = NULL);
void xmms_config_node_insert (xmms_config_node_t *parent_node, gint index, xmms_config_node_t *node, gboolean *ok = NULL);
gint xmms_config_node_element_count (xmms_config_node_t *node);
void xmms_config_node_element_remove (xmms_config_node_t *parent_node, gint index, gboolean *ok = NULL);
void xmms_config_node_element_remove (xmms_config_node_t *parent_node, xmms_config_node_t *node, gboolean *ok = NULL);

xmms_config_node_t *xmms_config_node_get_element (xmms_config_node_t *parent_node, gint index);
xmms_config_node_t *xmms_config_node_get_element (xmms_config_node_t *parent_node, const gchar *name);

gint xmms_config_node_get_element_int (xmms_config_node_t *parent_node, gint index, gboolean *ok = NULL);
gfloat xmms_config_node_get_element_float (xmms_config_node_t *parent_node, gint index, gboolean *ok = NULL);
const gchar *xmms_config_node_get_element_string (xmms_config_node_t *parent_node, gint index, gboolean *ok = NULL);

void xmms_config_node_set_element_int (xmms_config_node_t *parent_node, gint index, gint value, gboolean *ok = NULL);
void xmms_config_node_set_element_float (xmms_config_node_t *parent_node, gint index, gfloat value, gboolean *ok = NULL);
void xmms_config_node_set_element_string (xmms_config_node_t *parent_node, gint index, const gchar* value, gboolean *ok = NULL);

void xmms_config_node_set_from_hash (xmms_config_node_t *parent_node, GHashTable table);

Command Line interaction

The command line client will be able to manipulate values in the usual way, so it only needs to be enhanced for array and list usage.

You will be able to set the elements for exisitng elements of a list or array from the command line by separating the values by commas. They values will be converted internally to the type for each node. So for example for the config properties:

alsa.device = default
alsa.mixer = PCM
alsa.mixer_dev = default
alsa.mixer_index = 0

You will be able to do:

nyxmms server config alsa default,PCM,default,0

The user can also dynamically resize lists and arrays. The command line user will be able to make lists longer, but not shorter (as the server might count on some properties it created being there). So for example, the user could set a chain of ladspa plugins like this:

nyxmms server config ladpsa.plugin amp.so,tap_reverb.so,tap_tubewarmth.so

and the ladspa plugin list will be resized to accomodate them if it can’t already.

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