389 lines
10 KiB
Go
389 lines
10 KiB
Go
|
// Package sanitize provides functions for sanitizing text.
|
||
|
|
package sanitize
|
||
|
|
|
||
|
|
import (
|
||
|
|
"bytes"
|
||
|
|
"html"
|
||
|
|
"html/template"
|
||
|
|
"io"
|
||
|
|
"path"
|
||
|
|
"regexp"
|
||
|
|
"strings"
|
||
|
|
|
||
|
|
parser "golang.org/x/net/html"
|
||
|
|
)
|
||
|
|
|
||
|
|
var (
|
||
|
|
ignoreTags = []string{"title", "script", "style", "iframe", "frame", "frameset", "noframes", "noembed", "embed", "applet", "object", "base"}
|
||
|
|
|
||
|
|
defaultTags = []string{"h1", "h2", "h3", "h4", "h5", "h6", "div", "span", "hr", "p", "br", "b", "i", "strong", "em", "ol", "ul", "li", "a", "img", "pre", "code", "blockquote", "article", "section"}
|
||
|
|
|
||
|
|
defaultAttributes = []string{"id", "class", "src", "href", "title", "alt", "name", "rel"}
|
||
|
|
)
|
||
|
|
|
||
|
|
// HTMLAllowing sanitizes html, allowing some tags.
|
||
|
|
// Arrays of allowed tags and allowed attributes may optionally be passed as the second and third arguments.
|
||
|
|
func HTMLAllowing(s string, args ...[]string) (string, error) {
|
||
|
|
|
||
|
|
allowedTags := defaultTags
|
||
|
|
if len(args) > 0 {
|
||
|
|
allowedTags = args[0]
|
||
|
|
}
|
||
|
|
allowedAttributes := defaultAttributes
|
||
|
|
if len(args) > 1 {
|
||
|
|
allowedAttributes = args[1]
|
||
|
|
}
|
||
|
|
|
||
|
|
// Parse the html
|
||
|
|
tokenizer := parser.NewTokenizer(strings.NewReader(s))
|
||
|
|
|
||
|
|
buffer := bytes.NewBufferString("")
|
||
|
|
ignore := ""
|
||
|
|
|
||
|
|
for {
|
||
|
|
tokenType := tokenizer.Next()
|
||
|
|
token := tokenizer.Token()
|
||
|
|
|
||
|
|
switch tokenType {
|
||
|
|
|
||
|
|
case parser.ErrorToken:
|
||
|
|
err := tokenizer.Err()
|
||
|
|
if err == io.EOF {
|
||
|
|
return buffer.String(), nil
|
||
|
|
}
|
||
|
|
return "", err
|
||
|
|
|
||
|
|
case parser.StartTagToken:
|
||
|
|
|
||
|
|
if len(ignore) == 0 && includes(allowedTags, token.Data) {
|
||
|
|
token.Attr = cleanAttributes(token.Attr, allowedAttributes)
|
||
|
|
buffer.WriteString(token.String())
|
||
|
|
} else if includes(ignoreTags, token.Data) {
|
||
|
|
ignore = token.Data
|
||
|
|
}
|
||
|
|
|
||
|
|
case parser.SelfClosingTagToken:
|
||
|
|
|
||
|
|
if len(ignore) == 0 && includes(allowedTags, token.Data) {
|
||
|
|
token.Attr = cleanAttributes(token.Attr, allowedAttributes)
|
||
|
|
buffer.WriteString(token.String())
|
||
|
|
} else if token.Data == ignore {
|
||
|
|
ignore = ""
|
||
|
|
}
|
||
|
|
|
||
|
|
case parser.EndTagToken:
|
||
|
|
if len(ignore) == 0 && includes(allowedTags, token.Data) {
|
||
|
|
token.Attr = []parser.Attribute{}
|
||
|
|
buffer.WriteString(token.String())
|
||
|
|
} else if token.Data == ignore {
|
||
|
|
ignore = ""
|
||
|
|
}
|
||
|
|
|
||
|
|
case parser.TextToken:
|
||
|
|
// We allow text content through, unless ignoring this entire tag and its contents (including other tags)
|
||
|
|
if ignore == "" {
|
||
|
|
buffer.WriteString(token.String())
|
||
|
|
}
|
||
|
|
case parser.CommentToken:
|
||
|
|
// We ignore comments by default
|
||
|
|
case parser.DoctypeToken:
|
||
|
|
// We ignore doctypes by default - html5 does not require them and this is intended for sanitizing snippets of text
|
||
|
|
default:
|
||
|
|
// We ignore unknown token types by default
|
||
|
|
|
||
|
|
}
|
||
|
|
|
||
|
|
}
|
||
|
|
|
||
|
|
}
|
||
|
|
|
||
|
|
// HTML strips html tags, replace common entities, and escapes <>&;'" in the result.
|
||
|
|
// Note the returned text may contain entities as it is escaped by HTMLEscapeString, and most entities are not translated.
|
||
|
|
func HTML(s string) (output string) {
|
||
|
|
|
||
|
|
// Shortcut strings with no tags in them
|
||
|
|
if !strings.ContainsAny(s, "<>") {
|
||
|
|
output = s
|
||
|
|
} else {
|
||
|
|
|
||
|
|
// First remove line breaks etc as these have no meaning outside html tags (except pre)
|
||
|
|
// this means pre sections will lose formatting... but will result in less unintentional paras.
|
||
|
|
s = strings.Replace(s, "\n", "", -1)
|
||
|
|
|
||
|
|
// Then replace line breaks with newlines, to preserve that formatting
|
||
|
|
s = strings.Replace(s, "</p>", "\n", -1)
|
||
|
|
s = strings.Replace(s, "<br>", "\n", -1)
|
||
|
|
s = strings.Replace(s, "</br>", "\n", -1)
|
||
|
|
s = strings.Replace(s, "<br/>", "\n", -1)
|
||
|
|
s = strings.Replace(s, "<br />", "\n", -1)
|
||
|
|
|
||
|
|
// Walk through the string removing all tags
|
||
|
|
b := bytes.NewBufferString("")
|
||
|
|
inTag := false
|
||
|
|
for _, r := range s {
|
||
|
|
switch r {
|
||
|
|
case '<':
|
||
|
|
inTag = true
|
||
|
|
case '>':
|
||
|
|
inTag = false
|
||
|
|
default:
|
||
|
|
if !inTag {
|
||
|
|
b.WriteRune(r)
|
||
|
|
}
|
||
|
|
}
|
||
|
|
}
|
||
|
|
output = b.String()
|
||
|
|
}
|
||
|
|
|
||
|
|
// Remove a few common harmless entities, to arrive at something more like plain text
|
||
|
|
output = strings.Replace(output, "‘", "'", -1)
|
||
|
|
output = strings.Replace(output, "’", "'", -1)
|
||
|
|
output = strings.Replace(output, "“", "\"", -1)
|
||
|
|
output = strings.Replace(output, "”", "\"", -1)
|
||
|
|
output = strings.Replace(output, " ", " ", -1)
|
||
|
|
output = strings.Replace(output, """, "\"", -1)
|
||
|
|
output = strings.Replace(output, "'", "'", -1)
|
||
|
|
|
||
|
|
// Translate some entities into their plain text equivalent (for example accents, if encoded as entities)
|
||
|
|
output = html.UnescapeString(output)
|
||
|
|
|
||
|
|
// In case we have missed any tags above, escape the text - removes <, >, &, ' and ".
|
||
|
|
output = template.HTMLEscapeString(output)
|
||
|
|
|
||
|
|
// After processing, remove some harmless entities &, ' and " which are encoded by HTMLEscapeString
|
||
|
|
output = strings.Replace(output, """, "\"", -1)
|
||
|
|
output = strings.Replace(output, "'", "'", -1)
|
||
|
|
output = strings.Replace(output, "& ", "& ", -1) // NB space after
|
||
|
|
output = strings.Replace(output, "&amp; ", "& ", -1) // NB space after
|
||
|
|
|
||
|
|
return output
|
||
|
|
}
|
||
|
|
|
||
|
|
// We are very restrictive as this is intended for ascii url slugs
|
||
|
|
var illegalPath = regexp.MustCompile(`[^[:alnum:]\~\-\./]`)
|
||
|
|
|
||
|
|
// Path makes a string safe to use as a URL path,
|
||
|
|
// removing accents and replacing separators with -.
|
||
|
|
// The path may still start at / and is not intended
|
||
|
|
// for use as a file system path without prefix.
|
||
|
|
func Path(s string) string {
|
||
|
|
// Start with lowercase string
|
||
|
|
filePath := strings.ToLower(s)
|
||
|
|
filePath = strings.Replace(filePath, "..", "", -1)
|
||
|
|
filePath = path.Clean(filePath)
|
||
|
|
|
||
|
|
// Remove illegal characters for paths, flattening accents
|
||
|
|
// and replacing some common separators with -
|
||
|
|
filePath = cleanString(filePath, illegalPath)
|
||
|
|
|
||
|
|
// NB this may be of length 0, caller must check
|
||
|
|
return filePath
|
||
|
|
}
|
||
|
|
|
||
|
|
// Remove all other unrecognised characters apart from
|
||
|
|
var illegalName = regexp.MustCompile(`[^[:alnum:]-.]`)
|
||
|
|
|
||
|
|
// Name makes a string safe to use in a file name by first finding the path basename, then replacing non-ascii characters.
|
||
|
|
func Name(s string) string {
|
||
|
|
// Start with lowercase string
|
||
|
|
fileName := strings.ToLower(s)
|
||
|
|
fileName = path.Clean(path.Base(fileName))
|
||
|
|
|
||
|
|
// Remove illegal characters for names, replacing some common separators with -
|
||
|
|
fileName = cleanString(fileName, illegalName)
|
||
|
|
|
||
|
|
// NB this may be of length 0, caller must check
|
||
|
|
return fileName
|
||
|
|
}
|
||
|
|
|
||
|
|
// Replace these separators with -
|
||
|
|
var baseNameSeparators = regexp.MustCompile(`[./]`)
|
||
|
|
|
||
|
|
// BaseName makes a string safe to use in a file name, producing a sanitized basename replacing . or / with -.
|
||
|
|
// No attempt is made to normalise a path or normalise case.
|
||
|
|
func BaseName(s string) string {
|
||
|
|
|
||
|
|
// Replace certain joining characters with a dash
|
||
|
|
baseName := baseNameSeparators.ReplaceAllString(s, "-")
|
||
|
|
|
||
|
|
// Remove illegal characters for names, replacing some common separators with -
|
||
|
|
baseName = cleanString(baseName, illegalName)
|
||
|
|
|
||
|
|
// NB this may be of length 0, caller must check
|
||
|
|
return baseName
|
||
|
|
}
|
||
|
|
|
||
|
|
// A very limited list of transliterations to catch common european names translated to urls.
|
||
|
|
// This set could be expanded with at least caps and many more characters.
|
||
|
|
var transliterations = map[rune]string{
|
||
|
|
'À': "A",
|
||
|
|
'Á': "A",
|
||
|
|
'Â': "A",
|
||
|
|
'Ã': "A",
|
||
|
|
'Ä': "A",
|
||
|
|
'Å': "AA",
|
||
|
|
'Æ': "AE",
|
||
|
|
'Ç': "C",
|
||
|
|
'È': "E",
|
||
|
|
'É': "E",
|
||
|
|
'Ê': "E",
|
||
|
|
'Ë': "E",
|
||
|
|
'Ì': "I",
|
||
|
|
'Í': "I",
|
||
|
|
'Î': "I",
|
||
|
|
'Ï': "I",
|
||
|
|
'Ð': "D",
|
||
|
|
'Ł': "L",
|
||
|
|
'Ñ': "N",
|
||
|
|
'Ò': "O",
|
||
|
|
'Ó': "O",
|
||
|
|
'Ô': "O",
|
||
|
|
'Õ': "O",
|
||
|
|
'Ö': "OE",
|
||
|
|
'Ø': "OE",
|
||
|
|
'Œ': "OE",
|
||
|
|
'Ù': "U",
|
||
|
|
'Ú': "U",
|
||
|
|
'Ü': "UE",
|
||
|
|
'Û': "U",
|
||
|
|
'Ý': "Y",
|
||
|
|
'Þ': "TH",
|
||
|
|
'ẞ': "SS",
|
||
|
|
'à': "a",
|
||
|
|
'á': "a",
|
||
|
|
'â': "a",
|
||
|
|
'ã': "a",
|
||
|
|
'ä': "ae",
|
||
|
|
'å': "aa",
|
||
|
|
'æ': "ae",
|
||
|
|
'ç': "c",
|
||
|
|
'è': "e",
|
||
|
|
'é': "e",
|
||
|
|
'ê': "e",
|
||
|
|
'ë': "e",
|
||
|
|
'ì': "i",
|
||
|
|
'í': "i",
|
||
|
|
'î': "i",
|
||
|
|
'ï': "i",
|
||
|
|
'ð': "d",
|
||
|
|
'ł': "l",
|
||
|
|
'ñ': "n",
|
||
|
|
'ń': "n",
|
||
|
|
'ò': "o",
|
||
|
|
'ó': "o",
|
||
|
|
'ô': "o",
|
||
|
|
'õ': "o",
|
||
|
|
'ō': "o",
|
||
|
|
'ö': "oe",
|
||
|
|
'ø': "oe",
|
||
|
|
'œ': "oe",
|
||
|
|
'ś': "s",
|
||
|
|
'ù': "u",
|
||
|
|
'ú': "u",
|
||
|
|
'û': "u",
|
||
|
|
'ū': "u",
|
||
|
|
'ü': "ue",
|
||
|
|
'ý': "y",
|
||
|
|
'ÿ': "y",
|
||
|
|
'ż': "z",
|
||
|
|
'þ': "th",
|
||
|
|
'ß': "ss",
|
||
|
|
}
|
||
|
|
|
||
|
|
// Accents replaces a set of accented characters with ascii equivalents.
|
||
|
|
func Accents(s string) string {
|
||
|
|
// Replace some common accent characters
|
||
|
|
b := bytes.NewBufferString("")
|
||
|
|
for _, c := range s {
|
||
|
|
// Check transliterations first
|
||
|
|
if val, ok := transliterations[c]; ok {
|
||
|
|
b.WriteString(val)
|
||
|
|
} else {
|
||
|
|
b.WriteRune(c)
|
||
|
|
}
|
||
|
|
}
|
||
|
|
return b.String()
|
||
|
|
}
|
||
|
|
|
||
|
|
var (
|
||
|
|
// If the attribute contains data: or javascript: anywhere, ignore it
|
||
|
|
// we don't allow this in attributes as it is so frequently used for xss
|
||
|
|
// NB we allow spaces in the value, and lowercase.
|
||
|
|
illegalAttr = regexp.MustCompile(`(d\s*a\s*t\s*a|j\s*a\s*v\s*a\s*s\s*c\s*r\s*i\s*p\s*t\s*)\s*:`)
|
||
|
|
|
||
|
|
// We are far more restrictive with href attributes.
|
||
|
|
legalHrefAttr = regexp.MustCompile(`\A[/#][^/\\]?|mailto:|http://|https://`)
|
||
|
|
)
|
||
|
|
|
||
|
|
// cleanAttributes returns an array of attributes after removing malicious ones.
|
||
|
|
func cleanAttributes(a []parser.Attribute, allowed []string) []parser.Attribute {
|
||
|
|
if len(a) == 0 {
|
||
|
|
return a
|
||
|
|
}
|
||
|
|
|
||
|
|
var cleaned []parser.Attribute
|
||
|
|
for _, attr := range a {
|
||
|
|
if includes(allowed, attr.Key) {
|
||
|
|
|
||
|
|
val := strings.ToLower(attr.Val)
|
||
|
|
|
||
|
|
// Check for illegal attribute values
|
||
|
|
if illegalAttr.FindString(val) != "" {
|
||
|
|
attr.Val = ""
|
||
|
|
}
|
||
|
|
|
||
|
|
// Check for legal href values - / mailto:// http:// or https://
|
||
|
|
if attr.Key == "href" {
|
||
|
|
if legalHrefAttr.FindString(val) == "" {
|
||
|
|
attr.Val = ""
|
||
|
|
}
|
||
|
|
}
|
||
|
|
|
||
|
|
// If we still have an attribute, append it to the array
|
||
|
|
if attr.Val != "" {
|
||
|
|
cleaned = append(cleaned, attr)
|
||
|
|
}
|
||
|
|
}
|
||
|
|
}
|
||
|
|
return cleaned
|
||
|
|
}
|
||
|
|
|
||
|
|
// A list of characters we consider separators in normal strings and replace with our canonical separator - rather than removing.
|
||
|
|
var (
|
||
|
|
separators = regexp.MustCompile(`[ &_=+:]`)
|
||
|
|
|
||
|
|
dashes = regexp.MustCompile(`[\-]+`)
|
||
|
|
)
|
||
|
|
|
||
|
|
// cleanString replaces separators with - and removes characters listed in the regexp provided from string.
|
||
|
|
// Accents, spaces, and all characters not in A-Za-z0-9 are replaced.
|
||
|
|
func cleanString(s string, r *regexp.Regexp) string {
|
||
|
|
|
||
|
|
// Remove any trailing space to avoid ending on -
|
||
|
|
s = strings.Trim(s, " ")
|
||
|
|
|
||
|
|
// Flatten accents first so that if we remove non-ascii we still get a legible name
|
||
|
|
s = Accents(s)
|
||
|
|
|
||
|
|
// Replace certain joining characters with a dash
|
||
|
|
s = separators.ReplaceAllString(s, "-")
|
||
|
|
|
||
|
|
// Remove all other unrecognised characters - NB we do allow any printable characters
|
||
|
|
s = r.ReplaceAllString(s, "")
|
||
|
|
|
||
|
|
// Remove any multiple dashes caused by replacements above
|
||
|
|
s = dashes.ReplaceAllString(s, "-")
|
||
|
|
|
||
|
|
return s
|
||
|
|
}
|
||
|
|
|
||
|
|
// includes checks for inclusion of a string in a []string.
|
||
|
|
func includes(a []string, s string) bool {
|
||
|
|
for _, as := range a {
|
||
|
|
if as == s {
|
||
|
|
return true
|
||
|
|
}
|
||
|
|
}
|
||
|
|
return false
|
||
|
|
}
|