net: sntp: implement SNTP server library #96040

lfelten · 2025-09-15T20:46:24Z

Implementation of SNTP server functionality (RFC 5905)

Zephyr software example is also provided.

subsys/net/lib/sntp/sntp_server.c

+ret = sendto(data->sock, &sntp_reply, sizeof(struct sntp_pkt), 0, &client_addr,
+ client_addr_len);


subsys/net/lib/sntp/sntp_server.c

Implementation of SNTP server functionality (RFC 5905) Zephyr software example is also provided. Signed-off-by: Lothar Felten <lothar.felten@gmail.com>

pdgendt · 2025-09-16T07:03:36Z

@jukkar can probably comment on this, but shouldn't we use a socket service for this?

sonarqubecloud · 2025-09-16T07:17:04Z

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jukkar · 2025-09-16T08:45:04Z

subsys/net/lib/sntp/sntp_server.c

+char recv_buffer[SNTP_SERVER_RX_BUFFER_SIZE];
+};
+
+static struct sntp_pkt sntp_reply;


Why having a global reply buffer as this prevents multiple threads to send data at the same time? Can't we allocate this from stack in each receive function?

jukkar · 2025-09-16T08:46:30Z

subsys/net/lib/sntp/sntp_server.c

+return ret;
+}
+
+static void sntp_udp4_thread(void)


I think we could use socket service API here to avoid these IPv4 and IPv6 threads and save some memory.

Thanks, I'll look into the socket service API and I'll rewrite the code.

jukkar · 2025-09-16T08:50:24Z

can probably comment on this, but shouldn't we use a socket service for this?

Yes, I think so. Noticed your comment after giving mine about the same issue.

kartben · 2025-09-16T08:38:28Z

subsys/net/lib/sntp/sntp_server.c

+while (ret == 0) {
+sntp_process_packet(&data_ipv4);


infinite loop

Suggested change

while (ret == 0) {

sntp_process_packet(&data_ipv4);

while (ret == 0) {

ret = sntp_process_packet(&data_ipv4);

kartben · 2025-09-16T08:39:33Z

subsys/net/lib/sntp/Kconfig

+endif # SNTP client
+
+config SNTP_SERVER
+bool "SNTP client support"


Suggested change

bool "SNTP client support"

bool "SNTP server support"

kartben · 2025-09-16T08:51:32Z

subsys/net/lib/sntp/sntp_server.c

+sntp_reply.orig_tm_s = pkt->tx_tm_s;
+sntp_reply.orig_tm_f = pkt->tx_tm_f;
+sntp_reply.rx_tm_s = htonl(systime.tv_sec + OFFSET_1970_JAN_1);
+sntp_reply.rx_tm_f = htonl((systime.tv_nsec));


NTP timestamps use a 32-bit fractional second in units of 2⁻³² seconds, not nanoseconds.
Need to convert, something like:

uint32_t frac = (uint32_t)((((uint64_t)systime.tv_nsec) << 32) / 1000000000ULL); sntp_reply.rx_tm_f = htonl(frac);

kartben · 2025-09-16T08:51:52Z

subsys/net/lib/sntp/sntp_server.c

+return ret;
+}
+sntp_reply.tx_tm_s = htonl(systime.tv_sec + OFFSET_1970_JAN_1);
+sntp_reply.tx_tm_f = htonl((systime.tv_nsec));


kartben · 2025-09-16T08:54:43Z

samples/net/sockets/sntp_server/src/main.c

+return 0;
+}
+tp.tv_sec = t.seconds;
+tp.tv_nsec = t.fraction / 1000;


again, wrong handling of the fractional part, I think

Copilot

Pull Request Overview

This PR implements SNTP server functionality (RFC 5905) with automatic IPv4/IPv6 thread management and includes a complete example application.

Introduces SNTP server library that can handle client time requests on both IPv4 and IPv6
Refactors existing SNTP code to separate client and server components with shared constants
Provides configuration options for server thread stack size and priority

Reviewed Changes

Copilot reviewed 14 out of 14 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
subsys/net/lib/sntp/sntp_server.c	Core SNTP server implementation with packet processing and socket handling
subsys/net/lib/sntp/sntp_pkt.h	Shared SNTP constants moved from client code
subsys/net/lib/sntp/sntp.c	Refactored to use shared constants and make packet dump function public
subsys/net/lib/sntp/Kconfig	Configuration options for SNTP client/server separation
subsys/net/lib/sntp/CMakeLists.txt	Build system updates for conditional compilation
samples/net/sockets/sntp_server/*	Complete example application demonstrating SNTP server usage
samples/net/cloud/aws_iot_mqtt/prj.conf	Updated to use new SNTP_CLIENT config
include/zephyr/net/sntp_server.h	Public API header for SNTP server functionality

_{Tip: Customize your code reviews with copilot-instructions.md. Create the file or learn how to get started.}

Copilot · 2025-09-16T09:05:32Z

subsys/net/lib/sntp/sntp_server.c

+sntp_reply.li = SNTP_LEAP_INDICATOR_CLOCK_INVALID;
+sntp_reply.mode = SNTP_MODE_SERVER;
+sntp_reply.stratum = SNTP_STRATUM_KOD;
+sntp_reply.mode = SNTP_MODE_SERVER;


Duplicate assignment of sntp_reply.mode on line 48 and 50. Remove the redundant assignment on line 50.

Suggested change

sntp_reply.mode = SNTP_MODE_SERVER;

Copilot · 2025-09-16T09:05:33Z

subsys/net/lib/sntp/sntp_server.c

+sntp_reply.mode = SNTP_MODE_SERVER;
+sntp_reply.stratum = SNTP_STRATUM_KOD;
+sntp_reply.mode = SNTP_MODE_SERVER;
+strncpy((char *)(&sntp_reply.ref_id), "X", sizeof(sntp_reply.ref_id));


strncpy does not guarantee null termination. Use strlcpy or ensure null termination manually to prevent potential buffer overrun issues.

Suggested change

strncpy((char *)(&sntp_reply.ref_id), "X", sizeof(sntp_reply.ref_id));

strncpy((char *)(&sntp_reply.ref_id), "X", sizeof(sntp_reply.ref_id));

((char *)&sntp_reply.ref_id)[sizeof(sntp_reply.ref_id) - 1] = '\0';

subsys/net/lib/sntp/sntp_server.c

Copilot · 2025-09-16T09:05:33Z

subsys/net/lib/sntp/sntp_server.c

+int sntp_server_clock_source(unsigned char *refid, unsigned char stratum, char precision)
+{
+sntp_reply.stratum = stratum;
+strncpy((char *)(&sntp_reply.ref_id), refid, sizeof(sntp_reply.ref_id));


strncpy does not guarantee null termination. Use strlcpy or ensure null termination manually to prevent potential buffer overrun issues.

Suggested change

strncpy((char *)(&sntp_reply.ref_id), refid, sizeof(sntp_reply.ref_id));

strncpy((char *)(&sntp_reply.ref_id), refid, sizeof(sntp_reply.ref_id));

((char *)&sntp_reply.ref_id)[sizeof(sntp_reply.ref_id) - 1] = '\0';

jukkar

The sample changes should be separated to two separate commits, one for server sample and the other for aws changes. The actual sntp server changes should also be in separate commit. So in total three commits in the PR.

jukkar · 2025-09-16T14:10:23Z

samples/net/sockets/sntp_server/src/main.c

+
+LOG_INF("waiting for network");
+wait_for_network();
+ret = sntp_simple("ptbtime1.ptb.de", SYS_FOREVER_MS, &t);


The address of the server should be set via kconfig option. The server sample can have its own Kconfig file where the server name can be stored (see examples how to do this in other network samples). Note that the server name should be empty by default so that user is forced to set it according to his/hers network setup.

zephyrbot added area: Networking area: Sockets Networking sockets area: Samples Samples labels Sep 15, 2025

zephyrbot requested review from JarmouniA, jukkar, kartben, nashif, pdgendt, rlubos and ssharks September 15, 2025 20:47

zephyrbot assigned rlubos and jukkar Sep 15, 2025

lfelten force-pushed the sntp_server branch from 37cb0d0 to 1cb30ca Compare September 15, 2025 20:55

github-advanced-security bot found potential problems Sep 15, 2025

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lfelten force-pushed the sntp_server branch from 1cb30ca to 187609c Compare September 16, 2025 06:00

pdgendt reviewed Sep 16, 2025

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subsys/net/lib/sntp/sntp_server.c Show resolved Hide resolved

lfelten force-pushed the sntp_server branch from 187609c to ff6765a Compare September 16, 2025 06:49

net: sntp: implement SNTP server library

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Implementation of SNTP server functionality (RFC 5905) Zephyr software example is also provided. Signed-off-by: Lothar Felten <lothar.felten@gmail.com>

lfelten force-pushed the sntp_server branch from ff6765a to eecfced Compare September 16, 2025 06:57

jukkar reviewed Sep 16, 2025

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kartben requested changes Sep 16, 2025

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kartben requested a review from Copilot September 16, 2025 09:03

Copilot AI reviewed Sep 16, 2025

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net: sntp: implement SNTP server library #96040

net: sntp: implement SNTP server library #96040

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		ret = sendto(data->sock, &sntp_reply, sizeof(struct sntp_pkt), 0, &client_addr,
		client_addr_len);

	strncpy((char *)(&sntp_reply.ref_id), "X", sizeof(sntp_reply.ref_id));
	strncpy((char *)(&sntp_reply.ref_id), "X", sizeof(sntp_reply.ref_id));
	((char *)&sntp_reply.ref_id)[sizeof(sntp_reply.ref_id) - 1] = '\0';

	strncpy((char *)(&sntp_reply.ref_id), refid, sizeof(sntp_reply.ref_id));
	strncpy((char *)(&sntp_reply.ref_id), refid, sizeof(sntp_reply.ref_id));
	((char *)&sntp_reply.ref_id)[sizeof(sntp_reply.ref_id) - 1] = '\0';

net: sntp: implement SNTP server library #96040

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lfelten commented Sep 15, 2025

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Pull Request Overview

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