syscall, internal/syscall/windows: remove utf16PtrToString parameter

CL 208617 introduced syscall.utf16PtrToString and
internal/syscall/windows.UTF16PtrToString functions.

Original version of CL 208617 did not include syscall.utf16PtrToString
and internal/syscall/windows.UTF16PtrToString max parameter. The
parameter was added by Brad at the request of Ian. Ian said:

"In some cases it seems at least possible that the null terminator is
not present. I think it would be safer if we passed a maximum length
here."

The syscall.utf16PtrToString and
internal/syscall/windows.UTF16PtrToString function are designed to work
with only null terminated strings. So max parameter is superfluous.

This change removes max parameter.

Updates #34972

Change-Id: Ifea65dbd86bca8a08353579c6b9636c6f963d165
Reviewed-on: https://go-review.googlesource.com/c/go/+/228858
Run-TryBot: Alex Brainman <alex.brainman@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Bryan C. Mills <bcmills@google.com>

src/go/build/deps_test.go

@@ -152,7 +152,7 @@ var pkgDeps = map[string][]string{
 	"syscall/js":                        {"L0"},
 	"internal/oserror":                  {"L0"},
 	"internal/syscall/unix":             {"L0", "syscall"},
-	"internal/syscall/windows":          {"L0", "syscall", "internal/syscall/windows/sysdll", "unicode/utf16"},
+	"internal/syscall/windows":          {"L0", "syscall", "internal/syscall/windows/sysdll", "internal/unsafeheader", "unicode/utf16"},
 	"internal/syscall/windows/registry": {"L0", "syscall", "internal/syscall/windows/sysdll", "unicode/utf16"},
 	"internal/syscall/execenv":          {"L0", "syscall", "internal/syscall/windows", "unicode/utf16"},
 	"time": {

src/internal/syscall/windows/syscall_windows.go

@@ -5,6 +5,7 @@
 package windows
 
 import (
+	"internal/unsafeheader"
 	"sync"
 	"syscall"
 	"unicode/utf16"
@@ -13,20 +14,24 @@ import (
 
 // UTF16PtrToString is like UTF16ToString, but takes *uint16
 // as a parameter instead of []uint16.
-// max is how many times p can be advanced looking for the null terminator.
+func UTF16PtrToString(p *uint16) string {
-// If max is hit, the string is truncated at that point.
-func UTF16PtrToString(p *uint16, max int) string {
 	if p == nil {
 		return ""
 	}
 	// Find NUL terminator.
 	end := unsafe.Pointer(p)
 	n := 0
-	for *(*uint16)(end) != 0 && n < max {
+	for *(*uint16)(end) != 0 {
 		end = unsafe.Pointer(uintptr(end) + unsafe.Sizeof(*p))
 		n++
 	}
-	s := (*[(1 << 30) - 1]uint16)(unsafe.Pointer(p))[:n:n]
+	// Turn *uint16 into []uint16.
+	var s []uint16
+	hdr := (*unsafeheader.Slice)(unsafe.Pointer(&s))
+	hdr.Data = unsafe.Pointer(p)
+	hdr.Cap = n
+	hdr.Len = n
+	// Decode []uint16 into string.
 	return string(utf16.Decode(s))
 }
 

src/net/interface_windows.go

@@ -58,7 +58,7 @@ func interfaceTable(ifindex int) ([]Interface, error) {
 		if ifindex == 0 || ifindex == int(index) {
 			ifi := Interface{
 				Index: int(index),
-				Name:  windows.UTF16PtrToString(aa.FriendlyName, 10000),
+				Name:  windows.UTF16PtrToString(aa.FriendlyName),
 			}
 			if aa.OperStatus == windows.IfOperStatusUp {
 				ifi.Flags |= FlagUp

src/net/lookup_windows.go

@@ -234,7 +234,7 @@ func (*Resolver) lookupCNAME(ctx context.Context, name string) (string, error) {
 	defer syscall.DnsRecordListFree(r, 1)
 
 	resolved := resolveCNAME(syscall.StringToUTF16Ptr(name), r)
-	cname := windows.UTF16PtrToString(resolved, 256)
+	cname := windows.UTF16PtrToString(resolved)
 	return absDomainName([]byte(cname)), nil
 }
 
@@ -278,7 +278,7 @@ func (*Resolver) lookupMX(ctx context.Context, name string) ([]*MX, error) {
 	mxs := make([]*MX, 0, 10)
 	for _, p := range validRecs(r, syscall.DNS_TYPE_MX, name) {
 		v := (*syscall.DNSMXData)(unsafe.Pointer(&p.Data[0]))
-		mxs = append(mxs, &MX{absDomainName([]byte(windows.UTF16PtrToString(v.NameExchange, 256))), v.Preference})
+		mxs = append(mxs, &MX{absDomainName([]byte(windows.UTF16PtrToString(v.NameExchange))), v.Preference})
 	}
 	byPref(mxs).sort()
 	return mxs, nil
@@ -319,7 +319,7 @@ func (*Resolver) lookupTXT(ctx context.Context, name string) ([]string, error) {
 		d := (*syscall.DNSTXTData)(unsafe.Pointer(&p.Data[0]))
 		s := ""
 		for _, v := range (*[1 << 10]*uint16)(unsafe.Pointer(&(d.StringArray[0])))[:d.StringCount:d.StringCount] {
-			s += windows.UTF16PtrToString(v, 1<<20)
+			s += windows.UTF16PtrToString(v)
 		}
 		txts = append(txts, s)
 	}
@@ -344,7 +344,7 @@ func (*Resolver) lookupAddr(ctx context.Context, addr string) ([]string, error)
 	ptrs := make([]string, 0, 10)
 	for _, p := range validRecs(r, syscall.DNS_TYPE_PTR, arpa) {
 		v := (*syscall.DNSPTRData)(unsafe.Pointer(&p.Data[0]))
-		ptrs = append(ptrs, absDomainName([]byte(windows.UTF16PtrToString(v.Host, 256))))
+		ptrs = append(ptrs, absDomainName([]byte(windows.UTF16PtrToString(v.Host))))
 	}
 	return ptrs, nil
 }

src/os/exec_windows.go

@@ -98,7 +98,7 @@ func findProcess(pid int) (p *Process, err error) {
 }
 
 func init() {
-	cmd := windows.UTF16PtrToString(syscall.GetCommandLine(), 0xffff)
+	cmd := windows.UTF16PtrToString(syscall.GetCommandLine())
 	if len(cmd) == 0 {
 		arg0, _ := Executable()
 		Args = []string{arg0}

src/os/user/lookup_windows.go

@@ -44,7 +44,7 @@ func lookupFullNameServer(servername, username string) (string, error) {
 	}
 	defer syscall.NetApiBufferFree(p)
 	i := (*syscall.UserInfo10)(unsafe.Pointer(p))
-	return windows.UTF16PtrToString(i.FullName, 1024), nil
+	return windows.UTF16PtrToString(i.FullName), nil
 }
 
 func lookupFullName(domain, username, domainAndUser string) (string, error) {
@@ -167,7 +167,7 @@ func listGroupsForUsernameAndDomain(username, domain string) ([]string, error) {
 		if entry.Name == nil {
 			continue
 		}
-		sid, err := lookupGroupName(windows.UTF16PtrToString(entry.Name, 1024))
+		sid, err := lookupGroupName(windows.UTF16PtrToString(entry.Name))
 		if err != nil {
 			return nil, err
 		}

src/syscall/security_windows.go

@@ -163,7 +163,7 @@ func (sid *SID) String() (string, error) {
 		return "", e
 	}
 	defer LocalFree((Handle)(unsafe.Pointer(s)))
-	return utf16PtrToString(s, 256), nil
+	return utf16PtrToString(s), nil
 }
 
 // Len returns the length, in bytes, of a valid security identifier sid.

src/syscall/syscall_windows.go

@@ -10,6 +10,7 @@ import (
 	errorspkg "errors"
 	"internal/oserror"
 	"internal/race"
+	"internal/unsafeheader"
 	"runtime"
 	"sync"
 	"unicode/utf16"
@@ -59,20 +60,24 @@ func UTF16ToString(s []uint16) string {
 
 // utf16PtrToString is like UTF16ToString, but takes *uint16
 // as a parameter instead of []uint16.
-// max is how many times p can be advanced looking for the null terminator.
+func utf16PtrToString(p *uint16) string {
-// If max is hit, the string is truncated at that point.
-func utf16PtrToString(p *uint16, max int) string {
 	if p == nil {
 		return ""
 	}
 	// Find NUL terminator.
 	end := unsafe.Pointer(p)
 	n := 0
-	for *(*uint16)(end) != 0 && n < max {
+	for *(*uint16)(end) != 0 {
 		end = unsafe.Pointer(uintptr(end) + unsafe.Sizeof(*p))
 		n++
 	}
-	s := (*[(1 << 30) - 1]uint16)(unsafe.Pointer(p))[:n:n]
+	// Turn *uint16 into []uint16.
+	var s []uint16
+	hdr := (*unsafeheader.Slice)(unsafe.Pointer(&s))
+	hdr.Data = unsafe.Pointer(p)
+	hdr.Cap = n
+	hdr.Len = n
+	// Decode []uint16 into string.
 	return string(utf16.Decode(s))
 }