Add getOutputMessage() accessor to Statement

Symmetrical with the existing getInputMessage(), provides direct access
to the raw output message buffer for consumers that need to read
fetched row data at the raw byte level.

Closes asfernandes#42 (REQ-2).

Author: fdcastel

src/fb-cpp/Statement.h

@@ -408,6 +408,14 @@ namespace fbcpp
 			return outMetadata;
 		}
 
+		///
+		/// @brief Provides direct access to the raw output message buffer.
+		///
+		std::vector<std::byte>& getOutputMessage() noexcept
+		{
+			return outMessage;
+		}
+
 		///
 		/// @brief Returns the type classification reported by the server.
 		///

src/test/Statement.cpp

@@ -336,6 +336,27 @@ BOOST_AUTO_TEST_CASE(descriptorMetadataFields)
 	BOOST_CHECK(inDescriptors[0].alias.empty());
 }
 
+BOOST_AUTO_TEST_CASE(getOutputMessageMatchesMetadataLength)
+{
+	const auto database = getTempFile("Statement-getOutputMessageMatchesMetadataLength.fdb");
+
+	Attachment attachment{CLIENT, database, AttachmentOptions().setCreateDatabase(true)};
+	FbDropDatabase attachmentDrop{attachment};
+
+	Transaction transaction{attachment};
+	Statement stmt{attachment, transaction, "select 42 from rdb$database"};
+
+	auto& outMsg = stmt.getOutputMessage();
+	BOOST_CHECK(!outMsg.empty());
+
+	// After fetch, the output message buffer contains the fetched data.
+	BOOST_REQUIRE(stmt.execute(transaction));
+	BOOST_CHECK_EQUAL(stmt.getInt32(0).value(), 42);
+
+	// The buffer reference should remain the same object.
+	BOOST_CHECK_EQUAL(&outMsg, &stmt.getOutputMessage());
+}
+
 BOOST_AUTO_TEST_SUITE_END()