NullPtr: Change SAPI to accept regular `nullptr` for sandboxed API calls.

This change allows to use a `nullptr` instead to having to instantiate a `sapi::v::NullPtr` object.

```
sapi::v::NullPtr null;
SAPI_RETURN_IF_ERROR(api.testNullPtr(&null);
```

Becomes:

```
SAPI_RETURN_IF_ERROR(api.testNullPtr(nullptr);
```

PiperOrigin-RevId: 602333882
Change-Id: Ie2517dbedab8c514d7a102c4ef4bad90b34a219d

2 files changed, 15 insertions, 3 deletions

diff --git a/sandboxed_api/sandbox.cc b/sandboxed_api/sandbox.cc
index 5541b75..02cc51c 100644
--- a/sandboxed_api/sandbox.cc
+++ b/sandboxed_api/sandbox.cc
@@ -324,6 +324,14 @@ absl::Status Sandbox::Call(const std::string& func, v::Callable* ret,
   // Copy all arguments into rfcall.
   int i = 0;
   for (auto* arg : args) {
+    if (arg == nullptr) {
+      rfcall.arg_type[i] = v::Type::kPointer;
+      rfcall.arg_size[i] = sizeof(void*);
+      rfcall.args[i].arg_int = 0;
+      VLOG(1) << "CALL ARG: (" << i << "): nullptr";
+      ++i;
+      continue;
+    }
     rfcall.arg_size[i] = arg->GetSize();
     rfcall.arg_type[i] = arg->GetType();
 
@@ -357,7 +365,6 @@ absl::Status Sandbox::Call(const std::string& func, v::Callable* ret,
       }
       rfcall.args[i].arg_int = fd->GetRemoteFd();
     }
-
     VLOG(1) << "CALL ARG: (" << i << "), Type: " << arg->GetTypeString()
             << ", Size: " << arg->GetSize() << ", Val: " << arg->ToString();
     ++i;
@@ -382,7 +389,9 @@ absl::Status Sandbox::Call(const std::string& func, v::Callable* ret,
 
   // Synchronize all pointers after the call if it's needed.
   for (auto* arg : args) {
-    SAPI_RETURN_IF_ERROR(SynchronizePtrAfter(arg));
+    if (arg != nullptr) {
+      SAPI_RETURN_IF_ERROR(SynchronizePtrAfter(arg));
+    }
   }
 
   VLOG(1) << "CALL EXIT: Type: " << ret->GetTypeString()
diff --git a/sandboxed_api/var_ptr.h b/sandboxed_api/var_ptr.h
index ad2568c..2c9894f 100644
--- a/sandboxed_api/var_ptr.h
+++ b/sandboxed_api/var_ptr.h
@@ -20,6 +20,7 @@
 #include <memory>
 #include <string>
 
+#include "absl/base/attributes.h"
 #include "absl/base/macros.h"
 #include "absl/strings/str_format.h"
 #include "sandboxed_api/var_abstract.h"
@@ -79,7 +80,9 @@ class Ptr : public Reg<Var*> {
 };
 
 // Good, old nullptr
-class NullPtr : public Ptr {
+class ABSL_DEPRECATED(
+    "Use regular `nullptr` or `NULL` instead. This class will eventually get "
+    "removed") NullPtr : public Ptr {
  public:
   NullPtr() : Ptr(&void_obj_, SyncType::kSyncNone) {}