public final class HTMLFilter { /** * regex flag union representing /si modifiers in php **/ private static final int REGEX_FLAGS_SI = Pattern.CASE_INSENSITIVE | Pattern.DOTALL; private static final Pattern P_COMMENTS = Pattern.compile("<!--(.*?)-->", Pattern.DOTALL); private static final Pattern P_COMMENT = Pattern.compile("^!--(.*)--$", REGEX_FLAGS_SI); private static final Pattern P_TAGS = Pattern.compile("<(.*?)>", Pattern.DOTALL); private static final Pattern P_END_TAG = Pattern.compile("^/([a-z0-9]+)", REGEX_FLAGS_SI); private static final Pattern P_START_TAG = Pattern.compile("^([a-z0-9]+)(.*?)(/?)$", REGEX_FLAGS_SI); private static final Pattern P_QUOTED_ATTRIBUTES = Pattern.compile("([a-z0-9]+)=(["'])(.*?)\2", REGEX_FLAGS_SI); private static final Pattern P_UNQUOTED_ATTRIBUTES = Pattern.compile("([a-z0-9]+)(=)([^"\s']+)", REGEX_FLAGS_SI); private static final Pattern P_PROTOCOL = Pattern.compile("^([^:]+):", REGEX_FLAGS_SI); private static final Pattern P_ENTITY = Pattern.compile("&#(\d+);?"); private static final Pattern P_ENTITY_UNICODE = Pattern.compile("&#x([0-9a-f]+);?"); private static final Pattern P_ENCODE = Pattern.compile("%([0-9a-f]{2});?"); private static final Pattern P_VALID_ENTITIES = Pattern.compile("&([^&;]*)(?=(;|&|$))"); private static final Pattern P_VALID_QUOTES = Pattern.compile("(>|^)([^<]+?)(<|$)", Pattern.DOTALL); private static final Pattern P_END_ARROW = Pattern.compile("^>"); private static final Pattern P_BODY_TO_END = Pattern.compile("<([^>]*?)(?=<|$)"); private static final Pattern P_XML_CONTENT = Pattern.compile("(^|>)([^<]*?)(?=>)"); private static final Pattern P_STRAY_LEFT_ARROW = Pattern.compile("<([^>]*?)(?=<|$)"); private static final Pattern P_STRAY_RIGHT_ARROW = Pattern.compile("(^|>)([^<]*?)(?=>)"); private static final Pattern P_AMP = Pattern.compile("&"); private static final Pattern P_QUOTE = Pattern.compile("""); private static final Pattern P_LEFT_ARROW = Pattern.compile("<"); private static final Pattern P_RIGHT_ARROW = Pattern.compile(">"); private static final Pattern P_BOTH_ARROWS = Pattern.compile("<>"); // @xxx could grow large... maybe use sesat's ReferenceMap private static final ConcurrentMap<String, Pattern> P_REMOVE_PAIR_BLANKS = new ConcurrentHashMap<>(); private static final ConcurrentMap<String, Pattern> P_REMOVE_SELF_BLANKS = new ConcurrentHashMap<>(); /** * set of allowed html elements, along with allowed attributes for each element **/ private final Map<String, List<String>> vAllowed; /** * counts of open tags for each (allowable) html element **/ private final Map<String, Integer> vTagCounts = new HashMap<>(); /** * html elements which must always be self-closing (e.g. "<img />") **/ private final String[] vSelfClosingTags; /** * html elements which must always have separate opening and closing tags (e.g. "<b></b>") **/ private final String[] vNeedClosingTags; /** * set of disallowed html elements **/ private final String[] vDisallowed; /** * attributes which should be checked for valid protocols **/ private final String[] vProtocolAtts; /** * allowed protocols **/ private final String[] vAllowedProtocols; /** * tags which should be removed if they contain no content (e.g. "<b></b>" or "<b />") **/ private final String[] vRemoveBlanks; /** * entities allowed within html markup **/ private final String[] vAllowedEntities; /** * flag determining whether comments are allowed in input String. */ private final boolean stripComment; private final boolean encodeQuotes; /** * flag determining whether to try to make tags when presented with "unbalanced" angle brackets (e.g. "<b text </b>" * becomes "<b> text </b>"). If set to false, unbalanced angle brackets will be html escaped. */ private final boolean alwaysMakeTags; /** * Default constructor. */ public HTMLFilter() { vAllowed = new HashMap<>(); final ArrayList<String> a_atts = new ArrayList<>(); a_atts.add("href"); a_atts.add("target"); vAllowed.put("a", a_atts); final ArrayList<String> img_atts = new ArrayList<>(); img_atts.add("src"); img_atts.add("width"); img_atts.add("height"); img_atts.add("alt"); vAllowed.put("img", img_atts); final ArrayList<String> no_atts = new ArrayList<>(); vAllowed.put("b", no_atts); vAllowed.put("strong", no_atts); vAllowed.put("i", no_atts); vAllowed.put("em", no_atts); vSelfClosingTags = new String[] { "img" }; vNeedClosingTags = new String[] { "a", "b", "strong", "i", "em" }; vDisallowed = new String[] {}; vAllowedProtocols = new String[] { "http", "mailto", "https" }; // no ftp. vProtocolAtts = new String[] { "src", "href" }; vRemoveBlanks = new String[] { "a", "b", "strong", "i", "em" }; vAllowedEntities = new String[] { "amp", "gt", "lt", "quot" }; stripComment = true; encodeQuotes = true; alwaysMakeTags = true; } /** * Map-parameter configurable constructor. * * @param conf map containing configuration. keys match field names. */ @SuppressWarnings("unchecked") public HTMLFilter(final Map<String, Object> conf) { assert conf.containsKey("vAllowed") : "configuration requires vAllowed"; assert conf.containsKey("vSelfClosingTags") : "configuration requires vSelfClosingTags"; assert conf.containsKey("vNeedClosingTags") : "configuration requires vNeedClosingTags"; assert conf.containsKey("vDisallowed") : "configuration requires vDisallowed"; assert conf.containsKey("vAllowedProtocols") : "configuration requires vAllowedProtocols"; assert conf.containsKey("vProtocolAtts") : "configuration requires vProtocolAtts"; assert conf.containsKey("vRemoveBlanks") : "configuration requires vRemoveBlanks"; assert conf.containsKey("vAllowedEntities") : "configuration requires vAllowedEntities"; vAllowed = Collections.unmodifiableMap((HashMap<String, List<String>>) conf.get("vAllowed")); vSelfClosingTags = (String[]) conf.get("vSelfClosingTags"); vNeedClosingTags = (String[]) conf.get("vNeedClosingTags"); vDisallowed = (String[]) conf.get("vDisallowed"); vAllowedProtocols = (String[]) conf.get("vAllowedProtocols"); vProtocolAtts = (String[]) conf.get("vProtocolAtts"); vRemoveBlanks = (String[]) conf.get("vRemoveBlanks"); vAllowedEntities = (String[]) conf.get("vAllowedEntities"); stripComment = conf.containsKey("stripComment") ? (Boolean) conf.get("stripComment") : true; encodeQuotes = conf.containsKey("encodeQuotes") ? (Boolean) conf.get("encodeQuotes") : true; alwaysMakeTags = conf.containsKey("alwaysMakeTags") ? (Boolean) conf.get("alwaysMakeTags") : true; } private void reset() { vTagCounts.clear(); } // --------------------------------------------------------------- // my versions of some PHP library functions public static String chr(final int decimal) { return String.valueOf((char) decimal); } public static String htmlSpecialChars(final String s) { String result = s; result = regexReplace(P_AMP, "&", result); result = regexReplace(P_QUOTE, """, result); result = regexReplace(P_LEFT_ARROW, "<", result); result = regexReplace(P_RIGHT_ARROW, ">", result); return result; } // --------------------------------------------------------------- /** * given a user submitted input String, filter out any invalid or restricted html. * * @param input text (i.e. submitted by a user) than may contain html * @return "clean" version of input, with only valid, whitelisted html elements allowed */ public String filter(final String input) { reset(); String s = input; s = escapeComments(s); s = balanceHTML(s); s = checkTags(s); s = processRemoveBlanks(s); s = validateEntities(s); return s; } public boolean isAlwaysMakeTags() { return alwaysMakeTags; } public boolean isStripComments() { return stripComment; } private String escapeComments(final String s) { final Matcher m = P_COMMENTS.matcher(s); final StringBuffer buf = new StringBuffer(); if (m.find()) { final String match = m.group(1); // (.*?) m.appendReplacement(buf, Matcher.quoteReplacement("<!--" + htmlSpecialChars(match) + "-->")); } m.appendTail(buf); return buf.toString(); } private String balanceHTML(String s) { if (alwaysMakeTags) { // // try and form html // s = regexReplace(P_END_ARROW, "", s); s = regexReplace(P_BODY_TO_END, "<$1>", s); s = regexReplace(P_XML_CONTENT, "$1<$2", s); } else { // // escape stray brackets // s = regexReplace(P_STRAY_LEFT_ARROW, "<$1", s); s = regexReplace(P_STRAY_RIGHT_ARROW, "$1$2><", s); // // the last regexp causes '<>' entities to appear // (we need to do a lookahead assertion so that the last bracket can // be used in the next pass of the regexp) // s = regexReplace(P_BOTH_ARROWS, "", s); } return s; } private String checkTags(String s) { Matcher m = P_TAGS.matcher(s); final StringBuffer buf = new StringBuffer(); while (m.find()) { String replaceStr = m.group(1); replaceStr = processTag(replaceStr); m.appendReplacement(buf, Matcher.quoteReplacement(replaceStr)); } m.appendTail(buf); // these get tallied in processTag // (remember to reset before subsequent calls to filter method) final StringBuilder sBuilder = new StringBuilder(buf.toString()); for (String key : vTagCounts.keySet()) { for (int ii = 0; ii < vTagCounts.get(key); ii++) { sBuilder.append("</").append(key).append(">"); } } s = sBuilder.toString(); return s; } private String processRemoveBlanks(final String s) { String result = s; for (String tag : vRemoveBlanks) { if (!P_REMOVE_PAIR_BLANKS.containsKey(tag)) { P_REMOVE_PAIR_BLANKS.putIfAbsent(tag, Pattern.compile("<" + tag + "(\s[^>]*)?></" + tag + ">")); } result = regexReplace(P_REMOVE_PAIR_BLANKS.get(tag), "", result); if (!P_REMOVE_SELF_BLANKS.containsKey(tag)) { P_REMOVE_SELF_BLANKS.putIfAbsent(tag, Pattern.compile("<" + tag + "(\s[^>]*)?/>")); } result = regexReplace(P_REMOVE_SELF_BLANKS.get(tag), "", result); } return result; } private static String regexReplace(final Pattern regex_pattern, final String replacement, final String s) { Matcher m = regex_pattern.matcher(s); return m.replaceAll(replacement); } private String processTag(final String s) { // ending tags Matcher m = P_END_TAG.matcher(s); if (m.find()) { final String name = m.group(1).toLowerCase(); if (allowed(name)) { if (false == inArray(name, vSelfClosingTags)) { if (vTagCounts.containsKey(name)) { vTagCounts.put(name, vTagCounts.get(name) - 1); return "</" + name + ">"; } } } } // starting tags m = P_START_TAG.matcher(s); if (m.find()) { final String name = m.group(1).toLowerCase(); final String body = m.group(2); String ending = m.group(3); // debug( "in a starting tag, name='" + name + "'; body='" + body + "'; ending='" + ending + "'" ); if (allowed(name)) { final StringBuilder params = new StringBuilder(); final Matcher m2 = P_QUOTED_ATTRIBUTES.matcher(body); final Matcher m3 = P_UNQUOTED_ATTRIBUTES.matcher(body); final List<String> paramNames = new ArrayList<>(); final List<String> paramValues = new ArrayList<>(); while (m2.find()) { paramNames.add(m2.group(1)); // ([a-z0-9]+) paramValues.add(m2.group(3)); // (.*?) } while (m3.find()) { paramNames.add(m3.group(1)); // ([a-z0-9]+) paramValues.add(m3.group(3)); // ([^"\s']+) } String paramName, paramValue; for (int ii = 0; ii < paramNames.size(); ii++) { paramName = paramNames.get(ii).toLowerCase(); paramValue = paramValues.get(ii); // debug( "paramName='" + paramName + "'" ); // debug( "paramValue='" + paramValue + "'" ); // debug( "allowed? " + vAllowed.get( name ).contains( paramName ) ); if (allowedAttribute(name, paramName)) { if (inArray(paramName, vProtocolAtts)) { paramValue = processParamProtocol(paramValue); } params.append(' ').append(paramName).append("="").append(paramValue).append("""); } } if (inArray(name, vSelfClosingTags)) { ending = " /"; } if (inArray(name, vNeedClosingTags)) { ending = ""; } if (ending == null || ending.length() < 1) { if (vTagCounts.containsKey(name)) { vTagCounts.put(name, vTagCounts.get(name) + 1); } else { vTagCounts.put(name, 1); } } else { ending = " /"; } return "<" + name + params + ending + ">"; } else { return ""; } } // comments m = P_COMMENT.matcher(s); if (!stripComment && m.find()) { return "<" + m.group() + ">"; } return ""; } private String processParamProtocol(String s) { s = decodeEntities(s); final Matcher m = P_PROTOCOL.matcher(s); if (m.find()) { final String protocol = m.group(1); if (!inArray(protocol, vAllowedProtocols)) { // bad protocol, turn into local anchor link instead s = "#" + s.substring(protocol.length() + 1); if (s.startsWith("#//")) { s = "#" + s.substring(3); } } } return s; } private String decodeEntities(String s) { StringBuffer buf = new StringBuffer(); Matcher m = P_ENTITY.matcher(s); while (m.find()) { final String match = m.group(1); final int decimal = Integer.decode(match).intValue(); m.appendReplacement(buf, Matcher.quoteReplacement(chr(decimal))); } m.appendTail(buf); s = buf.toString(); buf = new StringBuffer(); m = P_ENTITY_UNICODE.matcher(s); while (m.find()) { final String match = m.group(1); final int decimal = Integer.valueOf(match, 16).intValue(); m.appendReplacement(buf, Matcher.quoteReplacement(chr(decimal))); } m.appendTail(buf); s = buf.toString(); buf = new StringBuffer(); m = P_ENCODE.matcher(s); while (m.find()) { final String match = m.group(1); final int decimal = Integer.valueOf(match, 16).intValue(); m.appendReplacement(buf, Matcher.quoteReplacement(chr(decimal))); } m.appendTail(buf); s = buf.toString(); s = validateEntities(s); return s; } private String validateEntities(final String s) { StringBuffer buf = new StringBuffer(); // validate entities throughout the string Matcher m = P_VALID_ENTITIES.matcher(s); while (m.find()) { final String one = m.group(1); // ([^&;]*) final String two = m.group(2); // (?=(;|&|$)) m.appendReplacement(buf, Matcher.quoteReplacement(checkEntity(one, two))); } m.appendTail(buf); return encodeQuotes(buf.toString()); } private String encodeQuotes(final String s) { if (encodeQuotes) { StringBuffer buf = new StringBuffer(); Matcher m = P_VALID_QUOTES.matcher(s); while (m.find()) { final String one = m.group(1); // (>|^) final String two = m.group(2); // ([^<]+?) final String three = m.group(3); // (<|$) // 不替换双引号为"，防止json格式无效 regexReplace(P_QUOTE, """, two) m.appendReplacement(buf, Matcher.quoteReplacement(one + two + three)); } m.appendTail(buf); return buf.toString(); } else { return s; } } private String checkEntity(final String preamble, final String term) { return ";".equals(term) && isValidEntity(preamble) ? '&' + preamble : "&" + preamble; } private boolean isValidEntity(final String entity) { return inArray(entity, vAllowedEntities); } private static boolean inArray(final String s, final String[] array) { for (String item : array) { if (item != null && item.equals(s)) { return true; } } return false; } private boolean allowed(final String name) { return (vAllowed.isEmpty() || vAllowed.containsKey(name)) && !inArray(name, vDisallowed); } private boolean allowedAttribute(final String name, final String paramName) { return allowed(name) && (vAllowed.isEmpty() || vAllowed.get(name).contains(paramName)); } }