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utils-markdown.go
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utils-markdown.go
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package main
import (
"bytes"
"encoding/xml"
"io"
"regexp"
"strings"
"github.com/microcosm-cc/bluemonday"
"github.com/russross/blackfriday/v2"
)
var htmlEscaper *strings.Replacer
var htmlPolicy *bluemonday.Policy
func init() {
// Use bluemonday policy for life of program
htmlPolicy = bluemonday.NewPolicy()
// Disallow images
// Allow elements
htmlPolicy.AllowElements(
"h1", "h2", "h3", "h4", "h5", "h6",
"p", "span", "em", "strong", "del", "sup", "sub",
"ul", "ol", "li",
"table", "thead", "tbody", "th", "tr", "td",
"blockquote",
"pre", "code",
"hr", "br")
// Allow links
htmlPolicy.AllowAttrs("href", "title").OnElements("a")
// Validate URLs using net/url.Parse and require 'mailto:', 'http://' or 'https://'
htmlPolicy.AllowURLSchemes("mailto", "http", "https")
htmlPolicy.AllowRelativeURLs(true) // links within crowdspec
htmlPolicy.RequireParseableURLs(true)
htmlPolicy.RequireNoFollowOnLinks(true)
htmlPolicy.AddTargetBlankToFullyQualifiedLinks(true)
// Allow code blocks with language class
htmlPolicy.AllowAttrs("class").Matching(regexp.MustCompile("^language-[a-zA-Z0-9]+$")).OnElements("code")
// Allow simple styles to dress up tables
htmlPolicy.AllowAttrs("style").OnElements("table", "thead", "tbody", "th", "td")
// style="border-spacing:50px;" and style="border-spacing:3em;" on table
var matchValue = regexp.MustCompile("^(\\d{1,3})(px|rem|em)(?: (\\d{1,3})(px|rem|em))?$")
var checkRange = func(a string, min, max int) bool {
v, err := AtoInt(a)
if err != nil {
return false
}
return v >= min && v <= max
}
const maxPx = 50
const maxEm = 3
htmlPolicy.AllowStyles("border-spacing").MatchingHandler(func(s string) bool {
if matchValue.MatchString(s) {
var parts = matchValue.FindStringSubmatch(s)
// first unit will be defined as px|rem|em
if parts[2] == "px" {
if !checkRange(parts[1], 0, maxPx) {
return false
}
} else if parts[2] == "rem" || parts[2] == "em" {
if !checkRange(parts[1], 0, maxEm) {
return false
}
}
// second unit may be defined
if parts[4] == "px" {
if !checkRange(parts[3], 0, maxPx) {
return false
}
} else if parts[4] == "rem" || parts[4] == "em" {
if !checkRange(parts[3], 0, maxEm) {
return false
}
}
return true
}
return false
}).OnElements("table")
// style="width:1000px;" and style="width:5%;" on table, th, td
htmlPolicy.AllowStyles("width").MatchingHandler(func(w string) bool {
w = strings.TrimSpace(w)
if strings.HasSuffix(w, "%") {
i, err := AtoInt(w[:len(w)-1])
return err == nil && i >= 5 && i <= 100
} else if strings.HasSuffix(w, "px") {
i, err := AtoInt(w[:len(w)-2])
return err == nil && i >= 25 && i <= 1000
}
return false
}).OnElements("table", "th", "td")
// style="white-space:nowrap;" on applicable elements
htmlPolicy.AllowStyles("white-space").MatchingEnum(
"nowrap", "pre", "pre-wrap", "pre-line",
).OnElements("table", "thead", "tbody", "tr", "th", "td")
// style="text-align:left;" on applicable elements
htmlPolicy.AllowStyles("text-align").MatchingEnum(
"left", "center", "right",
).OnElements("table", "thead", "tbody", "tr", "th", "td")
// style="vertival-align:top;" on applicable elements
htmlPolicy.AllowStyles("vertical-align").MatchingEnum(
"top", "middle", "bottom",
).OnElements("table", "thead", "tbody", "tr", "th", "td")
}
func renderMarkdown(markdown string) (string, error) {
var output = blackfriday.Run([]byte(markdown),
blackfriday.WithExtensions(
blackfriday.SpaceHeadings|
blackfriday.Autolink|
blackfriday.Strikethrough|
blackfriday.FencedCode|
blackfriday.Tables|
blackfriday.BackslashLineBreak))
output = htmlPolicy.SanitizeBytes(output)
// Validate HTML
var decoder = xml.NewDecoder(bytes.NewBuffer(output))
for {
// xml.Decoder.Token guarantees start/end tags are properly nested and closed
_, err := decoder.Token()
if err != nil {
if err == io.EOF {
break
}
return "", err
}
}
// log.Println("Output:" + string(output))
return string(output), nil
}