Pull request: 3435 openwrt detect

Merge in DNS/adguard-home from 3435-openwrt-detect to master

Updates #3435.

Squashed commit of the following:

commit 04b10f407ced1c85ac8089f980d79e9bbfe14e95
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Fri Aug 13 19:02:55 2021 +0300

    aghos: fix windows build

commit d387cec5f9cae9256dccef8c666c02f2fb7449a2
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Fri Aug 13 18:22:12 2021 +0300

    aghos: imp code, tests

commit 2450b98522eb032ec8658f3ef2384fc77b627cc6
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Fri Aug 13 13:43:46 2021 +0300

    all: imp code, docs

commit 7fabba3a8dc70fe61dbaa8fd5445453816fe9ac7
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Fri Aug 13 04:04:09 2021 +0300

    all: log changes

commit 7cc1235308caf09eb4c80c05a4f328b8d6909ec7
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Fri Aug 13 03:33:13 2021 +0300

    querylog: repl with golibs

commit 84592087d3b2aca23613950bb203ff3c862624dc
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Fri Aug 13 03:16:37 2021 +0300

    aghos: use filewalker

commit e4f2964b0e031c7a9a053e85c0ff7c792c772929
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Fri Aug 13 00:34:20 2021 +0300

    aghos: mv recurrentchecker from aghnet

internal/aghos/filewalker.go

@@ -0,0 +1,119 @@
+package aghos
+
+import (
+	"fmt"
+	"io"
+	"os"
+	"path/filepath"
+
+	"github.com/AdguardTeam/AdGuardHome/internal/aghio"
+	"github.com/AdguardTeam/golibs/errors"
+	"github.com/AdguardTeam/golibs/stringutil"
+)
+
+// FileWalker is the signature of a function called for files in the file tree.
+// As opposed to filepath.Walk it only walk the files (not directories) matching
+// the provided pattern and those returned by function itself.  All patterns
+// should be valid for filepath.Glob.  If cont is false, the walking terminates.
+// Each opened file is also limited for reading to MaxWalkedFileSize.
+//
+// TODO(e.burkov):  Consider moving to the separate package like pathutil.
+//
+// TODO(e.burkov):  Think about passing filename or any additional data.
+type FileWalker func(r io.Reader) (patterns []string, cont bool, err error)
+
+// MaxWalkedFileSize is the maximum length of the file that FileWalker can
+// check.
+const MaxWalkedFileSize = 1024 * 1024
+
+// checkFile tries to open and process a single file located on sourcePath.
+func checkFile(c FileWalker, sourcePath string) (patterns []string, cont bool, err error) {
+	var f *os.File
+	f, err = os.Open(sourcePath)
+	if err != nil {
+		if errors.Is(err, os.ErrNotExist) {
+			// Ignore non-existing files since this may only happen
+			// when the file was removed after filepath.Glob matched
+			// it.
+			return nil, true, nil
+		}
+
+		return nil, false, err
+	}
+	defer func() { err = errors.WithDeferred(err, f.Close()) }()
+
+	var r io.Reader
+	// Ignore the error since LimitReader function returns error only if
+	// passed limit value is less than zero, but the constant used.
+	//
+	// TODO(e.burkov):  Make variable.
+	r, _ = aghio.LimitReader(f, MaxWalkedFileSize)
+
+	return c(r)
+}
+
+// handlePatterns parses the patterns and ignores duplicates using srcSet.
+// srcSet must be non-nil.
+func handlePatterns(srcSet *stringutil.Set, patterns ...string) (sub []string, err error) {
+	sub = make([]string, 0, len(patterns))
+	for _, p := range patterns {
+		var matches []string
+		matches, err = filepath.Glob(p)
+		if err != nil {
+			// Enrich error with the pattern because filepath.Glob
+			// doesn't do it.
+			return nil, fmt.Errorf("invalid pattern %q: %w", p, err)
+		}
+
+		for _, m := range matches {
+			if srcSet.Has(m) {
+				continue
+			}
+
+			srcSet.Add(m)
+			sub = append(sub, m)
+		}
+	}
+
+	return sub, nil
+}
+
+// Walk starts walking the files defined by initPattern.  It only returns true
+// if c signed to stop walking.
+func (c FileWalker) Walk(initPattern string) (ok bool, err error) {
+	// The slice of sources keeps the order in which the files are walked
+	// since srcSet.Values() returns strings in undefined order.
+	srcSet := stringutil.NewSet()
+	var src []string
+	src, err = handlePatterns(srcSet, initPattern)
+	if err != nil {
+		return false, err
+	}
+
+	var filename string
+	defer func() { err = errors.Annotate(err, "checking %q: %w", filename) }()
+
+	for i := 0; i < len(src); i++ {
+		var patterns []string
+		var cont bool
+		filename = src[i]
+		patterns, cont, err = checkFile(c, src[i])
+		if err != nil {
+			return false, err
+		}
+
+		if !cont {
+			return true, nil
+		}
+
+		var subsrc []string
+		subsrc, err = handlePatterns(srcSet, patterns...)
+		if err != nil {
+			return false, err
+		}
+
+		src = append(src, subsrc...)
+	}
+
+	return false, nil
+}