Tcl_CreateChannel(3) Tcl Library Procedures Tcl_CreateChannel(3)_________________________________________________________________NAME
Tcl_CreateChannel, Tcl_GetChannelInstanceData,
Tcl_GetChannelType, Tcl_GetChannelName, Tcl_GetChan-
nelFile, Tcl_GetChannelMode, Tcl_GetChannelBufferSize,
Tcl_SetDefaultTranslation, Tcl_SetChannelBufferSize - pro-
cedures for creating and manipulating channels
SYNOPSIS
#include <tcl.h>
Tcl_Channel
Tcl_CreateChannel(typePtr, channelName, instanceData, mask)
ClientData
Tcl_GetChannelInstanceData(channel)
Tcl_ChannelType *
Tcl_GetChannelType(channel)
char *
Tcl_GetChannelName(channel)
Tcl_File
Tcl_GetChannelFile(channel, direction)
int
Tcl_GetChannelFlags(channel)
void
Tcl_SetDefaultTranslation(channel, transMode)
int
Tcl_GetChannelBufferSize(channel)
void
Tcl_SetChannelBufferSize(channel, size)
ARGUMENTS
Tcl_ChannelType *typePtr (in) Points to a
structure con-
taining the
addresses of
procedures that
can be called to
perform I/O and
other functions
on the channel.
char *channelName (in) The name of this
channel, such as
file3; must not
Tcl 7.5 1
Tcl_CreateChannel(3) Tcl Library Procedures Tcl_CreateChannel(3)
be in use by any
other channel.
Can be NULL, in
which case the
channel is cre-
ated without a
name.
ClientData instanceData (in) Arbitrary one-
word value to be
associated with
this channel.
This value is
passed to proce-
dures in typePtr
when they are
invoked.
int mask (in) OR-ed combina-
tion of
TCL_READABLE and
TCL_WRITABLE to
indicate whether
a channel is
readable and
writable.
Tcl_Channel channel (in) The channel to
operate on.
int direction (in) TCL_READABLE
means the input
file is wanted;
TCL_WRITABLE
means the output
file is wanted.
Tcl_EolTranslation transMode(in)
The translation
mode; one of the
constants
TCL_TRANS-
LATE_AUTO,
TCL_TRANS-
LATE_CR,
TCL_TRANSLATE_LF
and TCL_TRANS-
LATE_CRLF.
int size (in) The size, in
bytes, of
buffers to allo-
cate in this
channel.
Tcl 7.5 2
Tcl_CreateChannel(3) Tcl Library Procedures Tcl_CreateChannel(3)_________________________________________________________________DESCRIPTION
Tcl uses a two-layered channel architecture. It provides a
generic upper layer to enable C and Tcl programs to per-
form 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 Tcl_OpenFileChannel.
The lower layer provides type-specific channel drivers for
each type of file, socket and device supported on each
platform. This manual entry describes the C APIs used by
the generic layer to communicate with type-specific chan-
nel drivers to perform the input and output operations. It
also explains how new types of channels can be added by
providing new channel drivers.
Channel drivers consist of a number of components: First,
each channel driver provides a Tcl_ChannelType structure
containing pointers to functions implementing the various
operations used by the generic layer to communicate with
the channel driver. The Tcl_ChannelType structure and the
functions referenced by it are described in the section
TCL_CHANNELTYPE, below.
Second, channel drivers usually provide a Tcl command to
create instances of that type of channel. For example, the
Tcl open command creates channels that use the file and
command channel drivers, and the Tcl socket command cre-
ates channels that use TCP sockets for network communica-
tion.
Third, a channel driver optionally provides a C function
to open channel instances of that type. For example,
Tcl_OpenFileChannel opens a channel that uses the file
channel driver, and Tcl_OpenTcpClient opens a channel that
uses the TCP network protocol. These creation functions
typically use Tcl_CreateChannel internally to open the
channel.
To add a new type of channel you must implement a C API or
a Tcl command that opens a channel by invoking Tcl_Create-
Channel. When your driver calls Tcl_CreateChannel it
passes in a Tcl_ChannelType structure describing the
driver's I/O procedures. The generic layer will then
invoke the functions referenced in that structure to per-
form operations on the channel.
Tcl_CreateChannel opens a new channel and associates the
supplied typePtr and instanceData with it. The channel is
opened in the mode indicated by mask. For a discussion of
channel drivers, their operations and the Tcl_ChannelType
structure, see the section TCL_CHANNELTYPE, below.
Tcl 7.5 3
Tcl_CreateChannel(3) Tcl Library Procedures Tcl_CreateChannel(3)
Tcl_GetChannelInstanceData returns the instance data asso-
ciated with the channel in channel. This is the same as
the instanceData argument in the call to Tcl_CreateChannel
that created this channel.
Tcl_GetChannelType returns a pointer to the Tcl_Channel-
Type structure used by the channel in the channel argu-
ment. This is the same as the typePtr argument in the call
to Tcl_CreateChannel that created this channel.
Tcl_GetChannelName returns a string containing the name
associated with the channel, or NULL if the channelName
argument to Tcl_CreateChannel was NULL.
Tcl_GetChannelFile returns the inFile associated with
channel if direction is TCL_READABLE, or the outFile if
direction is TCL_WRITABLE. The operation returns NULL if
the channel is not based on Tcl_Files or if the channel is
not open for the specified direction.
Tcl_GetChannelMode returns an OR-ed combination of
TCL_READABLE and TCL_WRITABLE, indicating whether the
channel is open for input and output.
Tcl_SetDefaultTranslation sets the default end of line
translation mode. This mode will be installed as the
translation mode for the channel if an attempt is made to
output on the channel while it is still in TCL_TRANS-
LATE_AUTO mode. For a description of end of line transla-
tion modes, see the manual entry for fconfigure.
Tcl_GetChannelBufferSize returns the size, in bytes, of
buffers allocated to store input or output in chan. If the
value was not set by a previous call to Tcl_SetChannel-
BufferSize, described below, then the default value of
4096 is returned.
Tcl_SetChannelBufferSize sets the size, in bytes, of
buffers that will be allocated in subsequent operations on
the channel to store input or output. The size argument
should be between ten and one million, allowing buffers of
ten bytes to one million bytes. If size is outside this
range, Tcl_SetChannelBufferSize sets the buffer size to
4096.
TCL_CHANNELTYPE
A channel driver provides a Tcl_ChannelType 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 Tcl_ChannelType structure
contains the following fields:
typedef struct Tcl_ChannelType {
Tcl 7.5 4
Tcl_CreateChannel(3) Tcl Library Procedures Tcl_CreateChannel(3)
char *typeName;
Tcl_DriverBlockModeProc *blockModeProc;
Tcl_DriverCloseProc *closeProc;
Tcl_DriverInputProc *inputProc;
Tcl_DriverOutputProc *outputProc;
Tcl_DriverSeekProc *seekProc;
Tcl_DriverSetOptionProc *setOptionProc;
Tcl_DriverGetOptionProc *getOptionProc;
Tcl_DriverWatchChannelProc *watchChannelProc;
Tcl_DriverChannelReadyProc *channelReadyProc;
Tcl_DriverGetFileProc *getFileProc;
} Tcl_ChannelType;
The driver must provide implementations for all functions
except blockModeProc, seekProc, setOptionProc, and getOp-
tionProc, which may be specified as NULL to indicate that
the channel does not support seeking. Other functions
that can not be implemented for this type of device should
return EINVAL when invoked to indicate that they are not
implemented.
TYPENAME
The typeName field contains a null-terminated string that
identifies the type of the device implemented by this
driver, e.g. file or socket.
BLOCKMODEPROC
The blockModeProc field contains the address of a function
called by the generic layer to set blocking and nonblock-
ing mode on the device. BlockModeProc should match the
following prototype:
typedef int Tcl_DriverBlockModeProc(
ClientData instanceData,
int mode);
The instanceData is the same as the value passed to
Tcl_CreateChannel when this channel was created. The mode
argument is either TCL_MODE_BLOCKING or TCL_MODE_NONBLOCK-
ING to set the device into blocking or nonblocking mode.
The function should return zero if the operation was suc-
cessful, or a nonzero POSIX error code if the operation
failed.
If the operation is successful, the function can modify
the supplied instanceData 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.
Tcl 7.5 5
Tcl_CreateChannel(3) Tcl Library Procedures Tcl_CreateChannel(3)CLOSEPROC
The closeProc field contains the address of a function
called by the generic layer to clean up driver-related
information when the channel is closed. CloseProc must
match the following prototype:
typedef int Tcl_DriverCloseProc(
ClientData instanceData,
Tcl_Interp *interp);
The instanceData argument is the same as the value pro-
vided to Tcl_CreateChannel 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 closeProc.
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 interp is
not NULL, the procedure should store an error message in
interp->result.
INPUTPROC
The inputProc 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. InputProc must
match the following prototype:
typedef int Tcl_DriverInputProc(
ClientData instanceData,
char *buf,
int bufSize,
int *errorCodePtr);
InstanceData is the same as the value passed to Tcl_Creat-
eChannel when the channel was created. The buf argument
points to an array of bytes in which to store input from
the device, and the bufSize argument indicates how many
bytes are available at buf.
The errorCodePtr 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.
The function should read data from the input device encap-
sulated by the channel and store it at buf. On success,
the function should return a nonnegative integer indicat-
ing how many bytes were read from the input device and
stored at buf. On error, the function should return -1. If
an error occurs after some data has been read from the
Tcl 7.5 6
Tcl_CreateChannel(3) Tcl Library Procedures Tcl_CreateChannel(3)
device, that data is lost.
If inputProc can determine that the input device has some
data available but less than requested by the bufSize
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 EAGAIN error. If the input device has no data available
whatsoever and the channel is in blocking mode, the func-
tion 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.
OUTPUTPROC
The outputProc field contains the address of a function
called by the generic layer to transfer data from an
internal buffer to the output device. OutputProc must
match the following prototype:
typedef int Tcl_DriverOutputProc(
ClientData instanceData,
char *buf,
int toWrite,
int *errorCodePtr);
InstanceData is the same as the value passed to Tcl_Creat-
eChannel when the channel was created. The buf argument
contains an array of bytes to be written to the device,
and the toWrite argument indicates how many bytes are to
be written from the buf argument.
The errorCodePtr 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.
The function should write the data at buf to the output
device encapsulated by the channel. On success, the func-
tion should return a nonnegative integer indicating how
many bytes were written to the output device. The return
value is normally the same as toWrite, 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.
If the channel is nonblocking and the output device is
unable to absorb any data whatsoever, the function should
return -1 with an EAGAIN error without writing any data.
Tcl 7.5 7
Tcl_CreateChannel(3) Tcl Library Procedures Tcl_CreateChannel(3)SEEKPROC
The seekProc 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. SeekProc must match the following prototype:
typedef int Tcl_DriverSeekProc(
ClientData instanceData,
long offset,
int seekMode,
int *errorCodePtr);
The instanceData argument is the same as the value given
to Tcl_CreateChannel when this channel was created. Off-
set and seekMode have the same meaning as for the
Tcl_SeekChannel procedure (described in the manual entry
for Tcl_OpenFileChannel).
The errorCodePtr argument points to an integer variable
provided by the generic layer for returning errno values
from the function. The function should set this variable
to a POSIX error code if an error occurs. The function
should store an EINVAL error code if the channel type does
not implement seeking.
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.
SETOPTIONPROC
The setOptionProc field contains the address of a function
called by the generic layer to set a channel type specific
option on a channel. setOptionProc must match the follow-
ing prototype:
typedef int Tcl_DriverSetOptionProc(
ClientData instanceData,
Tcl_Interp *interp,
char *optionName,
char *optionValue);
optionName is the name of an option to set, and optionVa-
lue is the new value for that option, as a string. The
instanceData is the same as the value given to Tcl_Create-
Channel when this channel was created. The function should
do whatever channel type specific action is required to
implement the new value of the option.
Some options are handled by the generic code and this
function is never called to set them, e.g. -blockmode.
Other options are specific to each channel type and the
setOptionProc procedure of the channel driver will get
called to implement them. The setOptionProc field can be
Tcl 7.5 8
Tcl_CreateChannel(3) Tcl Library Procedures Tcl_CreateChannel(3)
NULL, which indicates that this channel type supports no
type specific options.
If the option value is successfully modified to the new
value, the function returns TCL_OK. It returns TCL_ERROR
if the optionName is unrecognized or if optionValue speci-
fies a value for the option that is not supported. In this
case, the function leaves an error message in the result
field of interp if interp is not NULL. The function should
also call Tcl_SetErrno to store an appropriate POSIX error
code.
GETOPTIONPROC
The getOptionProc 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. getOptionProc must
match the following prototype:
typedef int Tcl_DriverGetOptionProc(
ClientData instanceData,
char *optionName,
Tcl_DString *dsPtr);
OptionName 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 dsPtr. If optionName is NULL, the function stores
in dsPtr an alternating list of all supported options and
their current values. On success, the function returns
TCL_OK. If an error occurs, the function returns TCL_ERROR
and calls Tcl_SetErrno to store an appropriate POSIX error
code.
Some options are handled by the generic code and this
function is never called to retrieve their value, e.g.
-blockmode. Other options are specific to each channel
type and the getOptionProc procedure of the channel driver
will get called to implement them. The getOptionProc field
can be NULL, which indicates that this channel type sup-
ports no type specific options.
WATCHCHANNELPROC
The watchChannelProc field contains the address of a func-
tion called by the generic layer to initialize the event
notification mechanism to notice events of interest on
this channel. WatchChannelProc should match the following
prototype:
typeded void Tcl_DriverWatchChannelProc(
ClientData instanceData,
int mask);
Tcl 7.5 9
Tcl_CreateChannel(3) Tcl Library Procedures Tcl_CreateChannel(3)
The instanceData is the same as the value passed to
Tcl_CreateChannel when this channel was created. The mask
argument is an OR-ed combination of TCL_READABLE,
TCL_WRITABLE and TCL_EXCEPTION; it indicates events the
caller is interested in noticing on this channel.
The function should initialize device type specific mecha-
nisms to notice when an event of interest is present on
the channel. It may invoke Tcl_SetMaxBlockTime to specify
an upper limit on the length of time to wait for an event,
and it may invoke Tcl_WatchFile if the channel implementa-
tion is based on Tcl_Files.
CHANNELREADYPROC
The channelReadyProc field contains the address of a func-
tion called by the generic layer to sense whether events
of interest have occurred for this channel. Channel-
ReadyProc should match the following prototype:
typedef int Tcl_DriverChannelReadyProc(
ClientData instanceData,
int mask);
InstanceData is the same as the value passed to Tcl_Creat-
eChannel when this channel was created. The mask argument
is an OR-ed combination of TCL_READABLE, TCL_WRITABLE and
TCL_EXCEPTION indicating what events are of interest. The
function returns a mask containing an OR-ed combination of
a subset of the flags in mask to indicate what events have
actually occurred on the channel.
The function should use a device type dependent mechanism
to detect whether events of interest have occurred on the
channel. It may invoke Tcl_FileReady if the channel imple-
mentation is based on Tcl_Files.
GETFILEPROC
The getFileProc field contains the address of a function
called by the generic layer to retrieve a Tcl_File from
the channel. GetFileProc should match the following pro-
totype:
typedef Tcl_File Tcl_DriverGetFileProc(
ClientData instanceData,
int direction);
InstanceData is the same as the value passed to Tcl_Creat-
eChannel when this channel was created. The direction
argument is either TCL_READABLE to retrieve the Tcl_File
used for input, or TCL_WRITABLE to retrieve the Tcl_File
used for output.
Tcl 7.5 10
Tcl_CreateChannel(3) Tcl Library Procedures Tcl_CreateChannel(3)
If the channel implementation is based on Tcl_Files, the
function should retrieve the appropriate Tcl_File associ-
ated with the channel, according the direction argument;
it can return NULL if the channel is not open for that
direction. If the channel implementation does not use
Tcl_Files, the function should always return NULL.
SEE ALSOTcl_Close(3), Tcl_OpenFileChannel(3), Tcl_SetErrno(3),
Tcl_SetMaxBlockTime(3), Tcl_WatchFile(3), Tcl_FileReady(3)KEYWORDS
blocking, channel driver, channel registration, channel
type, nonblocking
Tcl 7.5 11
