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-'\"
-'\" Copyright (c) 1996-1997 Sun Microsystems, Inc.
-'\" Copyright (c) 1997-2000 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_CreateChannel 3 8.4 Tcl "Tcl Library Procedures"
-.so man.macros
-.BS
-'\" Note:  do not modify the .SH NAME line immediately below!
-.SH NAME
-Tcl_CreateChannel, Tcl_GetChannelInstanceData, Tcl_GetChannelType, Tcl_GetChannelName, Tcl_GetChannelHandle, Tcl_GetChannelMode, Tcl_GetChannelBufferSize, Tcl_SetChannelBufferSize, Tcl_NotifyChannel, Tcl_BadChannelOption, Tcl_ChannelName, Tcl_ChannelVersion, Tcl_ChannelBlockModeProc, Tcl_ChannelCloseProc, Tcl_ChannelClose2Proc, Tcl_ChannelInputProc, Tcl_ChannelOutputProc, Tcl_ChannelSeekProc, Tcl_ChannelWideSeekProc, Tcl_ChannelTruncateProc, Tcl_ChannelSetOptionProc, Tcl_ChannelGetOptionProc, Tcl_ChannelWatchProc, Tcl_ChannelGetHandleProc, Tcl_ChannelFlushProc, Tcl_ChannelHandlerProc, Tcl_ChannelThreadActionProc, Tcl_IsChannelShared, Tcl_IsChannelRegistered, Tcl_CutChannel, Tcl_SpliceChannel, Tcl_IsChannelExisting, Tcl_ClearChannelHandlers, Tcl_GetChannelThread, Tcl_ChannelBuffered \- procedures for creating and manipulating channels
-.SH SYNOPSIS
-.nf
-\fB#include <tcl.h>\fR
-.sp
-Tcl_Channel
-\fBTcl_CreateChannel\fR(\fItypePtr, channelName, instanceData, mask\fR)
-.sp
-ClientData
-\fBTcl_GetChannelInstanceData\fR(\fIchannel\fR)
-.sp
-const Tcl_ChannelType *
-\fBTcl_GetChannelType\fR(\fIchannel\fR)
-.sp
-const char *
-\fBTcl_GetChannelName\fR(\fIchannel\fR)
-.sp
-int
-\fBTcl_GetChannelHandle\fR(\fIchannel, direction, handlePtr\fR)
-.sp
-Tcl_ThreadId
-\fBTcl_GetChannelThread\fR(\fIchannel\fR)
-.sp
-int
-\fBTcl_GetChannelMode\fR(\fIchannel\fR)
-.sp
-int
-\fBTcl_GetChannelBufferSize\fR(\fIchannel\fR)
-.sp
-\fBTcl_SetChannelBufferSize\fR(\fIchannel, size\fR)
-.sp
-\fBTcl_NotifyChannel\fR(\fIchannel, mask\fR)
-.sp
-int
-\fBTcl_BadChannelOption\fR(\fIinterp, optionName, optionList\fR)
-.sp
-int
-\fBTcl_IsChannelShared\fR(\fIchannel\fR)
-.sp
-int
-\fBTcl_IsChannelRegistered\fR(\fIinterp, channel\fR)
-.sp
-int
-\fBTcl_IsChannelExisting\fR(\fIchannelName\fR)
-.sp
-void
-\fBTcl_CutChannel\fR(\fIchannel\fR)
-.sp
-void
-\fBTcl_SpliceChannel\fR(\fIchannel\fR)
-.sp
-void
-\fBTcl_ClearChannelHandlers\fR(\fIchannel\fR)
-.sp
-int
-\fBTcl_ChannelBuffered\fR(\fIchannel\fR)
-.sp
-const char *
-\fBTcl_ChannelName\fR(\fItypePtr\fR)
-.sp
-Tcl_ChannelTypeVersion
-\fBTcl_ChannelVersion\fR(\fItypePtr\fR)
-.sp
-Tcl_DriverBlockModeProc *
-\fBTcl_ChannelBlockModeProc\fR(\fItypePtr\fR)
-.sp
-Tcl_DriverCloseProc *
-\fBTcl_ChannelCloseProc\fR(\fItypePtr\fR)
-.sp
-Tcl_DriverClose2Proc *
-\fBTcl_ChannelClose2Proc\fR(\fItypePtr\fR)
-.sp
-Tcl_DriverInputProc *
-\fBTcl_ChannelInputProc\fR(\fItypePtr\fR)
-.sp
-Tcl_DriverOutputProc *
-\fBTcl_ChannelOutputProc\fR(\fItypePtr\fR)
-.sp
-Tcl_DriverSeekProc *
-\fBTcl_ChannelSeekProc\fR(\fItypePtr\fR)
-.sp
-Tcl_DriverWideSeekProc *
-\fBTcl_ChannelWideSeekProc\fR(\fItypePtr\fR)
-.sp
-Tcl_DriverThreadActionProc *
-\fBTcl_ChannelThreadActionProc\fR(\fItypePtr\fR)
-.sp
-Tcl_DriverTruncateProc *
-\fBTcl_ChannelTruncateProc\fR(\fItypePtr\fR)
-.sp
-Tcl_DriverSetOptionProc *
-\fBTcl_ChannelSetOptionProc\fR(\fItypePtr\fR)
-.sp
-Tcl_DriverGetOptionProc *
-\fBTcl_ChannelGetOptionProc\fR(\fItypePtr\fR)
-.sp
-Tcl_DriverWatchProc *
-\fBTcl_ChannelWatchProc\fR(\fItypePtr\fR)
-.sp
-Tcl_DriverGetHandleProc *
-\fBTcl_ChannelGetHandleProc\fR(\fItypePtr\fR)
-.sp
-Tcl_DriverFlushProc *
-\fBTcl_ChannelFlushProc\fR(\fItypePtr\fR)
-.sp
-Tcl_DriverHandlerProc *
-\fBTcl_ChannelHandlerProc\fR(\fItypePtr\fR)
-.sp
-.SH ARGUMENTS
-.AS "const Tcl_ChannelType" *channelName
-.AP "const Tcl_ChannelType" *typePtr in
-Points to a structure containing the addresses of procedures that
-can be called to perform I/O and other functions on the channel.
-.AP "const char" *channelName in
-The name of this channel, such as \fBfile3\fR; must not be in use
-by any other channel. Can be NULL, in which case the channel is
-created without a name. If the created channel is assigned to one
-of the standard channels (\fBstdin\fR, \fBstdout\fR or \fBstderr\fR),
-the assigned channel name will be the name of the standard channel.
-.AP ClientData instanceData in
-Arbitrary one-word value to be associated with this channel.  This
-value is passed to procedures in \fItypePtr\fR when they are invoked.
-.AP int mask in
-OR-ed combination of \fBTCL_READABLE\fR and \fBTCL_WRITABLE\fR to indicate
-whether a channel is readable and writable.
-.AP Tcl_Channel channel in
-The channel to operate on.
-.AP int direction in
-\fBTCL_READABLE\fR means the input handle is wanted; \fBTCL_WRITABLE\fR
-means the output handle is wanted.
-.AP ClientData *handlePtr out
-Points to the location where the desired OS-specific handle should be
-stored.
-.AP int size in
-The size, in bytes, of buffers to allocate in this channel.
-.AP int mask in
-An OR-ed combination of \fBTCL_READABLE\fR, \fBTCL_WRITABLE\fR
-and \fBTCL_EXCEPTION\fR that indicates events that have occurred on
-this channel.
-.AP Tcl_Interp *interp in
-Current interpreter. (can be NULL)
-.AP "const char" *optionName in
-Name of the invalid option.
-.AP "const char" *optionList in
-Specific options list (space separated words, without
-.QW \- )
-to append to the standard generic options list.
-Can be NULL for generic options error message only.
-.BE
-.SH DESCRIPTION
-.PP
-Tcl uses a two-layered channel architecture. It provides a generic upper
-layer to enable C and Tcl programs to perform input and output using the
-same APIs for a variety of files, devices, sockets etc. The generic C APIs
-are described in the manual entry for \fBTcl_OpenFileChannel\fR.
-.PP
-The lower layer provides type-specific channel drivers for each type
-of device supported on each platform.  This manual entry describes the
-C APIs used to communicate between the generic layer and the
-type-specific channel drivers.  It also explains how new types of
-channels can be added by providing new channel drivers.
-.PP
-Channel drivers consist of a number of components: First, each channel
-driver provides a \fBTcl_ChannelType\fR structure containing pointers to
-functions implementing the various operations used by the generic layer to
-communicate with the channel driver. The \fBTcl_ChannelType\fR structure
-and the functions referenced by it are described in the section
-\fBTCL_CHANNELTYPE\fR, below.
-.PP
-Second, channel drivers usually provide a Tcl command to create
-instances of that type of channel. For example, the Tcl \fBopen\fR
-command creates channels that use the file and command channel
-drivers, and the Tcl \fBsocket\fR command creates channels that use
-TCP sockets for network communication.
-.PP
-Third, a channel driver optionally provides a C function to open
-channel instances of that type. For example, \fBTcl_OpenFileChannel\fR
-opens a channel that uses the file channel driver, and
-\fBTcl_OpenTcpClient\fR opens a channel that uses the TCP network
-protocol.  These creation functions typically use
-\fBTcl_CreateChannel\fR internally to open the channel.
-.PP
-To add a new type of channel you must implement a C API or a Tcl command
-that opens a channel by invoking \fBTcl_CreateChannel\fR.
-When your driver calls \fBTcl_CreateChannel\fR it passes in
-a \fBTcl_ChannelType\fR structure describing the driver's I/O
-procedures.
-The generic layer will then invoke the functions referenced in that
-structure to perform operations on the channel.
-.PP
-\fBTcl_CreateChannel\fR opens a new channel and associates the supplied
-\fItypePtr\fR and \fIinstanceData\fR with it. The channel is opened in the
-mode indicated by \fImask\fR.
-For a discussion of channel drivers, their operations and the
-\fBTcl_ChannelType\fR structure, see the section \fBTCL_CHANNELTYPE\fR, below.
-.PP
-\fBTcl_CreateChannel\fR interacts with the code managing the standard
-channels. Once a standard channel was initialized either through a
-call to \fBTcl_GetStdChannel\fR or a call to \fBTcl_SetStdChannel\fR
-closing this standard channel will cause the next call to
-\fBTcl_CreateChannel\fR to make the new channel the new standard
-channel too. See \fBTcl_StandardChannels\fR for a general treatise
-about standard channels and the behavior of the Tcl library with
-regard to them.
-.PP
-\fBTcl_GetChannelInstanceData\fR returns the instance data associated with
-the channel in \fIchannel\fR. This is the same as the \fIinstanceData\fR
-argument in the call to \fBTcl_CreateChannel\fR that created this channel.
-.PP
-\fBTcl_GetChannelType\fR returns a pointer to the \fBTcl_ChannelType\fR
-structure used by the channel in the \fIchannel\fR argument. This is
-the same as the \fItypePtr\fR argument in the call to
-\fBTcl_CreateChannel\fR that created this channel.
-.PP
-\fBTcl_GetChannelName\fR returns a string containing the name associated
-with the channel, or NULL if the \fIchannelName\fR argument to
-\fBTcl_CreateChannel\fR was NULL.
-.PP
-\fBTcl_GetChannelHandle\fR places the OS-specific device handle
-associated with \fIchannel\fR for the given \fIdirection\fR in the
-location specified by \fIhandlePtr\fR and returns \fBTCL_OK\fR.  If
-the channel does not have a device handle for the specified direction,
-then \fBTCL_ERROR\fR is returned instead.  Different channel drivers
-will return different types of handle.  Refer to the manual entries
-for each driver to determine what type of handle is returned.
-.PP
-\fBTcl_GetChannelThread\fR returns the id of the thread currently managing
-the specified \fIchannel\fR. This allows channel drivers to send their file
-events to the correct event queue even for a multi-threaded core.
-.PP
-\fBTcl_GetChannelMode\fR returns an OR-ed combination of \fBTCL_READABLE\fR
-and \fBTCL_WRITABLE\fR, indicating whether the channel is open for input
-and output.
-.PP
-\fBTcl_GetChannelBufferSize\fR returns the size, in bytes, of buffers
-allocated to store input or output in \fIchannel\fR. If the value was not set
-by a previous call to \fBTcl_SetChannelBufferSize\fR, described below, then
-the default value of 4096 is returned.
-.PP
-\fBTcl_SetChannelBufferSize\fR sets the size, in bytes, of buffers that
-will be allocated in subsequent operations on the channel to store input or
-output. The \fIsize\fR argument should be between one and one million,
-allowing buffers of one byte to one million bytes. If \fIsize\fR is
-outside this range, \fBTcl_SetChannelBufferSize\fR sets the buffer size to
-4096.
-.PP
-\fBTcl_NotifyChannel\fR is called by a channel driver to indicate to
-the generic layer that the events specified by \fImask\fR have
-occurred on the channel.  Channel drivers are responsible for invoking
-this function whenever the channel handlers need to be called for the
-channel.  See \fBWATCHPROC\fR below for more details.
-.PP
-\fBTcl_BadChannelOption\fR is called from driver specific
-\fIsetOptionProc\fR or \fIgetOptionProc\fR to generate a complete
-error message.
-.PP
-\fBTcl_ChannelBuffered\fR returns the number of bytes of input
-currently buffered in the internal buffer (push back area) of the
-channel itself. It does not report about the data in the overall
-buffers for the stack of channels the supplied channel is part of.
-.PP
-\fBTcl_IsChannelShared\fR checks the refcount of the specified
-\fIchannel\fR and returns whether the \fIchannel\fR was shared among
-multiple interpreters (result == 1) or not (result == 0).
-.PP
-\fBTcl_IsChannelRegistered\fR checks whether the specified \fIchannel\fR is
-registered in the given \fIinterp\fRreter (result == 1) or not
-(result == 0).
-.PP
-\fBTcl_IsChannelExisting\fR checks whether a channel with the specified
-name is registered in the (thread)-global list of all channels (result
-== 1) or not (result == 0).
-.PP
-\fBTcl_CutChannel\fR removes the specified \fIchannel\fR from the
-(thread)global list of all channels (of the current thread).
-Application to a channel still registered in some interpreter
-is not allowed.
-Also notifies the driver if the \fBTcl_ChannelType\fR version is
-\fBTCL_CHANNEL_VERSION_4\fR (or higher), and
-\fBTcl_DriverThreadActionProc\fR is defined for it.
-.PP
-\fBTcl_SpliceChannel\fR adds the specified \fIchannel\fR to the
-(thread)global list of all channels (of the current thread).
-Application to a channel registered in some interpreter is not allowed.
-Also notifies the driver if the \fBTcl_ChannelType\fR version is
-\fBTCL_CHANNEL_VERSION_4\fR (or higher), and
-\fBTcl_DriverThreadActionProc\fR is defined for it.
-.PP
-\fBTcl_ClearChannelHandlers\fR removes all channel handlers and event
-scripts associated with the specified \fIchannel\fR, thus shutting
-down all event processing for this channel.
-.SH TCL_CHANNELTYPE
-.PP
-A channel driver provides a \fBTcl_ChannelType\fR structure that contains
-pointers to functions that implement the various operations on a channel;
-these operations are invoked as needed by the generic layer.  The structure
-was versioned starting in Tcl 8.3.2/8.4 to correct a problem with stacked
-channel drivers.  See the \fBOLD CHANNEL TYPES\fR section below for
-details about the old structure.
-.PP
-The \fBTcl_ChannelType\fR structure contains the following fields:
-.PP
-.CS
-typedef struct Tcl_ChannelType {
-        const char *\fItypeName\fR;
-        Tcl_ChannelTypeVersion \fIversion\fR;
-        Tcl_DriverCloseProc *\fIcloseProc\fR;
-        Tcl_DriverInputProc *\fIinputProc\fR;
-        Tcl_DriverOutputProc *\fIoutputProc\fR;
-        Tcl_DriverSeekProc *\fIseekProc\fR;
-        Tcl_DriverSetOptionProc *\fIsetOptionProc\fR;
-        Tcl_DriverGetOptionProc *\fIgetOptionProc\fR;
-        Tcl_DriverWatchProc *\fIwatchProc\fR;
-        Tcl_DriverGetHandleProc *\fIgetHandleProc\fR;
-        Tcl_DriverClose2Proc *\fIclose2Proc\fR;
-        Tcl_DriverBlockModeProc *\fIblockModeProc\fR;
-        Tcl_DriverFlushProc *\fIflushProc\fR;
-        Tcl_DriverHandlerProc *\fIhandlerProc\fR;
-        Tcl_DriverWideSeekProc *\fIwideSeekProc\fR;
-        Tcl_DriverThreadActionProc *\fIthreadActionProc\fR;
-        Tcl_DriverTruncateProc *\fItruncateProc\fR;
-} \fBTcl_ChannelType\fR;
-.CE
-.PP
-It is not necessary to provide implementations for all channel
-operations.  Those which are not necessary may be set to NULL in the
-struct: \fIblockModeProc\fR, \fIseekProc\fR, \fIsetOptionProc\fR,
-\fIgetOptionProc\fR, \fIgetHandleProc\fR, and \fIclose2Proc\fR, in addition to
-\fIflushProc\fR, \fIhandlerProc\fR, \fIthreadActionProc\fR, and
-\fItruncateProc\fR.  Other functions that cannot be implemented in a
-meaningful way should return \fBEINVAL\fR when called, to indicate
-that the operations they represent are not available. Also note that
-\fIwideSeekProc\fR can be NULL if \fIseekProc\fR is.
-.PP
-The user should only use the above structure for \fBTcl_ChannelType\fR
-instantiation.  When referencing fields in a \fBTcl_ChannelType\fR
-structure, the following functions should be used to obtain the values:
-\fBTcl_ChannelName\fR, \fBTcl_ChannelVersion\fR,
-\fBTcl_ChannelBlockModeProc\fR, \fBTcl_ChannelCloseProc\fR,
-\fBTcl_ChannelClose2Proc\fR, \fBTcl_ChannelInputProc\fR,
-\fBTcl_ChannelOutputProc\fR, \fBTcl_ChannelSeekProc\fR,
-\fBTcl_ChannelWideSeekProc\fR, \fBTcl_ChannelThreadActionProc\fR,
-\fBTcl_ChannelTruncateProc\fR,
-\fBTcl_ChannelSetOptionProc\fR, \fBTcl_ChannelGetOptionProc\fR,
-\fBTcl_ChannelWatchProc\fR, \fBTcl_ChannelGetHandleProc\fR,
-\fBTcl_ChannelFlushProc\fR, or \fBTcl_ChannelHandlerProc\fR.
-.PP
-The change to the structures was made in such a way that standard channel
-types are binary compatible.  However, channel types that use stacked
-channels (i.e. TLS, Trf) have new versions to correspond to the above change
-since the previous code for stacked channels had problems.
-.SS TYPENAME
-.PP
-The \fItypeName\fR field contains a null-terminated string that
-identifies the type of the device implemented by this driver, e.g.
-\fBfile\fR or \fBsocket\fR.
-.PP
-This value can be retrieved with \fBTcl_ChannelName\fR, which returns
-a pointer to the string.
-.SS VERSION
-.PP
-
-The \fIversion\fR field should be set to the version of the structure
-that you require. \fBTCL_CHANNEL_VERSION_2\fR is the minimum recommended.
-\fBTCL_CHANNEL_VERSION_3\fR must be set to specify the \fIwideSeekProc\fR member.
-\fBTCL_CHANNEL_VERSION_4\fR must be set to specify the \fIthreadActionProc\fR member
-(includes \fIwideSeekProc\fR).
-\fBTCL_CHANNEL_VERSION_5\fR must be set to specify the
-\fItruncateProc\fR members (includes
-\fIwideSeekProc\fR and \fIthreadActionProc\fR).
-If it is not set to any of these, then this
-\fBTcl_ChannelType\fR is assumed to have the original structure.  See
-\fBOLD CHANNEL TYPES\fR for more details.  While Tcl will recognize
-and function with either structures, stacked channels must be of at
-least \fBTCL_CHANNEL_VERSION_2\fR to function correctly.
-.PP
-This value can be retrieved with \fBTcl_ChannelVersion\fR, which returns
-one of
-\fBTCL_CHANNEL_VERSION_5\fR,
-\fBTCL_CHANNEL_VERSION_4\fR,
-\fBTCL_CHANNEL_VERSION_3\fR,
-\fBTCL_CHANNEL_VERSION_2\fR or \fBTCL_CHANNEL_VERSION_1\fR.
-.SS BLOCKMODEPROC
-.PP
-The \fIblockModeProc\fR field contains the address of a function called by
-the generic layer to set blocking and nonblocking mode on the device.
-\fIBlockModeProc\fR should match the following prototype:
-.PP
-.CS
-typedef int \fBTcl_DriverBlockModeProc\fR(
-        ClientData \fIinstanceData\fR,
-        int \fImode\fR);
-.CE
-.PP
-The \fIinstanceData\fR is the same as the value passed to
-\fBTcl_CreateChannel\fR when this channel was created.  The \fImode\fR
-argument is either \fBTCL_MODE_BLOCKING\fR or \fBTCL_MODE_NONBLOCKING\fR to
-set the device into blocking or nonblocking mode. The function should
-return zero if the operation was successful, or a nonzero POSIX error code
-if the operation failed.
-.PP
-If the operation is successful, the function can modify the supplied
-\fIinstanceData\fR to record that the channel entered blocking or
-nonblocking mode and to implement the blocking or nonblocking behavior.
-For some device types, the blocking and nonblocking behavior can be
-implemented by the underlying operating system; for other device types, the
-behavior must be emulated in the channel driver.
-.PP
-This value can be retrieved with \fBTcl_ChannelBlockModeProc\fR, which returns
-a pointer to the function.
-.PP
-A channel driver \fBnot\fR supplying a \fIblockModeProc\fR has to be
-very, very careful. It has to tell the generic layer exactly which
-blocking mode is acceptable to it, and should this also document for
-the user so that the blocking mode of the channel is not changed to an
-unacceptable value. Any confusion here may lead the interpreter into a
-(spurious and difficult to find) deadlock.
-.SS "CLOSEPROC AND CLOSE2PROC"
-.PP
-The \fIcloseProc\fR field contains the address of a function called by the
-generic layer to clean up driver-related information when the channel is
-closed. \fICloseProc\fR must match the following prototype:
-.PP
-.CS
-typedef int \fBTcl_DriverCloseProc\fR(
-        ClientData \fIinstanceData\fR,
-        Tcl_Interp *\fIinterp\fR);
-.CE
-.PP
-The \fIinstanceData\fR argument is the same as the value provided to
-\fBTcl_CreateChannel\fR when the channel was created. The function should
-release any storage maintained by the channel driver for this channel, and
-close the input and output devices encapsulated by this channel. All queued
-output will have been flushed to the device before this function is called,
-and no further driver operations will be invoked on this instance after
-calling the \fIcloseProc\fR. If the close operation is successful, the
-procedure should return zero; otherwise it should return a nonzero POSIX
-error code. In addition, if an error occurs and \fIinterp\fR is not NULL,
-the procedure should store an error message in the interpreter's result.
-.PP
-Alternatively, channels that support closing the read and write sides
-independently may set \fIcloseProc\fR to \fBTCL_CLOSE2PROC\fR and set
-\fIclose2Proc\fR to the address of a function that matches the
-following prototype:
-.PP
-.CS
-typedef int \fBTcl_DriverClose2Proc\fR(
-        ClientData \fIinstanceData\fR,
-        Tcl_Interp *\fIinterp\fR,
-        int \fIflags\fR);
-.CE
-.PP
-The \fIclose2Proc\fR will be called with \fIflags\fR set to an OR'ed
-combination of \fBTCL_CLOSE_READ\fR or \fBTCL_CLOSE_WRITE\fR to
-indicate that the driver should close the read and/or write side of
-the channel.  The channel driver may be invoked to perform
-additional operations on the channel after \fIclose2Proc\fR is
-called to close one or both sides of the channel.  If \fIflags\fR is
-\fB0\fR (zero), the driver should close the channel in the manner
-described above for \fIcloseProc\fR.  No further operations will be
-invoked on this instance after \fIclose2Proc\fR is called with all
-flags cleared.  In all cases, the \fIclose2Proc\fR function should
-return zero if the close operation was successful; otherwise it should
-return a nonzero POSIX error code. In addition, if an error occurs and
-\fIinterp\fR is not NULL, the procedure should store an error message
-in the interpreter's result.
-.PP
-The \fIcloseProc\fR and \fIclose2Proc\fR values can be retrieved with
-\fBTcl_ChannelCloseProc\fR or \fBTcl_ChannelClose2Proc\fR, which
-return a pointer to the respective function.
-.SS INPUTPROC
-.PP
-The \fIinputProc\fR field contains the address of a function called by the
-generic layer to read data from the file or device and store it in an
-internal buffer. \fIInputProc\fR must match the following prototype:
-.PP
-.CS
-typedef int \fBTcl_DriverInputProc\fR(
-        ClientData \fIinstanceData\fR,
-        char *\fIbuf\fR,
-        int \fIbufSize\fR,
-        int *\fIerrorCodePtr\fR);
-.CE
-.PP
-\fIInstanceData\fR is the same as the value passed to
-\fBTcl_CreateChannel\fR when the channel was created.  The \fIbuf\fR
-argument points to an array of bytes in which to store input from the
-device, and the \fIbufSize\fR argument indicates how many bytes are
-available at \fIbuf\fR.
-.PP
-The \fIerrorCodePtr\fR argument points to an integer variable provided by
-the generic layer. If an error occurs, the function should set the variable
-to a POSIX error code that identifies the error that occurred.
-.PP
-The function should read data from the input device encapsulated by the
-channel and store it at \fIbuf\fR.  On success, the function should return
-a nonnegative integer indicating how many bytes were read from the input
-device and stored at \fIbuf\fR. On error, the function should return -1. If
-an error occurs after some data has been read from the device, that data is
-lost.
-.PP
-If \fIinputProc\fR can determine that the input device has some data
-available but less than requested by the \fIbufSize\fR argument, the
-function should only attempt to read as much data as is available and
-return without blocking. If the input device has no data available
-whatsoever and the channel is in nonblocking mode, the function should
-return an \fBEAGAIN\fR error. If the input device has no data available
-whatsoever and the channel is in blocking mode, the function should block
-for the shortest possible time until at least one byte of data can be read
-from the device; then, it should return as much data as it can read without
-blocking.
-.PP
-This value can be retrieved with \fBTcl_ChannelInputProc\fR, which returns
-a pointer to the function.
-.SS OUTPUTPROC
-.PP
-The \fIoutputProc\fR field contains the address of a function called by the
-generic layer to transfer data from an internal buffer to the output device.
-\fIOutputProc\fR must match the following prototype:
-.PP
-.CS
-typedef int \fBTcl_DriverOutputProc\fR(
-        ClientData \fIinstanceData\fR,
-        const char *\fIbuf\fR,
-        int \fItoWrite\fR,
-        int *\fIerrorCodePtr\fR);
-.CE
-.PP
-\fIInstanceData\fR is the same as the value passed to
-\fBTcl_CreateChannel\fR when the channel was created. The \fIbuf\fR
-argument contains an array of bytes to be written to the device, and the
-\fItoWrite\fR argument indicates how many bytes are to be written from the
-\fIbuf\fR argument.
-.PP
-The \fIerrorCodePtr\fR argument points to an integer variable provided by
-the generic layer. If an error occurs, the function should set this
-variable to a POSIX error code that identifies the error.
-.PP
-The function should write the data at \fIbuf\fR to the output device
-encapsulated by the channel. On success, the function should return a
-nonnegative integer indicating how many bytes were written to the output
-device.  The return value is normally the same as \fItoWrite\fR, but may be
-less in some cases such as if the output operation is interrupted by a
-signal. If an error occurs the function should return -1.  In case of
-error, some data may have been written to the device.
-.PP
-If the channel is nonblocking and the output device is unable to absorb any
-data whatsoever, the function should return -1 with an \fBEAGAIN\fR error
-without writing any data.
-.PP
-This value can be retrieved with \fBTcl_ChannelOutputProc\fR, which returns
-a pointer to the function.
-.SS "SEEKPROC AND WIDESEEKPROC"
-.PP
-The \fIseekProc\fR field contains the address of a function called by the
-generic layer to move the access point at which subsequent input or output
-operations will be applied. \fISeekProc\fR must match the following
-prototype:
-.PP
-.CS
-typedef int \fBTcl_DriverSeekProc\fR(
-        ClientData \fIinstanceData\fR,
-        long \fIoffset\fR,
-        int \fIseekMode\fR,
-        int *\fIerrorCodePtr\fR);
-.CE
-.PP
-The \fIinstanceData\fR argument is the same as the value given to
-\fBTcl_CreateChannel\fR when this channel was created.  \fIOffset\fR and
-\fIseekMode\fR have the same meaning as for the \fBTcl_Seek\fR
-procedure (described in the manual entry for \fBTcl_OpenFileChannel\fR).
-.PP
-The \fIerrorCodePtr\fR argument points to an integer variable provided by
-the generic layer for returning \fBerrno\fR values from the function.  The
-function should set this variable to a POSIX error code if an error occurs.
-The function should store an \fBEINVAL\fR error code if the channel type
-does not implement seeking.
-.PP
-The return value is the new access point or -1 in case of error. If an
-error occurred, the function should not move the access point.
-.PP
-If there is a non-NULL \fIseekProc\fR field, the \fIwideSeekProc\fR
-field may contain the address of an alternative function to use which
-handles wide (i.e. larger than 32-bit) offsets, so allowing seeks
-within files larger than 2GB.  The \fIwideSeekProc\fR will be called
-in preference to the \fIseekProc\fR, but both must be defined if the
-\fIwideSeekProc\fR is defined.  \fIWideSeekProc\fR must match the
-following prototype:
-.PP
-.CS
-typedef Tcl_WideInt \fBTcl_DriverWideSeekProc\fR(
-        ClientData \fIinstanceData\fR,
-        Tcl_WideInt \fIoffset\fR,
-        int \fIseekMode\fR,
-        int *\fIerrorCodePtr\fR);
-.CE
-.PP
-The arguments and return values mean the same thing as with
-\fIseekProc\fR above, except that the type of offsets and the return
-type are different.
-.PP
-The \fIseekProc\fR value can be retrieved with
-\fBTcl_ChannelSeekProc\fR, which returns a pointer to the function,
-and similarly the \fIwideSeekProc\fR can be retrieved with
-\fBTcl_ChannelWideSeekProc\fR.
-.SS SETOPTIONPROC
-.PP
-The \fIsetOptionProc\fR field contains the address of a function called by
-the generic layer to set a channel type specific option on a channel.
-\fIsetOptionProc\fR must match the following prototype:
-.PP
-.CS
-typedef int \fBTcl_DriverSetOptionProc\fR(
-        ClientData \fIinstanceData\fR,
-        Tcl_Interp *\fIinterp\fR,
-        const char *\fIoptionName\fR,
-        const char *\fInewValue\fR);
-.CE
-.PP
-\fIoptionName\fR is the name of an option to set, and \fInewValue\fR is
-the new value for that option, as a string. The \fIinstanceData\fR is the
-same as the value given to \fBTcl_CreateChannel\fR when this channel was
-created. The function should do whatever channel type specific action is
-required to implement the new value of the option.
-.PP
-Some options are handled by the generic code and this function is never
-called to set them, e.g. \fB\-blockmode\fR. Other options are specific to
-each channel type and the \fIsetOptionProc\fR procedure of the channel
-driver will get called to implement them. The \fIsetOptionProc\fR field can
-be NULL, which indicates that this channel type supports no type specific
-options.
-.PP
-If the option value is successfully modified to the new value, the function
-returns \fBTCL_OK\fR.
-It should call \fBTcl_BadChannelOption\fR which itself returns
-\fBTCL_ERROR\fR if the \fIoptionName\fR is
-unrecognized.
-If \fInewValue\fR specifies a value for the option that
-is not supported or if a system call error occurs,
-the function should leave an error message in the
-\fIresult\fR field of \fIinterp\fR if \fIinterp\fR is not NULL. The
-function should also call \fBTcl_SetErrno\fR to store an appropriate POSIX
-error code.
-.PP
-This value can be retrieved with \fBTcl_ChannelSetOptionProc\fR, which returns
-a pointer to the function.
-.SS GETOPTIONPROC
-.PP
-The \fIgetOptionProc\fR field contains the address of a function called by
-the generic layer to get the value of a channel type specific option on a
-channel. \fIgetOptionProc\fR must match the following prototype:
-.PP
-.CS
-typedef int \fBTcl_DriverGetOptionProc\fR(
-        ClientData \fIinstanceData\fR,
-        Tcl_Interp *\fIinterp\fR,
-        const char *\fIoptionName\fR,
-        Tcl_DString *\fIoptionValue\fR);
-.CE
-.PP
-\fIOptionName\fR is the name of an option supported by this type of
-channel. If the option name is not NULL, the function stores its current
-value, as a string, in the Tcl dynamic string \fIoptionValue\fR.
-If \fIoptionName\fR is NULL, the function stores in \fIoptionValue\fR an
-alternating list of all supported options and their current values.
-On success, the function returns \fBTCL_OK\fR.
-It should call \fBTcl_BadChannelOption\fR which itself returns
-\fBTCL_ERROR\fR if the \fIoptionName\fR is
-unrecognized. If a system call error occurs,
-the function should leave an error message in the
-result of \fIinterp\fR if \fIinterp\fR is not NULL. The
-function should also call \fBTcl_SetErrno\fR to store an appropriate POSIX
-error code.
-.PP
-Some options are handled by the generic code and this function is never
-called to retrieve their value, e.g. \fB\-blockmode\fR. Other options are
-specific to each channel type and the \fIgetOptionProc\fR procedure of the
-channel driver will get called to implement them. The \fIgetOptionProc\fR
-field can be NULL, which indicates that this channel type supports no type
-specific options.
-.PP
-This value can be retrieved with \fBTcl_ChannelGetOptionProc\fR, which returns
-a pointer to the function.
-.SS WATCHPROC
-.PP
-The \fIwatchProc\fR field contains the address of a function called
-by the generic layer to initialize the event notification mechanism to
-notice events of interest on this channel.
-\fIWatchProc\fR should match the following prototype:
-.PP
-.CS
-typedef void \fBTcl_DriverWatchProc\fR(
-        ClientData \fIinstanceData\fR,
-        int \fImask\fR);
-.CE
-.PP
-The \fIinstanceData\fR is the same as the value passed to
-\fBTcl_CreateChannel\fR when this channel was created. The \fImask\fR
-argument is an OR-ed combination of \fBTCL_READABLE\fR, \fBTCL_WRITABLE\fR
-and \fBTCL_EXCEPTION\fR; it indicates events the caller is interested in
-noticing on this channel.
-.PP
-The function should initialize device type specific mechanisms to
-notice when an event of interest is present on the channel.  When one
-or more of the designated events occurs on the channel, the channel
-driver is responsible for calling \fBTcl_NotifyChannel\fR to inform
-the generic channel module.  The driver should take care not to starve
-other channel drivers or sources of callbacks by invoking
-Tcl_NotifyChannel too frequently.  Fairness can be insured by using
-the Tcl event queue to allow the channel event to be scheduled in sequence
-with other events.  See the description of \fBTcl_QueueEvent\fR for
-details on how to queue an event.
-.PP
-This value can be retrieved with \fBTcl_ChannelWatchProc\fR, which returns
-a pointer to the function.
-.SS GETHANDLEPROC
-.PP
-The \fIgetHandleProc\fR field contains the address of a function called by
-the generic layer to retrieve a device-specific handle from the channel.
-\fIGetHandleProc\fR should match the following prototype:
-.PP
-.CS
-typedef int \fBTcl_DriverGetHandleProc\fR(
-        ClientData \fIinstanceData\fR,
-        int \fIdirection\fR,
-        ClientData *\fIhandlePtr\fR);
-.CE
-.PP
-\fIInstanceData\fR is the same as the value passed to
-\fBTcl_CreateChannel\fR when this channel was created. The \fIdirection\fR
-argument is either \fBTCL_READABLE\fR to retrieve the handle used
-for input, or \fBTCL_WRITABLE\fR to retrieve the handle used for
-output.
-.PP
-If the channel implementation has device-specific handles, the
-function should retrieve the appropriate handle associated with the
-channel, according the \fIdirection\fR argument.  The handle should be
-stored in the location referred to by \fIhandlePtr\fR, and
-\fBTCL_OK\fR should be returned.  If the channel is not open for the
-specified direction, or if the channel implementation does not use
-device handles, the function should return \fBTCL_ERROR\fR.
-.PP
-This value can be retrieved with \fBTcl_ChannelGetHandleProc\fR, which returns
-a pointer to the function.
-.SS FLUSHPROC
-.PP
-The \fIflushProc\fR field is currently reserved for future use.
-It should be set to NULL.
-\fIFlushProc\fR should match the following prototype:
-.PP
-.CS
-typedef int \fBTcl_DriverFlushProc\fR(
-        ClientData \fIinstanceData\fR);
-.CE
-.PP
-This value can be retrieved with \fBTcl_ChannelFlushProc\fR, which returns
-a pointer to the function.
-.SS HANDLERPROC
-.PP
-The \fIhandlerProc\fR field contains the address of a function called by
-the generic layer to notify the channel that an event occurred.  It should
-be defined for stacked channel drivers that wish to be notified of events
-that occur on the underlying (stacked) channel.
-\fIHandlerProc\fR should match the following prototype:
-.PP
-.CS
-typedef int \fBTcl_DriverHandlerProc\fR(
-        ClientData \fIinstanceData\fR,
-        int \fIinterestMask\fR);
-.CE
-.PP
-\fIInstanceData\fR is the same as the value passed to \fBTcl_CreateChannel\fR
-when this channel was created.  The \fIinterestMask\fR is an OR-ed
-combination of \fBTCL_READABLE\fR or \fBTCL_WRITABLE\fR; it indicates what
-type of event occurred on this channel.
-.PP
-This value can be retrieved with \fBTcl_ChannelHandlerProc\fR, which returns
-a pointer to the function.
-
-.SS "THREADACTIONPROC"
-.PP
-The \fIthreadActionProc\fR field contains the address of the function
-called by the generic layer when a channel is created, closed, or
-going to move to a different thread, i.e. whenever thread-specific
-driver state might have to initialized or updated. It can be NULL.
-The action \fITCL_CHANNEL_THREAD_REMOVE\fR is used to notify the
-driver that it should update or remove any thread-specific data it
-might be maintaining for the channel.
-.PP
-The action \fITCL_CHANNEL_THREAD_INSERT\fR is used to notify the
-driver that it should update or initialize any thread-specific data it
-might be maintaining using the calling thread as the associate. See
-\fBTcl_CutChannel\fR and \fBTcl_SpliceChannel\fR for more detail.
-.PP
-.CS
-typedef void \fBTcl_DriverThreadActionProc\fR(
-        ClientData \fIinstanceData\fR,
-        int \fIaction\fR);
-.CE
-.PP
-\fIInstanceData\fR is the same as the value passed to
-\fBTcl_CreateChannel\fR when this channel was created.
-.PP
-These values can be retrieved with \fBTcl_ChannelThreadActionProc\fR,
-which returns a pointer to the function.
-.SS "TRUNCATEPROC"
-.PP
-The \fItruncateProc\fR field contains the address of the function
-called by the generic layer when a channel is truncated to some
-length. It can be NULL.
-.PP
-.CS
-typedef int \fBTcl_DriverTruncateProc\fR(
-        ClientData \fIinstanceData\fR,
-        Tcl_WideInt \fIlength\fR);
-.CE
-.PP
-\fIInstanceData\fR is the same as the value passed to
-\fBTcl_CreateChannel\fR when this channel was created, and
-\fIlength\fR is the new length of the underlying file, which should
-not be negative. The result should be 0 on success or an errno code
-(suitable for use with \fBTcl_SetErrno\fR) on failure.
-.PP
-These values can be retrieved with \fBTcl_ChannelTruncateProc\fR,
-which returns a pointer to the function.
-.SH TCL_BADCHANNELOPTION
-.PP
-This procedure generates a
-.QW "bad option"
-error message in an
-(optional) interpreter.  It is used by channel drivers when
-an invalid Set/Get option is requested. Its purpose is to concatenate
-the generic options list to the specific ones and factorize
-the generic options error message string.
-.PP
-It always returns \fBTCL_ERROR\fR
-.PP
-An error message is generated in \fIinterp\fR's result value to
-indicate that a command was invoked with a bad option.
-The message has the form
-.CS
-    bad option "blah": should be one of
-    <...generic options...>+<...specific options...>
-.CE
-so you get for instance:
-.CS
-    bad option "-blah": should be one of -blocking,
-    -buffering, -buffersize, -eofchar, -translation,
-    -peername, or -sockname
-.CE
-when called with \fIoptionList\fR equal to
-.QW "peername sockname"
-.PP
-.QW blah
-is the \fIoptionName\fR argument and
-.QW "<specific options>"
-is a space separated list of specific option words.
-The function takes good care of inserting minus signs before
-each option, commas after, and an
-.QW or
-before the last option.
-.SH "OLD CHANNEL TYPES"
-The original (8.3.1 and below) \fBTcl_ChannelType\fR structure contains
-the following fields:
-.PP
-.CS
-typedef struct Tcl_ChannelType {
-    const char *\fItypeName\fR;
-    Tcl_DriverBlockModeProc *\fIblockModeProc\fR;
-    Tcl_DriverCloseProc *\fIcloseProc\fR;
-    Tcl_DriverInputProc *\fIinputProc\fR;
-    Tcl_DriverOutputProc *\fIoutputProc\fR;
-    Tcl_DriverSeekProc *\fIseekProc\fR;
-    Tcl_DriverSetOptionProc *\fIsetOptionProc\fR;
-    Tcl_DriverGetOptionProc *\fIgetOptionProc\fR;
-    Tcl_DriverWatchProc *\fIwatchProc\fR;
-    Tcl_DriverGetHandleProc *\fIgetHandleProc\fR;
-    Tcl_DriverClose2Proc *\fIclose2Proc\fR;
-} \fBTcl_ChannelType\fR;
-.CE
-.PP
-It is still possible to create channel with the above structure.  The
-internal channel code will determine the version.  It is imperative to use
-the new \fBTcl_ChannelType\fR structure if you are creating a stacked
-channel driver, due to problems with the earlier stacked channel
-implementation (in 8.2.0 to 8.3.1).
-.PP
-Prior to 8.4.0 (i.e. during the later releases of 8.3 and early part
-of the 8.4 development cycle) the \fBTcl_ChannelType\fR structure
-contained the following fields:
-.PP
-.CS
-typedef struct Tcl_ChannelType {
-    const char *\fItypeName\fR;
-    Tcl_ChannelTypeVersion \fIversion\fR;
-    Tcl_DriverCloseProc *\fIcloseProc\fR;
-    Tcl_DriverInputProc *\fIinputProc\fR;
-    Tcl_DriverOutputProc *\fIoutputProc\fR;
-    Tcl_DriverSeekProc *\fIseekProc\fR;
-    Tcl_DriverSetOptionProc *\fIsetOptionProc\fR;
-    Tcl_DriverGetOptionProc *\fIgetOptionProc\fR;
-    Tcl_DriverWatchProc *\fIwatchProc\fR;
-    Tcl_DriverGetHandleProc *\fIgetHandleProc\fR;
-    Tcl_DriverClose2Proc *\fIclose2Proc\fR;
-    Tcl_DriverBlockModeProc *\fIblockModeProc\fR;
-    Tcl_DriverFlushProc *\fIflushProc\fR;
-    Tcl_DriverHandlerProc *\fIhandlerProc\fR;
-    Tcl_DriverTruncateProc *\fItruncateProc\fR;
-} \fBTcl_ChannelType\fR;
-.CE
-.PP
-When the above structure is registered as a channel type, the
-\fIversion\fR field should always be \fBTCL_CHANNEL_VERSION_2\fR.
-.SH "SEE ALSO"
-Tcl_Close(3), Tcl_OpenFileChannel(3), Tcl_SetErrno(3), Tcl_QueueEvent(3), Tcl_StackChannel(3), Tcl_GetStdChannel(3)
-.SH KEYWORDS
-blocking, channel driver, channel registration, channel type, nonblocking