Eliminate std::function: fn-pointer callbacks, per-test test_state structs, udp.cpp with link-time udp::client::handler, udp::address

firmware/lib/udp.cpp

@@ -0,0 +1,31 @@
+#include "udp.h"
+#include "eth.h"
+#include "ipv4.h"
+#include "net.h"
+#include "parse_buffer.h"
+
+namespace udp {
+
+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;
+
+    size_t options_len = ip->header_len() - sizeof(ipv4::header);
+    if (options_len > 0 && !pb.skip(options_len)) return;
+
+    auto* uhdr = pb.consume<header>();
+    if (!uhdr) return;
+    if (uhdr->dst_port != PICOMAP_PORT_BE) return;
+
+    size_t udp_len = __builtin_bswap16(uhdr->length);
+    if (udp_len < sizeof(header)) return;
+    size_t payload_len = udp_len - sizeof(header);
+    if (pb.remaining_size() < payload_len) return;
+
+    address from{eth_hdr->src, ip->src, uhdr->src_port};
+    client::handler(pb.remaining().subspan(0, payload_len), from);
+}
+
+} // namespace udp