1 files changed, 200 insertions, 0 deletions
diff --git a/src/os/user/cgo_lookup_unix.go b/src/os/user/cgo_lookup_unix.go
new file mode 100644
index 0000000..402429b
--- /dev/null
+++ b/src/os/user/cgo_lookup_unix.go
@@ -0,0 +1,200 @@
+// Copyright 2011 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build (cgo || darwin) && !osusergo && unix && !android
+
+package user
+
+import (
+	"fmt"
+	"runtime"
+	"strconv"
+	"strings"
+	"syscall"
+	"unsafe"
+)
+
+func current() (*User, error) {
+	return lookupUnixUid(syscall.Getuid())
+}
+
+func lookupUser(username string) (*User, error) {
+	var pwd _C_struct_passwd
+	var found bool
+	nameC := make([]byte, len(username)+1)
+	copy(nameC, username)
+
+	err := retryWithBuffer(userBuffer, func(buf []byte) syscall.Errno {
+		var errno syscall.Errno
+		pwd, found, errno = _C_getpwnam_r((*_C_char)(unsafe.Pointer(&nameC[0])),
+			(*_C_char)(unsafe.Pointer(&buf[0])), _C_size_t(len(buf)))
+		return errno
+	})
+	if err != nil {
+		return nil, fmt.Errorf("user: lookup username %s: %v", username, err)
+	}
+	if !found {
+		return nil, UnknownUserError(username)
+	}
+	return buildUser(&pwd), err
+}
+
+func lookupUserId(uid string) (*User, error) {
+	i, e := strconv.Atoi(uid)
+	if e != nil {
+		return nil, e
+	}
+	return lookupUnixUid(i)
+}
+
+func lookupUnixUid(uid int) (*User, error) {
+	var pwd _C_struct_passwd
+	var found bool
+
+	err := retryWithBuffer(userBuffer, func(buf []byte) syscall.Errno {
+		var errno syscall.Errno
+		pwd, found, errno = _C_getpwuid_r(_C_uid_t(uid),
+			(*_C_char)(unsafe.Pointer(&buf[0])), _C_size_t(len(buf)))
+		return errno
+	})
+	if err != nil {
+		return nil, fmt.Errorf("user: lookup userid %d: %v", uid, err)
+	}
+	if !found {
+		return nil, UnknownUserIdError(uid)
+	}
+	return buildUser(&pwd), nil
+}
+
+func buildUser(pwd *_C_struct_passwd) *User {
+	u := &User{
+		Uid:      strconv.FormatUint(uint64(_C_pw_uid(pwd)), 10),
+		Gid:      strconv.FormatUint(uint64(_C_pw_gid(pwd)), 10),
+		Username: _C_GoString(_C_pw_name(pwd)),
+		Name:     _C_GoString(_C_pw_gecos(pwd)),
+		HomeDir:  _C_GoString(_C_pw_dir(pwd)),
+	}
+	// The pw_gecos field isn't quite standardized. Some docs
+	// say: "It is expected to be a comma separated list of
+	// personal data where the first item is the full name of the
+	// user."
+	u.Name, _, _ = strings.Cut(u.Name, ",")
+	return u
+}
+
+func lookupGroup(groupname string) (*Group, error) {
+	var grp _C_struct_group
+	var found bool
+
+	cname := make([]byte, len(groupname)+1)
+	copy(cname, groupname)
+
+	err := retryWithBuffer(groupBuffer, func(buf []byte) syscall.Errno {
+		var errno syscall.Errno
+		grp, found, errno = _C_getgrnam_r((*_C_char)(unsafe.Pointer(&cname[0])),
+			(*_C_char)(unsafe.Pointer(&buf[0])), _C_size_t(len(buf)))
+		return errno
+	})
+	if err != nil {
+		return nil, fmt.Errorf("user: lookup groupname %s: %v", groupname, err)
+	}
+	if !found {
+		return nil, UnknownGroupError(groupname)
+	}
+	return buildGroup(&grp), nil
+}
+
+func lookupGroupId(gid string) (*Group, error) {
+	i, e := strconv.Atoi(gid)
+	if e != nil {
+		return nil, e
+	}
+	return lookupUnixGid(i)
+}
+
+func lookupUnixGid(gid int) (*Group, error) {
+	var grp _C_struct_group
+	var found bool
+
+	err := retryWithBuffer(groupBuffer, func(buf []byte) syscall.Errno {
+		var errno syscall.Errno
+		grp, found, errno = _C_getgrgid_r(_C_gid_t(gid),
+			(*_C_char)(unsafe.Pointer(&buf[0])), _C_size_t(len(buf)))
+		return syscall.Errno(errno)
+	})
+	if err != nil {
+		return nil, fmt.Errorf("user: lookup groupid %d: %v", gid, err)
+	}
+	if !found {
+		return nil, UnknownGroupIdError(strconv.Itoa(gid))
+	}
+	return buildGroup(&grp), nil
+}
+
+func buildGroup(grp *_C_struct_group) *Group {
+	g := &Group{
+		Gid:  strconv.Itoa(int(_C_gr_gid(grp))),
+		Name: _C_GoString(_C_gr_name(grp)),
+	}
+	return g
+}
+
+type bufferKind _C_int
+
+var (
+	userBuffer  = bufferKind(_C__SC_GETPW_R_SIZE_MAX)
+	groupBuffer = bufferKind(_C__SC_GETGR_R_SIZE_MAX)
+)
+
+func (k bufferKind) initialSize() _C_size_t {
+	sz := _C_sysconf(_C_int(k))
+	if sz == -1 {
+		// DragonFly and FreeBSD do not have _SC_GETPW_R_SIZE_MAX.
+		// Additionally, not all Linux systems have it, either. For
+		// example, the musl libc returns -1.
+		return 1024
+	}
+	if !isSizeReasonable(int64(sz)) {
+		// Truncate.  If this truly isn't enough, retryWithBuffer will error on the first run.
+		return maxBufferSize
+	}
+	return _C_size_t(sz)
+}
+
+// retryWithBuffer repeatedly calls f(), increasing the size of the
+// buffer each time, until f succeeds, fails with a non-ERANGE error,
+// or the buffer exceeds a reasonable limit.
+func retryWithBuffer(kind bufferKind, f func([]byte) syscall.Errno) error {
+	buf := make([]byte, kind.initialSize())
+	for {
+		errno := f(buf)
+		if errno == 0 {
+			return nil
+		} else if runtime.GOOS == "aix" && errno+1 == 0 {
+			// On AIX getpwuid_r appears to return -1,
+			// not ERANGE, on buffer overflow.
+		} else if errno != syscall.ERANGE {
+			return errno
+		}
+		newSize := len(buf) * 2
+		if !isSizeReasonable(int64(newSize)) {
+			return fmt.Errorf("internal buffer exceeds %d bytes", maxBufferSize)
+		}
+		buf = make([]byte, newSize)
+	}
+}
+
+const maxBufferSize = 1 << 20
+
+func isSizeReasonable(sz int64) bool {
+	return sz > 0 && sz <= maxBufferSize
+}
+
+// Because we can't use cgo in tests:
+func structPasswdForNegativeTest() _C_struct_passwd {
+	sp := _C_struct_passwd{}
+	*_C_pw_uidp(&sp) = 1<<32 - 2
+	*_C_pw_gidp(&sp) = 1<<32 - 3
+	return sp
+}