diff options
Diffstat (limited to 'doc/refchan.n')
| -rw-r--r-- | doc/refchan.n | 278 |
1 files changed, 278 insertions, 0 deletions
diff --git a/doc/refchan.n b/doc/refchan.n new file mode 100644 index 0000000..a35ec53 --- /dev/null +++ b/doc/refchan.n @@ -0,0 +1,278 @@ +'\" +'\" Copyright (c) 2006 Andreas Kupries +'\" +'\" See the file "license.terms" for information on usage and redistribution +'\" of this file, and for a DISCLAIMER OF ALL WARRANTIES. +'\" +'\" RCS: @(#) $Id: refchan.n,v 1.1 2006/03/17 17:24:10 andreas_kupries Exp $ +.so man.macros +.TH reflectedchan n 8.5 Tcl "Tcl Built-In Commands" +.BS +'\" Note: do not modify the .SH NAME line immediately below! +.SH NAME +reflectedchan \- Command handler API of reflected channels, version 1 +.SH SYNOPSIS +\fBcmdPrefix \fIoption\fR ?\fIarg arg ...\fR? +.BE +.SH DESCRIPTION +.PP +The Tcl-level handler for a reflected channel has to be a command with +subcommands (termed an \fIensemble\fR, as it is a command such as that +created by \fBnamespace ensemble create\fR, though the implementation +of handlers for reflected channel \fIis not\fR tied to \fBnamespace +ensemble\fRs in any way). Note that \fIcmdPrefix\fR is whatever was +specified in the call to \fBchan create\fR, and may consist of +multiple arguments; this will be expanded to multiple words in place +of the prefix. +.PP +Of all the possible subcommands, the handler \fImust\fR support +\fBinitialize\fR, \fBfinalize\fR, and \fBwatch\fR. Support for the +other subcommands is optional. +.SS "MANDATORY SUBCOMMANDS" +.TP +\fIcmdPrefix \fBinitialize \fIchannel mode\fR +. +An invokation of this subcommand will be the first call the +\fIcmdPrefix\fR will receive for the specified new \fBchannel\fR. It +is the responsibility of this subcommand to set up any internal data +structures required to keep track of the channel and its state. +.RS +.PP +The return value of the method has to be a list containing the names +of all subcommands supported by the \fIcmdPrefix\fR. This also tells +the Tcl core which version of the API for reflected channels is used by +this command handler. +.PP +Any error thrown by the method will abort the creation of the channel +and no channel will be created. The thrown error will appear as error +thrown by \fBchan create\fR. Any exception other than an \fBerror\fR +(e.g. \fBbreak\fR, etc.) is treated as (and converted to) an error. +.PP +\fBNote:\fR If the creation of the channel was aborted due to failures +here, then the \fBfinalize\fR subcommand will not be called. +.PP +The \fImode\fR argument tells the handler whether the channel was +opened for reading, writing, or both. It is a list containing any of +the strings "\fBread\fR" or "\fBwrite\fR". The list will always +contain at least one element. +.PP +The subcommand must throw an error if the chosen mode is not +supported by the \fIcmdPrefix\fR. +.RE +.TP +\fIcmdPrefix \fBfinalize \fIchannel\fR +. +An invokation of this subcommand will be the last call the +\fIcmdPrefix\fR will receive for the specified \fIchannel\fR. It will +be generated just before the destruction of the data structures of the +channel held by the Tcl core. The command handler \fImust not\fR +access the \fIchannel\fR anymore in no way. Upon this subcommand being +called, any internal resources allocated to this channel must be +cleaned up. +.RS +.PP +The return value of this subcommand is ignored. +.PP +If the subcommand throws an error the command which caused its +invocation (usually \fBclose\fR) will appear to have thrown this +error. Any exception beyond \fIerror\fR (e.g. \fIbreak\fR, etc.) is +treated as (and converted to) an error. +.PP +This subcommand is not invoked if the creation of the channel was +aborted during \fBinitialize\fR (See above). +.RE +.TP +\fIcmdPrefix \fBwatch \fIchannel eventspec\fR +. +This subcommand notifies the \fIcmdPrefix\fR that the specified +\fIchannel\fR is interested in the events listed in the +\fIeventspec\fR. This argument is a list containing any of "\fBread\fR" +and "\fBwrite\fR". The list may be empty, which signals that the +channel does not wish to be notified of any events. In that situation, +the handler should disable event generation completely. +.RS +.PP +\fBWarning:\fR Any return value of the subcommand is ignored. This +includes all errors thrown by the subcommand, break, continue, and +custom return codes. +.PP +This subcommand interacts with \fBchan postevent\fR. Trying to post an +event which was not listed in the last call to \fBwatch\fR will cause +\fBchan postenvent\fR to throw an error. +.RE +.SS "OPTIONAL SUBCOMMANDS" +.TP +\fIcmdPrefix \fBread \fIchannel count\fR +. +This \fIoptional\fR subcommand is called when the user requests data +from a channel. \fIcount\fR specifies how many \fBbytes\fR have been +requested. If the subcommand is not supported then it is not possible +to read from the channel handled by the command. +.RS +.PP +The return value of this subcommand is taken as the requested data +\fIbytes\fR. If the returned data contains more bytes than requested, +an error will be signalled and later thrown by the command which +performed the read (usually \fBgets\fR or \fBread\fR). However, +returning fewer bytes than requested is acceptable. +.PP +If the subcommand throws an error, the command which caused its +invocation (usually \fBgets\fR, or \fBread\fR) will appear to have +thrown this error. Any exception beyond \fIerror\fR, (e.g. +\fIbreak\fR, etc.) is treated as and converted to an error. +.RE +.TP +\fIcmdPrefix \fBwrite \fIchannel data\fR +. +This \fIoptional\fR subcommand is called when the user writes data to +the channel. The \fIdata\fR argument contains \fIbytes\fR, not +characters. Any type of transformation (EOL, encoding) configured for +the channel has already been applied at this point. If this subcommand +is not supported then it is not possible to write to the channel +handled by the command. +.RS +.PP +The return value of the subcommand is taken as the number of bytes +written by the channel. Anything non-numeric will cause an error to be +signaled and later thrown by the command which performed the write. A +negative value implies that the write failed. Returning a value +greater than the number of bytes given to the handler, or zero, is +forbidden and will cause the Tcl core to throw an error. +.PP +If the subcommand throws an error the command which caused its +invocation (usually \fBputs\fR) will appear to have thrown this error. +Any exception beyond \fIerror\fR (e.g. \fIbreak\fR, etc.) is treated +as and converted to an error. +.RE +.TP +\fIcmdPrefix \fBseek \fIchannel offset base\fR +. +This \fIoptional\fR subcommand is responsible for the handling of +\fBseek\fR and \fBtell\fR requests on the channel. If it is not +supported then seeking will not be possible for the channel. +.RS +.PP +The \fIbase\fR argument is one of +.TP 10 +\fBstart\fR +. +Seeking is relative to the beginning of the channel. +.TP 10 +\fBcurrent\fR +. +Seeking is relative to the current seek position. +.TP 10 +\fBend\fR +. +Seeking is relative to the end of the channel. +.PP +The \fIbase\fR argument of the builtin \fBchan seek\fR command takes +the same names. +.PP +The \fIoffset\fR is an integer number specifying the amount of +\fBbytes\fR to seek forward or backward. A positive number should seek +forward, and a negative number should seek backward. +.PP +A channel may provide only limited seeking. For example sockets can +seek forward, but not backward. +.PP +The return value of the subcommand is taken as the (new) location of +the channel, counted from the start. This has to be an integer number +greater than or equal to zero. +.PP +If the subcommand throws an error the command which caused its +invocation (usually \fBseek\fR, or \fBtell\fR) will appear to have +thrown this error. Any exception beyond \fIerror\fR (e.g. \fIbreak\fR, +etc.) is treated as and converted to an error. +.PP +The offset/base combination of 0/"\fBcurrent\fR" signals a \fBtell\fR +request, i.e. seek nothing relative to the current location, making +the new location identical to the current one, which is then returned. +.RE +.TP +\fIcmdPrefix \fBconfigure \fIchannel option value\fR +. +This \fIoptional\fR subcommand is for writing the type specific +options. The \fIoption\fR argument indicates the option to be written, +and the \fIvalue\fR argument indicates the value to set the option to. +.RS +.PP +This subcommand will never try to update more than one option at a +time; that is behavior implemented in the Tcl channel core. +.PP +The return value of the subcommand is ignored. +.PP +If the subcommand throws an error the command which performed the +(re)configuration or query (usually \fBfconfigure\fR or \fBchan +configure\fR) will appear to have thrown this error. Any exception +beyond \fIerror\fR (e.g. \fIbreak\fR, etc.) is treated as and +converted to an error. +.RE +.TP +\fIcmdPrefix \fBcget \fIchannel option\fR +. +This \fIoptional\fR subcommand is used when reading a single type +specific option. If this subcommand is supported then the subcommand +\fBcgetall\fR must be supported as well. +.RS +.PP +The subcommand should return the value of the specified \fIoption\fR. +.PP +If the subcommand throws an error, the command which performed the +(re)configuration or query (usually \fBfconfigure\fR) will appear to +have thrown this error. Any exception beyond \fIerror\fR (e.g. +\fIbreak\fR, etc.) is treated as and converted to an error. +.RE +.TP +\fIcmdPrefix \fBcgetall \fIchannel\fR +. +This \fIoptional\fR subcommand is used for reading all type specific +options. If this subcommand is supported then the subcommand +\fBcget\fR has to be supported as well. +.RS +.PP +The subcommand should return a list of all options and their values. +This list must have an even number of elements. +.PP +If the subcommand throws an error the command which performed the +(re)configuration or query (usually \fBfconfigure\fR) will appear to +have thrown this error. Any exception beyond \fIerror\fR (e.g. +\fIbreak\fR, etc.) is treated as and converted to an error. +.RE +.TP +\fIcmdPrefix \fBblocking \fIchannel mode\fR +. +This \fIoptional\fR subcommand handles changes to the blocking mode of +the channel. The \fImode\fR is a boolean flag. A true value means that +the channel has to be set to blocking, and a false value means that +the channel should be non-blocking. +.RS +.PP +The return value of the subcommand is ignored. +.PP +If the subcommand throws an error the command which caused its +invocation (usually \fBfconfigure\fR) will appear to have thrown this +error. Any exception beyond \fIerror\fR (e.g. \fIbreak\fR, etc.) is +treated as and converted to an error. +.RE +.SH NOTES +Some of the functions supported in channels defined in Tcl's C +interface are not available to channels reflected to the Tcl level. +.PP +The function \fBTcl_DriverGetHandleProc\fR is not supported; i.e. +reflected channels do not have OS specific handles. +.PP +The function \fBTcl_DriverHandlerProc\fI is not supported. This driver +function is relevant only for stacked channels, i.e. transformations. +Reflected channels are always base channels, not transformations. +.PP +The function \fBTcl_DriverFlushProc\fR is not supported. This is +because the current generic I/O layer of Tcl does not use this +function anywhere at all. Therefore support at the Tcl level makes no +sense either. This may be altered in the future (through extending the +API defined here and changing its version number) should the function +be used at some time in the future. +.SH "SEE ALSO" +chan(n) +.SH KEYWORDS +channel, reflection |