extract ipv4 into its own static library

include/ipv4.h

@@ -1,73 +0,0 @@
-#pragma once
-#include <array>
-#include <cstdint>
-#include <cstdio>
-#include <span>
-#include <string>
-#include "eth.h"
-#include "span_writer.h"
-
-namespace ipv4 {
-
-using ip4_addr = std::array<uint8_t, 4>;
-
-inline std::string to_string(const ip4_addr& ip) {
-    char buf[16];
-    snprintf(buf, sizeof(buf), "%u.%u.%u.%u", ip[0], ip[1], ip[2], ip[3]);
-    return buf;
-}
-
-struct __attribute__((packed)) header {
-    uint8_t ver_ihl;
-    uint8_t dscp_ecn;
-    uint16_t total_len;
-    uint16_t identification;
-    uint16_t flags_frag;
-    uint8_t ttl;
-    uint8_t protocol;
-    uint16_t checksum;
-    ip4_addr src;
-    ip4_addr dst;
-
-    size_t header_len() const { return (ver_ihl & 0x0F) * 4; }
-    size_t total() const { return __builtin_bswap16(total_len); }
-};
-static_assert(sizeof(header) == 20);
-
-uint16_t checksum(const void* data, size_t len);
-
-static constexpr ip4_addr SUBNET_BROADCAST = {169, 254, 255, 255};
-
-template <typename Buf>
-void prepend(Buf& buf, const eth::mac_addr& dst_mac, const eth::mac_addr& src_mac,
-             ip4_addr src_ip, ip4_addr dst_ip, uint8_t protocol,
-             size_t payload_len, uint8_t ttl = 64) {
-    auto* h = buf.template prepend<header>();
-    h->ver_ihl = 0x45;
-    h->dscp_ecn = 0;
-    h->total_len = __builtin_bswap16(sizeof(header) + payload_len);
-    h->identification = 0;
-    h->flags_frag = 0;
-    h->ttl = ttl;
-    h->protocol = protocol;
-    h->checksum = 0;
-    h->src = src_ip;
-    h->dst = dst_ip;
-    h->checksum = checksum(h, sizeof(header));
-    eth::prepend(buf, dst_mac, src_mac, eth::ETH_IPV4);
-}
-
-void handle(std::span<const uint8_t> frame, span_writer& tx);
-
-void init();
-const ip4_addr& get_ip();
-
-bool addressed_to_us(ip4_addr dst);
-
-using protocol_handler = void (*)(std::span<const uint8_t> frame, span_writer& tx);
-void register_protocol(uint8_t protocol, protocol_handler fn);
-
-using addr_filter = bool (*)(const ip4_addr& dst);
-void register_addr_filter(addr_filter fn);
-
-} // namespace ipv4