forgejo/modules/highlight/highlight.go

// Copyright 2015 The Gogs Authors. All rights reserved.
// Copyright 2020 The Gitea Authors. All rights reserved.
// Use of this source code is governed by a MIT-style
// license that can be found in the LICENSE file.

package highlight

import (
	"bufio"
	"bytes"
	"fmt"
	gohtml "html"
	"io"
	"path/filepath"
	"strings"
	"sync"

	"code.gitea.io/gitea/modules/analyze"
	"code.gitea.io/gitea/modules/log"
	"code.gitea.io/gitea/modules/setting"

	"github.com/alecthomas/chroma"
	"github.com/alecthomas/chroma/formatters/html"
	"github.com/alecthomas/chroma/lexers"
	"github.com/alecthomas/chroma/styles"
	lru "github.com/hashicorp/golang-lru"
)

// don't index files larger than this many bytes for performance purposes
const sizeLimit = 1024 * 1024

var (
	// For custom user mapping
	highlightMapping = map[string]string{}

	once sync.Once

	cache *lru.TwoQueueCache
)

// NewContext loads custom highlight map from local config
func NewContext() {
	once.Do(func() {
		if setting.Cfg != nil {
			keys := setting.Cfg.Section("highlight.mapping").Keys()
			for i := range keys {
				highlightMapping[keys[i].Name()] = keys[i].Value()
			}
		}
		// The size 512 is simply a conservative rule of thumb
		c, err := lru.New2Q(512)
		if err != nil {
			panic(fmt.Sprintf("failed to initialize LRU cache for highlighter: %s", err))
		}
		cache = c
	})
}

// Code returns a HTML version of code string with chroma syntax highlighting classes
func Code(fileName, language, code string) string {
	NewContext()

	// diff view newline will be passed as empty, change to literal '\n' so it can be copied
	// preserve literal newline in blame view
	if code == "" || code == "\n" {
		return "\n"
	}

	if len(code) > sizeLimit {
		return code
	}

	var lexer chroma.Lexer

	if len(language) > 0 {
		lexer = lexers.Get(language)

		if lexer == nil {
			// Attempt stripping off the '?'
			if idx := strings.IndexByte(language, '?'); idx > 0 {
				lexer = lexers.Get(language[:idx])
			}
		}
	}

	if lexer == nil {
		if val, ok := highlightMapping[filepath.Ext(fileName)]; ok {
			// use mapped value to find lexer
			lexer = lexers.Get(val)
		}
	}

	if lexer == nil {
		if l, ok := cache.Get(fileName); ok {
			lexer = l.(chroma.Lexer)
		}
	}

	if lexer == nil {
		lexer = lexers.Match(fileName)
		if lexer == nil {
			lexer = lexers.Fallback
		}
		cache.Add(fileName, lexer)
	}
	return CodeFromLexer(lexer, code)
}

// CodeFromLexer returns a HTML version of code string with chroma syntax highlighting classes
func CodeFromLexer(lexer chroma.Lexer, code string) string {
	formatter := html.New(html.WithClasses(true),
		html.WithLineNumbers(false),
		html.PreventSurroundingPre(true),
	)

	htmlbuf := bytes.Buffer{}
	htmlw := bufio.NewWriter(&htmlbuf)

	iterator, err := lexer.Tokenise(nil, code)
	if err != nil {
		log.Error("Can't tokenize code: %v", err)
		return code
	}
	// style not used for live site but need to pass something
	err = formatter.Format(htmlw, styles.GitHub, iterator)
	if err != nil {
		log.Error("Can't format code: %v", err)
		return code
	}

	_ = htmlw.Flush()
	// Chroma will add newlines for certain lexers in order to highlight them properly
	// Once highlighted, strip them here, so they don't cause copy/paste trouble in HTML output
	return strings.TrimSuffix(htmlbuf.String(), "\n")
}

// File returns a slice of chroma syntax highlighted HTML lines of code
func File(fileName, language string, code []byte) ([]string, error) {
	NewContext()

	if len(code) > sizeLimit {
		return PlainText(code), nil
	}

	formatter := html.New(html.WithClasses(true),
		html.WithLineNumbers(false),
		html.PreventSurroundingPre(true),
	)

	htmlBuf := bytes.Buffer{}
	htmlWriter := bufio.NewWriter(&htmlBuf)

	var lexer chroma.Lexer

	// provided language overrides everything
	if language != "" {
		lexer = lexers.Get(language)
	}

	if lexer == nil {
		if val, ok := highlightMapping[filepath.Ext(fileName)]; ok {
			lexer = lexers.Get(val)
		}
	}

	if lexer == nil {
		guessLanguage := analyze.GetCodeLanguage(fileName, code)

		lexer = lexers.Get(guessLanguage)
		if lexer == nil {
			lexer = lexers.Match(fileName)
			if lexer == nil {
				lexer = lexers.Fallback
			}
		}
	}

	iterator, err := lexer.Tokenise(nil, string(code))
	if err != nil {
		return nil, fmt.Errorf("can't tokenize code: %w", err)
	}

	err = formatter.Format(htmlWriter, styles.GitHub, iterator)
	if err != nil {
		return nil, fmt.Errorf("can't format code: %w", err)
	}

	_ = htmlWriter.Flush()

	// at the moment, Chroma generates stable output `<span class="line"><span class="cl">...\n</span></span>` for each line
	htmlStr := htmlBuf.String()
	lines := strings.Split(htmlStr, `<span class="line"><span class="cl">`)
	m := make([]string, 0, len(lines))
	for i := 1; i < len(lines); i++ {
		line := lines[i]
		line = strings.TrimSuffix(line, "</span></span>")
		m = append(m, line)
	}
	return m, nil
}

// PlainText returns non-highlighted HTML for code
func PlainText(code []byte) []string {
	r := bufio.NewReader(bytes.NewReader(code))
	m := make([]string, 0, bytes.Count(code, []byte{'\n'})+1)
	for {
		content, err := r.ReadString('\n')
		if err != nil && err != io.EOF {
			log.Error("failed to read string from buffer: %v", err)
			break
		}
		if content == "" && err == io.EOF {
			break
		}
		s := gohtml.EscapeString(content)
		m = append(m, s)
	}
	return m
}