time: unify three readFile implementations into one

Undoes this part of https://golang.org/cl/5447061 by using the
OS-specific open and close functions, and adding a read function.

Change-Id: If37ef43eb5df8554fc03f3922bbc2f785129bb9c
Reviewed-on: https://go-review.googlesource.com/66271
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Joe Tsai <joetsai@google.com>

src/time/sys_plan9.go

@@ -16,36 +16,6 @@ func interrupt() {
 	// cannot predict pid, don't want to kill group
 }
 
-// readFile reads and returns the content of the named file.
-// It is a trivial implementation of ioutil.ReadFile, reimplemented
-// here to avoid depending on io/ioutil or os.
-// It returns an error if name exceeds maxFileSize bytes.
-func readFile(name string) ([]byte, error) {
-	f, err := syscall.Open(name, syscall.O_RDONLY)
-	if err != nil {
-		return nil, err
-	}
-	defer syscall.Close(f)
-	var (
-		buf [4096]byte
-		ret []byte
-		n   int
-	)
-	for {
-		n, err = syscall.Read(f, buf[:])
-		if n > 0 {
-			ret = append(ret, buf[:n]...)
-		}
-		if n == 0 || err != nil {
-			break
-		}
-		if len(ret) > maxFileSize {
-			return nil, fileSizeError(name)
-		}
-	}
-	return ret, err
-}
-
 func open(name string) (uintptr, error) {
 	fd, err := syscall.Open(name, syscall.O_RDONLY)
 	if err != nil {
@@ -54,6 +24,10 @@ func open(name string) (uintptr, error) {
 	return uintptr(fd), nil
 }
 
+func read(fd uintptr, buf []byte) (int, error) {
+	return syscall.Read(int(fd), buf)
+}
+
 func closefd(fd uintptr) {
 	syscall.Close(int(fd))
 }

src/time/sys_unix.go

@@ -16,36 +16,6 @@ func interrupt() {
 	syscall.Kill(syscall.Getpid(), syscall.SIGCHLD)
 }
 
-// readFile reads and returns the content of the named file.
-// It is a trivial implementation of ioutil.ReadFile, reimplemented
-// here to avoid depending on io/ioutil or os.
-// It returns an error if name exceeds maxFileSize bytes.
-func readFile(name string) ([]byte, error) {
-	f, err := syscall.Open(name, syscall.O_RDONLY, 0)
-	if err != nil {
-		return nil, err
-	}
-	defer syscall.Close(f)
-	var (
-		buf [4096]byte
-		ret []byte
-		n   int
-	)
-	for {
-		n, err = syscall.Read(f, buf[:])
-		if n > 0 {
-			ret = append(ret, buf[:n]...)
-		}
-		if n == 0 || err != nil {
-			break
-		}
-		if len(ret) > maxFileSize {
-			return nil, fileSizeError(name)
-		}
-	}
-	return ret, err
-}
-
 func open(name string) (uintptr, error) {
 	fd, err := syscall.Open(name, syscall.O_RDONLY, 0)
 	if err != nil {
@@ -54,6 +24,10 @@ func open(name string) (uintptr, error) {
 	return uintptr(fd), nil
 }
 
+func read(fd uintptr, buf []byte) (int, error) {
+	return syscall.Read(int(fd), buf)
+}
+
 func closefd(fd uintptr) {
 	syscall.Close(int(fd))
 }

src/time/sys_windows.go

@@ -13,36 +13,6 @@ import (
 func interrupt() {
 }
 
-// readFile reads and returns the content of the named file.
-// It is a trivial implementation of ioutil.ReadFile, reimplemented
-// here to avoid depending on io/ioutil or os.
-// It returns an error if name exceeds maxFileSize bytes.
-func readFile(name string) ([]byte, error) {
-	f, err := syscall.Open(name, syscall.O_RDONLY, 0)
-	if err != nil {
-		return nil, err
-	}
-	defer syscall.Close(f)
-	var (
-		buf [4096]byte
-		ret []byte
-		n   int
-	)
-	for {
-		n, err = syscall.Read(f, buf[:])
-		if n > 0 {
-			ret = append(ret, buf[:n]...)
-		}
-		if n == 0 || err != nil {
-			break
-		}
-		if len(ret) > maxFileSize {
-			return nil, fileSizeError(name)
-		}
-	}
-	return ret, err
-}
-
 func open(name string) (uintptr, error) {
 	fd, err := syscall.Open(name, syscall.O_RDONLY, 0)
 	if err != nil {
@@ -51,6 +21,10 @@ func open(name string) (uintptr, error) {
 	return uintptr(fd), nil
 }
 
+func read(fd uintptr, buf []byte) (int, error) {
+	return syscall.Read(syscall.Handle(fd), buf)
+}
+
 func closefd(fd uintptr) {
 	syscall.Close(syscall.Handle(fd))
 }

src/time/zoneinfo_read.go

@@ -403,3 +403,33 @@ func loadLocation(name string, sources []string) (z *Location, firstErr error) {
 	}
 	return nil, errors.New("unknown time zone " + name)
 }
+
+// readFile reads and returns the content of the named file.
+// It is a trivial implementation of ioutil.ReadFile, reimplemented
+// here to avoid depending on io/ioutil or os.
+// It returns an error if name exceeds maxFileSize bytes.
+func readFile(name string) ([]byte, error) {
+	f, err := open(name)
+	if err != nil {
+		return nil, err
+	}
+	defer closefd(f)
+	var (
+		buf [4096]byte
+		ret []byte
+		n   int
+	)
+	for {
+		n, err = read(f, buf[:])
+		if n > 0 {
+			ret = append(ret, buf[:n]...)
+		}
+		if n == 0 || err != nil {
+			break
+		}
+		if len(ret) > maxFileSize {
+			return nil, fileSizeError(name)
+		}
+	}
+	return ret, err
+}