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);
+    }
+}