engdavidiogo opened a new issue, #16044:
URL: https://github.com/apache/nuttx/issues/16044
### Description
**Summary**
I'm developing a simple HTTP server that listens for TCP connections on the
wlan1 interface (SoftAP mode).
The main loop uses `select()` with a timeout to wait for incoming
connections. However, even when a client is connected and sending valid HTTP
requests, the `select()` function never returns a positive value, which
prevents `accept()` from being called.
**The Problem**
- The TCP socket is properly configured using `socket()`, `bind()`, and
`listen()`, associated with the IP address of the SoftAP interface (`wlan1`).
- The main loop uses `select()` with a 1-second timeout to wait for
activity.
- Even when a **client is connected** and sends an **HTTP request,
`select()` always returns 0** (timeout).
- As a result, `FD_ISSET(server_sock, &read_fds)` is never true.
- This prevents `accept()` from being called, making the HTTP server
**completely inaccessible**, even with active network traffic.
**Expected behavior**
- A client connects to the SoftAP (`wlan1`).
- The client sends a valid HTTP request (e.g., `GET /state`).
- `server_sock` should be marked as readable.
- `select()` should return 1.
- `FD_ISSET(server_sock, &read_fds)` should be true.
- `accept()` should be called and the client handled.
**Current Behavior**
- `select()` **always returns** `0` (timeout), even when the client is
actively connected and sending requests.
- `FD_ISSET(server_sock, &read_fds)` is never true.
- `accept()` is never called.
- The server remains "active", but is completely unresponsive.
**Socket Configuration Example**
```c
server_sock = socket(AF_INET, SOCK_STREAM, 0);
netlib_get_ipv4addr("wlan1", &softap_ip);
server_addr.sin_family = AF_INET;
server_addr.sin_port = htons(80);
server_addr.sin_addr = softap_ip;
bind(server_sock, (struct sockaddr *)&server_addr, sizeof(server_addr));
listen(server_sock, 5);
```
**Main Loop with `select()`**
```c
while (webserver_running)
{
fd_set read_fds;
struct timeval timeout;
FD_ZERO(&read_fds);
FD_SET(server_sock, &read_fds);
timeout.tv_sec = 1;
timeout.tv_usec = 0;
int sel_ret = select(server_sock + 1, &read_fds, NULL, NULL, &timeout);
if (sel_ret < 0)
{
break; // select() failed
}
else if (sel_ret == 0)
{
continue; // Timeout, no activity
}
if (FD_ISSET(server_sock, &read_fds))
{
int client_sock = accept(server_sock, ...);
if (client_sock >= 0)
{
handle_client(client_sock);
}
}
}
```
**Questions**
1. Is this behavior **expected** when using NuttX sockets in SoftAP mode?
2. Is there any known limitation with `select()` or socket monitoring on the
`wlan1` interface?
3. Is the way I'm using `select()` appropriate in this context? Am I missing
something important?
4. Could it be that the current implementation of `select()` is not
correctly monitoring `SOCK_STREAM` sockets on the SoftAP (`wlan1`) interface?
*I would be grateful for any analysis or guidance!*
**Platform**
**Board:** *ESP32-C6 (ESP32C6-DevKitC)*
### Verification
- [x] I have verified before submitting the report.
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