Add a generic length prefixed attester

pubsub/include/marlin/pubsub/attestation/LpfAttester.hpp

@@ -0,0 +1,66 @@
+#ifndef MARLIN_PUBSUB_ATTESTATION_LPFATTESTER_HPP
+#define MARLIN_PUBSUB_ATTESTATION_LPFATTESTER_HPP
+
+#include <stdint.h>
+#include <marlin/core/WeakBuffer.hpp>
+#include <ctime>
+#include <optional>
+
+
+namespace marlin {
+namespace pubsub {
+
+struct LpfAttester {
+	template<typename HeaderType>
+	constexpr uint64_t attestation_size(
+		uint64_t,
+		uint16_t,
+		uint8_t const*,
+		uint64_t,
+		HeaderType prev_header
+	) {
+		return prev_header.attestation_size == 0 ? 2 : prev_header.attestation_size;
+	}
+
+	template<typename HeaderType>
+	int attest(
+		uint64_t,
+		uint16_t,
+		uint8_t const*,
+		uint64_t,
+		HeaderType prev_header,
+		core::Buffer& out,
+		uint64_t offset = 0
+	) {
+		if(prev_header.attestation_size != 0) {
+			// FIXME: should probably add _unsafe to function
+			out.write_unsafe(offset, prev_header.attestation_data, prev_header.attestation_size);
+			return 1;
+		}
+
+		out.write_uint16_le_unsafe(offset, 0);
+
+		return 0;
+	}
+
+	template<typename HeaderType>
+	bool verify(
+		uint64_t,
+		uint16_t,
+		uint8_t const*,
+		uint64_t,
+		HeaderType
+	) {
+		return true;
+	}
+
+	std::optional<uint64_t> parse_size(core::Buffer& buf, uint64_t offset = 0) {
+		auto len = buf.read_uint16_le(offset);
+		return len;
+	}
+};
+
+} // namespace pubsub
+} // namespace marlin
+
+#endif // MARLIN_PUBSUB_ATTESTATION_LPFATTESTER_HPP