extract icmp into its own static library; replace all __attribute__((constructor)) self-registrations with explicit init() calls in dispatch_init

icmp/CMakeLists.txt

@@ -0,0 +1,11 @@
+add_library(icmp STATIC icmp.cpp)
+
+target_include_directories(icmp PUBLIC ${CMAKE_CURRENT_SOURCE_DIR})
+
+target_compile_options(icmp PRIVATE -Wall -Wextra -Wno-unused-parameter)
+
+target_link_libraries(icmp PUBLIC
+    util
+    eth
+    ipv4
+)

icmp/icmp.cpp

@@ -0,0 +1,66 @@
+#include "icmp.h"
+#include <cstring>
+#include "eth.h"
+#include "ipv4.h"
+#include "parse_buffer.h"
+#include "prepend_buffer.h"
+
+namespace icmp {
+
+void handle(std::span<const uint8_t> frame, span_writer& tx) {
+    parse_buffer pb(frame);
+    auto* eth_hdr = pb.consume<eth::header>();
+    auto* ip = pb.consume<ipv4::header>();
+    if (!ip) return;
+    if (!ipv4::addressed_to_us(ip->dst)) return;
+
+    size_t options_len = ip->header_len() - sizeof(ipv4::header);
+    if (options_len > 0 && !pb.skip(options_len)) return;
+
+    size_t icmp_len = ip->total() - ip->header_len();
+    if (pb.remaining_size() < icmp_len) return;
+
+    auto* icmp_pkt = pb.consume<echo>();
+    if (!icmp_pkt) return;
+    if (icmp_pkt->type != 8) return;
+
+    prepend_buffer<4096> buf;
+    memcpy(buf.append(icmp_len), pb.remaining().data() - sizeof(echo), icmp_len);
+
+    auto* reply = reinterpret_cast<echo*>(buf.data());
+    reply->type = 0;
+    reply->checksum = 0;
+    reply->checksum = ipv4::checksum(reply, icmp_len);
+
+    ipv4::prepend(buf, eth_hdr->src, eth::get_mac(), ipv4::get_ip(), ip->src, 1, icmp_len);
+    eth::send_raw(buf.span());
+}
+
+void init() {
+    ipv4::register_protocol(1, handle);
+}
+
+bool parse_echo_reply(std::span<const uint8_t> frame, ipv4::ip4_addr& src_ip, uint16_t expected_id) {
+    parse_buffer pb(frame);
+    auto* eth_hdr = pb.consume<eth::header>();
+    if (!eth_hdr) return false;
+    if (eth_hdr->ethertype != eth::ETH_IPV4) return false;
+
+    auto* ip = pb.consume<ipv4::header>();
+    if (!ip) return false;
+    if ((ip->ver_ihl >> 4) != 4) return false;
+    if (ip->protocol != 1) return false;
+
+    size_t options_len = ip->header_len() - sizeof(ipv4::header);
+    if (options_len > 0 && !pb.skip(options_len)) return false;
+
+    auto* icmp_pkt = pb.consume<echo>();
+    if (!icmp_pkt) return false;
+    if (icmp_pkt->type != 0) return false;
+    if (icmp_pkt->id != expected_id) return false;
+
+    src_ip = ip->src;
+    return true;
+}
+
+} // namespace icmp

icmp/icmp.h

@@ -0,0 +1,41 @@
+#pragma once
+#include <cstdint>
+#include <span>
+#include "eth.h"
+#include "ipv4.h"
+#include "span_writer.h"
+
+namespace icmp {
+
+struct __attribute__((packed)) echo {
+    uint8_t type;
+    uint8_t code;
+    uint16_t checksum;
+    uint16_t id;
+    uint16_t seq;
+};
+static_assert(sizeof(echo) == 8);
+
+void init();
+void handle(std::span<const uint8_t> frame, span_writer& tx);
+
+template <typename Buf>
+void prepend_echo_request(Buf& buf,
+                          eth::mac_addr src_mac, ipv4::ip4_addr src_ip,
+                          eth::mac_addr dst_mac, ipv4::ip4_addr dst_ip,
+                          uint16_t id, uint16_t seq,
+                          size_t payload_len = 0) {
+    auto* e = buf.template prepend<echo>();
+    e->type = 8;
+    e->code = 0;
+    e->checksum = 0;
+    e->id = id;
+    e->seq = seq;
+    size_t icmp_len = sizeof(echo) + payload_len;
+    e->checksum = ipv4::checksum(e, icmp_len);
+    ipv4::prepend(buf, dst_mac, src_mac, src_ip, dst_ip, 1, icmp_len);
+}
+
+bool parse_echo_reply(std::span<const uint8_t> frame, ipv4::ip4_addr& src_ip, uint16_t expected_id);
+
+} // namespace icmp