Add channel verification after setting monitor mode

- Add get_current_channel() function to query actual channel/frequency
- Add freq_to_channel() helper to convert frequency back to channel
- Display verified channel and frequency after setting monitor mode
- Warn if requested channel doesn't match actual channel

Co-authored-by: Cursor <cursoragent@cursor.com>

src/main.c

@@ -9,6 +9,7 @@
 #include "monitor.h"
 #include "capture.h"
 #include "frame_parser.h"
+#include <stdint.h>
 
 static volatile int running = 1;
 static uint64_t packet_count = 0;
@@ -120,7 +121,21 @@ int main(int argc, char **argv) {
         return 1;
     }
     
-    printf("Monitor mode activated\n");
+    // Verify channel was set correctly
+    uint32_t actual_freq = 0;
+    int actual_channel = get_current_channel(interface, &actual_freq);
+    if (actual_channel > 0) {
+        printf("Monitor mode activated\n");
+        printf("Channel verified: %d (%u MHz)\n", actual_channel, actual_freq);
+        if (actual_channel != channel) {
+            fprintf(stderr, "Warning: Channel mismatch! Requested %d, got %d\n", 
+                    channel, actual_channel);
+        }
+    } else {
+        printf("Monitor mode activated\n");
+        printf("Warning: Could not verify channel (may still be correct)\n");
+    }
+    
     printf("Capturing 802.11 frames... (Ctrl+C to stop)\n");
     printf("This output can be compared with ESP32 monitor debug logs\n");
     if (filter_enabled) {

src/monitor.c

@@ -179,6 +179,108 @@ static uint32_t channel_to_freq(int channel) {
     }
 }
 
+// Convert frequency in MHz to WiFi channel number
+static int freq_to_channel(uint32_t freq_mhz) {
+    if (freq_mhz >= 2412 && freq_mhz <= 2484) {
+        // 2.4 GHz: channel = (freq - 2412) / 5 + 1
+        return (int)((freq_mhz - 2412) / 5) + 1;
+    } else if (freq_mhz >= 5000 && freq_mhz <= 5825) {
+        // 5 GHz: channel = (freq - 5000) / 5
+        return (int)((freq_mhz - 5000) / 5);
+    } else {
+        // Invalid frequency
+        return 0;
+    }
+}
+
+// Callback to extract frequency from GET_INTERFACE response
+static int get_interface_cb(struct nl_msg *msg, void *arg) {
+    struct nlattr *tb[NL80211_ATTR_MAX + 1];
+    struct genlmsghdr *gnlh = (struct genlmsghdr *)nlmsg_data(nlmsg_hdr(msg));
+    uint32_t *freq_out = (uint32_t *)arg;
+    
+    nla_parse(tb, NL80211_ATTR_MAX, genlmsg_attrdata(gnlh, 0),
+              genlmsg_attrlen(gnlh, 0), NULL);
+    
+    if (tb[NL80211_ATTR_WIPHY_FREQ]) {
+        *freq_out = nla_get_u32(tb[NL80211_ATTR_WIPHY_FREQ]);
+    }
+    
+    return NL_OK;
+}
+
+// Get current channel from interface
+int get_current_channel(const char *interface, uint32_t *freq_out) {
+    struct nl_msg *msg;
+    struct nl_cb *cb;
+    int ifindex;
+    int err = 0;
+    uint32_t freq = 0;
+    
+    if (nl80211_init() < 0) {
+        return -1;
+    }
+    
+    ifindex = if_nametoindex(interface);
+    if (ifindex == 0) {
+        nl80211_cleanup();
+        return -1;
+    }
+    
+    msg = nlmsg_alloc();
+    if (!msg) {
+        nl80211_cleanup();
+        return -1;
+    }
+    
+    genlmsg_put(msg, NL_AUTO_PID, NL_AUTO_SEQ, nl80211_id, 0,
+                NLM_F_REQUEST, NL80211_CMD_GET_INTERFACE, 0);
+    
+    NLA_PUT_U32(msg, NL80211_ATTR_IFINDEX, ifindex);
+    
+    cb = nl_cb_alloc(NL_CB_DEFAULT);
+    if (!cb) {
+        nlmsg_free(msg);
+        nl80211_cleanup();
+        return -1;
+    }
+    
+    // Set up callback to receive response
+    nl_cb_set(cb, NL_CB_VALID, NL_CB_CUSTOM, get_interface_cb, &freq);
+    
+    err = nl_send_auto_complete(nl_sock, msg);
+    if (err < 0) {
+        nl_cb_put(cb);
+        nlmsg_free(msg);
+        nl80211_cleanup();
+        return -1;
+    }
+    
+    // Receive response
+    err = nl_recvmsgs(nl_sock, cb);
+    
+    nl_cb_put(cb);
+    nlmsg_free(msg);
+    
+    if (err < 0 || freq == 0) {
+        nl80211_cleanup();
+        return -1;
+    }
+    
+    if (freq_out) {
+        *freq_out = freq;
+    }
+    
+    nl80211_cleanup();
+    return freq_to_channel(freq);
+    
+nla_put_failure:
+    nl_cb_put(cb);
+    nlmsg_free(msg);
+    nl80211_cleanup();
+    return -1;
+}
+
 int set_channel(const char *interface, int channel) {
     struct nl_msg *msg;
     int ifindex;

src/monitor.h

@@ -27,4 +27,12 @@ int restore_managed_mode(const char *interface);
  */
 int set_channel(const char *interface, int channel);
 
+/**
+ * @brief Get current channel from interface
+ * @param interface Interface name
+ * @param freq_out Optional pointer to receive frequency in MHz
+ * @return Channel number on success, -1 on error
+ */
+int get_current_channel(const char *interface, uint32_t *freq_out);
+
 #endif /* MONITOR_H */