From 4cc41ea186cb3983466ff6103afa236312ca8ddd Mon Sep 17 00:00:00 2001
From: Brian Gianforcaro <bgianf@serenityos.org>
Date: Sat, 20 Nov 2021 00:40:57 -0800
Subject: [PATCH] Kernel: Add an error propagating KString::format(..) API :^)

In the continuous effort of better handling OOM in the kernel,
we want to move away from all AK::String usage. One of the final
pieces left to accomplish this goal is replacing all of the usages
of `String::formatted` with something that can actually propagate
failure.

The StringBuilder API was enhanced in the recent past to propagate
failure and thus a slightly modified version of what exists in
`AK::format` will work well for implementing failable format with
`KString`.
---
 Kernel/KString.cpp | 9 +++++++++
 Kernel/KString.h   | 9 +++++++++
 2 files changed, 18 insertions(+)

diff --git a/Kernel/KString.cpp b/Kernel/KString.cpp
index d20fd6e374..dbfad78d4c 100644
--- a/Kernel/KString.cpp
+++ b/Kernel/KString.cpp
@@ -4,6 +4,8 @@
  * SPDX-License-Identifier: BSD-2-Clause
  */
 
+#include <AK/Format.h>
+#include <AK/StringBuilder.h>
 #include <Kernel/KString.h>
 
 extern bool g_in_early_boot;
@@ -21,6 +23,13 @@ ErrorOr<NonnullOwnPtr<KString>> KString::try_create(StringView string)
     return new_string;
 }
 
+ErrorOr<NonnullOwnPtr<KString>> KString::vformatted(StringView fmtstr, AK::TypeErasedFormatParams& params)
+{
+    StringBuilder builder;
+    TRY(AK::vformat(builder, fmtstr, params));
+    return try_create(builder.string_view());
+}
+
 NonnullOwnPtr<KString> KString::must_create(StringView string)
 {
     // We can only enforce success during early boot.
diff --git a/Kernel/KString.h b/Kernel/KString.h
index e5ec4d0f79..ab4bc16b5d 100644
--- a/Kernel/KString.h
+++ b/Kernel/KString.h
@@ -21,6 +21,15 @@ public:
     [[nodiscard]] static ErrorOr<NonnullOwnPtr<KString>> try_create(StringView);
     [[nodiscard]] static NonnullOwnPtr<KString> must_create(StringView);
 
+    [[nodiscard]] static ErrorOr<NonnullOwnPtr<KString>> vformatted(StringView fmtstr, AK::TypeErasedFormatParams&);
+
+    template<typename... Parameters>
+    [[nodiscard]] static ErrorOr<NonnullOwnPtr<KString>> formatted(CheckedFormatString<Parameters...>&& fmtstr, const Parameters&... parameters)
+    {
+        AK::VariadicFormatParams variadic_format_parameters { parameters... };
+        return vformatted(fmtstr.view(), variadic_format_parameters);
+    }
+
     void operator delete(void*);
 
     ErrorOr<NonnullOwnPtr<KString>> try_clone() const;