code review 4440057: os/user: new package to look up users

src/pkg/os/user/lookup_unix.go

+// 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.
+
+package user
+
+import (
+        "fmt"
+        "os"
+        "runtime"
+        "strings"
+        "unsafe"
+)
+
+/*
+#include <unistd.h>
+#include <sys/types.h>
+#include <pwd.h>
+#include <stdlib.h>
+
+static int mygetpwuid_r(int uid, struct passwd *pwd,
+        char *buf, size_t buflen, struct passwd **result) {
+ return getpwuid_r(uid, pwd, buf, buflen, result);
+}
+*/
+import "C"
+
+// Lookup looks up a user by username. If the user cannot be found,
+// the returned error is of type UnknownUserError.
+func Lookup(username string) (*User, os.Error) {
+        return lookup(-1, username, true)
+}
+
+// LookupId looks up a user by userid. If the user cannot be found,
+// the returned error is of type UnknownUserIdError.
+func LookupId(uid int) (*User, os.Error) {
+        return lookup(uid, "", false)
+}
+
+func lookup(uid int, username string, lookupByName bool) (*User, os.Error) {
+        var pwd C.struct_passwd
+        var result *C.struct_passwd
+
+        var bufSize C.long
+        if runtime.GOOS == "freebsd" {
+                // FreeBSD doesn't have _SC_GETPW_R_SIZE_MAX
+                // and just returns -1.  So just use the same
+                // size that Linux returns
+                bufSize = 1024
+        } else {
+                bufSize = C.sysconf(C._SC_GETPW_R_SIZE_MAX)
+                if bufSize <= 0 || bufSize > 1<<20 {
+                        return nil, fmt.Errorf("user: unreasonable _SC_GETPW_R_SIZE_MAX of %d", bufSize)
+                }
+        }
+        buf := C.malloc(C.size_t(bufSize))
+        defer C.free(buf)
+        var rv C.int
+        if lookupByName {
+                nameC := C.CString(username)
+                defer C.free(unsafe.Pointer(nameC))
+                rv = C.getpwnam_r(nameC,
+                        &pwd,
+                        (*C.char)(buf),
+                        C.size_t(bufSize),
+                        &result)
+                if rv != 0 {
+                        return nil, fmt.Errorf("user: lookup username %s: %s", username, os.Errno(rv))
+                }
+                if result == nil {
+                        return nil, UnknownUserError(username)
+                }
+        } else {
+                // mygetpwuid_r is a wrapper around getpwuid_r to
+                // to avoid using uid_t because C.uid_t(uid) for
+                // unknown reasons doesn't work on linux.
+                rv = C.mygetpwuid_r(C.int(uid),
+                        &pwd,
+                        (*C.char)(buf),
+                        C.size_t(bufSize),
+                        &result)
+                if rv != 0 {
+                        return nil, fmt.Errorf("user: lookup userid %d: %s", uid, os.Errno(rv))
+                }
+                if result == nil {
+                        return nil, UnknownUserIdError(uid)
+                }
+        }
+        u := &User{
+                Uid:      int(pwd.pw_uid),
+                Gid:      int(pwd.pw_gid),
+                Username: C.GoString(pwd.pw_name),
+                Name:     C.GoString(pwd.pw_gecos),
+                HomeDir:  C.GoString(pwd.pw_dir),
+        }
+        // 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."
+        if i := strings.Index(u.Name, ","); i >= 0 {
+                u.Name = u.Name[:i]
+        }
+        return u, nil
+}