A web blog and personal homepage engine written in Go.
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// Package markdown implements a GitHub Flavored Markdown renderer.
package markdown
import (
"bytes"
"crypto/md5"
"errors"
"fmt"
"io"
"os/exec"
"regexp"
"strings"
"git.kirsle.net/apps/gophertype/pkg/console"
"git.kirsle.net/apps/gophertype/pkg/cache"
"github.com/microcosm-cc/bluemonday"
"github.com/shurcooL/github_flavored_markdown"
)
// Regexps for Markdown use cases.
var (
// TODO: Redis caching
// Cache interface{} = nil
// Match title from the first `# h1` heading.
reMarkdownTitle = regexp.MustCompile(`(?m:^#([^#\r\n]+)$)`)
// Match fenced code blocks with languages defined.
reFencedCode = regexp.MustCompile("```" + `([a-z]*)[\r\n]([\s\S]*?)[\r\n]\s*` + "```")
reFencedCodeClass = regexp.MustCompile("^highlight highlight-[a-zA-Z0-9]+$")
// Regexp to match fenced code blocks in rendered Markdown HTML.
// Tweak this if you change Markdown engines later.
reCodeBlock = regexp.MustCompile(`<div class="highlight highlight-(.+?)"><pre>(.+?)</pre></div>`)
reDecodeBlock = regexp.MustCompile(`\[?FENCED_CODE_%d_BLOCK?\]`)
)
// A container for parsed code blocks.
type codeBlock struct {
placeholder int
language string
source string
}
// TitleFromMarkdown tries to find a title from the source of a Markdown file.
//
// On error, returns "Untitled" along with the error. So if you're lazy and
// want a suitable default, you can safely ignore the error.
func TitleFromMarkdown(body string) (string, error) {
m := reMarkdownTitle.FindStringSubmatch(body)
if len(m) > 0 {
return m[1], nil
}
return "Untitled", errors.New(
"did not find a single h1 (denoted by # prefix) for Markdown title",
)
}
// RenderMarkdown renders markdown to HTML, safely. It uses blackfriday to
// render Markdown to HTML and then Bluemonday to sanitize the resulting HTML.
func RenderMarkdown(input string) string {
unsafe := []byte(RenderTrustedMarkdown(input))
// Sanitize HTML, but allow fenced code blocks to not get mangled in user
// submitted comments.
p := bluemonday.UGCPolicy()
p.AllowAttrs("class").Matching(reFencedCodeClass).OnElements("code")
html := p.SanitizeBytes(unsafe)
return string(html)
}
// RenderTrustedMarkdown renders markdown to HTML, but without applying
// bluemonday filtering afterward. This is for blog posts and website
// Markdown pages, not for user-submitted comments or things.
func RenderTrustedMarkdown(input string) string {
// Find and hang on to fenced code blocks.
codeBlocks := []codeBlock{}
matches := reFencedCode.FindAllStringSubmatch(input, -1)
for i, m := range matches {
language, source := m[1], m[2]
if language == "" {
continue
}
codeBlocks = append(codeBlocks, codeBlock{i, language, source})
input = strings.Replace(input, m[0], fmt.Sprintf(
"[?FENCED_CODE_%d_BLOCK?]",
i,
), 1)
}
// Render the HTML out.
html := string(github_flavored_markdown.Markdown([]byte(input)))
// Substitute fenced codes back in.
for _, block := range codeBlocks {
highlighted, err := Pygmentize(block.language, block.source)
if err != nil {
console.Error("Pygmentize error: %s", err)
}
html = strings.Replace(html,
fmt.Sprintf("[?FENCED_CODE_%d_BLOCK?]", block.placeholder),
highlighted,
1,
)
}
return string(html)
}
// Pygmentize searches for fenced code blocks in rendered Markdown HTML
// and runs Pygments to syntax highlight it.
//
// On error the original given source is returned back.
//
// The rendered result is cached in Redis if available, because the CLI
// call takes ~0.6s which is slow if you're rendering a lot of code blocks.
func Pygmentize(language, source string) (string, error) {
var result string
// Hash the source for the cache key.
h := md5.New()
io.WriteString(h, language+source)
hash := fmt.Sprintf("%x", h.Sum(nil))
cacheKey := "pygmentize:" + hash
// Do we have it cached?
if cached, err := cache.Get(cacheKey); err == nil && len(cached) > 0 {
return string(cached), nil
}
// Defer to the `pygmentize` command
bin := "pygmentize"
if _, err := exec.LookPath(bin); err != nil {
return source, errors.New("pygmentize not installed")
}
cmd := exec.Command(bin, "-l"+language, "-f"+"html", "-O encoding=utf-8")
cmd.Stdin = strings.NewReader(source)
var out bytes.Buffer
cmd.Stdout = &out
var stderr bytes.Buffer
cmd.Stderr = &stderr
if err := cmd.Run(); err != nil {
console.Error("Error running pygments: %s", stderr.String())
return source, err
}
result = out.String()
// Cache it in Redis if available.
err := cache.SetEx(cacheKey, result, 60*60*24) // cool md5's don't change
if err != nil {
console.Error("Couldn't cache Pygmentize output: %s", err)
}
return result, nil
}