Eliminate dead bytes from nodestore encoding:

The legacy nodestore encoding for blobs had an 8 byte prefix. Originally
the first 4 bytes stored the sequence number of the ledger to which the
encoded object belogned; the next 4 bytes were never specified rigidly
and some versions stored a redundant copy of the ledger sequence while
others simply set the bytes to 0.

Eventually that scheme was abandoned, and the first 8 bytes were just
set to 0 and ignored when reloading a blob.

This commit removes the unusued 8 byte legacy prefix. The change is
makes it impossible to load old databases with this code and for old
versions to load databases created with this code.

src/ripple/nodestore/impl/DecodedBlob.cpp

@@ -30,10 +30,8 @@ DecodedBlob::DecodedBlob(void const* key, void const* value, int valueBytes)
     /*  Data format:
 
         Bytes
-
+        0           uint8           One of NodeObjectType
-        0...7       Unused
+        1...end                     The body of the object data
-        8           char            One of NodeObjectType
-        9...end                     The body of the object data
     */
 
     m_success = false;
@@ -41,19 +39,17 @@ DecodedBlob::DecodedBlob(void const* key, void const* value, int valueBytes)
     // VFALCO NOTE Ledger indexes should have started at 1
     m_objectType = hotUNKNOWN;
     m_objectData = nullptr;
-    m_dataBytes = std::max(0, valueBytes - 9);
+    m_dataBytes = std::max(0, valueBytes - 1);
 
-    // VFALCO NOTE What about bytes 4 through 7 inclusive?
+    if (valueBytes != 0)
-
-    if (valueBytes > 8)
     {
         unsigned char const* byte = static_cast<unsigned char const*>(value);
-        m_objectType = safe_cast<NodeObjectType>(byte[8]);
+        m_objectType = safe_cast<NodeObjectType>(byte[0]);
     }
 
-    if (valueBytes > 9)
+    if (valueBytes > 1)
     {
-        m_objectData = static_cast<unsigned char const*>(value) + 9;
+        m_objectData = static_cast<unsigned char const*>(value) + 1;
 
         switch (m_objectType)
         {

src/ripple/nodestore/impl/EncodedBlob.cpp

@@ -28,14 +28,11 @@ EncodedBlob::prepare(std::shared_ptr<NodeObject> const& object)
 {
     m_key = object->getHash().begin();
 
-    auto ret = m_data.alloc(object->getData().size() + 9);
+    auto ret = m_data.alloc(object->getData().size() + 1);
 
-    // the first 8 bytes are unused
+    ret[0] = static_cast<std::uint8_t>(object->getType());
-    std::memset(ret, 0, 8);
 
-    ret[8] = static_cast<std::uint8_t>(object->getType());
+    std::memcpy(ret + 1, object->getData().data(), object->getData().size());
-
-    std::memcpy(ret + 9, object->getData().data(), object->getData().size());
 }
 
 }  // namespace NodeStore