linkinfo/default.go

package linkinfo

import (
	"errors"
	"fmt"
	"github.com/PuerkitoBio/goquery"
	"io"
	"io/ioutil"
	"net"
	"net/http"
	"net/url"
	"path"
	"strconv"
	"strings"
)

const (
	contentTypeHtml = "text/html"

	maxBodySizeBytes = 20971520
)

var privateIPBlocks []*net.IPNet

func init() {
	for _, cidr := range []string{
		"127.0.0.0/8",    // IPv4 loopback
		"10.0.0.0/8",     // RFC1918
		"172.16.0.0/12",  // RFC1918
		"192.168.0.0/16", // RFC1918
		"::1/128",        // IPv6 loopback
		"fe80::/10",      // IPv6 link-local
		"fc00::/7",       // IPv6 unique local addr
	} {
		_, block, err := net.ParseCIDR(cidr)
		if err != nil {
			panic(fmt.Errorf("parse error on %q: %v", cidr, err))
		}
		privateIPBlocks = append(privateIPBlocks, block)
	}
}

func isPrivateIP(ip net.IP) bool {
	for _, block := range privateIPBlocks {
		if block.Contains(ip) {
			return true
		}
	}
	return false
}

func (api *LinkInfoApi) DefaultLinkHandler(link string) (*LinkInfo, error) {
	redirects := make([]string, 0)

	u, err := url.Parse(link)

	if err != nil {
		return nil, err
	}

	if u.Host == "localhost" {
		return nil, errors.New("url is localhost")
	} else if ip := net.ParseIP(u.Host); ip != nil && isPrivateIP(ip) {
		return nil, errors.New("url is a local ip address")
	}

	var req *http.Request
	var res *http.Response

	for i := 0; i < 10; i++ {
		req, err = http.NewRequest(http.MethodHead, link, nil)

		if err != nil {
			return nil, err
		}

		if api.UserAgent != "" {
			req.Header.Set("User-Agent", api.UserAgent)
		}

		res, err = api.Client.Do(req)

		if err != nil {
			return nil, err
		}

		if (res.StatusCode == 301 || res.StatusCode == 302) && res.Header.Get("Location") != "" {
			link = res.Header.Get("Location")

			redirectUrl, err := url.Parse(link)

			if err != nil {
				return nil, err
			}

			if redirectUrl.Host == "localhost" {
				return nil, errors.New("url attempted to redirect to localhost")
			} else if ip := net.ParseIP(redirectUrl.Host); ip != nil && isPrivateIP(ip) {
				return nil, errors.New("host is a local ip address")
			}

			redirects = append(redirects, link)
		} else {
			break
		}
	}

	if res != nil && res.StatusCode != 200 {
		return nil, errors.New("invalid response, expected 200, got " + strconv.Itoa(res.StatusCode))
	}

	contentType := res.Header.Get("Content-Type")

	if contentType == "" {
		contentType = api.detectContentType(link, "application/octet-stream")
	}

	if idx := strings.Index(contentType, ";"); idx != -1 {
		contentType = contentType[:idx]
	}

	var contentLength int64

	if contentLengthStr := res.Header.Get("Content-Length"); contentLengthStr != "" {
		contentLength, err = strconv.ParseInt(contentLengthStr, 10, 64)
	}

	ret := &LinkInfo{
		ContentType:   contentType,
		ContentLength: contentLength,
	}

	switch contentType {
	case contentTypeHtml:
		if contentLength >= 0 && contentLength < maxBodySizeBytes {
			err = api.retrieveHtmlLinkTitle(ret, link)
			break
		}
		fallthrough
	default:
		ret.Title = fmt.Sprintf("%s (%s, %s)", path.Base(u.Path), contentType, ByteCountDecimal(contentLength))
	}

	return ret, err
}

func (api *LinkInfoApi) detectContentType(link, defaultType string) string {
	req, err := http.NewRequest("GET", link, nil)

	if err != nil {
		return defaultType
	}

	if api.UserAgent != "" {
		req.Header.Set("User-Agent", api.UserAgent)
	}

	req.Header.Set("Range", "bytes=0-512")

	res, err := api.Client.Do(req)

	if err != nil {
		return defaultType
	}

	defer res.Body.Close()

	b, err := ioutil.ReadAll(io.LimitReader(res.Body, 512))

	if err != nil {
		return defaultType
	}

	t := http.DetectContentType(b)

	if t == "" {
		t = defaultType
	}

	return t
}

var (
	attrKeys = []string{"property", "name", "itemprop"}
)

func (api *LinkInfoApi) retrieveHtmlLinkTitle(i *LinkInfo, link string) error {
	req, err := http.NewRequest(http.MethodGet, link, nil)

	if err != nil {
		return err
	}

	if api.UserAgent != "" {
		req.Header.Set("User-Agent", api.UserAgent)
	}

	res, err := api.Client.Do(req)

	if err != nil {
		return err
	}

	defer res.Body.Close()

	q, err := goquery.NewDocumentFromReader(io.LimitReader(res.Body, maxBodySizeBytes))

	if err != nil {
		return err
	}

	meta := q.Find("meta")

	metaTags := make(map[string]string)

	meta.Each(func(_ int, s *goquery.Selection) {
		var key, value string
		var exists bool

		for _, k := range attrKeys {
			key, exists = s.Attr(k)

			if exists {
				break
			}
		}

		if key == "" {
			return
		}

		value, exists = s.Attr("content")

		if !exists {
			return
		}

		metaTags[key] = value
	})

	var attr string
	var exists bool

	if attr, exists = metaTags["og:title"]; exists {
		i.Title = attr
	} else if tag := q.Find("head > title"); tag.Length() > 0 {
		i.Title = strings.TrimSpace(tag.Text())
	}

	if attr, exists = metaTags["og:description"]; exists {
		i.Description = attr
	} else if attr, exists = metaTags["description"]; exists {
		i.Description = attr
	}

	if attr, exists = metaTags["duration"]; exists {
		i.Duration = attr
	}

	return nil
}