examples/lwip_ipv4: add example for LWIP IPv4 client/server by krzysztof-cabaj · Pull Request #21519 · RIOT-OS/RIOT

krzysztof-cabaj · 2025-05-31T16:45:43Z

Contribution description

This PR adds new example which shows how to implement LWIP IPv4 client and server.

Moreover, this example can be used in CI to check, if new code do not break LWIP IPv4.
In the previous few months at least two problems with LWIP IPv4 are detected manually,
and they should be detected by CI - see PR #21316 or PR #21342.

Testing procedure

Check client and server commands as described in the README.md.

Issues/PRs references

None

examples/networking/misc/lwip_ipv4/main.c

riot-ci · 2025-06-03T14:54:04Z

Murdock results

✔️ PASSED

33365ca examples/lwip_ipv4: enable DHCP and server autostart

Success	Failures	Total	Runtime
17	0	17	01m:31s

Artifacts

Documentation preview

krzysztof-cabaj · 2025-06-03T17:35:11Z

I try to generate makefile.ci automatically using sudo make -C ./examples/networking/misc/lwip_ipv4 generate-Makefile.ci
but after around 1h and occupied 5GB of disk it still stuck at acd52832 board.

@crasbe could you add label CI: no fast fail so I could generate makefile.ci manually.

crasbe · 2025-06-03T19:04:48Z

I'll run it on my work computer tomorrow, then you can address the suggestions without triggering a full rebuild on every fixup.

crasbe · 2025-06-04T09:04:20Z

This is the result for generate-Makefile.ci for your example:

BOARD_INSUFFICIENT_MEMORY := \
    bluepill-stm32f030c8 \
    i-nucleo-lrwan1 \
    nucleo-c031c6 \
    nucleo-f030r8 \
    nucleo-f031k6 \
    nucleo-f042k6 \
    nucleo-l011k4 \
    nucleo-l031k6 \
    nucleo-l053r8 \
    samd10-xmini \
    slstk3400a \
    stk3200 \
    stm32f030f4-demo \
    stm32f0discovery \
    stm32g0316-disco \
    stm32l0538-disco \
    weact-g030f6 \
    #

krzysztof-cabaj · 2025-06-04T16:45:26Z

@crasbe Thanks for Makefile.ci generation.

examples/networking/misc/lwip_ipv4/main.c

benpicco · 2025-06-11T15:22:30Z

examples/networking/misc/lwip_ipv4/main.c

+        mutex_lock(&server_mutex);
+        server_running = 0;
+        mutex_unlock(&server_mutex);


What do you need that for?

My idea is that if due to some errors this thread ends - we could start server once again.
I tested this situation with similar code after sock_udp_recv function (lines 98-105). When RIOT receives UDP datagram longer than 64 bytes (buffer size) it ends with error, but I could restart server and later everything works well.

But why the need for a mutex?

This variable is changed by other thread (CLI thread in server command). Also I leave this in the example as example of synchronization. Yes, I known that probability of hazards or race is minimal.

I could leave this, remove mutex (in my opinion all should works fine, only in very rare case user have to issue server command once again, after error message that thread is started) or rewrite code to use _Atomic and atomic_compare_exchange_strong.

krzysztof-cabaj · 2025-06-13T10:30:54Z

All remarks from review fixed.
CI is green.

krzysztof-cabaj · 2025-06-18T08:57:33Z

Can me move this PR a little forward?

examples/networking/misc/lwip_ipv4/main.c

benpicco · 2025-06-18T11:53:51Z

examples/networking/misc/lwip_ipv4/main.c

+    }
+
+    if (data_len != (size_t)sock_udp_send(&sock, argv[3], data_len, NULL)) {
+        printf("Error sock_udp_send!\n");


You likely want to print the error.

Yes I want to print error.
Your comment concerns wrong condition? You suggest add only condition for <0?

sock_udp_send() gives you an error code that can tell the user why the send failed.

Ok. Thanks for hint!

I add printing error code to error message. Is that OK?

examples/networking/misc/lwip_ipv4/main.c

benpicco · 2025-06-18T11:56:29Z

examples/networking/misc/lwip_ipv4/main.c

+        mutex_lock(&server_mutex);
+        server_running = 0;
+        mutex_unlock(&server_mutex);


But why the need for a mutex?

examples/networking/misc/lwip_ipv4/main.c

krzysztof-cabaj · 2025-07-08T12:24:45Z

Can me move this PR little forward?

krzysztof-cabaj · 2025-08-08T07:56:08Z

@benpicco I fix most of your remarks and have questions to one or too.

Could you review the code once again and could we move this PR forward?

krzysztof-cabaj · 2025-08-18T12:08:03Z

Beginning of new week ... good time to finish this PR :)

@benpicco - can be move it little bit forward?

benpicco · 2025-12-17T12:41:19Z

Huh how did you get there?
Do you have a 'Submit Review' button on the Changes view?

krzysztof-cabaj

This should show all my pending comments.

krzysztof-cabaj · 2025-06-20T12:35:34Z

examples/networking/misc/lwip_ipv4/main.c

+        mutex_lock(&server_mutex);
+        server_running = 0;
+        mutex_unlock(&server_mutex);


This variable is changed by other thread (CLI thread in server command). Also I leave this in the example as example of synchronization. Yes, I known that probability of hazards or race is minimal.

I could leave this, remove mutex (in my opinion all should works fine, only in very rare case user have to issue server command once again, after error message that thread is started) or rewrite code to use _Atomic and atomic_compare_exchange_strong.

krzysztof-cabaj · 2025-06-20T14:55:07Z

examples/networking/misc/lwip_ipv4/main.c

+    }
+
+    if (data_len != (size_t)sock_udp_send(&sock, argv[3], data_len, NULL)) {
+        printf("Error sock_udp_send!\n");


Ok. Thanks for hint!

krzysztof-cabaj · 2025-06-20T15:51:16Z

examples/networking/misc/lwip_ipv4/main.c

+    }
+
+    if (data_len != (size_t)sock_udp_send(&sock, argv[3], data_len, NULL)) {
+        printf("Error sock_udp_send!\n");


I add printing error code to error message. Is that OK?

examples/networking/misc/lwip_ipv4/main.c

examples/networking/misc/lwip_ipv4/Makefile

examples/networking/misc/lwip_ipv4/main.c

krzysztof-cabaj · 2025-12-17T14:37:51Z

@benpicco thanks for spotting the problem and showing solution. I don't now why some of my comments are not send - I'm almost certain that I post all comments in this same manner.

I see that some of the comments are pending from June :(

I hope this allows us finalizing this PR without problems - and answers the question why you do not see my comments.

examples/networking/misc/lwip_ipv4/main.c

krzysztof-cabaj · 2025-12-19T08:59:04Z

@benpicco I try to fix all comments. If I missed something please let me known.

I leave two issues, which are not changed:

mutex - I still would like to leave this. We have two thread - CLI and server, which read and write this same variable server_running. In my opinion this needs synchronization.
Ending the server when too long packet is received. This is some kind of feature which allows clear closing of the server and restarting it with new port. If you agree with such solution I could add clear explanation in the README.md file.

krzysztof-cabaj · 2025-12-20T16:23:38Z

I simplify the example. Server thread is started automatically, and cannot be stopped.
This removes need for synchronization (usage of server_mutex variable) and CLI command for server start.
The README.md is updated accordingly.

benpicco

Thank you, that's much better.
An example shouldn't come with too many bells and whistles that will just confuse people.

krzysztof-cabaj · 2025-12-22T11:37:13Z

Murdock complains about small ROM and RAM for stm32c0116-dk.

I add this board to the Makefile.ci ... and also add stm32c0316-dk - this board has this same amount of RAM and ROM.

krzysztof-cabaj · 2025-12-23T08:34:35Z

Could we add this PR to merge queue once again ...
... I hope this time everything goes smooth.

maribu · 2025-12-23T09:06:30Z

Thx for adding this example ❤️

krzysztof-cabaj · 2025-12-23T14:08:22Z

@crasbe, @benpicco and @maribu thanks for support with my longest, and most commented PR.

krzysztof-cabaj requested a review from jia200x as a code owner May 31, 2025 16:45

github-actions bot added Area: doc Area: Documentation Area: examples Area: Example Applications labels May 31, 2025

krzysztof-cabaj force-pushed the examples-lwip_ipv4 branch from 30edfe6 to b6ba8d4 Compare May 31, 2025 16:53

benpicco reviewed Jun 2, 2025

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crasbe added Type: enhancement The issue suggests enhanceable parts / The PR enhances parts of the codebase / documentation CI: ready for build If set, CI server will compile all applications for all available boards for the labeled PR labels Jun 3, 2025

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benpicco reviewed Jun 11, 2025

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krzysztof-cabaj force-pushed the examples-lwip_ipv4 branch 3 times, most recently from 85936e5 to eeb5403 Compare June 20, 2025 17:45

krzysztof-cabaj force-pushed the examples-lwip_ipv4 branch from 376fdf3 to 5c2ae13 Compare August 18, 2025 12:11

krzysztof-cabaj commented Dec 17, 2025

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examples/lwip_ipv4: add initial version of the lwip_ipv4 example

3581007

krzysztof-cabaj force-pushed the examples-lwip_ipv4 branch from f836f51 to ab23020 Compare December 19, 2025 08:49

examples/lwip_ipv4: addition of example documentation

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krzysztof-cabaj force-pushed the examples-lwip_ipv4 branch from ab23020 to cfb07ac Compare December 20, 2025 16:17

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benpicco enabled auto-merge December 22, 2025 09:16

benpicco added CI: ready for build If set, CI server will compile all applications for all available boards for the labeled PR and removed CI: ready for build If set, CI server will compile all applications for all available boards for the labeled PR labels Dec 22, 2025

benpicco added this pull request to the merge queue Dec 22, 2025

github-merge-queue bot removed this pull request from the merge queue due to failed status checks Dec 22, 2025

krzysztof-cabaj added 3 commits December 22, 2025 12:34

examples/lwip_ipv4: add makefile.ci

fde797f

examples/lwip_ipv4: move licenses to SPDX format

a45d1b0

examples/lwip_ipv4: enable DHCP and server autostart

33365ca

krzysztof-cabaj force-pushed the examples-lwip_ipv4 branch from cfb07ac to 33365ca Compare December 22, 2025 11:35

maribu added this pull request to the merge queue Dec 23, 2025

Merged via the queue into RIOT-OS:master with commit 7ba922f Dec 23, 2025
25 checks passed

krzysztof-cabaj mentioned this pull request Dec 29, 2025

pkg/lwip: add LWP_IP4_ADDR_INIT macro #21969

Merged

leandrolanzieri added this to the Release 2026.01 milestone Jan 13, 2026

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Contribution description

Testing procedure

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Murdock results

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krzysztof-cabaj commented Jun 3, 2025

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krzysztof-cabaj commented Jun 13, 2025

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krzysztof-cabaj commented Jul 8, 2025

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krzysztof-cabaj commented May 31, 2025 •

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