Split net stack into eth/arp/ipv4/icmp, deferred handler responses, ping tests

firmware/lib/ipv4.cpp

@@ -0,0 +1,46 @@
+#include "ipv4.h"
+#include "icmp.h"
+
+namespace ipv4 {
+
+static constexpr ip4_addr IP_BROADCAST_ALL = {255, 255, 255, 255};
+
+uint16_t checksum(const void* data, size_t len) {
+    auto p = static_cast<const uint8_t*>(data);
+    uint32_t sum = 0;
+    for (size_t i = 0; i < len - 1; i += 2)
+        sum += (p[i] << 8) | p[i + 1];
+    if (len & 1)
+        sum += p[len - 1] << 8;
+    while (sum >> 16)
+        sum = (sum & 0xFFFF) + (sum >> 16);
+    return __builtin_bswap16(~sum);
+}
+
+static bool ip_match_or_broadcast(const ip4_addr& dst, const ip4_addr& our_ip, const ip4_addr& subnet_broadcast) {
+    return dst == our_ip || dst == IP_BROADCAST_ALL || dst == subnet_broadcast;
+}
+
+void handle(std::span<const uint8_t> frame, span_writer& tx,
+            eth::mac_addr our_mac, ip4_addr our_ip, ip4_addr subnet_broadcast,
+            std::function<void(std::span<const uint8_t>)> send_raw,
+            std::function<void(std::span<const uint8_t>, span_writer&)> handle_udp) {
+    if (frame.size() < sizeof(header)) return;
+    auto& ip = *reinterpret_cast<const header*>(frame.data());
+    if ((ip.ver_ihl >> 4) != 4) return;
+
+    switch (ip.protocol) {
+    case 1:
+        if (!ip_match_or_broadcast(ip.dst, our_ip, subnet_broadcast))
+            return;
+        icmp::handle(frame, tx, our_mac, our_ip, send_raw);
+        break;
+    case 17:
+        if (!ip_match_or_broadcast(ip.dst, our_ip, subnet_broadcast))
+            return;
+        handle_udp(frame, tx);
+        break;
+    }
+}
+
+} // namespace ipv4