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htmlconverter.go
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htmlconverter.go
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package main
import (
"C"
"bytes"
"fmt"
"regexp"
"github.com/alecthomas/chroma"
htmlFormatter "github.com/alecthomas/chroma/formatters/html"
"github.com/alecthomas/chroma/lexers"
"github.com/alecthomas/chroma/styles"
"github.com/samuelmeuli/nbtohtml"
"github.com/yuin/goldmark"
highlighting "github.com/yuin/goldmark-highlighting"
"github.com/yuin/goldmark/extension"
)
// Regex for YAML front matter in a Markdown document
var markdownFrontMatterRegex = regexp.MustCompile(`---\n[\s\S]*?\n---\n`)
// Enable syntax highlighting in Markdown
var markdownParser = goldmark.New(
goldmark.WithExtensions(
extension.GFM,
highlighting.NewHighlighting(
highlighting.WithFormatOptions(
htmlFormatter.WithClasses(true),
),
),
),
)
// Functions for conversion between C and Go strings. Required here because cgo cannot be used in
// tests.
func convertToCString(goString string) *C.char {
return C.CString(goString)
}
func convertToGoString(cString *C.char) string {
return C.GoString(cString)
}
// Convention: Because all functions return C strings, errors are implemented as return values which
// start with "error: ".
//export convertCodeToHTML
// convertCodeToHTML converts the provided source code string to HTML. Classes for syntax
// highlighting are generated using Chroma.
func convertCodeToHTML(source *C.char, lexer *C.char) *C.char {
sourceString := convertToGoString(source)
lexerString := convertToGoString(lexer)
htmlBuffer := new(bytes.Buffer)
// Set up lexer for programming language
var l chroma.Lexer
if lexerString != "" {
l = lexers.Get(lexerString)
}
if l == nil {
l = lexers.Analyse(sourceString)
}
if l == nil {
l = lexers.Fallback
}
l = chroma.Coalesce(l)
// Use classes instead of inline styles
formatter := htmlFormatter.New(htmlFormatter.WithClasses(true))
iterator, err := l.Tokenise(nil, sourceString)
if err != nil {
errMessage := fmt.Sprintf("error: Could not render source code (tokenization error): %d", err)
return convertToCString(errMessage)
}
err = formatter.Format(htmlBuffer, styles.GitHub, iterator)
if err != nil {
errMessage := fmt.Sprintf("error: Could not render source code (formatting error): %d", err)
return convertToCString(errMessage)
}
// Chroma escapes tags, so HTML should be safe from code injection
htmlString := htmlBuffer.String()
return convertToCString(htmlString)
}
//export convertMarkdownToHTML
// convertMarkdownToHTML converts the provided Markdown string to HTML using goldmark. Classes for
// syntax highlighting inside code blocks are generated using Chroma.
func convertMarkdownToHTML(source *C.char) *C.char {
sourceString := convertToGoString(source)
// Strip YAML front matter
sourceString = markdownFrontMatterRegex.ReplaceAllString(sourceString, "")
// Convert Markdown to HTML
var htmlBuffer bytes.Buffer
if err := markdownParser.Convert([]byte(sourceString), &htmlBuffer); err != nil {
errMessage := fmt.Sprintf("error: Could not convert Markdown to HTML: %d", err)
return convertToCString(errMessage)
}
// goldmark does not render raw HTML or potentially-dangerous URLs, so HTML should be safe from
// code injection
return convertToCString(htmlBuffer.String())
}
//export convertNotebookToHTML
// convertNotebookToHTML converts the provided Jupyter Notebook JSON to HTML using `nbtohtml`.
func convertNotebookToHTML(source *C.char) *C.char {
sourceString := convertToGoString(source)
html := new(bytes.Buffer)
err := nbtohtml.ConvertString(html, sourceString)
if err != nil {
errMessage := fmt.Sprintf("error: Could not convert Notebook to HTML: %d", err)
return convertToCString(errMessage)
}
htmlString := html.String()
return convertToCString(htmlString)
}
// Main function is required for `c-archive` builds.
func main() {}