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, 5 insertions, 5 deletions

diff --git a/src/encoding/pem/pem.go b/src/encoding/pem/pem.go
index a7272da5ad..e7adf88382 100644
--- a/src/encoding/pem/pem.go
+++ b/src/encoding/pem/pem.go
@@ -78,6 +78,7 @@ func removeSpacesAndTabs(data []byte) []byte {
 var pemStart = []byte("\n-----BEGIN ")
 var pemEnd = []byte("\n-----END ")
 var pemEndOfLine = []byte("-----")
+var colon = []byte(":")
 
 // Decode will find the next PEM formatted block (certificate, private key
 // etc) in the input. It returns that block and the remainder of the input. If
@@ -89,8 +90,8 @@ func Decode(data []byte) (p *Block, rest []byte) {
 	rest = data
 	if bytes.HasPrefix(data, pemStart[1:]) {
 		rest = rest[len(pemStart)-1 : len(data)]
-	} else if i := bytes.Index(data, pemStart); i >= 0 {
-		rest = rest[i+len(pemStart) : len(data)]
+	} else if _, after, ok := bytes.Cut(data, pemStart); ok {
+		rest = after
 	} else {
 		return nil, data
 	}
@@ -114,13 +115,12 @@ func Decode(data []byte) (p *Block, rest []byte) {
 		}
 		line, next := getLine(rest)
 
-		i := bytes.IndexByte(line, ':')
-		if i == -1 {
+		key, val, ok := bytes.Cut(line, colon)
+		if !ok {
 			break
 		}
 
 		// TODO(agl): need to cope with values that spread across lines.
-		key, val := line[:i], line[i+1:]
 		key = bytes.TrimSpace(key)
 		val = bytes.TrimSpace(val)
 		p.Headers[string(key)] = string(val)