LibC: Test behavior around overlong paths

This is what I used to write and evaluate my previous commits.

Userland/Tests/LibC/overlong_realpath.cpp

@@ -0,0 +1,114 @@
+/*
+ * Copyright (c) 2021, Ben Wiederhake <BenWiederhake.GitHub@gmx.de>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <AK/String.h>
+#include <AK/StringBuilder.h>
+#include <assert.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/stat.h>
+#include <unistd.h>
+
+// FIXME
+static const char* TEXT_FAIL = "\x1b[01;31m";
+static const char* TEXT_PASS = "\x1b[01;32m";
+static const char* TEXT_RESET = "\x1b[0m";
+
+static const char* TMPDIR_PATTERN = "/tmp/overlong_realpath_XXXXXX";
+static const char* PATH_LOREM_250 = "This-is-an-annoyingly-long-name-that-should-take-up-exactly-two-hundred-and-fifty-characters-and-is-surprisingly-difficult-to-fill-with-reasonably-meaningful-text-which-is-necessary-because-that-makes-it-easier-for-my-eyes-to-spot-any-corruption-fast";
+
+static const size_t ITERATION_DEPTH = 17;
+
+static bool check_result(const char* what, const String& expected, const char* actual)
+{
+    bool good = expected == actual;
+    printf("%s%s%s: %s = \"%s\" (%zu characters)\n", good ? TEXT_PASS : TEXT_FAIL, good ? "GOOD" : "FAIL", TEXT_RESET, what, actual, actual ? strlen(actual) : 0);
+    return good;
+}
+
+int main()
+{
+    // We want to construct a path that is over PATH_MAX characters long.
+    // This cannot be done in a single step.
+
+    // First, switch to a known environment:
+    char* tmp_dir = strdup("/tmp/overlong_realpath_XXXXXX");
+    if (!mkdtemp(tmp_dir)) {
+        perror("mkdtmp");
+        return 1;
+    }
+    if (chdir(tmp_dir) < 0) {
+        perror("chdir tmpdir");
+        return 1;
+    }
+
+    // Then, create a long path.
+    StringBuilder expected;
+    expected.append(tmp_dir);
+
+    // But first, demonstrate the functionality at a reasonable depth:
+    bool all_good = true;
+    auto expected_str = expected.build();
+    all_good &= check_result("getwd", expected_str, getwd(static_cast<char*>(calloc(1, PATH_MAX))));
+    all_good &= check_result("getcwd", expected_str, getcwd(nullptr, 0));
+    all_good &= check_result("realpath", expected_str, realpath(".", nullptr));
+
+    for (size_t i = 0; i < ITERATION_DEPTH; ++i) {
+        if (mkdir(PATH_LOREM_250, 0700) < 0) {
+            perror("mkdir iter");
+            printf("%sFAILED%s in iteration %zu.\n", TEXT_FAIL, TEXT_RESET, i);
+            return 1;
+        }
+        expected.append('/');
+        expected.append(PATH_LOREM_250);
+        if (chdir(PATH_LOREM_250) < 0) {
+            perror("chdir iter");
+            printf("%sFAILED%s in iteration %zu.\n", TEXT_FAIL, TEXT_RESET, i);
+            return 1;
+        }
+    }
+    printf("cwd should now be ridiculously large.\n");
+
+    // Evaluate
+    expected_str = expected.build();
+
+    all_good &= check_result("getwd", {}, getwd(static_cast<char*>(calloc(1, PATH_MAX))));
+    all_good &= check_result("getcwd", expected_str, getcwd(nullptr, 0));
+    all_good &= check_result("realpath", expected_str, realpath(".", nullptr));
+
+    ASSERT(strlen(PATH_LOREM_250) == 250);
+    ASSERT(strlen(TMPDIR_PATTERN) + ITERATION_DEPTH * (1 + strlen(PATH_LOREM_250)) == expected_str.length());
+    ASSERT(expected_str.length() > PATH_MAX);
+
+    if (all_good) {
+        printf("Overall: %sPASS%s\n", TEXT_PASS, TEXT_RESET);
+        return 0;
+    } else {
+        printf("Overall: %sFAIL%s\n", TEXT_FAIL, TEXT_RESET);
+        return 2;
+    }
+}