chore: refactor the string interface in c api

Signed-off-by: Jian Zhang <[email protected]>

include/leanstore/leanstore-c.h

@@ -20,8 +20,11 @@ typedef struct String {
   uint64_t mSize;
 } String;
 
-//! Creates a new string with the given bytes buffer
-String CreateString(const char* data, uint64_t size);
+//! Creates a new string, copying the data from the given buffer to the new string
+//! @param data the data buffer
+//! @param size the size of the data buffer
+//! @return the new string, which should be destroyed by the caller with DestroyString()
+String* CreateString(const char* data, uint64_t size);
 
 //! Destroys a string
 void DestroyString(String* str);
@@ -91,11 +94,9 @@ LeanStoreError BasicKvInsert(BasicKvHandle* handle, uint64_t workerId, StringSli
                              StringSlice val);
 
 //! Lookup a key in a basic key-value store at workerId
-//! NOTE:
-//!   1. The old content hold by val will be released and overwritten by the new content
-//!   2. The caller should destroy the val after use
-LeanStoreError BasicKvLookup(BasicKvHandle* handle, uint64_t workerId, StringSlice key,
-                             String* val);
+//! NOTE: The caller should destroy the val after use
+//! @return the value if the key exists, nullptr otherwise
+String* BasicKvLookup(BasicKvHandle* handle, uint64_t workerId, StringSlice key);
 
 //! Remove a key in a basic key-value store at workerId
 LeanStoreError BasicKvRemove(BasicKvHandle* handle, uint64_t workerId, StringSlice key);

src/leanstore-c.cpp

@@ -18,38 +18,35 @@
 // String API
 //------------------------------------------------------------------------------
 
-String CreateString(const char* data, uint64_t size) {
-  String str;
+String* CreateString(const char* data, uint64_t size) {
+  String* str = new String();
 
   if (data == nullptr || size == 0) {
-    str.mData = nullptr;
-    str.mSize = 0;
-    return str;
-  }
-
-  // allocate memory
-  str.mData = static_cast<char*>(malloc(size));
-  if (str.mData == nullptr) {
-    str.mSize = 0;
+    str->mData = nullptr;
+    str->mSize = 0;
     return str;
   }
 
-  // copy data
-  memcpy(str.mData, data, size);
-  str.mSize = size;
+  // allocate memory, copy data
+  str->mSize = size;
+  str->mData = new char[size];
+  memcpy(str->mData, data, size);
 
   return str;
 }
 
 void DestroyString(String* str) {
   if (str != nullptr) {
-    if (str->mData == nullptr) {
-      return;
+    if (str->mData != nullptr) {
+      // release memory
+      delete[] str->mData;
     }
 
-    free(str->mData);
     str->mData = nullptr;
     str->mSize = 0;
+
+    // release the string object
+    delete str;
   }
 }
 
@@ -150,17 +147,15 @@ LeanStoreError BasicKvInsert(BasicKvHandle* handle, uint64_t workerId, StringSli
   return ToLeanStoreError(opCode);
 }
 
-LeanStoreError BasicKvLookup(BasicKvHandle* handle, uint64_t workerId, StringSlice key,
-                             String* val) {
-  leanstore::OpCode opCode{leanstore::OpCode::kOK};
+String* BasicKvLookup(BasicKvHandle* handle, uint64_t workerId, StringSlice key) {
+  String* val{nullptr};
   handle->mStore->ExecSync(workerId, [&]() {
     auto copyValueOut = [&](leanstore::Slice valSlice) {
-      DestroyString(val); // release old content
-      *val = CreateString(reinterpret_cast<const char*>(valSlice.data()), valSlice.size());
+      val = CreateString(reinterpret_cast<const char*>(valSlice.data()), valSlice.size());
     };
-    opCode = handle->mBtree->Lookup(leanstore::Slice(key.mData, key.mSize), copyValueOut);
+    handle->mBtree->Lookup(leanstore::Slice(key.mData, key.mSize), copyValueOut);
   });
-  return ToLeanStoreError(opCode);
+  return val;
 }
 
 LeanStoreError BasicKvRemove(BasicKvHandle* handle, uint64_t workerId, StringSlice key) {