Import Tcl-core 8.6.6 (as of svn r86089)

doc/ChnlStack.3

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+'\"
+'\" Copyright (c) 1999-2000 Ajuba Solutions.
+'\"
+'\" See the file "license.terms" for information on usage and redistribution
+'\" of this file, and for a DISCLAIMER OF ALL WARRANTIES.
+.TH Tcl_StackChannel 3 8.3 Tcl "Tcl Library Procedures"
+.so man.macros
+.BS
+'\" Note:  do not modify the .SH NAME line immediately below!
+.SH NAME
+Tcl_StackChannel, Tcl_UnstackChannel, Tcl_GetStackedChannel, Tcl_GetTopChannel \- manipulate stacked I/O channels
+.SH SYNOPSIS
+.nf
+.nf
+\fB#include <tcl.h>\fR
+.sp
+Tcl_Channel
+\fBTcl_StackChannel\fR(\fIinterp, typePtr, clientData, mask, channel\fR)
+.sp
+int
+\fBTcl_UnstackChannel\fR(\fIinterp, channel\fR)
+.sp
+Tcl_Channel
+\fBTcl_GetStackedChannel\fR(\fIchannel\fR)
+.sp
+Tcl_Channel
+\fBTcl_GetTopChannel\fR(\fIchannel\fR)
+.sp
+.SH ARGUMENTS
+.AS Tcl_ChannelType clientData
+.AP Tcl_Interp *interp in
+Interpreter for error reporting.
+.AP "const Tcl_ChannelType" *typePtr in
+The new channel I/O procedures to use for \fIchannel\fR.
+.AP ClientData clientData in
+Arbitrary one-word value to pass to channel I/O procedures.
+.AP int mask in
+Conditions under which \fIchannel\fR will be used: OR-ed combination of
+\fBTCL_READABLE\fR, \fBTCL_WRITABLE\fR and \fBTCL_EXCEPTION\fR.
+This can be a subset of the operations currently allowed on \fIchannel\fR.
+.AP Tcl_Channel channel in
+An existing Tcl channel such as returned by \fBTcl_CreateChannel\fR.
+.BE
+
+.SH DESCRIPTION
+.PP
+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.
+.PP
+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 \fBTCL_CHANNEL_VERSION_2\fR
+\fBTcl_ChannelType\fR structure.  See \fBTcl_CreateChannel\fR for details.
+.PP
+\fBTcl_StackChannel\fR stacks a new \fIchannel\fR on an existing channel
+with the same name that was registered for \fIchannel\fR by
+\fBTcl_RegisterChannel\fR.
+.PP
+\fBTcl_StackChannel\fR 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.
+.PP
+The \fImask\fR 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 \fBTcl_StackChannel\fR call.
+.PP
+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.
+.PP
+\fBTcl_UnstackChannel\fR reverses the process.  The old channel is
+associated with the channel name, and the processing module added by
+\fBTcl_StackChannel\fR is destroyed.  If there is no old channel, then
+\fBTcl_UnstackChannel\fR is equivalent to \fBTcl_Close\fR.  If an error
+occurs unstacking the channel, \fBTCL_ERROR\fR is returned, otherwise
+\fBTCL_OK\fR is returned.
+.PP
+\fBTcl_GetTopChannel\fR returns the top channel in the stack of
+channels the supplied channel is part of.
+.PP
+\fBTcl_GetStackedChannel\fR returns the channel in the stack of
+channels which is just below the supplied channel.
+
+.SH "SEE ALSO"
+Notifier(3), Tcl_CreateChannel(3), Tcl_OpenFileChannel(3), vwait(n).
+
+.SH KEYWORDS
+channel, compression