Some code improvements

* Rewrite empty string checks more idiomatically.
* Change strings.ToLower comparisons to strings.EqualFold.
* Rewrite switch statement with only one case as if.

common/protocol/http/headers.go

@@ -11,7 +11,7 @@ import (
 // ParseXForwardedFor parses X-Forwarded-For header in http headers, and return the IP list in it.
 func ParseXForwardedFor(header http.Header) []net.Address {
 	xff := header.Get("X-Forwarded-For")
-	if len(xff) == 0 {
+	if xff == "" {
 		return nil
 	}
 	list := strings.Split(xff, ",")
@@ -38,7 +38,7 @@ func RemoveHopByHopHeaders(header http.Header) {
 
 	connections := header.Get("Connection")
 	header.Del("Connection")
-	if len(connections) == 0 {
+	if connections == "" {
 		return
 	}
 	for _, h := range strings.Split(connections, ",") {

common/protocol/http/sniff.go

@@ -44,7 +44,7 @@ var (
 
 func beginWithHTTPMethod(b []byte) error {
 	for _, m := range &methods {
-		if len(b) >= len(m) && strings.ToLower(string(b[:len(m)])) == m {
+		if len(b) >= len(m) && strings.EqualFold(string(b[:len(m)]), m) {
 			return nil
 		}
 

common/protocol/tls/sniff.go

@@ -81,8 +81,7 @@ func ReadClientHello(data []byte, h *SniffHeader) error {
 			return errNotClientHello
 		}
 
-		switch extension {
-		case 0x00: /* extensionServerName */
+		if extension == 0x00 { /* extensionServerName */
 			d := data[:length]
 			if len(d) < 2 {
 				return errNotClientHello

common/strmatcher/domain_matcher.go

@@ -51,7 +51,7 @@ func (g *DomainMatcherGroup) addMatcher(m domainMatcher, value uint32) {
 }
 
 func (g *DomainMatcherGroup) Match(domain string) uint32 {
-	if len(domain) == 0 {
+	if domain == "" {
 		return 0
 	}