Tcl_StackChannel, Tcl_UnstackChannel, Tcl_GetStackedChannel, Tcl_GetTopChannel -
manipulate stacked I/O channels
#include <tcl.h>
Tcl_Channel
Tcl_StackChannel(interp, typePtr, clientData, mask, channel)
int
Tcl_UnstackChannel(interp, channel)
Tcl_Channel
Tcl_GetStackedChannel(channel)
Tcl_Channel
Tcl_GetTopChannel(channel)
- Tcl_Interp *interp (in)
- Interpreter for error reporting.
- const Tcl_ChannelType *typePtr (in)
- The new channel I/O procedures to use for
channel.
- ClientData clientData (in)
- Arbitrary one-word value to pass to channel I/O
procedures.
- int mask (in)
- Conditions under which channel will be used: OR-ed
combination of TCL_READABLE, TCL_WRITABLE and
TCL_EXCEPTION. This can be a subset of the operations currently
allowed on channel.
- Tcl_Channel channel (in)
- An existing Tcl channel such as returned by
Tcl_CreateChannel.
These functions are for use by extensions that add processing layers to Tcl I/O
channels. Examples include compression and encryption modules. These functions
transparently stack and unstack a new channel on top of an existing one. Any
number of channels can be stacked together.
The implementation of the Tcl channel code was rewritten in 8.3.2 to correct
some problems with the previous implementation with regard to stacked
channels. Anyone using stacked channels or creating stacked channel drivers
should update to the new
TCL_CHANNEL_VERSION_2 Tcl_ChannelType
structure. See
Tcl_CreateChannel for details.
Tcl_StackChannel stacks a new
channel on an existing channel with
the same name that was registered for
channel by
Tcl_RegisterChannel.
Tcl_StackChannel works by creating a new channel structure and placing
itself on top of the channel stack. EOL translation, encoding and buffering
options are shared between all channels in the stack. The hidden channel does
no buffering, newline translations, or character set encoding. Instead, the
buffering, newline translations, and encoding functions all remain at the top
of the channel stack. A pointer to the new top channel structure is returned.
If an error occurs when stacking the channel, NULL is returned instead.
The
mask parameter specifies the operations that are allowed on the new
channel. These can be a subset of the operations allowed on the original
channel. For example, a read-write channel may become read-only after the
Tcl_StackChannel call.
Closing a channel closes the channels stacked below it. The close of stacked
channels is executed in a way that allows buffered data to be properly
flushed.
Tcl_UnstackChannel reverses the process. The old channel is associated
with the channel name, and the processing module added by
Tcl_StackChannel is destroyed. If there is no old channel, then
Tcl_UnstackChannel is equivalent to
Tcl_Close. If an error
occurs unstacking the channel,
TCL_ERROR is returned, otherwise
TCL_OK is returned.
Tcl_GetTopChannel returns the top channel in the stack of channels the
supplied channel is part of.
Tcl_GetStackedChannel returns the channel in the stack of channels which
is just below the supplied channel.
Notifier(3tcl),
Tcl_CreateChannel(3tcl),
Tcl_OpenFileChannel(3tcl),
vwait(3tcl).
channel, compression