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# -*- tcl -*-
# # ## ### ##### ######## #############
# (C) 2009 Andreas Kupries
# @@ Meta Begin
# Package tcl::chan::string 1
# Meta as::author {Andreas Kupries}
# Meta as::copyright 2009
# Meta as::license BSD
# Meta description Implementation of a channel representing
# Meta description an in-memory read-only random-access
# Meta description file. Based on using Tcl 8.5's channel
# Meta description reflection support. Exports a single
# Meta description command for the creation of new channels.
# Meta description One argument, the contents of the file.
# Meta description Result is the handle of the new channel.
# Meta description Similar to -> tcl::chan::memchan, except
# Meta description that the content is read-only. Seekable
# Meta description only within the bounds of the content.
# Meta platform tcl
# Meta require TclOO
# Meta require tcl::chan::events
# Meta require {Tcl 8.5}
# @@ Meta End
# # ## ### ##### ######## #############
package require Tcl 8.5
package require TclOO
package require tcl::chan::events
# # ## ### ##### ######## #############
namespace eval ::tcl::chan {}
proc ::tcl::chan::string {content} {
return [::chan create {read} [string::implementation new $content]]
}
oo::class create ::tcl::chan::string::implementation {
superclass ::tcl::chan::events ; # -> initialize, finalize, watch
constructor {thecontent} {
set content $thecontent
set at 0
next
}
method initialize {args} {
my Events
next {*}$args
}
variable content at
method read {c n} {
# First determine the location of the last byte to read,
# relative to the current location, and limited by the maximum
# location we are allowed to access per the size of the
# content.
set last [expr {min($at + $n,[string length $content])-1}]
# Then extract the relevant range from the content, move the
# seek location behind it, and return the extracted range. Not
# to forget, switch readable events based on the seek
# location.
set res [string range $content $at $last]
set at $last
incr at
my Events
return $res
}
method seek {c offset base} {
# offset == 0 && base == current
# <=> Seek nothing relative to current
# <=> Report current location.
if {!$offset && ($base eq "current")} {
return $at
}
# Compute the new location per the arguments.
set max [string length $content]
switch -exact -- $base {
start { set newloc $offset}
current { set newloc [expr {$at + $offset }] }
end { set newloc [expr {$max + $offset - 1}] }
}
# Check if the new location is beyond the range given by the
# content.
if {$newloc < 0} {
return -code error "Cannot seek before the start of the channel"
} elseif {$newloc >= $max} {
return -code error "Cannot seek after the end of the channel"
}
# Commit to new location, switch readable events, and report.
set at $newloc
my Events
return $at
}
method Events {} {
# Always readable -- Even if the seek location is at the end
# (or beyond). In that case the readable events are fired
# endlessly until the eof indicated by the seek location is
# properly processed by the event handler. Like for regular
# files -- Ticket [864a0c83e3].
my allow read
}
}
# # ## ### ##### ######## #############
package provide tcl::chan::string 1.0.2
return
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