Speed up wifi reconnect

src/JsonSettingsIO.cpp

@@ -407,6 +407,29 @@ bool JsonSettingsIO::saveWifi(const WifiCredentialStore& store, const char* path
     JsonObject obj = arr.add<JsonObject>();
     obj["ssid"] = cred.ssid;
     obj["password_obf"] = obfuscation::obfuscateToBase64(cred.password);
+    bool hasHint = cred.channel != 0;
+    for (int i = 0; i < 6 && !hasHint; i++) {
+      if (cred.bssid[i] != 0) hasHint = true;
+    }
+    if (hasHint) {
+      char bssidHex[13];
+      snprintf(bssidHex, sizeof(bssidHex), "%02x%02x%02x%02x%02x%02x", cred.bssid[0], cred.bssid[1], cred.bssid[2],
+               cred.bssid[3], cred.bssid[4], cred.bssid[5]);
+      obj["bssid"] = bssidHex;
+      obj["channel"] = cred.channel;
+    }
+    if (cred.ip[0] != 0) {
+      char buf[16];
+      snprintf(buf, sizeof(buf), "%d.%d.%d.%d", cred.ip[0], cred.ip[1], cred.ip[2], cred.ip[3]);
+      obj["ip"] = buf;
+      snprintf(buf, sizeof(buf), "%d.%d.%d.%d", cred.gateway[0], cred.gateway[1], cred.gateway[2], cred.gateway[3]);
+      obj["gw"] = buf;
+      snprintf(buf, sizeof(buf), "%d.%d.%d.%d", cred.mask[0], cred.mask[1], cred.mask[2], cred.mask[3]);
+      obj["mask"] = buf;
+      snprintf(buf, sizeof(buf), "%d.%d.%d.%d", cred.dns[0], cred.dns[1], cred.dns[2], cred.dns[3]);
+      obj["dns"] = buf;
+      obj["ts"] = cred.cacheTimestamp;
+    }
   }
 
   String json;
@@ -464,6 +487,48 @@ bool JsonSettingsIO::loadWifi(WifiCredentialStore& store, const char* json, bool
       cred.password = obj["password"] | std::string("");
       if (!cred.password.empty() && needsResave) *needsResave = true;
     }
+    const std::string bssidHex = obj["bssid"] | std::string("");
+    const int channel = obj["channel"] | 0;
+    if (bssidHex.size() == 12 && channel > 0 && channel <= 14) {
+      bool parseOk = true;
+      uint8_t parsed[6] = {0};
+      for (int i = 0; i < 6 && parseOk; i++) {
+        unsigned int byte = 0;
+        if (sscanf(bssidHex.c_str() + i * 2, "%2x", &byte) != 1) {
+          parseOk = false;
+        } else {
+          parsed[i] = static_cast<uint8_t>(byte);
+        }
+      }
+      if (parseOk) {
+        std::memcpy(cred.bssid, parsed, 6);
+        cred.channel = static_cast<uint8_t>(channel);
+      }
+    }
+    const auto parseQuad = [](const std::string& s, uint8_t out[4]) -> bool {
+      unsigned int a = 0, b = 0, c = 0, d = 0;
+      if (sscanf(s.c_str(), "%u.%u.%u.%u", &a, &b, &c, &d) != 4) return false;
+      if (a > 255 || b > 255 || c > 255 || d > 255) return false;
+      out[0] = a;
+      out[1] = b;
+      out[2] = c;
+      out[3] = d;
+      return true;
+    };
+    const std::string ipStr = obj["ip"] | std::string("");
+    const std::string gwStr = obj["gw"] | std::string("");
+    const std::string maskStr = obj["mask"] | std::string("");
+    const std::string dnsStr = obj["dns"] | std::string("");
+    if (!ipStr.empty()) {
+      uint8_t ip[4], gw[4], mask[4], dns[4];
+      if (parseQuad(ipStr, ip) && parseQuad(gwStr, gw) && parseQuad(maskStr, mask) && parseQuad(dnsStr, dns)) {
+        std::memcpy(cred.ip, ip, 4);
+        std::memcpy(cred.gateway, gw, 4);
+        std::memcpy(cred.mask, mask, 4);
+        std::memcpy(cred.dns, dns, 4);
+        cred.cacheTimestamp = obj["ts"] | 0u;
+      }
+    }
     store.credentials.push_back(cred);
   }
 

src/WifiCredentialStore.cpp

@@ -5,6 +5,8 @@
 #include <Logging.h>
 #include <ObfuscationUtils.h>
 
+#include <cstring>
+
 // Initialize the static instance
 WifiCredentialStore WifiCredentialStore::instance;
 
@@ -82,6 +84,54 @@ const WifiCredential* WifiCredentialStore::findCredential(const std::string& ssi
 
 bool WifiCredentialStore::hasSavedCredential(const std::string& ssid) const { return findCredential(ssid) != nullptr; }
 
+bool WifiCredentialStore::updateConnectionCache(const std::string& ssid, const uint8_t bssid[6], uint8_t channel,
+                                                const uint8_t ip[4], const uint8_t gateway[4], const uint8_t mask[4],
+                                                const uint8_t dns[4], uint32_t cacheTimestamp) {
+  const auto cred =
+      find_if(credentials.begin(), credentials.end(), [&ssid](const WifiCredential& c) { return c.ssid == ssid; });
+  if (cred == credentials.end()) {
+    return false;
+  }
+  const bool sameHint = (channel == cred->channel) && std::memcmp(bssid, cred->bssid, 6) == 0;
+  const bool sameIp = std::memcmp(ip, cred->ip, 4) == 0 && std::memcmp(gateway, cred->gateway, 4) == 0 &&
+                      std::memcmp(mask, cred->mask, 4) == 0 && std::memcmp(dns, cred->dns, 4) == 0;
+  // Timestamp updates are not worth a write on their own; only persist when topology changed.
+  if (sameHint && sameIp) {
+    return true;
+  }
+  std::memcpy(cred->bssid, bssid, 6);
+  cred->channel = channel;
+  std::memcpy(cred->ip, ip, 4);
+  std::memcpy(cred->gateway, gateway, 4);
+  std::memcpy(cred->mask, mask, 4);
+  std::memcpy(cred->dns, dns, 4);
+  cred->cacheTimestamp = cacheTimestamp;
+  return saveToFile();
+}
+
+bool WifiCredentialStore::clearConnectionCache(const std::string& ssid) {
+  const auto cred =
+      find_if(credentials.begin(), credentials.end(), [&ssid](const WifiCredential& c) { return c.ssid == ssid; });
+  if (cred == credentials.end()) {
+    return false;
+  }
+  bool empty = (cred->channel == 0) && (cred->ip[0] == 0);
+  for (int i = 0; i < 6 && empty; i++) {
+    if (cred->bssid[i] != 0) empty = false;
+  }
+  if (empty) {
+    return true;
+  }
+  std::memset(cred->bssid, 0, 6);
+  cred->channel = 0;
+  std::memset(cred->ip, 0, 4);
+  std::memset(cred->gateway, 0, 4);
+  std::memset(cred->mask, 0, 4);
+  std::memset(cred->dns, 0, 4);
+  cred->cacheTimestamp = 0;
+  return saveToFile();
+}
+
 void WifiCredentialStore::setLastConnectedSsid(const std::string& ssid) {
   if (lastConnectedSsid != ssid) {
     lastConnectedSsid = ssid;

src/WifiCredentialStore.h

@@ -1,10 +1,24 @@
 #pragma once
+#include <cstdint>
 #include <string>
 #include <vector>
 
 struct WifiCredential {
   std::string ssid;
   std::string password;  // Plaintext in memory; obfuscated with hardware key on disk
+  // Connection hint cached on successful connect. All-zero BSSID or channel==0 means
+  // "no hint, do a full scan". Used to skip channel scanning on reconnect.
+  uint8_t bssid[6] = {0, 0, 0, 0, 0, 0};
+  uint8_t channel = 0;
+
+  // Cached IP configuration to skip DHCP on reconnect. Valid only when ip[0] != 0 AND
+  // we connect to the same BSSID (cached above). cacheTimestamp is epoch seconds at
+  // capture; 0 means "unknown time, no TTL enforced".
+  uint8_t ip[4] = {0, 0, 0, 0};
+  uint8_t gateway[4] = {0, 0, 0, 0};
+  uint8_t mask[4] = {0, 0, 0, 0};
+  uint8_t dns[4] = {0, 0, 0, 0};
+  uint32_t cacheTimestamp = 0;
 };
 
 class WifiCredentialStore;
@@ -51,6 +65,16 @@ class WifiCredentialStore {
   bool removeCredential(const std::string& ssid);
   const WifiCredential* findCredential(const std::string& ssid) const;
 
+  // Update cached BSSID/channel hint AND IP configuration in one write. ip/gw/mask/dns
+  // may be all-zero to mean "no IP cache". cacheTimestamp is epoch seconds (0 if unsynced).
+  // Persists only if anything changed.
+  bool updateConnectionCache(const std::string& ssid, const uint8_t bssid[6], uint8_t channel, const uint8_t ip[4],
+                             const uint8_t gateway[4], const uint8_t mask[4], const uint8_t dns[4],
+                             uint32_t cacheTimestamp);
+  // Clear all cached hint + IP for this credential (after a hint-based connect failed
+  // and we want the next attempt to start fresh with full scan + DHCP).
+  bool clearConnectionCache(const std::string& ssid);
+
   // Get all stored credentials (for UI display)
   const std::vector<WifiCredential>& getCredentials() const { return credentials; }
 

src/activities/network/WifiSelectionActivity.cpp

@@ -2,12 +2,15 @@
 
 #include <GfxRenderer.h>
 #include <HTTPClient.h>
+#include <HalClock.h>
 #include <I18n.h>
 #include <Logging.h>
 #include <NetworkClient.h>
 #include <WiFi.h>
 #include <esp_mac.h>
 
+#include <cstring>
+#include <ctime>
 #include <map>
 
 #include "MappedInputManager.h"
@@ -46,6 +49,20 @@ String formatMacCompact(const uint8_t mac[6]) {
 void WifiSelectionActivity::onEnter() {
   Activity::onEnter();
 
+  // Timing instrumentation: split total connect time into association vs DHCP.
+  // STA_CONNECTED = association (auth + 4-way handshake done).
+  // STA_GOT_IP    = DHCP done.
+  evtIdConnected = WiFi.onEvent(
+      [this](WiFiEvent_t /*event*/, WiFiEventInfo_t /*info*/) {
+        LOG_DBG("WIFI", "EVT associated at %lu ms", millis() - connectionStartTime);
+      },
+      ARDUINO_EVENT_WIFI_STA_CONNECTED);
+  evtIdGotIp = WiFi.onEvent(
+      [this](WiFiEvent_t /*event*/, WiFiEventInfo_t /*info*/) {
+        LOG_DBG("WIFI", "EVT got_ip at %lu ms", millis() - connectionStartTime);
+      },
+      ARDUINO_EVENT_WIFI_STA_GOT_IP);
+
   // Load saved WiFi credentials - SD card operations need lock as we use SPI
   // for both
   {
@@ -109,6 +126,15 @@ void WifiSelectionActivity::onEnter() {
 void WifiSelectionActivity::onExit() {
   Activity::onExit();
 
+  if (evtIdConnected != 0) {
+    WiFi.removeEvent(evtIdConnected);
+    evtIdConnected = 0;
+  }
+  if (evtIdGotIp != 0) {
+    WiFi.removeEvent(evtIdGotIp);
+    evtIdGotIp = 0;
+  }
+
   LOG_DBG("WIFI", "Free heap at onExit start: %d bytes", ESP.getFreeHeap());
 
   // Stop any ongoing WiFi scan
@@ -195,23 +221,11 @@ void WifiSelectionActivity::tryNextAutoCycleCandidate() {
   connectionStartTime = millis();
   connectedIP.clear();
   connectionError.clear();
+  hintFallbackDone = false;
   requestUpdate();
 
-  WiFi.persistent(false);
-  WiFi.mode(WIFI_STA);
-  WiFi.disconnect(true, true);
-  delay(100);
-
-  uint8_t baseMac[6];
-  readDeviceBaseMac(baseMac);
-  String hostname = "CrossPoint-Reader-" + formatMacCompact(baseMac);
-  WiFi.setHostname(hostname.c_str());
-
-  if (selectedRequiresPassword && !enteredPassword.empty()) {
-    WiFi.begin(selectedSSID.c_str(), enteredPassword.c_str());
-  } else {
-    WiFi.begin(selectedSSID.c_str());
-  }
+  prepareForConnect();
+  issueWifiBegin(/*useHint=*/true);
 }
 
 void WifiSelectionActivity::processWifiScanResults() {
@@ -334,23 +348,96 @@ void WifiSelectionActivity::attemptConnection() {
   connectionStartTime = millis();
   connectedIP.clear();
   connectionError.clear();
+  hintFallbackDone = false;
   requestUpdate();
 
+  prepareForConnect();
+  issueWifiBegin(/*useHint=*/true);
+}
+
+void WifiSelectionActivity::prepareForConnect() {
   WiFi.persistent(false);  // Credentials are managed by WifiCredentialStore; suppress SDK NVS auto-connect
-  WiFi.mode(WIFI_STA);
-  WiFi.disconnect(true, true);  // Abort any in-progress SDK auto-connect and clear NVS-saved SSID
-  delay(100);
+
+  // Only switch mode if we're not already STA — the mode setter touches the netif and
+  // can take 50+ ms even when "no change" semantically.
+  if (WiFi.getMode() != WIFI_STA) {
+    WiFi.mode(WIFI_STA);
+  }
+
+  // Only do the heavy disconnect(true,true) — which erases NVS and tears down the WPA
+  // state machine — when there's actually something to tear down. From a fresh/idle
+  // state it's a pure cost (~50–80 ms on this SoC).
+  const wl_status_t status = WiFi.status();
+  const bool needsReset = (status == WL_CONNECTED) || (status == WL_CONNECT_FAILED) || (status == WL_CONNECTION_LOST) ||
+                          (status == WL_NO_SSID_AVAIL);
+  if (needsReset) {
+    WiFi.disconnect(true, true);
+  }
 
   // Use stable base MAC so hostname suffix is deterministic across WiFi states.
   uint8_t baseMac[6];
   readDeviceBaseMac(baseMac);
   String hostname = "CrossPoint-Reader-" + formatMacCompact(baseMac);
   WiFi.setHostname(hostname.c_str());
+}
 
-  if (selectedRequiresPassword && !enteredPassword.empty()) {
-    WiFi.begin(selectedSSID.c_str(), enteredPassword.c_str());
+void WifiSelectionActivity::issueWifiBegin(bool useHint) {
+  std::memset(currentAttemptBssid, 0, 6);
+  currentAttemptChannel = 0;
+  bool appliedStaticIp = false;
+
+  if (useHint) {
+    const auto* cred = WIFI_STORE.findCredential(selectedSSID);
+    if (cred && cred->channel != 0) {
+      std::memcpy(currentAttemptBssid, cred->bssid, 6);
+      currentAttemptChannel = cred->channel;
+
+      // Apply cached static IP only when the IP cache is keyed to this same BSSID and
+      // (if we have a synced clock) hasn't aged out. cacheTimestamp==0 means it was
+      // written before clock-sync; we trust it indefinitely in that case.
+      if (cred->ip[0] != 0) {
+        constexpr int64_t TTL_SECONDS = 7 * 24 * 60 * 60;
+        const time_t now = HalClock::now();
+        // Use signed arithmetic so we don't underflow when ts is in the future (which
+        // happens when NTP corrects the clock backwards between cache write and read).
+        // Future timestamps are treated as fresh (negative elapsed clamped to 0).
+        const int64_t elapsed =
+            (now == 0) ? 0 : (static_cast<int64_t>(now) - static_cast<int64_t>(cred->cacheTimestamp));
+        const bool ttlOk = (cred->cacheTimestamp == 0) || (now == 0) || (elapsed < TTL_SECONDS);
+        if (ttlOk) {
+          IPAddress ip(cred->ip[0], cred->ip[1], cred->ip[2], cred->ip[3]);
+          IPAddress gw(cred->gateway[0], cred->gateway[1], cred->gateway[2], cred->gateway[3]);
+          IPAddress mask(cred->mask[0], cred->mask[1], cred->mask[2], cred->mask[3]);
+          IPAddress dns(cred->dns[0], cred->dns[1], cred->dns[2], cred->dns[3]);
+          WiFi.config(ip, gw, mask, dns);
+          appliedStaticIp = true;
+        } else {
+          LOG_DBG("WIFI", "IP cache aged out (ts=%u, now=%ld), using DHCP", cred->cacheTimestamp, (long)now);
+        }
+      }
+    }
+  }
+
+  if (!appliedStaticIp) {
+    // Reset to DHCP in case a previous attempt left a static config behind.
+    WiFi.config(IPAddress(), IPAddress(), IPAddress(), IPAddress());
+  }
+
+  const char* pwd = (selectedRequiresPassword && !enteredPassword.empty()) ? enteredPassword.c_str() : nullptr;
+  const unsigned long preBeginMs = millis() - connectionStartTime;
+  if (currentAttemptChannel != 0) {
+    LOG_DBG("WIFI", "WiFi.begin -> %s ch=%d bssid=%02x:%02x:%02x:%02x:%02x:%02x staticIp=%s (pre-begin %lu ms)",
+            selectedSSID.c_str(), currentAttemptChannel, currentAttemptBssid[0], currentAttemptBssid[1],
+            currentAttemptBssid[2], currentAttemptBssid[3], currentAttemptBssid[4], currentAttemptBssid[5],
+            appliedStaticIp ? "yes" : "no", preBeginMs);
+    WiFi.begin(selectedSSID.c_str(), pwd, currentAttemptChannel, currentAttemptBssid, true);
   } else {
-    WiFi.begin(selectedSSID.c_str());
+    LOG_DBG("WIFI", "WiFi.begin -> %s (no hint, pre-begin %lu ms)", selectedSSID.c_str(), preBeginMs);
+    if (pwd) {
+      WiFi.begin(selectedSSID.c_str(), pwd);
+    } else {
+      WiFi.begin(selectedSSID.c_str());
+    }
   }
 }
 
@@ -399,11 +486,31 @@ void WifiSelectionActivity::checkConnectionStatus() {
     connectedIP = ipStr;
     autoConnecting = false;
 
-    // Save this as the last connected network - SD card operations need lock as
-    // we use SPI for both
+    LOG_DBG("WIFI", "Connected to %s in %lu ms (rssi=%d ch=%d ip=%s, hint=%s)", selectedSSID.c_str(),
+            millis() - connectionStartTime, WiFi.RSSI(), WiFi.channel(), ipStr,
+            currentAttemptChannel != 0 ? "yes" : "no");
+
+    // Save this as the last connected network and cache the full connection profile
+    // (BSSID/channel + IP/gw/mask/dns) so the next reconnect can skip both channel
+    // scanning and DHCP. SD card operations need lock as we use SPI for both.
     {
       RenderLock lock(*this);
       WIFI_STORE.setLastConnectedSsid(selectedSSID);
+      const uint8_t* actualBssid = WiFi.BSSID();
+      const int actualChannel = WiFi.channel();
+      if (actualBssid && actualChannel > 0 && actualChannel <= 255) {
+        const IPAddress gw = WiFi.gatewayIP();
+        const IPAddress mask = WiFi.subnetMask();
+        const IPAddress dns = WiFi.dnsIP();
+        const uint8_t ipBytes[4] = {ip[0], ip[1], ip[2], ip[3]};
+        const uint8_t gwBytes[4] = {gw[0], gw[1], gw[2], gw[3]};
+        const uint8_t maskBytes[4] = {mask[0], mask[1], mask[2], mask[3]};
+        const uint8_t dnsBytes[4] = {dns[0], dns[1], dns[2], dns[3]};
+        const time_t nowEpoch = HalClock::now();
+        WIFI_STORE.updateConnectionCache(selectedSSID, actualBssid, static_cast<uint8_t>(actualChannel), ipBytes,
+                                         gwBytes, maskBytes, dnsBytes,
+                                         nowEpoch > 0 ? static_cast<uint32_t>(nowEpoch) : 0u);
+      }
     }
 
     // Check for captive portal before declaring success
@@ -429,6 +536,25 @@ void WifiSelectionActivity::checkConnectionStatus() {
     return;
   }
 
+  // If this attempt used a hint and the hint hasn't paid off (channel may have changed
+  // because the AP is part of a mesh / roamed), retry once with a full scan before
+  // surfacing failure or moving to the next candidate. Triggered on either a hard
+  // failure status or a short timeout — whichever comes first.
+  const bool usingHint = currentAttemptChannel != 0;
+  const bool hintHardFail =
+      usingHint && !hintFallbackDone && (status == WL_CONNECT_FAILED || status == WL_NO_SSID_AVAIL);
+  const bool hintTimedOut =
+      usingHint && !hintFallbackDone && (millis() - connectionStartTime > HINT_ATTEMPT_TIMEOUT_MS);
+  if (hintHardFail || hintTimedOut) {
+    LOG_DBG("WIFI", "Hint attempt did not connect (%s after %lu ms), retrying with full scan",
+            hintHardFail ? "hard fail" : "timeout", millis() - connectionStartTime);
+    hintFallbackDone = true;
+    WiFi.disconnect(true, false);
+    connectionStartTime = millis();
+    issueWifiBegin(/*useHint=*/false);
+    return;
+  }
+
   const unsigned long timeout =
       state == WifiSelectionState::AUTO_CYCLING ? AUTO_CYCLE_TIMEOUT_MS : CONNECTION_TIMEOUT_MS;
 

src/activities/network/WifiSelectionActivity.h

@@ -86,8 +86,23 @@ class WifiSelectionActivity final : public Activity {
   // Connection timeouts
   static constexpr unsigned long CONNECTION_TIMEOUT_MS = 15000;
   static constexpr unsigned long AUTO_CYCLE_TIMEOUT_MS = 5000;
+  // Faster timeout for the first hint-based attempt before falling back to full scan.
+  // Hint-based connect on the correct channel usually completes in <2 s; if it doesn't,
+  // the AP has likely moved (mesh roam, channel change) so it's cheaper to bail and rescan.
+  static constexpr unsigned long HINT_ATTEMPT_TIMEOUT_MS = 3000;
   unsigned long connectionStartTime = 0;
 
+  // BSSID/channel hint used on the current attempt (channel==0 means no hint).
+  uint8_t currentAttemptBssid[6] = {0};
+  uint8_t currentAttemptChannel = 0;
+  // Whether we've already done the silent fallback retry without the hint for this
+  // user-initiated connection. Prevents loops if the AP genuinely isn't reachable.
+  bool hintFallbackDone = false;
+
+  // WiFi event handler IDs so we can deregister on exit.
+  uint16_t evtIdConnected = 0;
+  uint16_t evtIdGotIp = 0;
+
   void renderNetworkList() const;
   void renderPasswordEntry() const;
   void renderConnecting() const;
@@ -104,6 +119,14 @@ class WifiSelectionActivity final : public Activity {
   void selectNetwork(int index);
   void attemptConnection();
   void checkConnectionStatus();
+  // Issues WiFi.begin() either with the cached BSSID/channel hint (fast path) or without
+  // (full scan fallback). `useHint=false` clears currentAttemptChannel so the success path
+  // doesn't double-store the same hint.
+  void issueWifiBegin(bool useHint);
+  // Prepares the WiFi stack for a connect attempt: ensures STA mode and a clean state,
+  // sets a deterministic hostname. Skips the expensive disconnect(true,true) when WiFi
+  // is already idle so the warm reconnect path doesn't pay an NVS-erase cost.
+  void prepareForConnect();
   bool checkCaptivePortal();
   std::string getSignalStrengthIndicator(int32_t rssi) const;