A caller can stop waiting for a DNS result while the resolver keeps the request and callback. If another lwIP client continues polling, that callback can later use state which its owner has already released.
Add dns_cancel() to remove matching callbacks without canceling a query shared by other callers. Use it when stopping SNTP so a pending name lookup cannot outlive the client. Signed-off-by: James Hilliard <[email protected]> --- lib/lwip/lwip/src/apps/sntp/sntp.c | 3 +++ lib/lwip/lwip/src/core/dns.c | 26 ++++++++++++++++++++++++++ lib/lwip/lwip/src/include/lwip/dns.h | 1 + 3 files changed, 30 insertions(+) diff --git a/lib/lwip/lwip/src/apps/sntp/sntp.c b/lib/lwip/lwip/src/apps/sntp/sntp.c index 0e7f36520fa..a37699f65b7 100644 --- a/lib/lwip/lwip/src/apps/sntp/sntp.c +++ b/lib/lwip/lwip/src/apps/sntp/sntp.c @@ -711,6 +711,9 @@ void sntp_stop(void) { LWIP_ASSERT_CORE_LOCKED(); +#if SNTP_SERVER_DNS + dns_cancel(sntp_dns_found, NULL); +#endif if (sntp_pcb != NULL) { #if SNTP_MONITOR_SERVER_REACHABILITY u8_t i; diff --git a/lib/lwip/lwip/src/core/dns.c b/lib/lwip/lwip/src/core/dns.c index 6540f143bac..5762647ee27 100644 --- a/lib/lwip/lwip/src/core/dns.c +++ b/lib/lwip/lwip/src/core/dns.c @@ -387,6 +387,32 @@ dns_getserver(u8_t numdns) } } +/** + * @ingroup dns + * Cancel pending callbacks registered by dns_gethostbyname(). + * + * DNS queries shared with other callers continue so their result can still be + * cached and delivered. Only callbacks matching both arguments are removed. + * + * @param found callback passed to dns_gethostbyname() + * @param callback_arg callback argument passed to dns_gethostbyname() + */ +void +dns_cancel(dns_found_callback found, void *callback_arg) +{ + u8_t i; + + LWIP_ASSERT_CORE_LOCKED(); + + for (i = 0; i < DNS_MAX_REQUESTS; i++) { + if ((dns_requests[i].found == found) && + (dns_requests[i].arg == callback_arg)) { + dns_requests[i].found = NULL; + dns_requests[i].arg = NULL; + } + } +} + /** * The DNS resolver client timer - handle retries and timeouts and should * be called every DNS_TMR_INTERVAL milliseconds (every second by default). diff --git a/lib/lwip/lwip/src/include/lwip/dns.h b/lib/lwip/lwip/src/include/lwip/dns.h index 091341544f3..82579f09f35 100644 --- a/lib/lwip/lwip/src/include/lwip/dns.h +++ b/lib/lwip/lwip/src/include/lwip/dns.h @@ -111,6 +111,7 @@ err_t dns_gethostbyname(const char *hostname, ip_addr_t *addr, err_t dns_gethostbyname_addrtype(const char *hostname, ip_addr_t *addr, dns_found_callback found, void *callback_arg, u8_t dns_addrtype); +void dns_cancel(dns_found_callback found, void *callback_arg); #if DNS_LOCAL_HOSTLIST -- 2.53.0
