refactor: Add Reader class for CDBWrapper::Read

sedited · sedited · commit 6005165242cf · 2023-07-30T13:59:17.000+02:00
This wraps manipulating the data streams for reading and writing the db
keys and values in a class such that these can be used without
specifying template arguments by the dbwrapper implementation.

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.
diff --git a/src/dbwrapper.cpp b/src/dbwrapper.cpp
@@ -10,7 +10,6 @@
 #include <serialize.h>
 #include <span.h>
 #include <streams.h>
-#include <tinyformat.h>
 #include <util/fs.h>
 #include <util/fs_helpers.h>
 #include <util/strencodings.h>
@@ -301,6 +300,31 @@ std::vector<unsigned char> CDBWrapper::CreateObfuscateKey() const
     return ret;
 }
 
+bool CDBWrapper::ReadImpl(CDBWrapper::ReaderBase& reader) const
+{
+    DataStream ssKey{};
+    ssKey.reserve(DBWRAPPER_PREALLOC_KEY_SIZE);
+    reader.WriteKeyToStream(ssKey);
+    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);
+    }
+    try {
+        CDataStream ssValue{MakeByteSpan(strValue), SER_DISK, CLIENT_VERSION};
+        ssValue.Xor(obfuscate_key);
+        reader.ReadValueFromStream(ssValue);
+    } catch (const std::exception&) {
+        return false;
+    }
+    return true;
+}
+
 bool CDBWrapper::IsEmpty()
 {
     std::unique_ptr<CDBIterator> it(NewIterator());
diff --git a/src/dbwrapper.h b/src/dbwrapper.h
@@ -232,6 +232,36 @@ class CDBWrapper
     //! whether or not the database resides in memory
     bool m_is_memory;
 
+    class ReaderBase
+    {
+    public:
+        virtual void ReadValueFromStream(CDataStream& ssValue) = 0;
+        virtual void WriteKeyToStream(DataStream& ssKey) = 0;
+    };
+
+    template <typename K, typename V>
+    class Reader : public ReaderBase
+    {
+    private:
+        const K& key;
+        V& value;
+
+    public:
+        Reader(const K& key, V& value) : key{key}, value{value} {}
+
+        void ReadValueFromStream(CDataStream& ssValue) override
+        {
+            ssValue >> value;
+        }
+
+        void WriteKeyToStream(DataStream& ssKey) override
+        {
+            ssKey << key;
+        }
+    };
+
+    bool ReadImpl(ReaderBase& reader) const;
+
 public:
     CDBWrapper(const DBParams& params);
     ~CDBWrapper();
@@ -242,27 +272,8 @@ class CDBWrapper
     template <typename K, typename V>
     bool Read(const K& key, V& value) const
     {
-        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);
-        }
-        try {
-            CDataStream ssValue{MakeByteSpan(strValue), SER_DISK, CLIENT_VERSION};
-            ssValue.Xor(obfuscate_key);
-            ssValue >> value;
-        } catch (const std::exception&) {
-            return false;
-        }
-        return true;
+        Reader reader{key, value};
+        return ReadImpl(reader);
     }
 
     template <typename K, typename V>
