*(home): fix small filters update

✅ Closes: https://github.com/AdguardTeam/AdGuardHome/issues/1554

home/filter.go

@@ -24,12 +24,6 @@ var (
 	nextFilterID = time.Now().Unix() // semi-stable way to generate an unique ID
 )
 
-// type FilteringConf struct {
-// 	BlockLists []filter
-// 	AllowLists []filter
-// 	UserRules []string
-// }
-
 // Filtering - module object
 type Filtering struct {
 	// conf FilteringConf
@@ -447,8 +441,9 @@ func (f *Filtering) refreshFiltersIfNecessary(flags int) (int, bool) {
 }
 
 // Allows printable UTF-8 text with CR, LF, TAB characters
-func isPrintableText(data []byte) bool {
+func isPrintableText(data []byte, len int) bool {
-	for _, c := range data {
+	for i := 0; i < len; i++ {
+		c := data[i]
 		if (c >= ' ' && c != 0x7f) || c == '\n' || c == '\r' || c == '\t' {
 			continue
 		}
@@ -549,7 +544,7 @@ func (f *Filtering) updateIntl(filter *filter) (bool, error) {
 			firstChunkLen += copied
 
 			if firstChunkLen == len(firstChunk) || err == io.EOF {
-				if !isPrintableText(firstChunk) {
+				if !isPrintableText(firstChunk, firstChunkLen) {
 					return false, fmt.Errorf("data contains non-printable characters")
 				}
 

home/filter_test.go

@@ -1,6 +1,8 @@
 package home
 
 import (
+	"fmt"
+	"net"
 	"net/http"
 	"os"
 	"testing"
@@ -9,7 +11,28 @@ import (
 	"github.com/stretchr/testify/assert"
 )
 
+func testStartFilterListener() net.Listener {
+	http.HandleFunc("/filters/1.txt", func(w http.ResponseWriter, r *http.Request) {
+		content := `||example.org^$third-party
+||example.com^$third-party
+0.0.0.0 example.com
+`
+		_, _ = w.Write([]byte(content))
+	})
+
+	listener, err := net.Listen("tcp", ":0")
+	if err != nil {
+		panic(err)
+	}
+
+	go func() { _ = http.Serve(listener, nil) }()
+	return listener
+}
+
 func TestFilters(t *testing.T) {
+	l := testStartFilterListener()
+	defer func() { _ = l.Close() }()
+
 	dir := prepareTestDir()
 	defer func() { _ = os.RemoveAll(dir) }()
 	Context = homeContext{}
@@ -20,13 +43,14 @@ func TestFilters(t *testing.T) {
 	Context.filters.Init()
 
 	f := filter{
-		URL: "https://adguardteam.github.io/AdGuardSDNSFilter/Filters/filter.txt",
+		URL: fmt.Sprintf("http://127.0.0.1:%d/filters/1.txt", l.Addr().(*net.TCPAddr).Port),
 	}
 
 	// download
 	ok, err := Context.filters.update(&f)
 	assert.Equal(t, nil, err)
 	assert.True(t, ok)
+	assert.Equal(t, 3, f.RulesCount)
 
 	// refresh
 	ok, err = Context.filters.update(&f)