Replace shared_ptr in bignum with unique_ptr (#1518)

Co-authored-by: ruslan-ilesik <[email protected]>

Author: ruslan-ilesik

include/dpp/bignum.h

@@ -44,10 +44,28 @@ struct openssl_bignum;
  * for HTTPS.
 */
 class DPP_EXPORT bignumber {
+	/**
+	 * @brief Forward declaration of structure which implements proper destructor for unique_ptr<openssl_bignum> as type is incomplete in header
+	 * custom deleter defined where openssl_bignum is complete
+	 */
+	struct bn_deleter {
+
+		/**
+		 * @brief Deletes an `openssl_bignum` instance.
+		 *
+		 * This operator is invoked automatically by `std::unique_ptr` when the
+		 * managed object needs to be destroyed.
+		 *
+		 * @param p Pointer to the `openssl_bignum` instance to delete.
+		 */
+		void operator()(openssl_bignum* p) const noexcept;
+	};
+
 	/**
 	 * @brief Internal opaque struct to contain OpenSSL things
 	 */
-	std::shared_ptr<openssl_bignum> ssl_bn{nullptr};
+	std::unique_ptr<openssl_bignum, bn_deleter> ssl_bn;
+
 public:
 	/**
 	 * @brief Construct a new bignumber object

src/dpp/bignum.cpp

@@ -47,7 +47,11 @@ struct openssl_bignum {
 	}
 };
 
-bignumber::bignumber(const std::string& number_string) : ssl_bn(std::make_shared<openssl_bignum>()) {
+void bignumber::bn_deleter::operator()(openssl_bignum* p) const noexcept {
+	delete p;
+}
+
+bignumber::bignumber(const std::string &number_string): ssl_bn{new openssl_bignum(), bn_deleter{}} {
 	if (dpp::lowercase(number_string.substr(0, 2)) == "0x") {
 		BN_hex2bn(&ssl_bn->bn, number_string.substr(2, number_string.length() - 2).c_str());
 	} else {
@@ -71,7 +75,7 @@ inline uint64_t flip_bytes(uint64_t bytes) {
 	       | (((bytes) & 0x00000000000000ffull) << 56));
 }
 
-bignumber::bignumber(std::vector<uint64_t> bits): ssl_bn(std::make_shared<openssl_bignum>()) {
+bignumber::bignumber(std::vector<uint64_t> bits): ssl_bn{new openssl_bignum(), bn_deleter{}} {
 	std::reverse(bits.begin(), bits.end());
 	for (auto& chunk : bits) {
 		chunk = flip_bytes(chunk);