os/Chown (#4213)

src/os, src/syscall: add os.Chown

Author: leongross

src/os/file_anyos.go

@@ -147,6 +147,20 @@ func Chmod(name string, mode FileMode) error {
 	return nil
 }
 
+// Chown changes the numeric uid and gid of the named file.
+// If the file is a symbolic link, it changes the uid and gid of the link's target.
+// A uid or gid of -1 means to not change that value.
+// If there is an error, it will be of type *PathError.
+func Chown(name string, uid, gid int) error {
+	e := ignoringEINTR(func() error {
+		return syscall.Chown(name, uid, gid)
+	})
+	if e != nil {
+		return &PathError{Op: "chown", Path: name, Err: e}
+	}
+	return nil
+}
+
 // ignoringEINTR makes a function call and repeats it if it returns an
 // EINTR error. This appears to be required even though we install all
 // signal handlers with SA_RESTART: see #22838, #38033, #38836, #40846.

src/os/os_chmod_test.go

@@ -9,12 +9,15 @@
 package os_test
 
 import (
+	"errors"
+	"io/fs"
 	. "os"
 	"runtime"
 	"testing"
 )
 
 func TestChmod(t *testing.T) {
+	// Chmod
 	f := newFile("TestChmod", t)
 	defer Remove(f.Name())
 	defer f.Close()
@@ -28,4 +31,42 @@ func TestChmod(t *testing.T) {
 		t.Fatalf("chmod %s %#o: %s", f.Name(), fm, err)
 	}
 	checkMode(t, f.Name(), fm)
+
+}
+
+// Since testing syscalls requires a static, predictable environment that has to be controlled
+// by the CI, we don't test for success but for failures and verify that the error messages are as expected.
+// EACCES is returned when the user does not have the required permissions to change the ownership of the file
+// ENOENT is returned when the file does not exist
+// ENOTDIR is returned when the file is not a directory
+func TestChownErr(t *testing.T) {
+	if runtime.GOOS == "windows" || runtime.GOOS == "plan9" {
+		t.Log("skipping on " + runtime.GOOS)
+		return
+	}
+
+	var (
+		TEST_UID_ROOT = 0
+		TEST_GID_ROOT = 0
+	)
+
+	f := newFile("TestChown", t)
+	defer Remove(f.Name())
+	defer f.Close()
+
+	// EACCES
+	if err := Chown(f.Name(), TEST_UID_ROOT, TEST_GID_ROOT); err != nil {
+		errCmp := fs.PathError{Op: "chown", Path: f.Name(), Err: errors.New("operation not permitted")}
+		if errors.Is(err, &errCmp) {
+			t.Fatalf("chown(%s, uid=%v, gid=%v): got '%v', want 'operation not permitted'", f.Name(), TEST_UID_ROOT, TEST_GID_ROOT, err)
+		}
+	}
+
+	// ENOENT
+	if err := Chown("invalid", Geteuid(), Getgid()); err != nil {
+		errCmp := fs.PathError{Op: "chown", Path: "invalid", Err: errors.New("no such file or directory")}
+		if errors.Is(err, &errCmp) {
+			t.Fatalf("chown(%s, uid=%v, gid=%v): got '%v', want 'no such file or directory'", f.Name(), Geteuid(), Getegid(), err)
+		}
+	}
 }

src/syscall/syscall_libc.go

@@ -163,6 +163,15 @@ func Unlink(path string) (err error) {
 	return
 }
 
+func Chown(path string, uid, gid int) (err error) {
+	data := cstring(path)
+	fail := int(libc_chown(&data[0], uid, gid))
+	if fail < 0 {
+		err = getErrno()
+	}
+	return
+}
+
 func Faccessat(dirfd int, path string, mode uint32, flags int) (err error)
 
 func Kill(pid int, sig Signal) (err error) {
@@ -357,6 +366,11 @@ func libc_chdir(pathname *byte) int32
 //export chmod
 func libc_chmod(pathname *byte, mode uint32) int32
 
+// int chown(const char *pathname, uid_t owner, gid_t group);
+//
+//export chown
+func libc_chown(pathname *byte, owner, group int) int32
+
 // int mkdir(const char *pathname, mode_t mode);
 //
 //export mkdir