forgejo/modules/markup/markdown/meta.go

// 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 markdown

import (
	"errors"
	"strings"

	"gopkg.in/yaml.v2"
)

func isYAMLSeparator(line string) bool {
	line = strings.TrimSpace(line)
	for i := 0; i < len(line); i++ {
		if line[i] != '-' {
			return false
		}
	}
	return len(line) > 2
}

// ExtractMetadata consumes a markdown file, parses YAML frontmatter,
// and returns the frontmatter metadata separated from the markdown content
func ExtractMetadata(contents string, out interface{}) (string, error) {
	var front, body []string
	lines := strings.Split(contents, "\n")
	for idx, line := range lines {
		if idx == 0 {
			// First line has to be a separator
			if !isYAMLSeparator(line) {
				return "", errors.New("frontmatter must start with a separator line")
			}
			continue
		}
		if isYAMLSeparator(line) {
			front, body = lines[1:idx], lines[idx+1:]
			break
		}
	}

	if len(front) == 0 {
		return "", errors.New("could not determine metadata")
	}

	if err := yaml.Unmarshal([]byte(strings.Join(front, "\n")), out); err != nil {
		return "", err
	}
	return strings.Join(body, "\n"), nil
}