mdns: add mdns for local network routing #511

pkova · 2023-09-04T19:36:58Z

This PR implements mDNS for vere, significantly improving Urbit routing inside local networks. On startup vere will now broadcast a service with the format dinleb-rambep._ames._udp.local. Vere will also listen for any services on the local network with the signature of _ames._udp. Whenever new services are found vere will send the lane to arvo.

On macOS we can use Bonjour and don't need to pull down any dependencies at all. On Linux we can use Avahi, specifically the bonjour compatibility layer. The header we're using is dns_sd.h, documented here.

Tested on macos aarch64 and linux x86_64 so far. To try it out, build vere from this PR, start a fakezod and observe:

# macos
dns-sd -B _ames._udp

# linux
avahi-browse -r _ames._udp

You can also start another fake ship on the same network and do |ames-verb %rcv %odd to see your fakeships find eachother. For this second part you need the companion arvo PR, here's a pill that has it already:

./urbit -F zod -u https://urbit-foundation.s3.us-east-2.amazonaws.com/dear.pill

pkova · 2023-09-04T19:45:15Z

pkg/vere/vere.h

+      /* mdns_init(): initialize mdns.
+      */
+        void
+        mdns_init(uint16_t port, char* our, mdns_cb* cb, void* context);


Where should I put this signature? vere.h seems wrong but don't really know where it should go.

pkova · 2023-09-05T12:29:51Z

I wonder what we should do in the following scenario:

Someone boots a fresh ship on your local network. You receive the mDNS notification and send a %dear to arvo, but since this is a fresh boot you won't have peer-state for the ship yet and the lane will get dropped on the ground. You won't receive a mDNS notification about this lane until either ship restarts vere.

This reverts commit 3779c75.

joemfb · 2023-09-06T15:43:22Z

pkg/vere/io/ames.c

+*/
+static void
+_ames_put_dear(char* ship, unsigned long s_addr, uint16_t port, void* context)
+{


This should use c3 types: _ames_put_dear(c3_c*, c3_w, c3_s, void*)

joemfb · 2023-09-06T15:43:53Z

pkg/vere/io/ames.c

+  if (our == u3t(shp_u)) {
+    u3z(our);
+    return;
+  }


This early return leaks shp_u

joemfb · 2023-09-06T15:45:04Z

pkg/vere/io/ames.c

+  u3_auto_peer(
+               u3_auto_plan(&sam_u->car_u,
+                            u3_ovum_init(0, c3__a, wir, cad)),
+               0, 0, _mdns_dear_bail);


We don't need to track or handle failures with these events.

I get real ugly crashes on arvo versions that don't support %dear unless I handle the bail myself.

joemfb · 2023-09-06T16:02:19Z

pkg/vere/mdns.c

+  uv_poll_stop(payload->poll);
+  c3_free(payload->poll);
+  c3_free(payload->our);
+  c3_free(payload);


leave a comment explaining why we leak sref.

joemfb · 2023-09-06T16:27:06Z

pkg/vere/mdns.c

+  register_payload->cb = cb;
+  register_payload->context = context;
+  register_payload->our = our;
+


It looks like you don't need to save our in payload. I would try removing that, and also just passing our + 1 to DNSServiceRegister() (maybe after checking that '~' = *our).

joemfb · 2023-09-06T16:29:14Z

pkg/vere/mdns.c

+  char*         who;
+  char*         our;
+  uint16_t      port;
+  uv_poll_t*    poll;


It looks like poll always has the same lifetime as payload, so it can just be uv_poll_t (no *).

joemfb · 2023-09-06T16:30:12Z

pkg/vere/mdns.c

+  poll->data = (void *)sref;
+  payload->poll = poll;
+  uv_poll_init(loop, poll, fd);
+  uv_poll_start(poll, UV_READABLE, poll_cb);


If poll has the same lifetime as payload (see above), you can remove the malloc here and just uv_poll_init(loop, &(payload->poll), fd);`

pkova requested a review from a team as a code owner September 4, 2023 19:36

pkova requested a review from joemfb September 4, 2023 19:37

pkova mentioned this pull request Sep 4, 2023

lull, ames: add %dear task to receive lane from unix urbit/urbit#6783

Merged

pkova force-pushed the pkova/mdns branch 2 times, most recently from ada3336 to 47ac3d7 Compare September 4, 2023 19:43

pkova commented Sep 4, 2023

View reviewed changes

mdns: add mdns for local network routing

704a619

pkova force-pushed the pkova/mdns branch from 47ac3d7 to 704a619 Compare September 4, 2023 21:26

pkova added 2 commits September 5, 2023 13:20

bazel: host h2o from s3 since github is unable to serve it reliably

3779c75

bazel: mess with config options to make dbus build in CI

b3c381a

pkova force-pushed the pkova/mdns branch from 383c44d to b3c381a Compare September 5, 2023 11:15

mdns: free our on register_cb fail

fd96138

pkova added 2 commits September 5, 2023 16:45

bazel: revert serving h2o from our s3 since github incident is over

66b17cc

This reverts commit 3779c75.

mdns: fix wonky indentation

43e9207

pkova force-pushed the pkova/mdns branch from 0bc0dad to 43e9207 Compare September 5, 2023 13:51

mdns: stop polling as soon as we reach resolve_cb

390735c

joemfb reviewed Sep 6, 2023

View reviewed changes

pkg/vere/io/ames.c

if (our == u3t(shp_u)) {

u3z(our);

return;

}

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joemfb Sep 6, 2023

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This early return leaks shp_u

joemfb reviewed Sep 6, 2023

View reviewed changes

pkova force-pushed the pkova/mdns branch 2 times, most recently from 1a48dfa to de78b05 Compare September 8, 2023 12:36

mdns: address joes feedback

e99d9b5

pkova force-pushed the pkova/mdns branch from de78b05 to e99d9b5 Compare September 8, 2023 12:58

pkova added 2 commits September 11, 2023 13:41

bazel: remove unused options from expat.BUILD

7aaa3a9

ames: shp_u -> whu in _ames_put_dear

4ac9875

pkova and others added 4 commits September 11, 2023 14:12

mdns: use pointer arithmetic instead of memmove to desig

b173a02

Merge branch 'develop' into pkova/mdns

b229a66

mdns: handle poll lifetimes properly

14a2d7a

Merge branch 'develop' into pkova/mdns

ae110cb

pkova merged commit e7e06d0 into develop Dec 5, 2023
5 checks passed

pkova deleted the pkova/mdns branch December 5, 2023 12:00

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mdns: add mdns for local network routing #511

mdns: add mdns for local network routing #511

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mdns: add mdns for local network routing #511

mdns: add mdns for local network routing #511

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