Merge pull request #35 in DNS/adguard-dns from bugfix/343 to master

* commit '119d38fa8e8b5c5193fe20ad215a6daac833354b':
  Add trace() for debugging
  coredns -- don't try to be smart and replace 127.0.0.1 with NXDOMAIN yet -- need research on that first
  Fix 'index out of range' panic when adding a filter URL that has empty line in contents
  web UI -- Fix description of hosts rule syntax, it's other way around

client/src/components/Filters/UserRules.js

@@ -44,7 +44,7 @@ export default class UserRules extends Component {
                             domain and all its subdomains
                         </li>
                         <li>
-                            <code>example.org 127.0.0.1</code> - AdGuard DNS will now return
+                            <code>127.0.0.1 example.org</code> - AdGuard DNS will now return
                             127.0.0.1 address for the example.org domain (but not its subdomains).
                         </li>
                         <li>

control.go

@@ -1148,7 +1148,7 @@ func (filter *filter) update(now time.Time) (bool, error) {
 	d := dnsfilter.New()
 	for _, line := range lines {
 		line = strings.TrimSpace(line)
-		if line[0] == '!' {
+		if len(line) > 0 && line[0] == '!' {
 			if m := filterTitle.FindAllStringSubmatch(line, -1); len(m) > 0 && len(m[0]) >= 2 && !seenTitle {
 				log.Printf("Setting filter title to %s\n", m[0][1])
 				filter.Name = m[0][1]

coredns_plugin/coredns_plugin.go

@@ -384,7 +384,8 @@ func (p *plug) serveDNSInternal(ctx context.Context, w dns.ResponseWriter, r *dn
 		// is it in hosts?
 		if val, ok := p.hosts[host]; ok {
 			// it is, if it's a loopback host, reply with NXDOMAIN
-			if val.IsLoopback() {
+			// TODO: research if it's better than 127.0.0.1
+			if false && val.IsLoopback() {
 				rcode, err := writeNXdomain(ctx, w, r)
 				if err != nil {
 					return rcode, dnsfilter.Result{}, err

helpers.go

@@ -3,6 +3,7 @@ package main
 import (
 	"bufio"
 	"errors"
+	"fmt"
 	"io"
 	"net/http"
 	"path"
@@ -246,3 +247,17 @@ func _Func() string {
 	f := runtime.FuncForPC(pc[0])
 	return path.Base(f.Name())
 }
+
+func trace(format string, args ...interface{}) {
+	pc := make([]uintptr, 10) // at least 1 entry needed
+	runtime.Callers(2, pc)
+	f := runtime.FuncForPC(pc[0])
+	var buf strings.Builder
+	buf.WriteString(fmt.Sprintf("%s(): ", path.Base(f.Name())))
+	text := fmt.Sprintf(format, args...)
+	buf.WriteString(text)
+	if len(text) == 0 || text[len(text)-1] != '\n' {
+		buf.WriteRune('\n')
+	}
+	fmt.Print(buf.String())
+}