Documented channel transformations.

3 files changed, 196 insertions, 10 deletions

diff --git a/doc/chan.n b/doc/chan.n
index 85d087f..4b7b041 100644
--- a/doc/chan.n
+++ b/doc/chan.n
@@ -4,7 +4,7 @@
 '\" See the file "license.terms" for information on usage and redistribution
 '\" of this file, and for a DISCLAIMER OF ALL WARRANTIES.
 '\"
-'\" RCS: @(#) $Id: chan.n,v 1.19 2008/09/22 21:02:39 ferrieux Exp $
+'\" RCS: @(#) $Id: chan.n,v 1.20 2008/10/07 14:10:29 dkf Exp $
 .so man.macros
 .TH chan n 8.5 Tcl "Tcl Built-In Commands"
 .BS
@@ -330,7 +330,7 @@ This subcommand creates a new script level channel using the command
 prefix \fIcmdPrefix\fR as its handler. Any such channel is called a
 \fBreflected\fR channel. The specified command prefix, \fBcmdPrefix\fR,
 must be a non-empty list, and should provide the API described in the
-\fBreflectedchan\fR manual page. The handle of the new channel is
+\fBrefchan\fR manual page. The handle of the new channel is
 returned as the result of the \fBchan create\fR command, and the
 channel is open. Use either \fBclose\fR or \fBchan close\fR to remove
 the channel.
@@ -349,7 +349,7 @@ mode, or an error is thrown.
 .PP
 The command prefix is executed in the global namespace, at the top of
 call stack, following the appending of arguments as described in the
-\fBreflectedchan\fR manual page. Command resolution happens at the
+\fBrefchan\fR manual page. Command resolution happens at the
 time of the call. Renaming the command, or destroying it means that
 the next call of a handler method may fail, causing the channel
 command invoking the handler to fail as well. Depending on the
@@ -517,7 +517,7 @@ an extremely long line that exceeds the available memory to buffer it).
 Returns -1 if the channel was not opened for the mode in question.
 .TP
 \fBchan pipe\fR
-.
+.VS 8.6
 Creates a standalone pipe whose read- and write-side channels are
 returned as a 2-element list, the first element being the read side and
 the second the write side. Can be useful e.g. to redirect
@@ -525,6 +525,16 @@ separately stderr and stdout from a subprocess. To do this, spawn with "2>@" or
 ">@" redirection operators onto the write side of a pipe, and then
 immediately close it in the parent. This is necessary to get an EOF on
 the read side once the child has exited or otherwise closed its output. 
+.VE 8.6
+.TP
+\fBchan pop \fIchannelId\fR
+.VS 8.6
+Removes the topmost transformation from the channel \fIchannelId\fR, if there
+is any. If there are no transformations added to \fIchannelId\fR, this is
+equivalent to \fBchan close\fR of that channel. The result is normally the
+empty string, but can be an error in some situations (i.e. where the
+underlying system stream is closed and that results in an error).
+.VE 8.6
 .TP
 \fBchan postevent \fIchannelId eventSpec\fR
 .
@@ -551,7 +561,7 @@ other interpreter will cause this subcommand to report an error.
 Another restriction is that it is not possible to post events that the
 I/O core has not registered an interest in. Trying to do so will cause
 the method to throw an error. See the command handler method
-\fBwatch\fR described in \fBreflectedchan\fR, the document specifying
+\fBwatch\fR described in \fBrefchan\fR, the document specifying
 the API of command handlers for reflected channels.
 .PP
 This command is \fBsafe\fR and made accessible to safe interpreters.
@@ -562,6 +572,18 @@ a trusted interpreter. \fBChan event\fR handlers are \fIalways\fR
 executed in the interpreter that set them up.
 .RE
 .TP
+\fBchan push \fIchannelId cmdPrefix\fR
+.VS 8.6
+Adds a new transformation on top of the channel \fIchannelId\fR. The
+\fIcmdPrefix\fR argument describes a list of one or more words which represent
+a handler that will be used to implement the transformation. The command
+prefix must provide the API described in the \fBtranschan\fR manual page.
+The result of this subcommand is a handle to the transformation. Note that it
+is important to make sure that the transformation is capable of supporting the
+channel mode that it is used with or this can make the channel neither
+readable nor writable.
+.VE 8.6
+.TP
 \fBchan puts\fR ?\fB\-nonewline\fR? ?\fIchannelId\fR? \fIstring\fR
 .
 Writes \fIstring\fR to the channel named \fIchannelId\fR followed by a
@@ -744,6 +766,9 @@ while {[\fBchan gets\fR $f line] >= 0} {
 .SH "SEE ALSO"
 close(n), eof(n), fblocked(n), fconfigure(n), fcopy(n), file(n),
 fileevent(n), flush(n), gets(n), open(n), puts(n), read(n), seek(n),
-socket(n), tell(n), refchan(n)
+socket(n), tell(n), refchan(n), transchan(n)
 .SH KEYWORDS
 channel, input, output, events, offset
+'\" Local Variables:
+'\" mode: nroff
+'\" End:
diff --git a/doc/refchan.n b/doc/refchan.n
index d007c0f..4365512 100644
--- a/doc/refchan.n
+++ b/doc/refchan.n
@@ -4,13 +4,13 @@
 '\" 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 1.11 2008/03/26 09:59:22 dkf Exp $
+'\" RCS: @(#) $Id: refchan.n,v 1.12 2008/10/07 14:10:29 dkf Exp $
 .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
+refchan \- command handler API of reflected channels
 .SH SYNOPSIS
 \fBcmdPrefix \fIoption\fR ?\fIarg arg ...\fR?
 .BE
@@ -273,6 +273,6 @@ 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)
+chan(n), transchan(n)
 .SH KEYWORDS
-channel, reflection
+API, channel, ensemble, prefix, reflection
diff --git a/doc/transchan.n b/doc/transchan.n
new file mode 100644
index 0000000..8cb5b57
--- /dev/null
+++ b/doc/transchan.n
@@ -0,0 +1,161 @@
+'\" 
+'\" Copyright (c) 2008 Donal K. Fellows
+'\"
+'\" See the file "license.terms" for information on usage and redistribution
+'\" of this file, and for a DISCLAIMER OF ALL WARRANTIES.
+'\"
+'\" RCS: @(#) $Id: transchan.n,v 1.1 2008/10/07 14:10:29 dkf Exp $
+.so man.macros
+.TH transchan n 8.6 Tcl "Tcl Built-In Commands"
+.BS
+'\" Note:  do not modify the .SH NAME line immediately below!
+.SH NAME
+transchan \- command handler API of channel transforms
+.SH SYNOPSIS
+\fBcmdPrefix \fIoption\fR ?\fIarg arg ...\fR?
+.BE
+.SH DESCRIPTION
+.PP
+The Tcl-level handler for a channel transformation has to be a command with
+subcommands (termed an \fIensemble\fR despite not implying that it must be
+created with \fBnamespace ensemble create\fR; this mechanism is not tied to
+\fBnamespace ensemble\fR in any way). Note that \fIcmdPrefix\fR is whatever
+was specified in the call to \fBchan push\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 and \fBfinalize\fR. Transformations for writable channels
+must also support \fBwrite\fR, and transformations for readable channels must
+also support \fBread\fR.
+.PP
+Note that in the descriptions below \fIcmdPrefix\fR may be more than one word,
+and \fIhandle\fR is the value returned by the \fBchan push\fR call used to
+create the transformation.
+.SS "GENERIC SUBCOMMANDS"
+.PP
+The following subcommands are relevant to all types of channel.
+.TP
+\fIcmdPrefix \fBfinalize \fIhandle\fR
+.
+This mandatory subcommand is called last for the given \fIhandle\fR, and then
+never again, and it exists to allow for cleaning up any Tcl-level data
+structures associated with the transformation. \fIWarning!\fR Any errors
+thrown by this subcommand will be ignored. It is not guaranteed to be called
+if the interpreter is deleted.
+.TP
+\fIcmdPrefix \fBclear \fIhandle\fR
+.
+This optional subcommand is called to signify to the transformation that any
+data stored in internal buffers (either incoming or outgoing) must be
+cleared. It is called when a \fBchan seek\fR is performed on the channel being
+transformed.
+.TP
+\fIcmdPrefix \fBinitialize \fIhandle mode\fR
+.
+This mandatory subcommand is called first, and then never again (for the given
+\fIhandle\fR). Its responsibility is to initialize all parts of the
+transformation at the Tcl level. The \fImode\fR is a list containing any of
+\fBread\fR and \fBwrite\fR.
+.RS
+.TP
+\fBwrite\fR
+.
+implies that the channel is writable.
+.TP
+\fBread\fR
+.
+implies that the channel is readable.
+.PP
+The return value of the subcommand should be a list containing the names of
+all subcommands supported by this handler. Any error thrown by the subcommand
+will prevent the creation of the transformation. The thrown error will appear
+as error thrown by \fBchan push\fR.
+.RE
+.SS "READ-RELATED SUBCOMMANDS"
+.PP
+These subcommands are used for handling transformations applied to readable
+channels; though strictly \fBread\fR is optional, it must be supported if any
+of the others is or the channel will be made non-readable.
+.TP
+\fIcmdPrefix \fBdrain \fIhandle\fR
+.
+This optional subcommand is called whenever data in the transformation input
+(i.e. read) buffer has to be forced upward, i.e. towards the user or script.
+The result returned by the method is taken as the \fIbinary\fR data to push
+upward to the level above this transformation (the reader or a higher-level
+transformation).
+.RS
+.PP
+In other words, when this method is called the transformation cannot defer the
+actual transformation operation anymore and has to transform all data waiting
+in its internal read buffers and return the result of that action.
+.RE
+.TP
+\fIcmdPrefix \fBlimit? \fIhandle\fR
+.
+This optional subcommand is called to allow the Tcl I/O engine to determine
+how far ahead it should read. If present, it should return an integer number
+greater than zero which indicates how many bytes ahead should be read, or an
+integer less than zero to indicate that the I/O engine may read as far ahead
+as it likes.
+.TP
+\fIcmdPrefix \fBread \fIhandle buffer\fR
+.
+This subcommand, which must be present if the transformation is to work with
+readable channels, is called whenever the base channel, or a transformation
+below this transformation, pushes data upward. The \fIbuffer\fR contains the
+binary data which has been given to us from below. It is the responsibility of
+this subcommand to actually transform the data. The result returned by the
+subcommand is taken as the binary data to push further upward to the
+transformation above this transformation. This can also be the user or script
+that originally read from the channel.
+.RS
+.PP
+Note that the result is allowed to be empty, or even less than the data we
+received; the transformation is not required to transform everything given to
+it right now. It is allowed to store incoming data in internal buffers and to
+defer the actual transformation until it has more data.
+.RE
+.SS "WRITE-RELATED SUBCOMMANDS"
+.PP
+These subcommands are used for handling transformations applied to writable
+channels; though strictly \fBwrite\fR is optional, it must be supported if any
+of the others is or the channel will be made non-writable.
+.TP
+\fIcmdPrefix \fBflush \fIhandle\fR
+.
+This optional subcommand is called whenever data in the transformation 'write'
+buffer has to be forced downward, i.e. towards the base channel. The result
+returned by the subcommand is taken as the binary data to write to the
+transformation below the current transformation. This can be the base channel
+as well.
+.RS
+.PP
+In other words, when this subcommand is called the transformation cannot defer
+the actual transformation operation anymore and has to transform all data
+waiting in its internal write buffers and return the result of that action.
+.RE
+.TP
+\fIcmdPrefix \fBwrite \fIhandle buffer\fR
+.
+This subcommand, which must be present if the transformation is to work with
+writable channels, is called whenever the user, or a transformation above this
+transformation, writes data downward. The \fIbuffer\fR contains the binary
+data which has been written to us. It is the responsibility of this subcommand
+to actually transform the data.
+.RS
+.PP
+The result returned by the subcommand is taken as the binary data to write to
+the transformation below this transformation. This can be the base channel as
+well. Note that the result is allowed to be empty, or less than the data we
+got; the transformation is not required to transform everything which was
+written to it right now. It is allowed to store this data in internal buffers
+and to defer the actual transformation until it has more data.
+.RE
+.SH "SEE ALSO"
+chan(n), refchan(n)
+.SH KEYWORDS
+API, channel, ensemble, prefix, transformation
+'\" Local Variables:
+'\" mode: nroff
+'\" End: