Tcl_CreateChannel(3) Tcl (8.0) Tcl_CreateChannel(3)
_________________________________________________________________
NAME
Tcl_CreateChannel, Tcl_GetChannelInstanceData,
Tcl_GetChannelType, Tcl_GetChannelName,
Tcl_GetChannelHandle, Tcl_GetChannelMode,
Tcl_GetChannelBufferSize, Tcl_SetDefaultTranslation,
Tcl_SetChannelBufferSize, Tcl_NotifyChannel,
Tcl_BadChannelOption - procedures 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)
int |
Tcl_GetChannelHandle(channel, direction, handlePtr) |
int
Tcl_GetChannelFlags(channel)
Tcl_SetDefaultTranslation(channel, transMode)
int
Tcl_GetChannelBufferSize(channel)
Tcl_SetChannelBufferSize(channel, size)
Tcl_NotifyChannel(channel, mask) |
int |
Tcl_BadChannelOption(interp, optionName, optionList) |
ARGUMENTS
Tcl_ChannelType *typePtr (in) Points to a
structure
containing the
addresses of
procedures
that can be
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Tcl_CreateChannel(3) Tcl (8.0) Tcl_CreateChannel(3)
called to
perform I/O
and other
functions on
the channel.
char *channelName (in) The name of
this channel,
such as file3;
must not be in
use by any
other channel.
Can be NULL,
in which case
the channel is
created
without a
name.
ClientData instanceData (in) Arbitrary
one-word value
to be
associated
with this
channel. This
value is
passed to
procedures in
typePtr when
they are
invoked.
int mask (in) OR-ed
combination 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 handle |
is wanted; |
TCL_WRITABLE |
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Tcl_CreateChannel(3) Tcl (8.0) Tcl_CreateChannel(3)
means the |
output handle |
is wanted. |
ClientData *handlePtr (out) ||
Points to the |
location where |
the desired |
OS-specific |
handle should |
be stored.
Tcl_EolTranslation transMode (in) The
translation
mode; one of
the constants
TCL_TRANSLATE_AUTO,
TCL_TRANSLATE_CR,
TCL_TRANSLATE_LF
and
TCL_TRANSLATE_CRLF.
int size (in) The size, in
bytes, of
buffers to
allocate in
this channel. |
int mask (in) ||
An OR-ed |
combination of |
TCL_READABLE, |
TCL_WRITABLE |
and |
TCL_EXCEPTION |
that indicates |
events that |
have occurred |
on this |
channel. |
Tcl_Interp *interp (in) ||
Current |
interpreter. |
(can be NULL) |
char *optionName (in) ||
Name of the |
invalid |
option. |
char *optionList (in) ||
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Tcl_CreateChannel(3) Tcl (8.0) Tcl_CreateChannel(3)
Specific |
options list |
(space |
separated |
words, without |
"-") to append |
to the |
standard |
generic |
options list. |
Can be NULL |
for generic |
options error |
message only.
_________________________________________________________________
DESCRIPTION
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 Tcl_OpenFileChannel.
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.
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 creates
channels that use TCP sockets for network communication.
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
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Tcl_CreateChannel(3) Tcl (8.0) Tcl_CreateChannel(3)
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_CreateChannel. 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 perform
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_GetChannelInstanceData returns the instance data
associated 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_ChannelType
structure used by the channel in the channel argument. 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_GetChannelHandle places the OS-specific device handle |
associated with channel for the given direction in the |
location specified by handlePtr and returns TCL_OK. If the |
channel does not have a device handle for the specified |
direction, then TCL_ERROR 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.
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_TRANSLATE_AUTO mode. For a description of end of line
translation 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
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Tcl_CreateChannel(3) Tcl (8.0) Tcl_CreateChannel(3)
value was not set by a previous call to
Tcl_SetChannelBufferSize, 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_NotifyChannel is called by a channel driver to indicate |
to the generic layer that the events specified by mask 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 WATCHPROC below for |
more details.
Tcl_BadChannelOption is called from driver specific set or |
get option procs to generate a complete error message.
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 { |
char *typeName; |
Tcl_DriverBlockModeProc *blockModeProc; |
Tcl_DriverCloseProc *closeProc; |
Tcl_DriverInputProc *inputProc; |
Tcl_DriverOutputProc *outputProc; |
Tcl_DriverSeekProc *seekProc; |
Tcl_DriverSetOptionProc *setOptionProc; |
Tcl_DriverGetOptionProc *getOptionProc; |
Tcl_DriverWatchProc *watchProc; |
Tcl_DriverGetHandleProc *getHandleProc; |
} Tcl_ChannelType; |
The driver must provide implementations for all functions
except blockModeProc, seekProc, setOptionProc, and
getOptionProc, 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
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Tcl_CreateChannel(3) Tcl (8.0) Tcl_CreateChannel(3)
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 nonblocking
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_NONBLOCKING
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.
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.
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 provided
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
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Tcl_CreateChannel(3) Tcl (8.0) Tcl_CreateChannel(3)
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_CreateChannel 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
encapsulated by the channel and store it at buf. On
success, the function should return a nonnegative integer
indicating 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
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 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.
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:
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Tcl_CreateChannel(3) Tcl (8.0) Tcl_CreateChannel(3)
typedef int Tcl_DriverOutputProc(
ClientData instanceData,
char *buf,
int toWrite,
int *errorCodePtr);
InstanceData is the same as the value passed to
Tcl_CreateChannel 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 function
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.
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. Offset 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
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Tcl_CreateChannel(3) Tcl (8.0) Tcl_CreateChannel(3)
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 following
prototype:
typedef int Tcl_DriverSetOptionProc(
ClientData instanceData,
Tcl_Interp *interp,
char *optionName,
char *optionValue);
optionName is the name of an option to set, and optionValue
is the new value for that option, as a string. The
instanceData is the same as the value given to
Tcl_CreateChannel 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
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 should call |
Tcl_BadChannelOption which itself returns TCL_ERROR if the |
optionName is unrecognized. If optionValue 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 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
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Tcl_CreateChannel(3) Tcl (8.0) Tcl_CreateChannel(3)
the following prototype:
typedef int Tcl_DriverGetOptionProc(
ClientData instanceData,
Tcl_Interp *interp, |
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. It |
should call Tcl_BadChannelOption which itself returns |
TCL_ERROR if the optionName is unrecognized. If a system |
call error occurs, the function should leave 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.
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 supports no
type specific options.
WATCHPROC
The watchProc 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. WatchProc should match the following prototype: |
typedef void Tcl_DriverWatchProc( |
ClientData instanceData, |
int mask); |
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 |
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 Tcl_NotifyChannel to inform the generic channel |
module. The driver should take care not to starve other |
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Tcl_CreateChannel(3) Tcl (8.0) Tcl_CreateChannel(3)
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 Tcl_QueueEvent for details on how to queue an |
event. |
GETHANDLEPROC |
The getHandleProc field contains the address of a function |
called by the generic layer to retrieve a device-specific |
handle from the channel. GetHandleProc should match the |
following prototype: |
typedef int Tcl_DriverGetHandleProc( |
ClientData instanceData, |
int direction, |
ClientData *handlePtr); |
InstanceData is the same as the value passed to |
Tcl_CreateChannel when this channel was created. The |
direction argument is either TCL_READABLE to retrieve the |
handle used for input, or TCL_WRITABLE to retrieve the |
handle used for output. |
If the channel implementation has device-specific handles, |
the function should retrieve the appropriate handle |
associated with the channel, according the direction |
argument. The handle should be stored in the location |
referred to by handlePtr, and TCL_OK 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 TCL_ERROR.
TCL_BADCHANNELOPTION |
This procedure generates a "bad option" error message in an |
(optional) interpreter. It is used by channel drivers when |
a 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. |
It always return TCL_ERROR |
An error message is generated in interp's result object to |
indicate that a command was invoked with the a bad option |
The message has the form |
bad option "blah": should be one of |
<...generic options...>+<...specific options...> |
so you get for instance: |
bad option "-blah": should be one of -blocking, |
-buffering, -buffersize, -eofchar, -translation, |
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Tcl_CreateChannel(3) Tcl (8.0) Tcl_CreateChannel(3)-peername, or -sockname |
when called with optionList="peername sockname" |
"blah" is the optionName argument and "<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 "or" before the last |
option.
SEE ALSO
Tcl_Close(3), Tcl_OpenFileChannel(3), Tcl_SetErrno(3),
Tcl_QueueEvent(3)
KEYWORDS
blocking, channel driver, channel registration, channel
type, nonblocking
Page 13 (printed 2/19/99)
