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 <[email protected]> Run-TryBot: Russ Cox <[email protected]> TryBot-Result: Go Bot <[email protected]> Reviewed-by: Ian Lance Taylor <[email protected]>
cloudflare · Oct 6, 2021 · 4d8db00 · 4d8db00
1 parent 8e36ab0
commit 4d8db00
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Showing 78 changed files with 356 additions and 577 deletions.
diff --git a/misc/cgo/errors/errors_test.go b/misc/cgo/errors/errors_test.go
@@ -36,14 +36,13 @@ func check(t *testing.T, file string) {
  continue
  }
 
- frags := bytes.SplitAfterN(line, []byte("ERROR HERE: "), 2)
- if len(frags) == 1 {
+ _, frag, ok := bytes.Cut(line, []byte("ERROR HERE: "))
+ if !ok {
  continue
  }
- frag := fmt.Sprintf(":%d:.*%s", i+1, frags[1])
- re, err := regexp.Compile(frag)
+ re, err := regexp.Compile(fmt.Sprintf(":%d:.*%s", i+1, frag))
  if err != nil {
- t.Errorf("Invalid regexp after `ERROR HERE: `: %#q", frags[1])
+ t.Errorf("Invalid regexp after `ERROR HERE: `: %#q", frag)
  continue
  }
  errors = append(errors, re)

diff --git a/misc/cgo/testcshared/cshared_test.go b/misc/cgo/testcshared/cshared_test.go
@@ -200,7 +200,7 @@ func adbRun(t *testing.T, env []string, adbargs ...string) string {
  args := append(adbCmd(), "exec-out")
  // Propagate LD_LIBRARY_PATH to the adb shell invocation.
  for _, e := range env {
- if strings.Index(e, "LD_LIBRARY_PATH=") != -1 {
+ if strings.Contains(e, "LD_LIBRARY_PATH=") {
  adbargs = append([]string{e}, adbargs...)
  break
  }
@@ -326,7 +326,7 @@ func createHeaders() error {
  base, name := filepath.Split(args[0])
  args[0] = filepath.Join(base, "llvm-dlltool")
  var machine string
- switch strings.SplitN(name, "-", 2)[0] {
+ switch prefix, _, _ := strings.Cut(name, "-"); prefix {
  case "i686":
  machine = "i386"
  case "x86_64":

diff --git a/misc/cgo/testsanitizers/cc_test.go b/misc/cgo/testsanitizers/cc_test.go
@@ -344,7 +344,7 @@ func (c *config) checkCSanitizer() (skip bool, err error) {
  if os.IsNotExist(err) {
  return true, fmt.Errorf("%#q failed to produce executable: %v", strings.Join(cmd.Args, " "), err)
  }
- snippet := bytes.SplitN(out, []byte{'\n'}, 2)[0]
+ snippet, _, _ := bytes.Cut(out, []byte("\n"))
  return true, fmt.Errorf("%#q generated broken executable: %v\n%s", strings.Join(cmd.Args, " "), err, snippet)
  }
 

diff --git a/misc/ios/go_ios_exec.go b/misc/ios/go_ios_exec.go
@@ -148,9 +148,8 @@ func runOnDevice(appdir string) error {
  // Device IDs as listed with ios-deploy -c.
  deviceID = os.Getenv("GOIOS_DEVICE_ID")
 
- parts := strings.SplitN(appID, ".", 2)
- if len(parts) == 2 {
- bundleID = parts[1]
+ if _, id, ok := strings.Cut(appID, "."); ok {
+ bundleID = id
  }
 
  if err := signApp(appdir); err != nil {
@@ -291,11 +290,10 @@ func findDevImage() (string, error) {
  var iosVer, buildVer string
  lines := bytes.Split(out, []byte("\n"))
  for _, line := range lines {
- spl := bytes.SplitN(line, []byte(": "), 2)
- if len(spl) != 2 {
+ key, val, ok := strings.Cut(string(line), ": ")
+ if !ok {
  continue
  }
- key, val := string(spl[0]), string(spl[1])
  switch key {
  case "ProductVersion":
  iosVer = val

diff --git a/misc/linkcheck/linkcheck.go b/misc/linkcheck/linkcheck.go
@@ -81,10 +81,8 @@ func crawl(url string, sourceURL string) {
  }
  mu.Lock()
  defer mu.Unlock()
- var frag string
- if i := strings.Index(url, "#"); i >= 0 {
- frag = url[i+1:]
- url = url[:i]
+ if u, frag, ok := strings.Cut(url, "#"); ok {
+ url = u
  if frag != "" {
  uf := urlFrag{url, frag}
  neededFrags[uf] = append(neededFrags[uf], sourceURL)

diff --git a/src/archive/tar/strconv.go b/src/archive/tar/strconv.go
@@ -14,7 +14,7 @@ import (
 
 // hasNUL reports whether the NUL character exists within s.
 func hasNUL(s string) bool {
- return strings.IndexByte(s, 0) >= 0
+ return strings.Contains(s, "\x00")
 }
 
 // isASCII reports whether the input is an ASCII C-style string.
@@ -201,10 +201,7 @@ func parsePAXTime(s string) (time.Time, error) {
  const maxNanoSecondDigits = 9
 
  // Split string into seconds and sub-seconds parts.
- ss, sn := s, ""
- if pos := strings.IndexByte(s, '.'); pos >= 0 {
- ss, sn = s[:pos], s[pos+1:]
- }
+ ss, sn, _ := strings.Cut(s, ".")
 
  // Parse the seconds.
  secs, err := strconv.ParseInt(ss, 10, 64)
@@ -254,48 +251,32 @@ func formatPAXTime(ts time.Time) (s string) {
 // return the remainder as r.
 func parsePAXRecord(s string) (k, v, r string, err error) {
  // The size field ends at the first space.
- sp := strings.IndexByte(s, ' ')
- if sp == -1 {
+ nStr, rest, ok := strings.Cut(s, " ")
+ if !ok {
  return "", "", s, ErrHeader
  }
 
  // Parse the first token as a decimal integer.
- n, perr := strconv.ParseInt(s[:sp], 10, 0) // Intentionally parse as native int
- if perr != nil || n < 5 || int64(len(s)) < n {
+ n, perr := strconv.ParseInt(nStr, 10, 0) // Intentionally parse as native int
+ if perr != nil || n < 5 || n > int64(len(s)) {
  return "", "", s, ErrHeader
  }
-
- afterSpace := int64(sp + 1)
- beforeLastNewLine := n - 1
- // In some cases, "length" was perhaps padded/malformed, and
- // trying to index past where the space supposedly is goes past
- // the end of the actual record.
- // For example:
- // "0000000000000000000000000000000030 mtime=1432668921.098285006\n30 ctime=2147483649.15163319"
- // ^ ^
- // | |
- // | afterSpace=35
- // |
- // beforeLastNewLine=29
- // yet indexOf(firstSpace) MUST BE before endOfRecord.
- //
- // See https://golang.org/issues/40196.
- if afterSpace >= beforeLastNewLine {
+ n -= int64(len(nStr) + 1) // convert from index in s to index in rest
+ if n <= 0 {
  return "", "", s, ErrHeader
  }
 
  // Extract everything between the space and the final newline.
- rec, nl, rem := s[afterSpace:beforeLastNewLine], s[beforeLastNewLine:n], s[n:]
+ rec, nl, rem := rest[:n-1], rest[n-1:n], rest[n:]
  if nl != "\n" {
  return "", "", s, ErrHeader
  }
 
  // The first equals separates the key from the value.
- eq := strings.IndexByte(rec, '=')
- if eq == -1 {
+ k, v, ok = strings.Cut(rec, "=")
+ if !ok {
  return "", "", s, ErrHeader
  }
- k, v = rec[:eq], rec[eq+1:]
 
  if !validPAXRecord(k, v) {
  return "", "", s, ErrHeader
@@ -333,7 +314,7 @@ func formatPAXRecord(k, v string) (string, error) {
 // for the PAX version of the USTAR string fields.
 // The key must not contain an '=' character.
 func validPAXRecord(k, v string) bool {
- if k == "" || strings.IndexByte(k, '=') >= 0 {
+ if k == "" || strings.Contains(k, "=") {
  return false
  }
  switch k {

diff --git a/src/archive/tar/writer_test.go b/src/archive/tar/writer_test.go
@@ -988,9 +988,7 @@ func TestIssue12594(t *testing.T) {
  var blk block
  copy(blk[:], b.Bytes())
  prefix := string(blk.toUSTAR().prefix())
- if i := strings.IndexByte(prefix, 0); i >= 0 {
- prefix = prefix[:i] // Truncate at the NUL terminator
- }
+ prefix, _, _ = strings.Cut(prefix, "\x00") // Truncate at the NUL terminator
  if blk.getFormat() == FormatGNU && len(prefix) > 0 && strings.HasPrefix(name, prefix) {
  t.Errorf("test %d, found prefix in GNU format: %s", i, prefix)
  }

diff --git a/src/archive/zip/writer_test.go b/src/archive/zip/writer_test.go
@@ -362,7 +362,7 @@ func TestWriterDirAttributes(t *testing.T) {
  }
 
  binary.LittleEndian.PutUint32(sig[:], uint32(dataDescriptorSignature))
- if bytes.Index(b, sig[:]) != -1 {
+ if bytes.Contains(b, sig[:]) {
  t.Error("there should be no data descriptor")
  }
 }

diff --git a/src/cmd/doc/dirs.go b/src/cmd/doc/dirs.go
@@ -221,11 +221,7 @@ func findCodeRoots() []Dir {
  cmd.Stderr = os.Stderr
  out, _ := cmd.Output()
  for _, line := range strings.Split(string(out), "\n") {
- i := strings.Index(line, "\t")
- if i < 0 {
- continue
- }
- path, dir := line[:i], line[i+1:]
+ path, dir, _ := strings.Cut(line, "\t")
  if dir != "" {
  list = append(list, Dir{importPath: path, dir: dir, inModule: true})
  }

diff --git a/src/cmd/doc/pkg.go b/src/cmd/doc/pkg.go
@@ -315,9 +315,7 @@ func (pkg *Package) oneLineNodeDepth(node ast.Node, depth int) string {
  recv = "(" + recv + ") "
  }
  fnc := pkg.oneLineNodeDepth(n.Type, depth)
- if strings.Index(fnc, "func") == 0 {
- fnc = fnc[4:]
- }
+ fnc = strings.TrimPrefix(fnc, "func")
  return fmt.Sprintf("func %s%s%s", recv, name, fnc)
 
  case *ast.TypeSpec:

diff --git a/src/cmd/fix/typecheck.go b/src/cmd/fix/typecheck.go
@@ -544,8 +544,8 @@ func typecheck1(cfg *TypeConfig, f interface{}, typeof map[interface{}]string, a
  if strings.HasPrefix(t, "[") || strings.HasPrefix(t, "map[") {
  // Lazy: assume there are no nested [] in the array
  // length or map key type.
- if i := strings.Index(t, "]"); i >= 0 {
- typeof[n] = t[i+1:]
+ if _, elem, ok := strings.Cut(t, "]"); ok {
+ typeof[n] = elem
  }
  }
 
@@ -575,8 +575,7 @@ func typecheck1(cfg *TypeConfig, f interface{}, typeof map[interface{}]string, a
  t := expand(typeof[n])
  if strings.HasPrefix(t, "[") { // array or slice
  // Lazy: assume there are no nested [] in the array length.
- if i := strings.Index(t, "]"); i >= 0 {
- et := t[i+1:]
+ if _, et, ok := strings.Cut(t, "]"); ok {
  for _, e := range n.Elts {
  if kv, ok := e.(*ast.KeyValueExpr); ok {
  e = kv.Value
@@ -589,8 +588,7 @@ func typecheck1(cfg *TypeConfig, f interface{}, typeof map[interface{}]string, a
  }
  if strings.HasPrefix(t, "map[") { // map
  // Lazy: assume there are no nested [] in the map key type.
- if i := strings.Index(t, "]"); i >= 0 {
- kt, vt := t[4:i], t[i+1:]
+ if kt, vt, ok := strings.Cut(t[len("map["):], "]"); ok {
  for _, e := range n.Elts {
  if kv, ok := e.(*ast.KeyValueExpr); ok {
  if typeof[kv.Key] == "" {
@@ -629,12 +627,10 @@ func typecheck1(cfg *TypeConfig, f interface{}, typeof map[interface{}]string, a
  key, value = "int", "rune"
  } else if strings.HasPrefix(t, "[") {
  key = "int"
- if i := strings.Index(t, "]"); i >= 0 {
- value = t[i+1:]
- }
+ _, value, _ = strings.Cut(t, "]")
  } else if strings.HasPrefix(t, "map[") {
- if i := strings.Index(t, "]"); i >= 0 {
- key, value = t[4:i], t[i+1:]
+ if k, v, ok := strings.Cut(t[len("map["):], "]"); ok {
+ key, value = k, v
  }
  }
  changed := false

diff --git a/src/cmd/vet/vet_test.go b/src/cmd/vet/vet_test.go
@@ -241,8 +241,8 @@ func errorCheck(outStr string, wantAuto bool, fullshort ...string) (err error) {
  // Assume errmsg says "file:line: foo".
  // Cut leading "file:line: " to avoid accidental matching of file name instead of message.
  text := errmsg
- if i := strings.Index(text, " "); i >= 0 {
- text = text[i+1:]
+ if _, suffix, ok := strings.Cut(text, " "); ok {
+ text = suffix
  }
  if we.re.MatchString(text) {
  matched = true

diff --git a/src/crypto/ecdsa/ecdsa_test.go b/src/crypto/ecdsa/ecdsa_test.go
@@ -219,9 +219,9 @@ func TestVectors(t *testing.T) {
 
  if line[0] == '[' {
  line = line[1 : len(line)-1]
- parts := strings.SplitN(line, ",", 2)
+ curve, hash, _ := strings.Cut(line, ",")
 
- switch parts[0] {
+ switch curve {
  case "P-224":
  pub.Curve = elliptic.P224()
  case "P-256":
@@ -234,7 +234,7 @@ func TestVectors(t *testing.T) {
  pub.Curve = nil
  }
 
- switch parts[1] {
+ switch hash {
  case "SHA-1":
  h = sha1.New()
  case "SHA-224":

diff --git a/src/crypto/tls/handshake_client_test.go b/src/crypto/tls/handshake_client_test.go
@@ -97,18 +97,18 @@ func (o *opensslOutputSink) Write(data []byte) (n int, err error) {
  o.all = append(o.all, data...)
 
  for {
- i := bytes.IndexByte(o.line, '\n')
- if i < 0 {
+ line, next, ok := bytes.Cut(o.line, []byte("\n"))
+ if !ok {
  break
  }
 
- if bytes.Equal([]byte(opensslEndOfHandshake), o.line[:i]) {
+ if bytes.Equal([]byte(opensslEndOfHandshake), line) {
  o.handshakeComplete <- struct{}{}
  }
- if bytes.Equal([]byte(opensslReadKeyUpdate), o.line[:i]) {
+ if bytes.Equal([]byte(opensslReadKeyUpdate), line) {
  o.readKeyUpdate <- struct{}{}
  }
- o.line = o.line[i+1:]
+ o.line = next
  }
 
  return len(data), nil

diff --git a/src/crypto/tls/handshake_test.go b/src/crypto/tls/handshake_test.go
@@ -191,18 +191,17 @@ func parseTestData(r io.Reader) (flows [][]byte, err error) {
  // Otherwise the line is a line of hex dump that looks like:
  // 00000170 fc f5 06 bf (...) |.....X{&?......!|
  // (Some bytes have been omitted from the middle section.)
-
- if i := strings.IndexByte(line, ' '); i >= 0 {
- line = line[i:]
- } else {
+ _, after, ok := strings.Cut(line, " ")
+ if !ok {
  return nil, errors.New("invalid test data")
  }
+ line = after
 
- if i := strings.IndexByte(line, '|'); i >= 0 {
- line = line[:i]
- } else {
+ before, _, ok := strings.Cut(line, "|")
+ if !ok {
  return nil, errors.New("invalid test data")
  }
+ line = before
 
  hexBytes := strings.Fields(line)
  for _, hexByte := range hexBytes {

diff --git a/src/crypto/x509/pem_decrypt.go b/src/crypto/x509/pem_decrypt.go
@@ -127,12 +127,11 @@ func DecryptPEMBlock(b *pem.Block, password []byte) ([]byte, error) {
  return nil, errors.New("x509: no DEK-Info header in block")
  }
 
- idx := strings.Index(dek, ",")
- if idx == -1 {
+ mode, hexIV, ok := strings.Cut(dek, ",")
+ if !ok {
  return nil, errors.New("x509: malformed DEK-Info header")
  }
 
- mode, hexIV := dek[:idx], dek[idx+1:]
  ciph := cipherByName(mode)
  if ciph == nil {
  return nil, errors.New("x509: unknown encryption mode")

diff --git a/src/encoding/asn1/common.go b/src/encoding/asn1/common.go
@@ -94,14 +94,7 @@ type fieldParameters struct {
 func parseFieldParameters(str string) (ret fieldParameters) {
  var part string
  for len(str) > 0 {
- // This loop uses IndexByte and explicit slicing
- // instead of strings.Split(str, ",") to reduce allocations.
- i := strings.IndexByte(str, ',')
- if i < 0 {
- part, str = str, ""
- } else {
- part, str = str[:i], str[i+1:]
- }
+ part, str, _ = strings.Cut(str, ",")
  switch {
  case part == "optional":
  ret.optional = true