MirageFilterStream: libMirage Reference Manual

## MirageFilterStream MirageFilterStream — Filter I/O stream object. |

## Functions

gboolean | mirage_filter_stream_open ()
void | mirage_filter_stream_generate_info ()
const MirageFilterStreamInfo * | mirage_filter_stream_get_info ()
MirageStream * | mirage_filter_stream_get_underlying_stream ()
void | mirage_filter_stream_info_copy ()
void | mirage_filter_stream_info_free ()
goffset | mirage_filter_stream_simplified_get_position ()
void | mirage_filter_stream_simplified_set_stream_length ()

## Types and Values

struct | MirageFilterStream
struct | MirageFilterStreamClass
struct | MirageFilterStreamInfo

## Object Hierarchy

        GObject
        ╰── MirageObject
            ╰── MirageFilterStream

## Implemented Interfaces

MirageFilterStream implements MirageContextual and MirageStream.

## Includes

    #include <mirage-filter-stream.h>

## Description

MirageFilterStream is a basic unit of file access abstraction used in libMirage. It implements MirageStream interface to perform I/O operations.

When opening a file with libMirage, `mirage_context_create_input_stream()` function should be used. It creates a chain of MirageFilterStream objects on top of a MirageFileStream, and returns the top object on the chain. This allows transparent access to, for example, compressed data stored in the file. Alternatively, you can create a MirageFileStream yourself and open additional MirageFilterStream objects on top of it.

There are two ways to implement a MirageFilterStream. For full control over the logic for reading from parts and managing position in the stream, use "full interface", which requires implementation of three virtual functions: read, seek and tell. The second option is to use "simplified read interface", which provides framework for stream position management and reading logic, and requires that filter stream implements partial_read function. Additionally, it requires that filter stream implementation sets the file stream size using `mirage_filter_stream_simplified_set_stream_length()` function. In simplified_partial_read, the current position in the stream, which is managed by the framework, can be obtained using `mirage_filter_stream_simplified_get_position()`.

## Functions

### mirage_filter_stream_open ()

    gboolean
    mirage_filter_stream_open (MirageFilterStream *self,
                               MirageStream *stream,
                               gboolean writable,
                               GError **error);

Opens stream on top of provided underlying stream.

#### Parameters

self | a MirageFilterStream |
stream | an underlying stream. | [in]
writable | a flag indicating whether the stream should be opened in read/write mode or not. | [in]
error | location to store error, or `NULL`. | [out][allow-none]

#### Returns

`TRUE` on success, `FALSE` on failure

### mirage_filter_stream_generate_info ()

    void
    mirage_filter_stream_generate_info (MirageFilterStream *self,
                                        const gchar *id,
                                        const gchar *name,
                                        gboolean writable,
                                        gint num_types,
                                        ...);

Generates filter stream information from the input fields. It is intended as a function for creating filter stream information in filter stream implementations.

#### Parameters

self | a MirageFilterStream |
id | filter stream ID. | [in]
name | filter stream name. | [in]
writable | flag indicating whether filter stream supports write operation. | [in]
num_types | number of MIME types. | [in]
... | description and MIME type string pairs, one for each defined type. | [in]

### mirage_filter_stream_get_info ()

    const MirageFilterStreamInfo *
    mirage_filter_stream_get_info (MirageFilterStream *self);

Retrieves filter stream information.

#### Parameters

self | a MirageFilterStream |

#### Returns

a pointer to filter stream information structure. The structure belongs to object and therefore should not be modified.

[transfer none]

### mirage_filter_stream_get_underlying_stream ()

    MirageStream *
    mirage_filter_stream_get_underlying_stream
                                   (MirageFilterStream *self);

Retrieves filter stream's underlying stream.

#### Parameters

self | a MirageFilterStream |

#### Returns

a pointer to filter stream's underlying stream. The reference belongs to filter stream and should not be released.

[transfer none]

### mirage_filter_stream_info_copy ()

    void
    mirage_filter_stream_info_copy (const MirageFilterStreamInfo *info,
                                    MirageFilterStreamInfo *dest);

Copies parser information from `info` to `dest` .

#### Parameters

info | a MirageFilterStreamInfo to copy data from. | [in]
dest | a MirageFilterStreamInfo to copy data to. | [in]

### mirage_filter_stream_info_free ()

    void
    mirage_filter_stream_info_free (MirageFilterStreamInfo *info);

Frees the allocated fields in `info` (but not the structure itself!).

#### Parameters

info | a MirageFilterStreamInfo to free. | [in]

### mirage_filter_stream_simplified_get_position ()

    goffset
    mirage_filter_stream_simplified_get_position
                                   (MirageFilterStream *self);

Retrieves position in the stream.

This function is intented for use in filter stream implementations that are based on the simplified interface. It should be used by the implementation's simplified_partial_read function to determine position to read from without having to worry about position management and update.

#### Parameters

self | a MirageFilterStream |

#### Returns

position in the stream

### mirage_filter_stream_simplified_set_stream_length ()

    void
    mirage_filter_stream_simplified_set_stream_length
                                   (MirageFilterStream *self,
                                    gsize length);

Sets size of the stream.

This function is intented for use in filter stream implementations that are based on the simplified interface. It should be used by the implementation to set the stream size during stream parsing; the set stream size is then used by the read function that is implemented by the simplified interface.

#### Parameters

self | a MirageFilterStream |
length | length of the stream. | [in]

## Types and Values

### struct MirageFilterStream

    struct MirageFilterStream;

All the fields in the MirageFilterStream structure are private to the MirageFilterStream implementation and should never be accessed directly.

### struct MirageFilterStreamClass

    struct MirageFilterStreamClass {
        MirageObjectClass parent_class;

        /* Class members */
        gboolean (*open) (MirageFilterStream *self, MirageStream *stream, gboolean writable, GError **error);

        /* Functions implemented for MirageStream: */
        gssize (*read) (MirageFilterStream *self, void *buffer, gsize count, GError **error);
        gssize (*write) (MirageFilterStream *self, const void *buffer, gsize count, GError **error);
        gboolean (*seek) (MirageFilterStream *self, goffset offset, GSeekType type, GError **error);
        goffset (*tell) (MirageFilterStream *self);

        /* Simplified read/write interface */
        gssize (*simplified_partial_read) (MirageFilterStream *self, void *buffer, gsize count);
        gssize (*simplified_partial_write) (MirageFilterStream *self, const void *buffer, gsize count);
    };

The class structure for the MirageFilterStream type.

#### Members

`open` () | opens a filter stream on top underyling stream |
`read` () | reads data from stream |
`write` () | wrties data to stream |
`seek` () | seeks to a location within stream |
`tell` () | tells the current location within stream |
`simplified_partial_read` () | reads a chunk of requested data from stream (part of simplified interface) |
`simplified_partial_write` () | writes a chunk of requested data to stream (part of simplified interface) |

### struct MirageFilterStreamInfo

    struct MirageFilterStreamInfo {
        gchar *id;
        gchar *name;
        gboolean writable;
        gchar **description;
        gchar **mime_type;
    };

A structure containing filter stream information. It can be obtained with call to `mirage_filter_stream_get_info()`.

#### Members

gchar *`id`; | filter stream ID |
gchar *`name`; | filter stream name |
gboolean `writable`; | whether filter stream supports write operation |
gchar **`description`; | zero-terminated array of file type description strings. | [array zero-terminated=1]
gchar **`mime_type`; | zero-terminated array of file type MIME strings. | [array zero-terminated=1]

## See Also

MirageStream, MirageFileStream