From ca543f7da3ea3789e3b3a018b3c1f277f1509102 Mon Sep 17 00:00:00 2001
From: Greg Weber <greg@gregweber.info>
Date: Sun, 19 Sep 2010 14:45:53 -0700
Subject: [PATCH] rip off jgm's pandoc sanitization code

---
 README         |  2 +-
 SanitizeXSS.hs | 81 ++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 82 insertions(+), 1 deletion(-)
 create mode 100644 SanitizeXSS.hs

diff --git a/README b/README
index 010704f..3a4068d 100644
--- a/README
+++ b/README
@@ -1,5 +1,5 @@
 == Summary ==
-provides a function sanitizeHtmlXSS that removes XSS attacks from html.
+provides a function sanitizeXSS that removes XSS attacks from html.
 
 == Use Case ==
 All html from an untrusted source (user of a web application) should be ran through this function.
diff --git a/SanitizeXSS.hs b/SanitizeXSS.hs
new file mode 100644
index 0000000..63b19af
--- /dev/null
+++ b/SanitizeXSS.hs
@@ -0,0 +1,81 @@
+module SanitizeXSS where
+
+import Data.Set
+import Network.URI ( parseURIReference, URI (..) )
+
+import Data.Char ( toLower, isLower, isUpper, isAlpha, isAscii,
+                   isLetter, isDigit )
+
+import Network.URI ( isAllowedInURI, escapeURIString, unEscapeString )
+import Codec.Binary.UTF8.String ( encodeString, decodeString )
+
+
+sanitizeXSS :: String -> String
+sanitizeXSS unsafeHtml = error
+
+unSafeTag tag = tag `notElem` sanitaryTags
+unSafeAttributes tag = (attr `notElem` sanitaryAttributes ||
+         (attr `elem` ["href","src"] && unsanitaryURI val))
+
+-- | Returns @True@ if the specified URI is potentially a security risk.
+unsanitaryURI :: String -> Bool
+unsanitaryURI u =
+  let safeURISchemes = [ "", "http:", "https:", "ftp:", "mailto:", "file:",
+             "telnet:", "gopher:", "aaa:", "aaas:", "acap:", "cap:", "cid:",
+             "crid:", "dav:", "dict:", "dns:", "fax:", "go:", "h323:", "im:",
+             "imap:", "ldap:", "mid:", "news:", "nfs:", "nntp:", "pop:",
+             "pres:", "sip:", "sips:", "snmp:", "tel:", "urn:", "wais:",
+             "xmpp:", "z39.50r:", "z39.50s:", "aim:", "callto:", "cvs:",
+             "ed2k:", "feed:", "fish:", "gg:", "irc:", "ircs:", "lastfm:",
+             "ldaps:", "magnet:", "mms:", "msnim:", "notes:", "rsync:",
+             "secondlife:", "skype:", "ssh:", "sftp:", "smb:", "sms:",
+             "snews:", "webcal:", "ymsgr:"]
+  in  case parseURIReference (escapeURI u) of
+           -- uriScheme member of URI record data structure
+           Just p  -> (map toLower $ uriScheme p) `notElem` safeURISchemes
+           Nothing -> True
+
+
+-- | Escape unicode characters in a URI.  Characters that are
+-- already valid in a URI, including % and ?, are left alone.
+escapeURI :: String -> String
+escapeURI = escapeURIString isAllowedInURI . encodeString
+
+-- | Unescape unicode and some special characters in a URI, but
+-- without introducing spaces.
+unescapeURI :: String -> String
+unescapeURI = escapeURIString (\c -> isAllowedInURI c || not (isAscii c)) .
+               decodeString . unEscapeString
+
+
+
+
+sanitaryTags :: [[Char]]
+sanitaryTags = ["a", "abbr", "acronym", "address", "area", "b", "big",
+                "blockquote", "br", "button", "caption", "center",
+                "cite", "code", "col", "colgroup", "dd", "del", "dfn",
+                "dir", "div", "dl", "dt", "em", "fieldset", "font",
+                "form", "h1", "h2", "h3", "h4", "h5", "h6", "hr",
+                "i", "img", "input", "ins", "kbd", "label", "legend",
+                "li", "map", "menu", "ol", "optgroup", "option", "p",
+                "pre", "q", "s", "samp", "select", "small", "span",
+                "strike", "strong", "sub", "sup", "table", "tbody",
+                "td", "textarea", "tfoot", "th", "thead", "tr", "tt",
+                "u", "ul", "var"]
+
+sanitaryAttributes :: [[Char]]
+sanitaryAttributes = ["abbr", "accept", "accept-charset",
+                      "accesskey", "action", "align", "alt", "axis",
+                      "border", "cellpadding", "cellspacing", "char",
+                      "charoff", "charset", "checked", "cite", "class",
+                      "clear", "cols", "colspan", "color", "compact",
+                      "coords", "datetime", "dir", "disabled",
+                      "enctype", "for", "frame", "headers", "height",
+                      "href", "hreflang", "hspace", "id", "ismap",
+                      "label", "lang", "longdesc", "maxlength", "media",
+                      "method", "multiple", "name", "nohref", "noshade",
+                      "nowrap", "prompt", "readonly", "rel", "rev",
+                      "rows", "rowspan", "rules", "scope", "selected",
+                      "shape", "size", "span", "src", "start",
+                      "summary", "tabindex", "target", "title", "type",
+                      "usemap", "valign", "value", "vspace", "width"]