rpc: add GetTarget helper

Author: Sjors

Diff for: src/rpc/util.cpp

@@ -4,6 +4,7 @@
 
 #include <bitcoin-build-config.h> // IWYU pragma: keep
 
+#include <chain.h>
 #include <clientversion.h>
 #include <common/args.h>
 #include <common/messages.h>
@@ -13,6 +14,7 @@
 #include <key_io.h>
 #include <node/types.h>
 #include <outputtype.h>
+#include <pow.h>
 #include <rpc/util.h>
 #include <script/descriptor.h>
 #include <script/interpreter.h>
@@ -1418,3 +1420,9 @@ std::vector<RPCResult> ScriptPubKeyDoc() {
              {RPCResult::Type::STR, "type", "The type (one of: " + GetAllOutputTypes() + ")"},
          };
 }
+
+uint256 GetTarget(const CBlockIndex& blockindex, const uint256 pow_limit)
+{
+    arith_uint256 target{*CHECK_NONFATAL(DeriveTarget(blockindex.nBits, pow_limit))};
+    return ArithToUint256(target);
+}

Diff for: src/rpc/util.h

@@ -516,4 +516,14 @@ void PushWarnings(const std::vector<bilingual_str>& warnings, UniValue& obj);
 
 std::vector<RPCResult> ScriptPubKeyDoc();
 
+/***
+ * Get the target for a given block index.
+ *
+ * @param[in] blockindex    the block
+ * @param[in] pow_limit     PoW limit (consensus parameter)
+ *
+ * @return  the target
+ */
+uint256 GetTarget(const CBlockIndex& blockindex, const uint256 pow_limit);
+
 #endif // BITCOIN_RPC_UTIL_H