LibC+Tests: Simplify getpwuid_r() and getpwnam_r() and add tests

These functions are now implemented in terms of getpwent_r() which
allows us to remove two FIXMEs about global variable shenanigans.

I'm also adding tests for both APIs. :^)

Tests/LibC/CMakeLists.txt

@@ -20,6 +20,7 @@ set(TEST_SOURCES
     TestPThreadPriority.cpp
     TestPthreadSpinLocks.cpp
     TestPthreadRWLocks.cpp
+    TestPwd.cpp
     TestQsort.cpp
     TestRaise.cpp
     TestRealpath.cpp

Tests/LibC/TestPwd.cpp

@@ -0,0 +1,118 @@
+/*
+ * Copyright (c) 2022, Andreas Kling <kling@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <LibTest/TestCase.h>
+
+#include <AK/Vector.h>
+#include <pwd.h>
+
+struct PasswdEntry {
+    String name;
+    uid_t uid {};
+};
+
+static Vector<PasswdEntry> get_all_passwd_entries()
+{
+    Vector<PasswdEntry> entries;
+    setpwent();
+    while (auto* pwd = getpwent()) {
+        entries.append(PasswdEntry {
+            .name = pwd->pw_name,
+            .uid = pwd->pw_uid,
+        });
+    }
+    return entries;
+}
+
+TEST_CASE(getpwuid_r)
+{
+    // Verify that all known passwd entries can be found with getpwuid_r()
+    for (auto const& entry : get_all_passwd_entries()) {
+        struct passwd pwd_buffer = {};
+        char buffer[4096] = {};
+        struct passwd* result = nullptr;
+        auto rc = getpwuid_r(entry.uid, &pwd_buffer, buffer, sizeof(buffer), &result);
+        EXPECT_EQ(rc, 0);
+        EXPECT_EQ(entry.uid, result->pw_uid);
+        EXPECT_EQ(entry.name, result->pw_name);
+    }
+
+    // Verify that a bogus UID can't be found with getpwuid_r()
+    {
+        struct passwd pwd_buffer = {};
+        char buffer[4096] = {};
+        struct passwd* result = nullptr;
+        auto rc = getpwuid_r(99991999, &pwd_buffer, buffer, sizeof(buffer), &result);
+        EXPECT_EQ(rc, ENOENT);
+        EXPECT_EQ(result, nullptr);
+    }
+
+    // Verify that two calls to getpwuid_r() don't clobber each other.
+    {
+        struct passwd pwd_buffer1 = {};
+        char buffer1[4096] = {};
+        struct passwd* result1 = nullptr;
+        auto rc1 = getpwuid_r(0, &pwd_buffer1, buffer1, sizeof(buffer1), &result1);
+        EXPECT_EQ(rc1, 0);
+        EXPECT_NE(result1, nullptr);
+        EXPECT_EQ(result1, &pwd_buffer1);
+
+        struct passwd pwd_buffer2 = {};
+        char buffer2[4096] = {};
+        struct passwd* result2 = nullptr;
+        auto rc2 = getpwuid_r(0, &pwd_buffer2, buffer2, sizeof(buffer2), &result2);
+        EXPECT_EQ(rc2, 0);
+        EXPECT_NE(result2, nullptr);
+        EXPECT_EQ(result2, &pwd_buffer2);
+
+        EXPECT_NE(result1, result2);
+    }
+}
+
+TEST_CASE(getpwnam_r)
+{
+    // Verify that all known passwd entries can be found with getpwnam_r()
+    for (auto const& entry : get_all_passwd_entries()) {
+        struct passwd pwd_buffer = {};
+        char buffer[4096] = {};
+        struct passwd* result = nullptr;
+        auto rc = getpwnam_r(entry.name.characters(), &pwd_buffer, buffer, sizeof(buffer), &result);
+        EXPECT_EQ(rc, 0);
+        EXPECT_EQ(entry.uid, result->pw_uid);
+        EXPECT_EQ(entry.name, result->pw_name);
+    }
+
+    // Verify that a bogus name can't be found with getpwnam_r()
+    {
+        struct passwd pwd_buffer = {};
+        char buffer[4096] = {};
+        struct passwd* result = nullptr;
+        auto rc = getpwnam_r("99991999", &pwd_buffer, buffer, sizeof(buffer), &result);
+        EXPECT_EQ(rc, ENOENT);
+        EXPECT_EQ(result, nullptr);
+    }
+
+    // Verify that two calls to getpwnam_r() don't clobber each other.
+    {
+        struct passwd pwd_buffer1 = {};
+        char buffer1[4096] = {};
+        struct passwd* result1 = nullptr;
+        auto rc1 = getpwnam_r("root", &pwd_buffer1, buffer1, sizeof(buffer1), &result1);
+        EXPECT_EQ(rc1, 0);
+        EXPECT_NE(result1, nullptr);
+        EXPECT_EQ(result1, &pwd_buffer1);
+
+        struct passwd pwd_buffer2 = {};
+        char buffer2[4096] = {};
+        struct passwd* result2 = nullptr;
+        auto rc2 = getpwnam_r("root", &pwd_buffer2, buffer2, sizeof(buffer2), &result2);
+        EXPECT_EQ(rc2, 0);
+        EXPECT_NE(result2, nullptr);
+        EXPECT_EQ(result2, &pwd_buffer2);
+
+        EXPECT_NE(result1, result2);
+    }
+}

Userland/Libraries/LibC/pwd.cpp

@@ -20,12 +20,6 @@ extern "C" {
 static FILE* s_stream = nullptr;
 static unsigned s_line_number = 0;
 
-static String s_name;
-static String s_passwd;
-static String s_gecos;
-static String s_dir;
-static String s_shell;
-
 void setpwent()
 {
     s_line_number = 0;
@@ -163,91 +157,28 @@ int getpwent_r(struct passwd* passwd_buf, char* buffer, size_t buffer_size, stru
     }
 }
 
-static void construct_pwd(struct passwd* pwd, char* buf, struct passwd** result)
-{
-    auto* buf_name = &buf[0];
-    auto* buf_passwd = &buf[s_name.length() + 1];
-    auto* buf_gecos = &buf[s_name.length() + 1 + s_gecos.length() + 1];
-    auto* buf_dir = &buf[s_gecos.length() + 1 + s_name.length() + 1 + s_gecos.length() + 1];
-    auto* buf_shell = &buf[s_dir.length() + 1 + s_gecos.length() + 1 + s_name.length() + 1 + s_gecos.length() + 1];
-
-    bool ok = true;
-    ok = ok && s_name.copy_characters_to_buffer(buf_name, s_name.length() + 1);
-    ok = ok && s_passwd.copy_characters_to_buffer(buf_passwd, s_passwd.length() + 1);
-    ok = ok && s_gecos.copy_characters_to_buffer(buf_gecos, s_gecos.length() + 1);
-    ok = ok && s_dir.copy_characters_to_buffer(buf_dir, s_dir.length() + 1);
-    ok = ok && s_shell.copy_characters_to_buffer(buf_shell, s_shell.length() + 1);
-
-    VERIFY(ok);
-
-    *result = pwd;
-    pwd->pw_name = buf_name;
-    pwd->pw_passwd = buf_passwd;
-    pwd->pw_gecos = buf_gecos;
-    pwd->pw_dir = buf_dir;
-    pwd->pw_shell = buf_shell;
-}
-
-int getpwnam_r(char const* name, struct passwd* pwd, char* buf, size_t buflen, struct passwd** result)
+// https://pubs.opengroup.org/onlinepubs/9699919799/functions/getpwnam.html
+int getpwnam_r(char const* name, struct passwd* pwd, char* buffer, size_t bufsize, struct passwd** result)
 {
-    // FIXME: This is a HACK!
-    TemporaryChange name_change { s_name, {} };
-    TemporaryChange passwd_change { s_passwd, {} };
-    TemporaryChange gecos_change { s_gecos, {} };
-    TemporaryChange dir_change { s_dir, {} };
-    TemporaryChange shell_change { s_shell, {} };
-
     setpwent();
-    bool found = false;
-    while (auto* pw = getpwent()) {
-        if (!strcmp(pw->pw_name, name)) {
-            found = true;
-            break;
-        }
-    }
-
-    if (!found) {
-        *result = nullptr;
-        return 0;
+    for (;;) {
+        if (auto rc = getpwent_r(pwd, buffer, bufsize, result); rc != 0)
+            return rc;
+        if (strcmp(pwd->pw_name, name) == 0)
+            return 0;
     }
-
-    auto const total_buffer_length = s_name.length() + s_passwd.length() + s_gecos.length() + s_dir.length() + s_shell.length() + 5;
-    if (buflen < total_buffer_length)
-        return ERANGE;
-
-    construct_pwd(pwd, buf, result);
-    return 0;
 }
 
-int getpwuid_r(uid_t uid, struct passwd* pwd, char* buf, size_t buflen, struct passwd** result)
+// https://pubs.opengroup.org/onlinepubs/9699919799/functions/getpwuid.html
+int getpwuid_r(uid_t uid, struct passwd* pwd, char* buffer, size_t bufsize, struct passwd** result)
 {
-    // FIXME: This is a HACK!
-    TemporaryChange name_change { s_name, {} };
-    TemporaryChange passwd_change { s_passwd, {} };
-    TemporaryChange gecos_change { s_gecos, {} };
-    TemporaryChange dir_change { s_dir, {} };
-    TemporaryChange shell_change { s_shell, {} };
-
     setpwent();
-    bool found = false;
-    while (auto* pw = getpwent()) {
-        if (pw->pw_uid == uid) {
-            found = true;
-            break;
-        }
-    }
-
-    if (!found) {
-        *result = nullptr;
-        return 0;
+    for (;;) {
+        if (auto rc = getpwent_r(pwd, buffer, bufsize, result); rc != 0)
+            return rc;
+        if (pwd->pw_uid == uid)
+            return 0;
     }
-
-    auto const total_buffer_length = s_name.length() + s_passwd.length() + s_gecos.length() + s_dir.length() + s_shell.length() + 5;
-    if (buflen < total_buffer_length)
-        return ERANGE;
-
-    construct_pwd(pwd, buf, result);
-    return 0;
 }
 
 int putpwent(const struct passwd* p, FILE* stream)