Resize favicons before storing them

Some websites are using images of O(10kB) when not )O(100kB) for their
favicons. As miniflux only displays them with a 16x16 resolution, let's do our
best to resize them before storing them in the database. This should make
miniflux consume less bandwidth when serving pages, for the joy of mobile users
on a small data plan.

go.mod

@@ -13,6 +13,7 @@ require (
 	github.com/prometheus/client_golang v1.20.5
 	github.com/tdewolff/minify/v2 v2.21.2
 	golang.org/x/crypto v0.30.0
+	golang.org/x/image v0.23.0
 	golang.org/x/net v0.32.0
 	golang.org/x/oauth2 v0.24.0
 	golang.org/x/term v0.27.0

go.sum

@@ -70,6 +70,8 @@ golang.org/x/crypto v0.0.0-20190308221718-c2843e01d9a2/go.mod h1:djNgcEr1/C05ACk
 golang.org/x/crypto v0.0.0-20210921155107-089bfa567519/go.mod h1:GvvjBRRGRdwPK5ydBHafDWAxML/pGHZbMvKqRZ5+Abc=
 golang.org/x/crypto v0.30.0 h1:RwoQn3GkWiMkzlX562cLB7OxWvjH1L8xutO2WoJcRoY=
 golang.org/x/crypto v0.30.0/go.mod h1:kDsLvtWBEx7MV9tJOj9bnXsPbxwJQ6csT/x4KIN4Ssk=
+golang.org/x/image v0.23.0 h1:HseQ7c2OpPKTPVzNjG5fwJsOTCiiwS4QdsYi5XU6H68=
+golang.org/x/image v0.23.0/go.mod h1:wJJBTdLfCCf3tiHa1fNxpZmUI4mmoZvwMCPP0ddoNKY=
 golang.org/x/mod v0.6.0-dev.0.20220419223038-86c51ed26bb4/go.mod h1:jJ57K6gSWd91VN4djpZkiMVwK6gcyfeH4XE8wZrZaV4=
 golang.org/x/mod v0.8.0/go.mod h1:iBbtSCu2XBx23ZKBPSOrRkjjQPZFPuis4dIYUhu/chs=
 golang.org/x/net v0.0.0-20190620200207-3b0461eec859/go.mod h1:z5CRVTTTmAJ677TzLLGU+0bjPO0LkuOLi4/5GtJWs/s=

internal/reader/icon/finder.go

@@ -4,8 +4,14 @@
 package icon // import "miniflux.app/v2/internal/reader/icon"
 
 import (
+	"bufio"
+	"bytes"
 	"encoding/base64"
 	"fmt"
+	"image"
+	"image/gif"
+	"image/jpeg"
+	"image/png"
 	"io"
 	"log/slog"
 	"net/url"
@@ -19,6 +25,7 @@ import (
 	"miniflux.app/v2/internal/urllib"
 
 	"github.com/PuerkitoBio/goquery"
+	"golang.org/x/image/draw"
 	"golang.org/x/net/html/charset"
 )
 
@@ -180,9 +187,44 @@ func (f *IconFinder) DownloadIcon(iconURL string) (*model.Icon, error) {
 		Content:  responseBody,
 	}
 
+	icon = resizeIcon(icon)
+
 	return icon, nil
 }
 
+func resizeIcon(icon *model.Icon) *model.Icon {
+	var src image.Image
+	var err error
+
+	r := bytes.NewReader(icon.Content)
+	switch icon.MimeType {
+	case "image/jpeg":
+		src, err = jpeg.Decode(r)
+	case "image/png":
+		src, err = png.Decode(r)
+	case "image/gif":
+		src, err = gif.Decode(r)
+	default:
+		return icon
+	}
+	if err != nil {
+		return icon
+	}
+
+	dst := image.NewRGBA(image.Rect(0, 0, 16, 16))
+	draw.BiLinear.Scale(dst, dst.Rect, src, src.Bounds(), draw.Over, nil)
+
+	var b bytes.Buffer
+	w := bufio.NewWriter(&b)
+	if err = png.Encode(w, dst); err == nil {
+		icon.Content = b.Bytes()
+		icon.MimeType = "image/png"
+	}
+
+	return icon
+
+}
+
 func findIconURLsFromHTMLDocument(body io.Reader, contentType string) ([]string, error) {
 	queries := []string{
 		"link[rel='icon' i]",