github.com/zxy12/golang_with_comment@v0.0.0-20190701084843-0e6b2aff5ef3/os/user/listgroups_unix.go (about)

     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  // +build dragonfly darwin freebsd !android,linux netbsd openbsd
     6  
     7  package user
     8  
     9  import (
    10  	"fmt"
    11  	"strconv"
    12  	"unsafe"
    13  )
    14  
    15  /*
    16  #include <unistd.h>
    17  #include <sys/types.h>
    18  #include <stdlib.h>
    19  */
    20  import "C"
    21  
    22  func listGroups(u *User) ([]string, error) {
    23  	ug, err := strconv.Atoi(u.Gid)
    24  	if err != nil {
    25  		return nil, fmt.Errorf("user: list groups for %s: invalid gid %q", u.Username, u.Gid)
    26  	}
    27  	userGID := C.gid_t(ug)
    28  	nameC := C.CString(u.Username)
    29  	defer C.free(unsafe.Pointer(nameC))
    30  
    31  	n := C.int(256)
    32  	gidsC := make([]C.gid_t, n)
    33  	rv := getGroupList(nameC, userGID, &gidsC[0], &n)
    34  	if rv == -1 {
    35  		// More than initial buffer, but now n contains the correct size.
    36  		const maxGroups = 2048
    37  		if n > maxGroups {
    38  			return nil, fmt.Errorf("user: list groups for %s: member of more than %d groups", u.Username, maxGroups)
    39  		}
    40  		gidsC = make([]C.gid_t, n)
    41  		rv := getGroupList(nameC, userGID, &gidsC[0], &n)
    42  		if rv == -1 {
    43  			return nil, fmt.Errorf("user: list groups for %s failed (changed groups?)", u.Username)
    44  		}
    45  	}
    46  	gidsC = gidsC[:n]
    47  	gids := make([]string, 0, n)
    48  	for _, g := range gidsC[:n] {
    49  		gids = append(gids, strconv.Itoa(int(g)))
    50  	}
    51  	return gids, nil
    52  }