net: use bytealg.LastIndexByteString

There is no need to handwrite the "last" function, the bytealg package already provides "LastIndexByteString".

Change-Id: I6000705bffe8450a10cf8f3fa716a8d4605ada1f
GitHub-Last-Rev: 6627c65fb4
GitHub-Pull-Request: golang/go#62647
Reviewed-on: https://go-review.googlesource.com/c/go/+/527976
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>

src/net/dial.go

@@ -6,6 +6,7 @@ package net
 
 import (
 	"context"
+	"internal/bytealg"
 	"internal/godebug"
 	"internal/nettrace"
 	"syscall"
@@ -226,7 +227,7 @@ func (d *Dialer) fallbackDelay() time.Duration {
 }
 
 func parseNetwork(ctx context.Context, network string, needsProto bool) (afnet string, proto int, err error) {
-	i := last(network, ':')
+	i := bytealg.LastIndexByteString(network, ':')
 	if i < 0 { // no colon
 		switch network {
 		case "tcp", "tcp4", "tcp6":

src/net/ipsock.go

@@ -172,7 +172,7 @@ func SplitHostPort(hostport string) (host, port string, err error) {
 	j, k := 0, 0
 
 	// The port starts after the last colon.
-	i := last(hostport, ':')
+	i := bytealg.LastIndexByteString(hostport, ':')
 	if i < 0 {
 		return addrErr(hostport, missingPort)
 	}
@@ -219,7 +219,7 @@ func SplitHostPort(hostport string) (host, port string, err error) {
 func splitHostZone(s string) (host, zone string) {
 	// The IPv6 scoped addressing zone identifier starts after the
 	// last percent sign.
-	if i := last(s, '%'); i > 0 {
+	if i := bytealg.LastIndexByteString(s, '%'); i > 0 {
 		host, zone = s[:i], s[i+1:]
 	} else {
 		host = s

src/net/parse.go

@@ -180,17 +180,6 @@ func xtoi2(s string, e byte) (byte, bool) {
 	return byte(n), ok && ei == 2
 }
 
-// Index of rightmost occurrence of b in s.
-func last(s string, b byte) int {
-	i := len(s)
-	for i--; i >= 0; i-- {
-		if s[i] == b {
-			break
-		}
-	}
-	return i
-}
-
 // hasUpperCase tells whether the given string contains at least one upper-case.
 func hasUpperCase(s string) bool {
 	for i := range s {