Global: adds general cache layer

src/common/impl/FFcache.c

@@ -0,0 +1,53 @@
+#include "common/FFcache.h"
+
+// Entries are file scope statics owned by the cache owner, so they can be linked into a list
+// without any allocation. The list holds every entry that has been used at least once: an entry
+// that was never used has nothing to drop.
+static FFcacheEntry* entries = nullptr;
+
+static void registerEntry(FFcacheEntry* entry) {
+    if (entry->registered) {
+        return;
+    }
+
+    entry->registered = true;
+    entry->next = entries;
+    entries = entry;
+}
+
+void* ffCacheGet(FFcacheEntry* entry) {
+    if (ffCacheBeginInit(entry) && entry->init) {
+        entry->init(entry->storage);
+    }
+
+    return entry->storage;
+}
+
+bool ffCacheBeginInit(FFcacheEntry* entry) {
+    registerEntry(entry);
+
+    if (entry->initialized) {
+        return false;
+    }
+
+    entry->initialized = true;
+    return true;
+}
+
+void ffCacheInvalidate(FFcacheEntry* entry) {
+    if (!entry->initialized) {
+        return;
+    }
+
+    entry->initialized = false;
+
+    if (entry->destroy) {
+        entry->destroy(entry->storage);
+    }
+}
+
+void ffCacheInvalidateAll(void) {
+    for (FFcacheEntry* entry = entries; entry; entry = entry->next) {
+        ffCacheInvalidate(entry);
+    }
+}

src/common/impl/netif.c

@@ -1,22 +1,47 @@
 #include "common/netif.h"
+#include "common/FFcache.h"
 
-#ifndef _WIN32
-    #include <net/if.h>
-    #include <netinet/in.h>
-#endif
+#include <string.h>
+
+// netio, localip and dns resolve the default route on every round, and it can change while a
+// `--dynamic-interval` run is going on: a laptop switching from Wi-Fi to Ethernet, a VPN coming up.
+static FFNetifDefaultRouteResult defaultRouteV4;
+static FFNetifDefaultRouteResult defaultRouteV6;
+
+static void resetDefaultRoute(void* storage) {
+    // The impls only write the fields they found, so without this a round that finds no default
+    // route would keep reporting the interface of the previous one.
+    memset(storage, 0, sizeof(FFNetifDefaultRouteResult));
+}
+
+static void initDefaultRouteV4(void* storage) {
+    FFNetifDefaultRouteResult* result = storage;
+    result->status = ffNetifGetDefaultRouteImplV4(result) ? FF_NETIF_OK : FF_NETIF_INVALID;
+}
+
+static void initDefaultRouteV6(void* storage) {
+    FFNetifDefaultRouteResult* result = storage;
+    result->status = ffNetifGetDefaultRouteImplV6(result) ? FF_NETIF_OK : FF_NETIF_INVALID;
+}
+
+static FFcacheEntry ffCacheEntryDefaultRouteV4 = {
+    .name = "default route V4",
+    .storage = &defaultRouteV4,
+    .init = initDefaultRouteV4,
+    .destroy = resetDefaultRoute,
+};
+
+static FFcacheEntry ffCacheEntryDefaultRouteV6 = {
+    .name = "default route V6",
+    .storage = &defaultRouteV6,
+    .init = initDefaultRouteV6,
+    .destroy = resetDefaultRoute,
+};
 
 const FFNetifDefaultRouteResult* ffNetifGetDefaultRouteV4(void) {
-    static FFNetifDefaultRouteResult result;
-    if (result.status == FF_NETIF_UNINITIALIZED) {
-        result.status = ffNetifGetDefaultRouteImplV4(&result) ? FF_NETIF_OK : FF_NETIF_INVALID;
-    }
-    return &result;
+    return ffCacheGet(&ffCacheEntryDefaultRouteV4);
 }
 
 const FFNetifDefaultRouteResult* ffNetifGetDefaultRouteV6(void) {
-    static FFNetifDefaultRouteResult result;
-    if (result.status == FF_NETIF_UNINITIALIZED) {
-        result.status = ffNetifGetDefaultRouteImplV6(&result) ? FF_NETIF_OK : FF_NETIF_INVALID;
-    }
-    return &result;
+    return ffCacheGet(&ffCacheEntryDefaultRouteV6);
 }