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"
+
+// LookupId looks up a user by username. If the user isn't found,

[r, 2011/04/21 20:39:32]

s/isn't/cannot be/ here and below

+// os.ENOENT is returned.

[r, 2011/04/21 20:39:32]

is this overspecifying the error return?  we usually don't document so
specifically.

+func Lookup(username string) (*User, os.Error) {
+        return lookup(-1, username, true)
+}
+
+// LookupId looks up a user by userid. If the user isn't found,
+// os.ENOENT is returned.
+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 {

[r, 2011/04/21 20:39:32]

this test can go up a line

+                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)
+        } 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: getpwuid_r returned %d", rv)
+        }
+        if result == nil {
+                return nil, os.ENOENT
+        }
+        u := &User{
+                Uid:           int(pwd.pw_uid),
+                Gid:           int(pwd.pw_gid),
+                Username:      C.GoString(pwd.pw_name),
+                Name:          C.GoString(pwd.pw_gecos),
+                HomeDirectory: C.GoString(pwd.pw_dir),
+        }
+        // The pw_gecos field isn't quite standardized.  Some docs
+        // says: "It is expected to be a comma separated list of
+        // personal data where the first item is the full name of the
+        // user."
+        if strings.Contains(u.Name, ",") {
+                sp := strings.Split(u.Name, ",", 2)
+                u.Name = sp[0]
+        }
+        return u, nil
+}