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# libnd_filter

## Name

libnd_filter --

## Synopsis

    enum        LND_FilterMode;
    gboolean    (*LND_FilterInitFunc)           (LND_Filter *filter,
                                                 LND_Trace *trace,
                                                 void *filter_data);
    gboolean    (*LND_FilterFunc)               (LND_Filter *filter,
                                                 LND_Packet *packet,
                                                 void *filter_data);
    void        (*LND_FilterCleanupFunc)        (LND_Filter *filter,
                                                 void *filter_data);
    void        (*LND_FilterFreeFunc)           (void *filter_data);
    LND_Filter* libnd_filter_new                (const char *name,
                                                 LND_FilterInitFunc filter_init,
                                                 LND_FilterFunc filter_func,
                                                 LND_FilterCleanupFunc filter_cleanup,
                                                 LND_FilterFreeFunc filter_data_free,
                                                 void *filter_data);
    void        libnd_filter_free               (LND_Filter *filter);
    void        libnd_filter_set_factory        (LND_Filter *filter,
                                                 LND_FilterFactory *factory);
    gboolean    libnd_filter_apply              (LND_Filter *filter,
                                                 LND_Packet *packet);
    gboolean    libnd_filter_list_apply         (GList *filters,
                                                 LND_Packet *packet,
                                                 LND_FilterMode mode);
    void        libnd_filter_list_init          (GList *filters,
                                                 LND_Trace *trace);
    void        libnd_filter_list_cleanup       (GList *filters);

## Description

## Details

### enum LND_FilterMode

    typedef enum {
      LND_FILTER_MODE_AND,
      LND_FILTER_MODE_OR
    } LND_FilterMode;

### LND_FilterInitFunc ()

    gboolean    (*LND_FilterInitFunc)           (LND_Filter *filter,
                                                 LND_Trace *trace,
                                                 void *filter_data);

This is the signature for filter initializers.

`filter` :

  filter to initialize.

`trace` :

  trace to initialize the filter for.

`filter_data` :

  filter-specific data.

Returns :

  TRUE when initialization was successful, % FALSE otherwise.

### LND_FilterFunc ()

    gboolean    (*LND_FilterFunc)               (LND_Filter *filter,
                                                 LND_Packet *packet,
                                                 void *filter_data);

This is the signature for filter hooks.

`filter` :

  filter to apply.

`packet` :

  packet to filter.

`filter_data` :

  filter-specific data.

Returns :

  TRUE if the packet passes the filter, FALSE otherwise.

### LND_FilterCleanupFunc ()

    void        (*LND_FilterCleanupFunc)        (LND_Filter *filter,
                                                 void *filter_data);

This is the signature for filter cleanup callbacks.

`filter` :

  filter to clean up.

`filter_data` :

  filter-specific data.

### LND_FilterFreeFunc ()

    void        (*LND_FilterFreeFunc)           (void *filter_data);

This is the signature for callbacks called when a filter is released, to clean up the filter data the filter was using.

`filter_data` :

  filter-specific data.

### libnd_filter_new ()

    LND_Filter* libnd_filter_new                (const char *name,
                                                 LND_FilterInitFunc filter_init,
                                                 LND_FilterFunc filter_func,
                                                 LND_FilterCleanupFunc filter_cleanup,
                                                 LND_FilterFreeFunc filter_data_free,
                                                 void *filter_data);

The function creates and returns a new filter with the given callbacks that implement the filter behaviour. If you don't require some of the functionality (e.g., when your filter is not stateful) then just pass NULL. `filter_data` can be any data structure that contains the state your filter requires for operation. It is cleaned up when the filter is destroyed, using a call to @`filter_data_free()`.

`name` :

  name of the filter.

`filter_init` :

  initialization function to run before packets are iterated.

`filter_func` :

  actual filter function, run on every packet.

`filter_cleanup` :

  cleanup function, run after packets are iterated.

`filter_data_free` :

  cleanup function for filter data.

`filter_data` :

  arbitrary user data the filter might require.

Returns :

  new filter, or NULL if an error occurred.

### libnd_filter_free ()

    void        libnd_filter_free               (LND_Filter *filter);

The function releases all memory that `filter` occupies.

`filter` :

  filter to release.

### libnd_filter_set_factory ()

    void        libnd_filter_set_factory        (LND_Filter *filter,
                                                 LND_FilterFactory *factory);

If your filter is created through a factory, the factory should call this function to make sure there is a connection from an instantiated filter to the factory that created it.

`filter` :

  filter whose factory to set.

`factory` :

  `filter`'s new factory.

### libnd_filter_apply ()

    gboolean    libnd_filter_apply              (LND_Filter *filter,
                                                 LND_Packet *packet);

The function applies `filter` to `packet`.

`filter` :

  filter to apply.

`packet` :

  packet to apply filter to.

Returns :

  TRUE when the packet passed the filter, FALSE otherwise.

### libnd_filter_list_apply ()

    gboolean    libnd_filter_list_apply         (GList *filters,
                                                 LND_Packet *packet,
                                                 LND_FilterMode mode);

The function applies `filters` to `packet`. `filters` is assumed to be a list of LND_Filter*s. Depending on `mode`, the function returns TRUE only when `packet` passes all filters (LND_FILTER_MODE_AND), or when it passes at least one filter (LND_FILTER_MODE_OR).

`filters` :

  list of filters to apply.

`packet` :

  packet to apply filter to.

`mode` :

  mode to use for filtering.

Returns :

  TRUE when the packet passed the filter, FALSE otherwise.

### libnd_filter_list_init ()

    void        libnd_filter_list_init          (GList *filters,
                                                 LND_Trace *trace);

The function initializes all filters for `trace`.

`filters` :

  list of filters to initialize.

`trace` :

  trace to initialize with.

### libnd_filter_list_cleanup ()

    void        libnd_filter_list_cleanup       (GList *filters);

The function cleans up the state of all filters int `filters`.

`filters` :

  list of filters to clean up.

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