Pull request: all: fix lint and naming issues vol. 3

Merge in DNS/adguard-home from 2276-fix-lint-3 to master

Updates #2276.

Squashed commit of the following:

commit 6ee94cc6ed2a9762b70ef395b58b496434244b80
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Mon Dec 7 15:55:45 2020 +0300

    all: fix lint and naming issues vol. 3

internal/home/authglinet.go

@@ -0,0 +1,119 @@
+package home
+
+import (
+	"bytes"
+	"encoding/binary"
+	"io/ioutil"
+	"net"
+	"net/http"
+	"os"
+	"time"
+	"unsafe"
+
+	"github.com/AdguardTeam/AdGuardHome/internal/aghio"
+	"github.com/AdguardTeam/golibs/log"
+)
+
+// GLMode - enable GL-Inet compatibility mode
+var GLMode bool
+
+var glFilePrefix = "/tmp/gl_token_"
+
+const (
+	glTokenTimeoutSeconds = 3600
+	glCookieName          = "Admin-Token"
+)
+
+func glProcessRedirect(w http.ResponseWriter, r *http.Request) bool {
+	if !GLMode {
+		return false
+	}
+	// redirect to gl-inet login
+	host, _, _ := net.SplitHostPort(r.Host)
+	url := "http://" + host
+	log.Debug("Auth: redirecting to %s", url)
+	http.Redirect(w, r, url, http.StatusFound)
+	return true
+}
+
+func glProcessCookie(r *http.Request) bool {
+	if !GLMode {
+		return false
+	}
+
+	glCookie, glerr := r.Cookie(glCookieName)
+	if glerr != nil {
+		return false
+	}
+
+	log.Debug("Auth: GL cookie value: %s", glCookie.Value)
+	if glCheckToken(glCookie.Value) {
+		return true
+	}
+	log.Info("Auth: invalid GL cookie value: %s", glCookie)
+	return false
+}
+
+func glCheckToken(sess string) bool {
+	tokenName := glFilePrefix + sess
+	_, err := os.Stat(tokenName)
+	if err != nil {
+		log.Error("os.Stat: %s", err)
+		return false
+	}
+	tokenDate := glGetTokenDate(tokenName)
+	now := uint32(time.Now().UTC().Unix())
+	return now <= (tokenDate + glTokenTimeoutSeconds)
+}
+
+func archIsLittleEndian() bool {
+	var i int32 = 0x01020304
+	u := unsafe.Pointer(&i)
+	pb := (*byte)(u)
+	b := *pb
+	return (b == 0x04)
+}
+
+// MaxFileSize is a maximum file length in bytes.
+const MaxFileSize = 1024 * 1024
+
+func glGetTokenDate(file string) uint32 {
+	f, err := os.Open(file)
+	if err != nil {
+		log.Error("os.Open: %s", err)
+		return 0
+	}
+	defer f.Close()
+
+	fileReadCloser, err := aghio.LimitReadCloser(f, MaxFileSize)
+	if err != nil {
+		log.Error("LimitReadCloser: %s", err)
+		return 0
+	}
+	defer fileReadCloser.Close()
+
+	var dateToken uint32
+
+	// This use of ReadAll is now safe, because we limited reader.
+	bs, err := ioutil.ReadAll(fileReadCloser)
+	if err != nil {
+		log.Error("ioutil.ReadAll: %s", err)
+		return 0
+	}
+	buf := bytes.NewBuffer(bs)
+
+	if archIsLittleEndian() {
+		err := binary.Read(buf, binary.LittleEndian, &dateToken)
+		if err != nil {
+			log.Error("binary.Read: %s", err)
+			return 0
+		}
+	} else {
+		err := binary.Read(buf, binary.BigEndian, &dateToken)
+		if err != nil {
+			log.Error("binary.Read: %s", err)
+			return 0
+		}
+	}
+	return dateToken
+}