net: shell: dns: Add list command to show service records

Add "net dns list" command that will show DNS SD records
defined in the system.

Signed-off-by: Jukka Rissanen <jukka.rissanen@nordicsemi.no>

Author: jukkar

subsys/net/lib/shell/dns.c

@@ -10,6 +10,8 @@ LOG_MODULE_DECLARE(net_shell);
 
 #include <zephyr/net/socket.h>
 #include <zephyr/net/dns_resolve.h>
+#include <zephyr/net/dns_sd.h>
+#include "dns/dns_sd.h"
 
 #include "net_shell_private.h"
 
@@ -256,13 +258,62 @@ static int cmd_net_dns(const struct shell *sh, size_t argc, char *argv[])
 	return 0;
 }
 
+static int cmd_net_dns_list(const struct shell *sh, size_t argc, char *argv[])
+{
+#if defined(CONFIG_DNS_SD)
+#define MAX_PORT_LEN 6
+	char buf[MAX_PORT_LEN];
+	int n_records = 0;
+
+	DNS_SD_FOREACH(record) {
+		if (!dns_sd_rec_is_valid(record)) {
+			continue;
+		}
+
+		if (n_records == 0) {
+			PR("     DNS service records\n");
+		}
+
+		++n_records;
+
+		if (record->port != NULL) {
+			snprintk(buf, sizeof(buf), "%u", ntohs(*record->port));
+		}
+
+		PR("[%2d] %s.%s%s%s%s%s%s%s\n",
+		   n_records,
+		   record->instance != NULL ? record->instance : "",
+		   record->service != NULL ? record->service : "",
+		   record->proto != NULL ? "." : "",
+		   record->proto != NULL ? record->proto : "",
+		   record->domain != NULL ? "." : "",
+		   record->domain != NULL ? record->domain : "",
+		   record->port != NULL ? ":" : "",
+		   record->port != NULL ? buf : "");
+	}
+
+	if (n_records == 0) {
+		PR("No DNS service records found.\n");
+		return 0;
+	}
+#else
+	PR_INFO("DNS service discovery not supported. Set CONFIG_DNS_SD to "
+		"enable it.\n");
+#endif
+
+	return 0;
+}
+
 SHELL_STATIC_SUBCMD_SET_CREATE(net_cmd_dns,
 	SHELL_CMD(cancel, NULL, "Cancel all pending requests.",
 		  cmd_net_dns_cancel),
 	SHELL_CMD(query, NULL,
 		  "'net dns <hostname> [A or AAAA]' queries IPv4 address "
 		  "(default) or IPv6 address for a host name.",
 		  cmd_net_dns_query),
+	SHELL_CMD(list, NULL,
+		  "List local DNS service records.",
+		  cmd_net_dns_list),
 	SHELL_SUBCMD_SET_END
 );