all: use bytes.Cut, strings.Cut

Many uses of Index/IndexByte/IndexRune/Split/SplitN
can be written more clearly using the new Cut functions.
Do that. Also rewrite to other functions if that's clearer.

For #46336.

Change-Id: I68d024716ace41a57a8bf74455c62279bde0f448
Reviewed-on: https://go-review.googlesource.com/c/go/+/351711
Trust: Russ Cox <rsc@golang.org>
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

1 files changed, 12 insertions, 13 deletions

diff --git a/src/net/http/request.go b/src/net/http/request.go
index 0eb7042d7b..76c2317d28 100644
--- a/src/net/http/request.go
+++ b/src/net/http/request.go
@@ -940,7 +940,7 @@ func NewRequestWithContext(ctx context.Context, method, url string, body io.Read
 func (r *Request) BasicAuth() (username, password string, ok bool) {
 	auth := r.Header.Get("Authorization")
 	if auth == "" {
-		return
+		return "", "", false
 	}
 	return parseBasicAuth(auth)
 }
@@ -951,18 +951,18 @@ func parseBasicAuth(auth string) (username, password string, ok bool) {
 	const prefix = "Basic "
 	// Case insensitive prefix match. See Issue 22736.
 	if len(auth) < len(prefix) || !ascii.EqualFold(auth[:len(prefix)], prefix) {
-		return
+		return "", "", false
 	}
 	c, err := base64.StdEncoding.DecodeString(auth[len(prefix):])
 	if err != nil {
-		return
+		return "", "", false
 	}
 	cs := string(c)
-	s := strings.IndexByte(cs, ':')
-	if s < 0 {
-		return
+	username, password, ok = strings.Cut(cs, ":")
+	if !ok {
+		return "", "", false
 	}
-	return cs[:s], cs[s+1:], true
+	return username, password, true
 }
 
 // SetBasicAuth sets the request's Authorization header to use HTTP
@@ -980,13 +980,12 @@ func (r *Request) SetBasicAuth(username, password string) {
 
 // parseRequestLine parses "GET /foo HTTP/1.1" into its three parts.
 func parseRequestLine(line string) (method, requestURI, proto string, ok bool) {
-	s1 := strings.Index(line, " ")
-	s2 := strings.Index(line[s1+1:], " ")
-	if s1 < 0 || s2 < 0 {
-		return
+	method, rest, ok1 := strings.Cut(line, " ")
+	requestURI, proto, ok2 := strings.Cut(rest, " ")
+	if !ok1 || !ok2 {
+		return "", "", "", false
 	}
-	s2 += s1 + 1
-	return line[:s1], line[s1+1 : s2], line[s2+1:], true
+	return method, requestURI, proto, true
 }
 
 var textprotoReaderPool sync.Pool