# LISA HTTP SNTP

Enable `CONFIG_LISA_HTTPSNTP=y` and include `lisa_httpsntp.h`.
The component uses the existing HTTP client to issue HEAD requests and read
the Date header. It does not use UDP/NTP or change the system clock.

```c
const char *urls[] = {"http://www.aliyun.com/", "http://www.qq.com/"};
struct lisa_httpsntp_time now;
int ret = lisa_httpsntp_query(urls, 2, 2000, &now);
```

The result is UTC Unix seconds (2020 through 2099), with `nsec = 0`.
Only valid IMF-fixdate headers and HTTP 2xx/3xx responses are accepted.
The query tries URLs in order and leaves the output unchanged on failure.
Timeouts are milliseconds rounded up to seconds, separately for sending and
receiving on each server. DNS and TLS retain the underlying client's limits;
this is not an overall query deadline. Call from a worker thread.

HTTP Date offers second resolution, with additional network/cache delay; it
is unsuitable for precise clock discipline. HTTP is unauthenticated, as is
the existing plain SNTP service. HTTPS URLs use the SDK's existing certificate
configuration and require a usable initial clock when certificate date
verification is enabled. This component does not disable TLS verification.

snap-learn selects `CONFIG_PDK_NETWORK_PROBE_HTTPSNTP=y` to replace network
probe SNTP queries. `CONFIG_LISA_SNTP` remains enabled for the existing probe
lifecycle and LSChat dependency. Other apps retain their original backend.