LibCore: Introduce Core::Environment wrapper

Core::System already had some wrappers for *env() functions, which I've
copied over. But 1) the set of functions there was incomplete, and 2)
the environment feels like an object in its own right, so let's treat it
as one. :^)

Also add `Core::Environment::has(StringView)` for situations where we
just care if a variable is defined.

Userland/Libraries/LibCore/Environment.cpp

@@ -0,0 +1,169 @@
+/*
+ * Copyright (c) 2021-2022, Andreas Kling <kling@serenityos.org>
+ * Copyright (c) 2021-2022, Kenneth Myhra <kennethmyhra@serenityos.org>
+ * Copyright (c) 2021-2024, Sam Atkins <atkinssj@serenityos.org>
+ * Copyright (c) 2022, Matthias Zimmerman <matthias291999@gmail.com>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include "Environment.h"
+#include <AK/ByteString.h>
+
+#if defined(AK_OS_MACOS)
+#    include <crt_externs.h>
+#else
+extern char** environ;
+#endif
+
+namespace Core::Environment {
+
+char** raw_environ()
+{
+#if defined(AK_OS_MACOS)
+    return *_NSGetEnviron();
+#else
+    return environ;
+#endif
+}
+
+Entry Entry::from_chars(char const* input)
+{
+    return Entry::from_string({ input, strlen(input) });
+}
+
+Entry Entry::from_string(StringView input)
+{
+    auto split_index = input.find('=');
+    if (!split_index.has_value()) {
+        return Entry {
+            .full_entry = input,
+            .name = input,
+            .value = ""sv,
+        };
+    }
+
+    return Entry {
+        .full_entry = input,
+        .name = input.substring_view(0, *split_index),
+        .value = input.substring_view(*split_index + 1),
+    };
+}
+
+EntryIterator EntryIterator::begin()
+{
+    return EntryIterator(0);
+}
+
+EntryIterator EntryIterator::end()
+{
+    auto environment = raw_environ();
+
+    size_t env_count = 0;
+    for (size_t i = 0; environment[i]; ++i)
+        ++env_count;
+    return EntryIterator(env_count);
+}
+
+EntryIterator entries()
+{
+    return EntryIterator::begin();
+}
+
+size_t size()
+{
+    auto environment = raw_environ();
+
+    size_t environ_size = 0;
+    while (environment[environ_size])
+        ++environ_size;
+
+    return environ_size;
+}
+
+bool has(StringView name)
+{
+    return get(name).has_value();
+}
+
+Optional<StringView> get(StringView name, [[maybe_unused]] SecureOnly secure)
+{
+    StringBuilder builder;
+    builder.append(name);
+    builder.append('\0');
+    // Note the explicit null terminators above.
+
+#if defined(AK_OS_MACOS)
+    char* result = ::getenv(builder.string_view().characters_without_null_termination());
+#else
+    char* result;
+    if (secure == SecureOnly::Yes) {
+        result = ::secure_getenv(builder.string_view().characters_without_null_termination());
+    } else {
+        result = ::getenv(builder.string_view().characters_without_null_termination());
+    }
+#endif
+    if (result)
+        return StringView { result, strlen(result) };
+    return {};
+}
+
+ErrorOr<void> set(StringView name, StringView value, Overwrite overwrite)
+{
+    auto builder = TRY(StringBuilder::create());
+    TRY(builder.try_append(name));
+    TRY(builder.try_append('\0'));
+    TRY(builder.try_append(value));
+    TRY(builder.try_append('\0'));
+    // Note the explicit null terminators above.
+    auto c_name = builder.string_view().characters_without_null_termination();
+    auto c_value = c_name + name.length() + 1;
+    auto rc = ::setenv(c_name, c_value, overwrite == Overwrite::Yes ? 1 : 0);
+    if (rc < 0)
+        return Error::from_errno(errno);
+    return {};
+}
+
+ErrorOr<void> unset(StringView name)
+{
+    auto builder = TRY(StringBuilder::create());
+    TRY(builder.try_append(name));
+    TRY(builder.try_append('\0'));
+
+    // Note the explicit null terminator above.
+    auto rc = ::unsetenv(builder.string_view().characters_without_null_termination());
+    if (rc < 0)
+        return Error::from_errno(errno);
+    return {};
+}
+
+ErrorOr<void> put(StringView env)
+{
+#if defined(AK_OS_SERENITY)
+    auto rc = ::serenity_putenv(env.characters_without_null_termination(), env.length());
+#else
+    // Leak somewhat unavoidable here due to the putenv API.
+    auto leaked_new_env = strndup(env.characters_without_null_termination(), env.length());
+    auto rc = ::putenv(leaked_new_env);
+#endif
+    if (rc < 0)
+        return Error::from_errno(errno);
+    return {};
+}
+
+ErrorOr<void> clear()
+{
+#if defined(AK_OS_MACOS)
+    auto environment = raw_environ();
+    for (size_t environ_size = 0; environment[environ_size]; ++environ_size) {
+        environment[environ_size] = NULL;
+    }
+#else
+    auto rc = ::clearenv();
+    if (rc < 0)
+        return Error::from_errno(errno);
+#endif
+    return {};
+}
+
+}