refactor: Split dbwrapper CDBWrapper::Exists implementation

Keep the generic serialization in the header, while moving
leveldb-specifics to the implementation file.

The context of this commit is an effort to decouple the dbwrapper header
file from leveldb includes. To this end, the includes are moved to the
dbwrapper implementation file. This is done as part of the kernel
project to reduce the number of required includes for users of the
kernel.

Author: TheCharlatan

src/dbwrapper.cpp

@@ -313,6 +313,21 @@ std::optional<std::string> CDBWrapper::ReadImpl(Span<const std::byte> ssKey) con
     return strValue;
 }
 
+bool CDBWrapper::ExistsImpl(Span<const std::byte> ssKey) const
+{
+    leveldb::Slice slKey(CharCast(ssKey.data()), ssKey.size());
+
+    std::string strValue;
+    leveldb::Status status = pdb->Get(readoptions, slKey, &strValue);
+    if (!status.ok()) {
+        if (status.IsNotFound())
+            return false;
+        LogPrintf("LevelDB read failure: %s\n", status.ToString());
+        dbwrapper_private::HandleError(status);
+    }
+    return true;
+}
+
 bool CDBWrapper::IsEmpty()
 {
     std::unique_ptr<CDBIterator> it(NewIterator());

src/dbwrapper.h

@@ -6,7 +6,6 @@
 #define BITCOIN_DBWRAPPER_H
 
 #include <clientversion.h>
-#include <logging.h>
 #include <serialize.h>
 #include <span.h>
 #include <streams.h>
@@ -18,14 +17,14 @@
 #include <leveldb/db.h>
 #include <leveldb/options.h>
 #include <leveldb/slice.h>
-#include <leveldb/status.h>
 #include <memory>
 #include <optional>
 #include <stdexcept>
 #include <string>
 #include <vector>
 namespace leveldb {
 class Env;
+class Status;
 }
 
 static const size_t DBWRAPPER_PREALLOC_KEY_SIZE = 64;
@@ -236,6 +235,7 @@ class CDBWrapper
     bool m_is_memory;
 
     std::optional<std::string> ReadImpl(Span<const std::byte> ssKey) const;
+    bool ExistsImpl(Span<const std::byte> ssKey) const;
 
 public:
     CDBWrapper(const DBParams& params);
@@ -286,17 +286,7 @@ class CDBWrapper
         DataStream ssKey{};
         ssKey.reserve(DBWRAPPER_PREALLOC_KEY_SIZE);
         ssKey << key;
-        leveldb::Slice slKey(CharCast(ssKey.data()), ssKey.size());
-
-        std::string strValue;
-        leveldb::Status status = pdb->Get(readoptions, slKey, &strValue);
-        if (!status.ok()) {
-            if (status.IsNotFound())
-                return false;
-            LogPrintf("LevelDB read failure: %s\n", status.ToString());
-            dbwrapper_private::HandleError(status);
-        }
-        return true;
+        return ExistsImpl(ssKey);
     }
 
     template <typename K>