GI.Gio.Interfaces.Seekable

Seekable is implemented by streams (implementations of InputStream or OutputStream) that support seeking.

Seekable streams largely fall into two categories: resizable and fixed-size.

Seekable on fixed-sized streams is approximately the same as POSIX lseek() on a block device (for example: attempting to seek past the end of the device is an error). Fixed streams typically cannot be truncated.

Seekable on resizable streams is approximately the same as POSIX lseek() on a normal file. Seeking past the end and writing data will usually cause the stream to resize by introducing zero bytes.

Exported types

newtype Seekable

Memory-managed wrapper type.

Constructors

Seekable (ManagedPtr Seekable)

Instances

GObject Seekable

Defined in GI.Gio.Interfaces.Seekable

Methods

gobjectType :: IO GType

HasParentTypes Seekable

Defined in GI.Gio.Interfaces.Seekable

type ParentTypes Seekable

Defined in GI.Gio.Interfaces.Seekable

type ParentTypes Seekable = Object ': ([] :: [Type])

noSeekable :: Maybe Seekable

A convenience alias for Nothing :: Maybe Seekable.

class (GObject o, IsDescendantOf Seekable o) => IsSeekable o

Type class for types which can be safely cast to Seekable, for instance with toSeekable.

Instances

(GObject o, IsDescendantOf Seekable o) => IsSeekable o

Defined in GI.Gio.Interfaces.Seekable

toSeekable :: (MonadIO m, IsSeekable o) => o -> m Seekable

Cast to Seekable, for types for which this is known to be safe. For general casts, use castTo.

Methods

canSeek

seekableCanSeek

Arguments

:: (HasCallStack, MonadIO m, IsSeekable a)

=> a

seekable: a Seekable.

-> m Bool

Returns: True if seekable can be seeked. False otherwise.

Tests if the stream supports the SeekableIface.

canTruncate

seekableCanTruncate

Arguments

:: (HasCallStack, MonadIO m, IsSeekable a)

=> a

seekable: a Seekable.

-> m Bool

Returns: True if the stream can be truncated, False otherwise.

Tests if the length of the stream can be adjusted with seekableTruncate.

seek

seekableSeek

Arguments

:: (HasCallStack, MonadIO m, IsSeekable a, IsCancellable b)

=> a

seekable: a Seekable.

-> Int64

offset: a goffset.

-> SeekType

type: a SeekType.

-> Maybe b

cancellable: optional Cancellable object, Nothing to ignore.

-> m ()

(Can throw GError)

Seeks in the stream by the given offset, modified by type.

Attempting to seek past the end of the stream will have different results depending on if the stream is fixed-sized or resizable. If the stream is resizable then seeking past the end and then writing will result in zeros filling the empty space. Seeking past the end of a resizable stream and reading will result in EOF. Seeking past the end of a fixed-sized stream will fail.

Any operation that would result in a negative offset will fail.

If cancellable is not Nothing, then the operation can be cancelled by triggering the cancellable object from another thread. If the operation was cancelled, the error IOErrorEnumCancelled will be returned.

tell

seekableTell

Arguments

:: (HasCallStack, MonadIO m, IsSeekable a)

=> a

seekable: a Seekable.

-> m Int64

Returns: the offset from the beginning of the buffer.

Tells the current position within the stream.

truncate

seekableTruncate

Arguments

:: (HasCallStack, MonadIO m, IsSeekable a, IsCancellable b)

=> a

seekable: a Seekable.

-> Int64

offset: new length for seekable, in bytes.

-> Maybe b

cancellable: optional Cancellable object, Nothing to ignore.

-> m ()

(Can throw GError)

Sets the length of the stream to offset. If the stream was previously larger than offset, the extra data is discarded. If the stream was previouly shorter than offset, it is extended with NUL ('\0') bytes.

If cancellable is not Nothing, then the operation can be cancelled by triggering the cancellable object from another thread. If the operation was cancelled, the error IOErrorEnumCancelled will be returned. If an operation was partially finished when the operation was cancelled the partial result will be returned, without an error.