Add Base64 Encode Decode in Tcl (#5006)

Author: pascalecu

archive/t/tcl/base64-encode-decode.tcl

@@ -0,0 +1,43 @@
+#!/usr/bin/env tclsh
+
+proc usage {} {
+    puts stderr "Usage: please provide a mode and a string to encode/decode"
+    exit 1
+}
+
+if {$argc != 2} {
+    usage
+}
+
+set mode [lindex $argv 0]
+set text [lindex $argv 1]
+
+if {$text eq ""} {
+    usage
+}
+
+
+switch -- $mode {
+    encode {
+        set result [binary encode base64 $text]
+    }
+    decode {
+        if {[catch {binary decode base64 $text} result]} {
+            usage
+        }
+	# Tcl’s decoder sometimes tolerates invalid padding, so validate manually
+        # Check that input length is a multiple of 4 and only contains valid chars
+        if {![regexp {^[A-Za-z0-9+/]*={0,2}$} $text]} {
+            usage
+        }
+        if {[expr {[string length $text] % 4 != 0}]} {
+            usage
+        }
+    }
+    default {
+        usage
+    }
+}
+
+puts $result
+