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diff --git a/doc/refchan.n b/doc/refchan.n new file mode 100644 index 0000000..577c78a --- /dev/null +++ b/doc/refchan.n @@ -0,0 +1,340 @@ +'\" +'\" Copyright (c) 2006 Andreas Kupries <andreas_kupries@users.sourceforge.net> +'\" +'\" See the file "license.terms" for information on usage and redistribution +'\" of this file, and for a DISCLAIMER OF ALL WARRANTIES. +'\" +.so man.macros +.TH refchan n 8.5 Tcl "Tcl Built-In Commands" +.BS +.\" Note: do not modify the .SH NAME line immediately below! +.SH NAME +refchan \- 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 \fIchannelId mode\fR +. +An invocation of this subcommand will be the first call the +\fIcmdPrefix\fR will receive for the specified new \fIchannelId\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 \fIchannelId\fR +. +An invocation of this subcommand will be the last call the +\fIcmdPrefix\fR will receive for the specified \fIchannelId\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 \fIchannelId\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 \fIchannelId eventspec\fR +. +This subcommand notifies the \fIcmdPrefix\fR that the specified +\fIchannelId\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 postevent\fR to throw an error. +.RE +.SS "OPTIONAL SUBCOMMANDS" +.TP +\fIcmdPrefix \fBread \fIchannelId count\fR +. +This \fIoptional\fR subcommand is called when the user requests data from the +channel \fIchannelId\fR. \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 signaled 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 +Note that returning nothing (0 bytes) is a signal to the higher layers +that \fBEOF\fR has been reached on the channel. To signal that the +channel is out of data right now, but has not yet reached \fBEOF\fR, +it is necessary to throw the error "EAGAIN", i.e. to either +.PP +.CS +return -code error EAGAIN +.CE +or +.CS +error EAGAIN +.CE +.PP +For extensibility any error whose value is a negative integer number +will cause the higher layers to set the C-level variable "\fBerrno\fR" +to the absolute value of this number, signaling a system error. This +means that both +.PP +.CS +return -code error -11 +.CE +and +.CS +error -11 +.CE +.PP +are equivalent to the examples above, using the more readable string "EAGAIN". +No other error value has such a mapping to a symbolic string. +.PP +If the subcommand throws any other 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 \fIchannelId data\fR +. +This \fIoptional\fR subcommand is called when the user writes data to +the channel \fIchannelId\fR. 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 +To signal that the channel is not able to accept data for writing +right now, it is necessary to throw the error "EAGAIN", i.e. to either +.PP +.CS +return -code error EAGAIN +.CE +or +.CS +error EAGAIN +.CE +.PP +For extensibility any error whose value is a negative integer number +will cause the higher layers to set the C-level variable "\fBerrno\fR" +to the absolute value of this number, signaling a system error. +However, note that the exact mapping between these error numbers and +their meanings is operating system dependent. +.PP +For example, while on Linux both +.PP +.CS +return -code error -11 +.CE +and +.CS +error -11 +.CE +.PP +are equivalent to the examples above, using the more readable string "EAGAIN", +this is not true for BSD, where the equivalent number is -35. +.PP +The symbolic string however is the same across systems, and internally +translated to the correct number. No other error value has such a mapping +to a symbolic string. +.PP +If the subcommand throws any other 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 \fIchannelId offset base\fR +. +This \fIoptional\fR subcommand is responsible for the handling of +\fBseek\fR and \fBtell\fR requests on the channel \fIchannelId\fR. 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 \fIchannelId option value\fR +. +This \fIoptional\fR subcommand is for setting the type-specific options of +channel \fIchannelId\fR. 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 \fIchannelId option\fR +. +This \fIoptional\fR subcommand is used when reading a single type-specific +option of channel \fIchannelId\fR. 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 \fIchannelId\fR +. +This \fIoptional\fR subcommand is used for reading all type-specific options +of channel \fIchannelId\fR. 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 \fIchannelId mode\fR +. +This \fIoptional\fR subcommand handles changes to the blocking mode of the +channel \fIchannelId\fR. 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\fR 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 |