mesh: implement UDP gossip transport; wire mesh comms into main

Signed-off-by: NotAShelf <raf@notashelf.dev>
Change-Id: Iea0b2f250b01df78b1c7be73d69d28c06a6a6964

internal/mesh/gossip_test.go

@@ -0,0 +1,54 @@
+package mesh_test
+
+import (
+	"net"
+	"testing"
+	"time"
+
+	"notashelf.dev/ncro/internal/cache"
+	"notashelf.dev/ncro/internal/mesh"
+)
+
+func TestAnnounceAndReceive(t *testing.T) {
+	store := mesh.NewRouteStore()
+	node, err := mesh.NewNode("", store)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// Bind to an ephemeral port.
+	conn, err := net.ListenPacket("udp", "127.0.0.1:0")
+	if err != nil {
+		t.Fatal(err)
+	}
+	addr := conn.LocalAddr().String()
+	conn.Close()
+
+	if err := mesh.ListenAndServe(addr, store); err != nil {
+		t.Fatalf("ListenAndServe: %v", err)
+	}
+
+	routes := []cache.RouteEntry{
+		{
+			StorePath:   "test-pkg-abc",
+			UpstreamURL: "https://cache.nixos.org",
+			LatencyEMA:  25,
+			TTL:         time.Now().Add(time.Hour),
+		},
+	}
+
+	if err := mesh.Announce(addr, node, routes); err != nil {
+		t.Fatalf("Announce: %v", err)
+	}
+
+	// Give the listener goroutine time to process the packet.
+	time.Sleep(50 * time.Millisecond)
+
+	entry := store.Get("test-pkg-abc")
+	if entry == nil {
+		t.Fatal("route not merged into store after announce")
+	}
+	if entry.UpstreamURL != "https://cache.nixos.org" {
+		t.Errorf("UpstreamURL = %q", entry.UpstreamURL)
+	}
+}