Implement a DNS resolver.

* rex: Implement a simplistic DNS resolver.  Use it when looking up
host-specific keys in the database.
* vpnc.exp (startvpnc): Ignore SIGHUP.

1 files changed, 136 insertions, 9 deletions

diff --git a/rex b/rex
index 549d2a8..373ec4a 100755
--- a/rex
+++ b/rex
@@ -41,6 +41,106 @@ proc config_option {key} {
     return $config(option,$key)
 }
 
+# #######################################################################
+# A poor man's resolver.  Given the requirement of being as minimalistic
+# as possible, I cannot use any external libraries.  Therefore the task
+# of resolving host names and IP addresses is handled by calling "host"
+# and parsing its return.
+# #######################################################################
+
+namespace eval pmres { }
+
+proc ::pmres::hostorder {} {
+    global config
+
+    if {![info exists config(hostorder)]} {
+	set config(hostorder) {files dns}
+	if {[catch {open "/etc/nsswitch.conf" "r"} fd] == 0} {
+	    while {[gets $fd line] >= 0} {
+		if [regexp {[^[:space:]]*hosts:} "$line"] {
+		    set config(hostorder) [lrange [regexp -all -inline {[^[:space:]]+} $line] 1 end]
+		    break
+		}
+	    }
+	    close $fd
+	}
+    }
+    return $config(hostorder)
+}
+
+proc ::pmres::files_match {mode arg var} {
+    upvar $var res
+
+    if {[catch {open "/etc/hosts" "r"} fd] == 0} {
+	while {[gets $fd line] >= 0} {
+	    regsub "#.*" $line "" rec
+	    if {$rec == ""} {
+		continue
+	    }
+	    if {$mode == "-ip"} {
+		if {[lindex $rec 0] == $arg} {
+		    eval lappend res [lrange $rec 1 end]
+		}
+	    } else {
+		if {[lsearch -exact [lrange $rec 1 end] $arg] != -1} {
+		    lappend res [lindex $rec 0]
+		}
+	    }
+	}
+	close $fd
+    }
+}
+
+proc ::pmres::dns_match  {mode arg var} {
+    upvar $var res
+
+    if {[catch [list exec host $arg] ans] == 0} {
+	foreach line [split $ans "\n"] {
+	    if {$mode == "-ip"} {
+		if [regexp "domain name pointer" $line] {
+		    regsub {\.$} [lindex $line 4] "" t
+		    lappend res $t
+		}
+	    } else {
+		if [regexp "has address" $line] {
+		    lappend res [lindex $line 3]
+		} elseif [regexp "has IPv6 address" $line] {
+		    lappend res [lindex $line 4]
+		}
+	    }
+	}
+    }
+}
+
+proc ::pmres::resolve {args} {
+    set mode [lindex $args 0]
+    if {$mode == "-host" || $mode == "-ip"} {
+	set arg [lindex $args 1]
+    } else {
+	set arg [lindex $args 0]
+	if {[regexp {\d+\.\d+\.\d+\.\d+} $arg]} {
+	    set mode "-ip"
+	} elseif [regexp -nocase {(\d+)\.(\d+)\.(\d+)\.(\d+)\.in-addr.arpa} $arg o4 o3 o2 o1] {
+	    set mode "-ip"
+	    set arg "$o1.$o2.$o3.$o4"
+	} else {
+	    set mode "-host"
+	}
+    }
+    set res {}
+
+    foreach x [hostorder] {
+	set name "${x}_match"
+	if {[info procs "$name"] == "$name"} {
+	    eval $name $mode $arg res
+	}
+    }
+    return $res
+}	
+
+# #######################################################################
+# Database access functions
+# #######################################################################
 # rexdbget KEY [KEY...]
 # Iterate over KEYs, find first of them that is defined and return its value.
 proc rexdbget {args} {
@@ -49,12 +149,16 @@ proc rexdbget {args} {
     foreach key $args {
 	if [info exist config(option,hostgroup)] {
 	    set x "$config(option,hostgroup):$key"
+	    debug 3 "db: looking for $x"
 	    if {[info exist rexdb($x)]} {
+		debug 3 "db: found $x"
 		return $rexdb($x)
 	    }
 	}
 	
+	debug 3 "db: looking for $key"
 	if [info exist rexdb($key)] {
+	    debug 3 "db: found $key"
 	    return $rexdb($key)
 	}
     }
@@ -95,6 +199,9 @@ proc rexdbclr {args} {
     set rexdb(updated) 1
 }   
 
+# #######################################################################
+# Debugging and error reporting
+# #######################################################################
 proc debug {args} {
     global config
 
@@ -114,6 +221,10 @@ proc terror {args} {
     send_error "$argv0: $msg\n"
 }
 
+# #######################################################################
+# Various utility functions.
+# #######################################################################
+
 # Compare two version numbers. Return 0 if they are the same, a negative
 # value if "a" is older than "b", and a positive value otherwise.
 proc vercmp {va vb} {
@@ -242,6 +353,10 @@ proc getyn {args} {
     }
 }
 
+# #######################################################################
+# Program-specific database functions.
+# #######################################################################
+
 # Encrypt password
 proc passenc {pass} {
     binary scan [encoding convertto ebcdic $pass] H* enc
@@ -401,10 +516,12 @@ proc editdb {dbname} {
 proc hostuser {host} {
     global config
 
-    set key "$host:user"
-    set val [rexdbget $key user]
-    if {$val != ""} {
-	return $val
+    foreach hk [concat $host [::pmres::resolve $host]] { 
+	set key "$hk:user"
+	set val [rexdbget $key user]
+	if {$val != ""} {
+	    return $val
+	}
     }
 
     if [config_option interactive] {
@@ -432,12 +549,14 @@ proc hostuser {host} {
 proc hostpass {host} {
     global rexdb config
 
-    set key "$host:pass"
-    set val [rexdbget $key pass]
-    if {$val != ""} {
-	return [passdec $val]
+    foreach hk [concat $host [::pmres::resolve $host]] { 
+	set key "$hk:pass"
+	set val [rexdbget $key pass]
+	if {$val != ""} {
+	    return [passdec $val]
+	}
     }
-
+    
     if [config_option interactive] {
 	set x [getans -echo "Password on $host:"]
 	if {$x == ""} {
@@ -490,6 +609,11 @@ proc listgroups {} {
     }
 }
 
+# #######################################################################
+# A parser for GNU-style command line syntax.
+# Almost compatible with getopt_long(3), excepting several quirks.
+# #######################################################################
+
 # getopt [-progname name] [-longopts list] argc argv shortopts script
 proc getopt {args} {
     while 1 {
@@ -691,6 +815,9 @@ proc getopt {args} {
     return 0
 }
 
+# #######################################################################
+# The game begins...
+# #######################################################################
 set shortopts "CcdeEig:HhlNp:Ss:u:x:Vw"
 set longopts {
     debug         d