io.encodings.utf7: implementation of decoding for new codec utf7

basis/io/encodings/utf7/utf7-tests.factor

@@ -0,0 +1,31 @@
+USING:
+    io.encodings.string io.encodings.utf7
+    kernel
+    sequences
+    strings
+    tools.test ;
+IN: io.encodings.utf7.tests
+
+[
+    {
+        "~/b&AOU-g&APg-"
+        "b&AOU-x"
+        "b&APg-x"
+        "test"
+        "Skr&AOQ-ppost"
+        "Ting &- S&AOU-ger"
+        "~/F&APg-lder/mailb&AOU-x &- stuff + more"
+        "~peter/mail/&ZeVnLIqe-/&U,BTFw-"
+    }
+] [
+    {
+        "~/bågø"
+        "båx"
+        "bøx"
+        "test"
+        "Skräppost"
+        "Ting & Såger"
+        "~/Følder/mailbåx & stuff + more"
+        "~peter/mail/日本語/台北"
+    } [ utf7imap4 encode >string ] map
+] unit-test

basis/io/encodings/utf7/utf7.factor

@@ -0,0 +1,58 @@
+USING:
+    accessors
+    arrays
+    ascii
+    assocs
+    base64
+    byte-arrays
+    fry
+    io
+    io.encodings io.encodings.string io.encodings.utf16
+    kernel
+    sequences
+    splitting
+    strings ;
+IN: io.encodings.utf7
+
+SINGLETON: utf7
+SINGLETON: utf7imap4
+
+! This map encodes the difference between standard utf7 and the
+! dialect used by IMAP which wants slashes repladed with commas when
+! encoding and uses '&' instead of '+' as the escaping character.
+CONSTANT: dialect-data {
+    { utf7 { { "" "" } { "+" "-" } } }
+    { utf7imap4 { { "/" "," } { "&" "-" } } }
+}
+
+: >raw-base64 ( byte-array -- str )
+    >string utf16be encode >base64 [ CHAR: = = ] trim-tail ;
+
+: flush-buffer ( buffer repl-pair surround-pair -- result )
+    rot [ 2drop "" ] [
+        >raw-base64 -rot [ first2 replace ] [ first2 surround ] bi*
+    ] if-empty ;
+
+: escaped-char ( str1 begin end -- str )
+    -rot dupd = [ swap append ] [ nip ] if ;
+
+: encode-utf7-char ( result buffer dialect-info ch -- result buffer )
+    dup printable? [
+        1string -rot first2
+        [ flush-buffer swapd append swap ]
+        [ nip first2 escaped-char append ] 2bi ""
+    ] [ nip suffix ] if ;
+
+: encode-utf7-string ( str dialect -- str' )
+    { "" "" } swap dialect-data at [
+        '[ [ first2 ] dip _ swap encode-utf7-char 2array ] reduce
+    ] [
+        [ first2 ] dip first2 flush-buffer append
+    ] bi ;
+
+: stream-write-utf7 ( string stream encoding -- )
+    swapd encode-utf7-string >byte-array swap stream-write ;
+
+M: utf7 encode-string stream-write-utf7 ;
+
+M: utf7imap4 encode-string stream-write-utf7 ;