# safe.tcl --

#

# This file provide a safe loading/sourcing mechanism for safe interpreters.

# It implements a virtual path mecanism to hide the real pathnames from the

# slave. It runs in a master interpreter and sets up data structure and

# aliases that will be invoked when used from a slave interpreter.

# 

# See the safe.n man page for details.

#

# Copyright (c) 1996-1997 Sun Microsystems, Inc.

#

# See the file "license.terms" for information on usage and redistribution

# of this file, and for a DISCLAIMER OF ALL WARRANTIES.

#

# RCS: @(#) $Id: safe.tcl,v 1.9.2.3 2005/07/22 21:59:41 dgp Exp $

#

# The implementation is based on namespaces. These naming conventions

# are followed:

# Private procs starts with uppercase.

# Public  procs are exported and starts with lowercase

#

# Needed utilities package

package require opt 0.4.1;

# Create the safe namespace

namespace eval ::safe {

    # Exported API:

    namespace export interpCreate interpInit interpConfigure interpDelete \

	    interpAddToAccessPath interpFindInAccessPath setLogCmd

    ####

    #

    # Setup the arguments parsing

    #

    ####

    # Make sure that our temporary variable is local to this

    # namespace.  [Bug 981733]

    variable temp

    # Share the descriptions

    set temp [::tcl::OptKeyRegister {

	{-accessPath -list {} "access path for the slave"}

	{-noStatics "prevent loading of statically linked pkgs"}

	{-statics true "loading of statically linked pkgs"}

	{-nestedLoadOk "allow nested loading"}

	{-nested false "nested loading"}

	{-deleteHook -script {} "delete hook"}

    }]

    # create case (slave is optional)

    ::tcl::OptKeyRegister {

	{?slave? -name {} "name of the slave (optional)"}

    } ::safe::interpCreate

    # adding the flags sub programs to the command program

    # (relying on Opt's internal implementation details)

    lappend ::tcl::OptDesc(::safe::interpCreate) $::tcl::OptDesc($temp)

    # init and configure (slave is needed)

    ::tcl::OptKeyRegister {

	{slave -name {} "name of the slave"}

    } ::safe::interpIC

    # adding the flags sub programs to the command program

    # (relying on Opt's internal implementation details)

    lappend ::tcl::OptDesc(::safe::interpIC) $::tcl::OptDesc($temp)

    # temp not needed anymore

    ::tcl::OptKeyDelete $temp

    # Helper function to resolve the dual way of specifying staticsok

    # (either by -noStatics or -statics 0)

    proc InterpStatics {} {

	foreach v {Args statics noStatics} {

	    upvar $v $v

	}

	set flag [::tcl::OptProcArgGiven -noStatics];

	if {$flag && (!$noStatics == !$statics) 

	          && ([::tcl::OptProcArgGiven -statics])} {

	    return -code error\

		    "conflicting values given for -statics and -noStatics"

	}

	if {$flag} {

	    return [expr {!$noStatics}]

	} else {

	    return $statics

	}

    }

    # Helper function to resolve the dual way of specifying nested loading

    # (either by -nestedLoadOk or -nested 1)

    proc InterpNested {} {

	foreach v {Args nested nestedLoadOk} {

	    upvar $v $v

	}

	set flag [::tcl::OptProcArgGiven -nestedLoadOk];

	# note that the test here is the opposite of the "InterpStatics"

	# one (it is not -noNested... because of the wanted default value)

	if {$flag && (!$nestedLoadOk != !$nested) 

	          && ([::tcl::OptProcArgGiven -nested])} {

	    return -code error\

		    "conflicting values given for -nested and -nestedLoadOk"

	}

	if {$flag} {

	    # another difference with "InterpStatics"

	    return $nestedLoadOk

	} else {

	    return $nested

	}

    }

    ####

    #

    #  API entry points that needs argument parsing :

    #

    ####

    # Interface/entry point function and front end for "Create"

    proc interpCreate {args} {

	set Args [::tcl::OptKeyParse ::safe::interpCreate $args]

	InterpCreate $slave $accessPath \

		[InterpStatics] [InterpNested] $deleteHook

    }

    proc interpInit {args} {

	set Args [::tcl::OptKeyParse ::safe::interpIC $args]

	if {![::interp exists $slave]} {

	    return -code error "\"$slave\" is not an interpreter"

	}

	InterpInit $slave $accessPath \

		[InterpStatics] [InterpNested] $deleteHook;

    }

    proc CheckInterp {slave} {

	if {![IsInterp $slave]} {

	    return -code error \

		    "\"$slave\" is not an interpreter managed by ::safe::"

	}

    }

    # Interface/entry point function and front end for "Configure"

    # This code is awfully pedestrian because it would need

    # more coupling and support between the way we store the

    # configuration values in safe::interp's and the Opt package

    # Obviously we would like an OptConfigure

    # to avoid duplicating all this code everywhere. -> TODO

    # (the app should share or access easily the program/value

    #  stored by opt)

    # This is even more complicated by the boolean flags with no values

    # that we had the bad idea to support for the sake of user simplicity

    # in create/init but which makes life hard in configure...

    # So this will be hopefully written and some integrated with opt1.0

    # (hopefully for tcl8.1 ?)

    proc interpConfigure {args} {

	switch [llength $args] {

	    1 {

		# If we have exactly 1 argument

		# the semantic is to return all the current configuration

		# We still call OptKeyParse though we know that "slave"

		# is our given argument because it also checks

		# for the "-help" option.

		set Args [::tcl::OptKeyParse ::safe::interpIC $args]

		CheckInterp $slave

		set res {}

		lappend res [list -accessPath [Set [PathListName $slave]]]

		lappend res [list -statics    [Set [StaticsOkName $slave]]]

		lappend res [list -nested     [Set [NestedOkName $slave]]]

		lappend res [list -deleteHook [Set [DeleteHookName $slave]]]

		join $res

	    }

	    2 {

		# If we have exactly 2 arguments

		# the semantic is a "configure get"

		::tcl::Lassign $args slave arg

		# get the flag sub program (we 'know' about Opt's internal

		# representation of data)

		set desc [lindex [::tcl::OptKeyGetDesc ::safe::interpIC] 2]

		set hits [::tcl::OptHits desc $arg]

                if {$hits > 1} {

                    return -code error [::tcl::OptAmbigous $desc $arg]

                } elseif {$hits == 0} {

                    return -code error [::tcl::OptFlagUsage $desc $arg]

                }

		CheckInterp $slave

		set item [::tcl::OptCurDesc $desc]

		set name [::tcl::OptName $item]

		switch -exact -- $name {

		    -accessPath {

			return [list -accessPath [Set [PathListName $slave]]]

		    }

		    -statics {

			return [list -statics    [Set [StaticsOkName $slave]]]

		    }

		    -nested {

			return [list -nested     [Set [NestedOkName $slave]]]

		    }

		    -deleteHook {

			return [list -deleteHook [Set [DeleteHookName $slave]]]

		    }

		    -noStatics {

			# it is most probably a set in fact

			# but we would need then to jump to the set part

			# and it is not *sure* that it is a set action

			# that the user want, so force it to use the

			# unambigous -statics ?value? instead:

			return -code error\

				"ambigous query (get or set -noStatics ?)\

				use -statics instead"

		    }

		    -nestedLoadOk {

			return -code error\

				"ambigous query (get or set -nestedLoadOk ?)\

				use -nested instead"

		    }

		    default {

			return -code error "unknown flag $name (bug)"

		    }

		}

	    }

	    default {

		# Otherwise we want to parse the arguments like init and create

		# did

		set Args [::tcl::OptKeyParse ::safe::interpIC $args]

		CheckInterp $slave

		# Get the current (and not the default) values of

		# whatever has not been given:

		if {![::tcl::OptProcArgGiven -accessPath]} {

		    set doreset 1

		    set accessPath [Set [PathListName $slave]]

		} else {

		    set doreset 0

		}

		if {(![::tcl::OptProcArgGiven -statics]) \

			&& (![::tcl::OptProcArgGiven -noStatics]) } {

		    set statics    [Set [StaticsOkName $slave]]

		} else {

		    set statics    [InterpStatics]

		}

		if {([::tcl::OptProcArgGiven -nested]) \

			|| ([::tcl::OptProcArgGiven -nestedLoadOk]) } {

		    set nested     [InterpNested]

		} else {

		    set nested     [Set [NestedOkName $slave]]

		}

		if {![::tcl::OptProcArgGiven -deleteHook]} {

		    set deleteHook [Set [DeleteHookName $slave]]

		}

		# we can now reconfigure :

		InterpSetConfig $slave $accessPath $statics $nested $deleteHook

		# auto_reset the slave (to completly synch the new access_path)

		if {$doreset} {

		    if {[catch {::interp eval $slave {auto_reset}} msg]} {

			Log $slave "auto_reset failed: $msg"

		    } else {

			Log $slave "successful auto_reset" NOTICE

		    }

		}

	    }

	}

    }

    ####

    #

    #  Functions that actually implements the exported APIs

    #

    ####

    #

    # safe::InterpCreate : doing the real job

    #

    # This procedure creates a safe slave and initializes it with the

    # safe base aliases.

    # NB: slave name must be simple alphanumeric string, no spaces,

    # no (), no {},...  {because the state array is stored as part of the name}

    #

    # Returns the slave name.

    #

    # Optional Arguments : 

    # + slave name : if empty, generated name will be used

    # + access_path: path list controlling where load/source can occur,

    #                if empty: the master auto_path will be used.

    # + staticsok  : flag, if 0 :no static package can be loaded (load {} Xxx)

    #                      if 1 :static packages are ok.

    # + nestedok: flag, if 0 :no loading to sub-sub interps (load xx xx sub)

    #                      if 1 : multiple levels are ok.

    # use the full name and no indent so auto_mkIndex can find us

    proc ::safe::InterpCreate {

	slave 

	access_path

	staticsok

	nestedok

	deletehook

    } {

	# Create the slave.

	if {$slave ne ""} {

	    ::interp create -safe $slave

	} else {

	    # empty argument: generate slave name

	    set slave [::interp create -safe]

	}

	Log $slave "Created" NOTICE

	# Initialize it. (returns slave name)

	InterpInit $slave $access_path $staticsok $nestedok $deletehook

    }

    #

    # InterpSetConfig (was setAccessPath) :

    #    Sets up slave virtual auto_path and corresponding structure

    #    within the master. Also sets the tcl_library in the slave

    #    to be the first directory in the path.

    #    Nb: If you change the path after the slave has been initialized

    #    you probably need to call "auto_reset" in the slave in order that it

    #    gets the right auto_index() array values.

    proc ::safe::InterpSetConfig {slave access_path staticsok\

	    nestedok deletehook} {

	# determine and store the access path if empty

	if {$access_path eq ""} {

	    set access_path [uplevel \#0 set auto_path]

	    # Make sure that tcl_library is in auto_path

	    # and at the first position (needed by setAccessPath)

	    set where [lsearch -exact $access_path [info library]]

	    if {$where == -1} {

		# not found, add it.

		set access_path [concat [list [info library]] $access_path]

		Log $slave "tcl_library was not in auto_path,\

			added it to slave's access_path" NOTICE

	    } elseif {$where != 0} {

		# not first, move it first

		set access_path [concat [list [info library]]\

			[lreplace $access_path $where $where]]

		Log $slave "tcl_libray was not in first in auto_path,\

			moved it to front of slave's access_path" NOTICE

	    }

	    # Add 1st level sub dirs (will searched by auto loading from tcl

	    # code in the slave using glob and thus fail, so we add them

	    # here so by default it works the same).

	    set access_path [AddSubDirs $access_path]

	}

	Log $slave "Setting accessPath=($access_path) staticsok=$staticsok\

		nestedok=$nestedok deletehook=($deletehook)" NOTICE

	# clear old autopath if it existed

	set nname [PathNumberName $slave]

	if {[Exists $nname]} {

	    set n [Set $nname]

	    for {set i 0} {$i<$n} {incr i} {

		Unset [PathToken $i $slave]

	    }

	}

	# build new one

	set slave_auto_path {}

	set i 0

	foreach dir $access_path {

	    Set [PathToken $i $slave] $dir

	    lappend slave_auto_path "\$[PathToken $i]"

	    incr i

	}

	Set $nname $i

	Set [PathListName $slave] $access_path

	Set [VirtualPathListName $slave] $slave_auto_path

	Set [StaticsOkName $slave] $staticsok

	Set [NestedOkName $slave] $nestedok

	Set [DeleteHookName $slave] $deletehook

	SyncAccessPath $slave

    }

    #

    #

    # FindInAccessPath:

    #    Search for a real directory and returns its virtual Id

    #    (including the "$")

proc ::safe::interpFindInAccessPath {slave path} {

	set access_path [GetAccessPath $slave]

	set where [lsearch -exact $access_path $path]

	if {$where == -1} {

	    return -code error "$path not found in access path $access_path"

	}

	return "\$[PathToken $where]"

    }

    #

    # addToAccessPath:

    #    add (if needed) a real directory to access path

    #    and return its virtual token (including the "$").

proc ::safe::interpAddToAccessPath {slave path} {

	# first check if the directory is already in there

	if {![catch {interpFindInAccessPath $slave $path} res]} {

	    return $res

	}

	# new one, add it:

	set nname [PathNumberName $slave]

	set n [Set $nname]

	Set [PathToken $n $slave] $path

	set token "\$[PathToken $n]"

	Lappend [VirtualPathListName $slave] $token

	Lappend [PathListName $slave] $path

	Set $nname [expr {$n+1}]

	SyncAccessPath $slave

	return $token

    }

    # This procedure applies the initializations to an already existing

    # interpreter. It is useful when you want to install the safe base

    # aliases into a preexisting safe interpreter.

    proc ::safe::InterpInit {

	slave 

	access_path

	staticsok

	nestedok

	deletehook

    } {

	# Configure will generate an access_path when access_path is

	# empty.

	InterpSetConfig $slave $access_path $staticsok $nestedok $deletehook

	# These aliases let the slave load files to define new commands

	# NB we need to add [namespace current], aliases are always

	# absolute paths.

	::interp alias $slave source {} [namespace current]::AliasSource $slave

	::interp alias $slave load {} [namespace current]::AliasLoad $slave

	# This alias lets the slave use the encoding names, convertfrom,

	# convertto, and system, but not "encoding system <name>" to set

	# the system encoding.

	::interp alias $slave encoding {} [namespace current]::AliasEncoding \

		$slave

	# This alias lets the slave have access to a subset of the 'file'

	# command functionality.

	AliasSubset $slave file file dir.* join root.* ext.* tail \

		path.* split

	# This alias interposes on the 'exit' command and cleanly terminates

	# the slave.

	::interp alias $slave exit {} [namespace current]::interpDelete $slave

	# The allowed slave variables already have been set

	# by Tcl_MakeSafe(3)

	# Source init.tcl into the slave, to get auto_load and other

	# procedures defined:

	# We don't try to use the -rsrc on the mac because it would get

	# confusing if you would want to customize init.tcl

	# for a given set of safe slaves, on all the platforms

	# you just need to give a specific access_path and

	# the mac should be no exception. As there is no

	# obvious full "safe ressources" design nor implementation

	# for the mac, safe interps there will just don't

	# have that ability. (A specific app can still reenable

	# that using custom aliases if they want to).

	# It would also make the security analysis and the Safe Tcl security

	# model platform dependant and thus more error prone.

	if {[catch {::interp eval $slave\

		{source [file join $tcl_library init.tcl]}} msg]} {

	    Log $slave "can't source init.tcl ($msg)"

	    error "can't source init.tcl into slave $slave ($msg)"

	}

	return $slave

    }

    # Add (only if needed, avoid duplicates) 1 level of

    # sub directories to an existing path list.

    # Also removes non directories from the returned list.

    proc AddSubDirs {pathList} {

	set res {}

	foreach dir $pathList {

	    if {[file isdirectory $dir]} {

		# check that we don't have it yet as a children

		# of a previous dir

		if {[lsearch -exact $res $dir]<0} {

		    lappend res $dir

		}

		foreach sub [glob -directory $dir -nocomplain *] {

		    if {([file isdirectory $sub]) \

			    && ([lsearch -exact $res $sub]<0) } {

			# new sub dir, add it !

	                lappend res $sub

	            }

		}

	    }

	}

	return $res

    }

    # This procedure deletes a safe slave managed by Safe Tcl and

    # cleans up associated state:

proc ::safe::interpDelete {slave} {

        Log $slave "About to delete" NOTICE

	# If the slave has a cleanup hook registered, call it.

	# check the existance because we might be called to delete an interp

	# which has not been registered with us at all

	set hookname [DeleteHookName $slave]

	if {[Exists $hookname]} {

	    set hook [Set $hookname]

	    if {![::tcl::Lempty $hook]} {

		# remove the hook now, otherwise if the hook

		# calls us somehow, we'll loop

		Unset $hookname

		if {[catch {eval $hook [list $slave]} err]} {

		    Log $slave "Delete hook error ($err)"

		}

	    }

	}

	# Discard the global array of state associated with the slave, and

	# delete the interpreter.

	set statename [InterpStateName $slave]

	if {[Exists $statename]} {

	    Unset $statename

	}

	# if we have been called twice, the interp might have been deleted

	# already

	if {[::interp exists $slave]} {

	    ::interp delete $slave

	    Log $slave "Deleted" NOTICE

	}

	return

    }

    # Set (or get) the loging mecanism 

proc ::safe::setLogCmd {args} {

    variable Log

    if {[llength $args] == 0} {

	return $Log

    } else {

	if {[llength $args] == 1} {

	    set Log [lindex $args 0]

	} else {

	    set Log $args

	}

    }

}

    # internal variable

    variable Log {}

    # ------------------- END OF PUBLIC METHODS ------------

    #

    # sets the slave auto_path to the master recorded value.

    # also sets tcl_library to the first token of the virtual path.

    #

    proc SyncAccessPath {slave} {

	set slave_auto_path [Set [VirtualPathListName $slave]]

	::interp eval $slave [list set auto_path $slave_auto_path]

	Log $slave "auto_path in $slave has been set to $slave_auto_path"\

		NOTICE

	::interp eval $slave [list set tcl_library [lindex $slave_auto_path 0]]

    }

    # base name for storing all the slave states

    # the array variable name for slave foo is thus "Sfoo"

    # and for sub slave {foo bar} "Sfoo bar" (spaces are handled

    # ok everywhere (or should))

    # We add the S prefix to avoid that a slave interp called "Log"

    # would smash our "Log" variable.

    proc InterpStateName {slave} {

	return "S$slave"

    }

    # Check that the given slave is "one of us"

    proc IsInterp {slave} {

	expr {[Exists [InterpStateName $slave]] && [::interp exists $slave]}

    }

    # returns the virtual token for directory number N

    # if the slave argument is given, 

    # it will return the corresponding master global variable name

    proc PathToken {n {slave ""}} {

	if {$slave ne ""} {

	    return "[InterpStateName $slave](access_path,$n)"

	} else {

	    # We need to have a ":" in the token string so

	    # [file join] on the mac won't turn it into a relative

	    # path.

	    return "p(:$n:)"

	}

    }

    # returns the variable name of the complete path list

    proc PathListName {slave} {

	return "[InterpStateName $slave](access_path)"

    }

    # returns the variable name of the complete path list

    proc VirtualPathListName {slave} {

	return "[InterpStateName $slave](access_path_slave)"

    }

    # returns the variable name of the number of items

    proc PathNumberName {slave} {

	return "[InterpStateName $slave](access_path,n)"

    }

    # returns the staticsok flag var name

    proc StaticsOkName {slave} {

	return "[InterpStateName $slave](staticsok)"

    }

    # returns the nestedok flag var name

    proc NestedOkName {slave} {

	return "[InterpStateName $slave](nestedok)"

    }

    # Run some code at the namespace toplevel

    proc Toplevel {args} {

	namespace eval [namespace current] $args

    }

    # set/get values

    proc Set {args} {

	eval [linsert $args 0 Toplevel set]

    }

    # lappend on toplevel vars

    proc Lappend {args} {

	eval [linsert $args 0 Toplevel lappend]

    }

    # unset a var/token (currently just an global level eval)

    proc Unset {args} {

	eval [linsert $args 0 Toplevel unset]

    }

    # test existance 

    proc Exists {varname} {

	Toplevel info exists $varname

    }

    # short cut for access path getting

    proc GetAccessPath {slave} {

	Set [PathListName $slave]

    }

    # short cut for statics ok flag getting

    proc StaticsOk {slave} {

	Set [StaticsOkName $slave]

    }

    # short cut for getting the multiples interps sub loading ok flag

    proc NestedOk {slave} {

	Set [NestedOkName $slave]

    }

    # interp deletion storing hook name

    proc DeleteHookName {slave} {

	return [InterpStateName $slave](cleanupHook)

    }

    #

    # translate virtual path into real path

    #

    proc TranslatePath {slave path} {

	# somehow strip the namespaces 'functionality' out (the danger

	# is that we would strip valid macintosh "../" queries... :

	if {[regexp {(::)|(\.\.)} $path]} {

	    error "invalid characters in path $path"

	}

	set n [expr {[Set [PathNumberName $slave]]-1}]

	for {} {$n>=0} {incr n -1} {

	    # fill the token virtual names with their real value

	    set [PathToken $n] [Set [PathToken $n $slave]]

	}

	# replaces the token by their value

	subst -nobackslashes -nocommands $path

    }

    # Log eventually log an error

    # to enable error logging, set Log to {puts stderr} for instance

    proc Log {slave msg {type ERROR}} {

	variable Log

	if {[info exists Log] && [llength $Log]} {

	    eval $Log [list "$type for slave $slave : $msg"]

	}

    }

    # file name control (limit access to files/ressources that should be

    # a valid tcl source file)

    proc CheckFileName {slave file} {

	# This used to limit what can be sourced to ".tcl" and forbid files

	# with more than 1 dot and longer than 14 chars, but I changed that

	# for 8.4 as a safe interp has enough internal protection already

	# to allow sourcing anything. - hobbs

	if {![file exists $file]} {

	    # don't tell the file path

	    error "no such file or directory"

	}

	if {![file readable $file]} {

	    # don't tell the file path

	    error "not readable"

	}

    }

    # AliasSource is the target of the "source" alias in safe interpreters.

    proc AliasSource {slave args} {

	set argc [llength $args]

	# Allow only "source filename"

	# (and not mac specific -rsrc for instance - see comment in ::init

	# for current rationale)

	if {$argc != 1} {

	    set msg "wrong # args: should be \"source fileName\""

	    Log $slave "$msg ($args)"

	    return -code error $msg

	}

	set file [lindex $args 0]

	# get the real path from the virtual one.

	if {[catch {set file [TranslatePath $slave $file]} msg]} {

	    Log $slave $msg

	    return -code error "permission denied"

	}

	# check that the path is in the access path of that slave

	if {[catch {FileInAccessPath $slave $file} msg]} {

	    Log $slave $msg

	    return -code error "permission denied"

	}

	# do the checks on the filename :

	if {[catch {CheckFileName $slave $file} msg]} {

	    Log $slave "$file:$msg"

	    return -code error $msg

	}

	# passed all the tests , lets source it:

	if {[catch {::interp invokehidden $slave source $file} msg]} {

	    Log $slave $msg

	    return -code error "script error"

	}

	return $msg

    }

    # AliasLoad is the target of the "load" alias in safe interpreters.

    proc AliasLoad {slave file args} {

	set argc [llength $args]

	if {$argc > 2} {

	    set msg "load error: too many arguments"

	    Log $slave "$msg ($argc) {$file $args}"

	    return -code error $msg

	}

	# package name (can be empty if file is not).

	set package [lindex $args 0]

	# Determine where to load. load use a relative interp path

	# and {} means self, so we can directly and safely use passed arg.

	set target [lindex $args 1]

	if {$target ne ""} {

	    # we will try to load into a sub sub interp

	    # check that we want to authorize that.

	    if {![NestedOk $slave]} {

		Log $slave "loading to a sub interp (nestedok)\

			disabled (trying to load $package to $target)"

		return -code error "permission denied (nested load)"

	    }

	}

	# Determine what kind of load is requested

	if {$file eq ""} {

	    # static package loading

	    if {$package eq ""} {

		set msg "load error: empty filename and no package name"

		Log $slave $msg

		return -code error $msg

	    }

	    if {![StaticsOk $slave]} {

		Log $slave "static packages loading disabled\

			(trying to load $package to $target)"

		return -code error "permission denied (static package)"

	    }

	} else {

	    # file loading

	    # get the real path from the virtual one.

	    if {[catch {set file [TranslatePath $slave $file]} msg]} {

		Log $slave $msg

		return -code error "permission denied"

	    }

	    # check the translated path

	    if {[catch {FileInAccessPath $slave $file} msg]} {

		Log $slave $msg

		return -code error "permission denied (path)"

	    }

	}

	if {[catch {::interp invokehidden\

		$slave load $file $package $target} msg]} {

	    Log $slave $msg

	    return -code error $msg

	}

	return $msg

    }

    # FileInAccessPath raises an error if the file is not found in

    # the list of directories contained in the (master side recorded) slave's

    # access path.

    # the security here relies on "file dirname" answering the proper

    # result.... needs checking ?

    proc FileInAccessPath {slave file} {

	set access_path [GetAccessPath $slave]

	if {[file isdirectory $file]} {

	    error "\"$file\": is a directory"

	}

	set parent [file dirname $file]

	# Normalize paths for comparison since lsearch knows nothing of

	# potential pathname anomalies.

	set norm_parent [file normalize $parent]

	foreach path $access_path {

	    lappend norm_access_path [file normalize $path]

	}

	if {[lsearch -exact $norm_access_path $norm_parent] == -1} {

	    error "\"$file\": not in access_path"

	}

    }

    # This procedure enables access from a safe interpreter to only a subset of

    # the subcommands of a command:

    proc Subset {slave command okpat args} {

	set subcommand [lindex $args 0]

	if {[regexp $okpat $subcommand]} {

	    return [eval [linsert $args 0 $command]]

	}

	set msg "not allowed to invoke subcommand $subcommand of $command"

	Log $slave $msg

	error $msg

    }

    # This procedure installs an alias in a slave that invokes "safesubset"

    # in the master to execute allowed subcommands. It precomputes the pattern

    # of allowed subcommands; you can use wildcards in the pattern if you wish

    # to allow subcommand abbreviation.

    #

    # Syntax is: AliasSubset slave alias target subcommand1 subcommand2...

    proc AliasSubset {slave alias target args} {

	set pat ^(; set sep ""

	foreach sub $args {

	    append pat $sep$sub

	    set sep |

	}

	append pat )\$

	::interp alias $slave $alias {}\

		[namespace current]::Subset $slave $target $pat

    }

    # AliasEncoding is the target of the "encoding" alias in safe interpreters.

    proc AliasEncoding {slave args} {

	set argc [llength $args]

	set okpat "^(name.*|convert.*)\$"

	set subcommand [lindex $args 0]

	if {[regexp $okpat $subcommand]} {

	    return [eval [linsert $args 0 \

		    ::interp invokehidden $slave encoding]]

	}

	if {[string first $subcommand system] == 0} {

	    if {$argc == 1} {

		# passed all the tests , lets source it:

		if {[catch {::interp invokehidden \

			$slave encoding system} msg]} {

		    Log $slave $msg

		    return -code error "script error"

		}

	    } else {

		set msg "wrong # args: should be \"encoding system\""

		Log $slave $msg

		error $msg

	    }

	} else {

	    set msg "wrong # args: should be \"encoding option ?arg ...?\""

	    Log $slave $msg

	    error $msg

	}

	return $msg

    }

}