cgo_listgroups_unix.go

     1  // Copyright 2016 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  //go:build (cgo || darwin) && !osusergo && (darwin || dragonfly || freebsd || (linux && !android) || netbsd || openbsd || (solaris && !illumos))
     6  
     7  package user
     8  
     9  import (
    10  	"fmt"
    11  	"strconv"
    12  	"unsafe"
    13  )
    14  
    15  const maxGroups = 2048
    16  
    17  func listGroups(u *User) ([]string, error) {
    18  	ug, err := strconv.Atoi(u.Gid)
    19  	if err != nil {
    20  		return nil, fmt.Errorf("user: list groups for %s: invalid gid %q", u.Username, u.Gid)
    21  	}
    22  	userGID := _C_gid_t(ug)
    23  	nameC := make([]byte, len(u.Username)+1)
    24  	copy(nameC, u.Username)
    25  
    26  	n := _C_int(256)
    27  	gidsC := make([]_C_gid_t, n)
    28  	rv := getGroupList((*_C_char)(unsafe.Pointer(&nameC[0])), userGID, &gidsC[0], &n)
    29  	if rv == -1 {
    30  		// Mac is the only Unix that does not set n properly when rv == -1, so
    31  		// we need to use different logic for Mac vs. the other OS's.
    32  		if err := groupRetry(u.Username, nameC, userGID, &gidsC, &n); err != nil {
    33  			return nil, err
    34  		}
    35  	}
    36  	gidsC = gidsC[:n]
    37  	gids := make([]string, 0, n)
    38  	for _, g := range gidsC[:n] {
    39  		gids = append(gids, strconv.Itoa(int(g)))
    40  	}
    41  	return gids, nil
    42  }
    43  
    44  // groupRetry retries getGroupList with much larger size for n. The result is
    45  // stored in gids.
    46  func groupRetry(username string, name []byte, userGID _C_gid_t, gids *[]_C_gid_t, n *_C_int) error {
    47  	// More than initial buffer, but now n contains the correct size.
    48  	if *n > maxGroups {
    49  		return fmt.Errorf("user: %q is a member of more than %d groups", username, maxGroups)
    50  	}
    51  	*gids = make([]_C_gid_t, *n)
    52  	rv := getGroupList((*_C_char)(unsafe.Pointer(&name[0])), userGID, &(*gids)[0], n)
    53  	if rv == -1 {
    54  		return fmt.Errorf("user: list groups for %s failed", username)
    55  	}
    56  	return nil
    57  }
    58
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