pwa-launcher/pkg/net.go

package app

import (
	"fmt"
	"image"
	"io"
	"log"
	"net/http"
	"net/url"
	"path/filepath"
	"strconv"
	"strings"

	"golang.org/x/net/html"
)

// Insights parsed from a web URL.
type Insights struct {
	Title string
	Icons []Icon
}

// Icon found for the web URL.
type Icon struct {
	Size string
	URL  string
	Data image.Image // raw image data, if available
}

// Width returns the icon's width.
func (i Icon) Width() int {
	parts := strings.Split(i.Size, "x")
	if len(parts) > 1 {
		w, _ := strconv.Atoi(parts[0])
		return w
	}
	return 0
}

// Parse a web page and return page insights.
func Parse(url string) (Insights, error) {
	log.Printf("### Parse HTML on %s for Title and Icon URLs", url)
	var (
		result = Insights{
			Icons: []Icon{},
		}
		inTag = ""
	)

	resp, err := http.Get(url)
	if err != nil {
		return result, fmt.Errorf("HTTP error: %s", err)
	}
	defer resp.Body.Close()

	z := html.NewTokenizer(resp.Body)
	parsing := true
	for parsing {
		tt := z.Next()
		token := z.Token()
		switch tt {
		case html.ErrorToken:
			fmt.Printf("error: %s\n", z.Err())
			if z.Err() == io.EOF {
				// successful error condition
				parsing = false
				break
			}
			return result, fmt.Errorf("HTML parsing error: %s", z.Err())

		case html.TextToken:
			if inTag == "title" && result.Title == "" {
				result.Title += token.Data
			}

		case html.StartTagToken:
			inTag = token.Data

			// Looking for <link rel="shortcut icon">
			if token.Data == "link" {
				attr := AttrDict(token)
				rel, _ := attr["rel"]
				sizes, _ := attr["sizes"]
				href, _ := attr["href"]

				// Ensure "//" URIs start with "https://"
				href = AddScheme(href)

				if rel == "shortcut icon" {
					log.Printf(`Found <link rel="shortcut icon"> URL: %s`, href)
					if sizes == "" {
						sizes = "16x16"
					}

					// If an ico file, extract the PNGs.
					if filepath.Ext(href) == ".ico" {
						log.Printf("The favicon is a .ico file, extracting PNGs")
						if resp, err := http.Get(href); err == nil {
							if pngs, err := IcoToPNG(resp.Body); err == nil {
								for _, png := range pngs {
									size := png.Bounds().Size()
									result.Icons = append(result.Icons, Icon{
										Size: fmt.Sprintf("%dx%d", size.X, size.Y),
										URL:  href,
										Data: png,
									})
								}
								resp.Body.Close()
								continue
							} else {
								log.Printf("Error extracting PNG from %s: %s", href, err)
							}
							resp.Body.Close()
						} else {
							log.Printf("HTTP error downloading %s: %s", href, err)
						}
					}

					result.Icons = append(result.Icons, Icon{
						Size: sizes,
						URL:  href,
					})
				}
			}

		case html.EndTagToken, html.SelfClosingTagToken:
			inTag = ""
		}

	}

	return result, nil
}

// DetectIcons checks well-known icon URLs on a base domain.
func DetectIcons(weburl string) ([]Icon, error) {
	var result = []Icon{}

	uri, err := url.Parse(weburl)
	if err != nil {
		return result, err
	}

	baseURL := uri.Scheme + "://" + uri.Host
	log.Printf("### Auto-detecting Icon URLs from site %s", baseURL)

	tryURI := []string{
		"/apple-touch-icon.png",
		"/apple-touch-icon-180x180.png",
		"/apple-touch-icon-152x152.png",
		"/apple-touch-icon-144x144.png",
		"/apple-touch-icon-120x120.png",
		"/apple-touch-icon-114x114.png",
		"/apple-touch-icon-76x76.png",
		"/apple-touch-icon-72x72.png",
		"/apple-touch-icon-57x57.png",
		"/apple-touch-icon-60x60.png",
		"/favicon.ico",
	}
	for _, uri := range tryURI {
		resp, err := http.Get(baseURL + uri)
		if err != nil {
			continue
		}
		defer resp.Body.Close()

		// PNG images?
		if filepath.Ext(uri) == ".png" {
			png, err := ParsePNG(resp.Body)
			if err != nil {
				continue
			}

			size := png.Bounds().Size()
			result = append(result, Icon{
				Size: fmt.Sprintf("%dx%d", size.X, size.Y),
				URL:  baseURL + uri,
			})
		} else if filepath.Ext(uri) == ".ico" {
			// Extract the PNG images from the icon.
			pngs, err := IcoToPNG(resp.Body)
			if err != nil {
				continue
			}

			for _, png := range pngs {
				size := png.Bounds().Size()
				result = append(result, Icon{
					Size: fmt.Sprintf("%dx%d", size.X, size.Y),
					URL:  baseURL + uri,
					Data: png,
				})
			}
		}

		log.Printf("Found icon: %s", uri)
		_ = resp
	}

	return result, nil
}

// AttrDict converts an HTML Token attributes list into a hash map.
func AttrDict(token html.Token) map[string]string {
	var result = map[string]string{}
	for _, attr := range token.Attr {
		result[attr.Key] = attr.Val
	}
	return result
}

// AddScheme ensures an HTTP URL has a valid scheme, converting "//" into
// "https://"
func AddScheme(uri string) string {
	if strings.HasPrefix(uri, "//") {
		return "https:" + uri
	}
	return uri
}