Tcl_StackChannel - TopChannel - 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_StackChannel(3tcl) Tcl Library Procedures Tcl_StackChannel(3tcl)
______________________________________________________________________________
NAME
Tcl_StackChannel, Tcl_UnstackChannel, Tcl_GetStackedChannel, Tcl_Get-
TopChannel - manipulate stacked I/O channels
SYNOPSIS
#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)
ARGUMENTS
Tcl_Interp *interp (in) Interpreter for error report-
ing.
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 proce-
dures.
int mask (in) Conditions under which channel
will be used: OR-ed combina-
tion of TCL_READABLE,
TCL_WRITABLE and TCL_EXCEP-
TION. 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_CreateChan-
nel.
______________________________________________________________________________
DESCRIPTION
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 encod-
ing 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 origi-
nal 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.
ATTRIBUTES
See attributes(7) for descriptions of the following attributes:
+---------------+------------------+
|ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+---------------+------------------+
|Availability | runtime/tcl-8 |
+---------------+------------------+
|Stability | Uncommitted |
+---------------+------------------+
SEE ALSO
Notifier(3), Tcl_CreateChannel(3), Tcl_OpenFileChannel(3), vwait(n).
KEYWORDS
channel, compression
NOTES
Source code for open source software components in Oracle Solaris can
be found at https://www.oracle.com/downloads/opensource/solaris-source-
code-downloads.html.
This software was built from source available at
https://github.com/oracle/solaris-userland. The original community
source was downloaded from http://prdownloads.sourceforge.net/tcl/tcl-
core8.6.7-src.tar.gz.
Further information about this software can be found on the open source
community website at https://www.tcl.tk/.
Tcl 8.3 Tcl_StackChannel(3tcl)