mdns: add mdns for local network routing (#511)

This PR implements [mDNS](https://en.wikipedia.org/wiki/Multicast_DNS)
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](https://developer.apple.com/bonjour/) and
don't need to pull down any dependencies at all. On Linux we can use
[Avahi](https://www.avahi.org/), specifically the bonjour compatibility
layer. The header we're using is
[dns_sd.h](https://github.com/lathiat/avahi/blob/master/avahi-compat-libdns_sd/dns_sd.h),
[documented
here](https://developer.apple.com/library/archive/documentation/Networking/Conceptual/dns_discovery_api/Introduction.html#//apple_ref/doc/uid/TP40002475-SW1).

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
```

WORKSPACE.bazel

@@ -121,6 +121,15 @@ versioned_http_archive(
     version = "9681279cfaa6e6399bb7ca3afbbc27fc2e19df4b",
 )
 
+versioned_http_archive(
+    name = "avahi",
+    build_file = "//bazel/third_party/avahi:avahi.BUILD",
+    sha256 = "060309d7a333d38d951bc27598c677af1796934dbd98e1024e7ad8de798fedda",
+    strip_prefix = "avahi-{version}",
+    url = "https://github.com/lathiat/avahi/releases/download/v{version}/avahi-{version}.tar.gz",
+    version = "0.8",
+)
+
 versioned_http_archive(
     name = "bazel_gazelle",
     sha256 = "efbbba6ac1a4fd342d5122cbdfdb82aeb2cf2862e35022c752eaddffada7c3f3",
@@ -145,6 +154,25 @@ versioned_http_archive(
     version = "7.85.0",
 )
 
+versioned_http_archive(
+    name = "dbus",
+    build_file = "//bazel/third_party/dbus:dbus.BUILD",
+    sha256 = "a6bd5bac5cf19f0c3c594bdae2565a095696980a683a0ef37cb6212e093bde35",
+    strip_prefix = "dbus-{version}",
+    url = "https://dbus.freedesktop.org/releases/dbus/dbus-{version}.tar.xz",
+    version = "1.14.8",
+)
+
+versioned_http_archive(
+    name = "expat",
+    build_file = "//bazel/third_party/expat:expat.BUILD",
+    strip_prefix = "expat-{version}",
+    sha256 = "ef2420f0232c087801abf705e89ae65f6257df6b7931d37846a193ef2e8cdcbe",
+    # TODO: fix the R_2_5_0 nonsense
+    url = "https://github.com/libexpat/libexpat/releases/download/R_2_5_0/expat-{version}.tar.xz",
+    version = "2.5.0",
+)
+
 versioned_http_archive(
     name = "gmp",
     build_file = "//bazel/third_party/gmp:gmp.BUILD",

bazel/third_party/avahi/avahi.BUILD

@@ -0,0 +1,30 @@
+load("@rules_foreign_cc//foreign_cc:defs.bzl", "configure_make")
+
+filegroup(
+    name = "all",
+    srcs = glob(["**"]),
+)
+
+cc_library(
+    name = "dns-sd",
+    hdrs = ["dns_sd.h"],
+    visibility = ["//visibility:public"],
+)
+
+configure_make(
+    name = "avahi",
+    args = select({
+        "@platforms//os:macos": ["--jobs=`sysctl -n hw.logicalcpu`"],
+        "//conditions:default": ["--jobs=`nproc`"],
+    }),
+    configure_options = ["--with-dbus-system-address='unix:path=/var/run/dbus/system_bus_socket' --with-xml=none --disable-libevent --disable-glib --disable-gobject --disable-gdbm --disable-qt3 --disable-qt4 --disable-qt5 --disable-gtk --disable-gtk3 --disable-mono --disable-monodoc --disable-python --disable-libdaemon --enable-compat-libdns_sd --disable-rpath"],
+    lib_source = ":all",
+    # out_include_dir = "avahi-compat-libdns_sd",
+    deps = ["@dbus"],
+    configure_in_place = True,
+    autogen = True,
+    autoconf = True,
+    autogen_command = "bootstrap.sh",
+    out_static_libs = ["libdns_sd.a", "libavahi-client.a", "libavahi-common.a"],
+    visibility = ["//visibility:public"],
+)

bazel/third_party/dbus/dbus.BUILD

@@ -0,0 +1,21 @@
+load("@rules_foreign_cc//foreign_cc:defs.bzl", "configure_make")
+
+filegroup(
+    name = "all",
+    srcs = glob(["**"]),
+)
+
+configure_make(
+    name = "dbus",
+    lib_name = "libdbus-1",
+    args = select({
+        "@platforms//os:macos": ["--jobs=`sysctl -n hw.logicalcpu`"],
+        "//conditions:default": ["--jobs=`nproc`"],
+    }),
+    copts = ["-O3"],
+    configure_options = ["--disable-selinux --without-x --disable-tests"],
+    lib_source = ":all",
+    configure_in_place = True,
+    deps = ["@expat"],
+    visibility = ["//visibility:public"],
+)

bazel/third_party/expat/expat.BUILD

@@ -0,0 +1,18 @@
+load("@rules_foreign_cc//foreign_cc:defs.bzl", "configure_make")
+
+filegroup(
+    name = "all",
+    srcs = glob(["**"]),
+)
+
+configure_make(
+    name = "expat",
+    args = select({
+        "@platforms//os:macos": ["--jobs=`sysctl -n hw.logicalcpu`"],
+        "//conditions:default": ["--jobs=`nproc`"],
+    }),
+    copts = ["-O3"],
+    lib_source = ":all",
+    out_static_libs = ["libexpat.a"],
+    visibility = ["//visibility:public"],
+)

pkg/c3/motes.h

@@ -308,6 +308,7 @@
 #   define c3__deep   c3_s4('d','e','e','p')
 #   define c3__defn   c3_s4('d','e','f','n')
 #   define c3__del    c3_s3('d','e','l')
+#   define c3__dear   c3_s4('d','e','a','r')
 #   define c3__delc   c3_s4('d','e','l','c')
 #   define c3__delt   c3_s4('d','e','l','t')
 #   define c3__dept   c3_s4('d','e','p','t')

pkg/vere/BUILD.bazel

@@ -119,7 +119,13 @@ vere_library(
     hdrs = [
         "db/lmdb.h",
         "vere.h",
-    ],
+        "mdns.h",
+    ] + select({
+        "@platforms//os:macos": [],
+        "@platforms//os:linux": [
+            "dns_sd.h",
+        ],
+        }),
     includes = ["."],
     linkstatic = True,
     visibility = ["//pkg:__subpackages__"],
@@ -133,7 +139,12 @@ vere_library(
         "@lmdb",
         "@openssl",
         "@uv",
-    ],
+    ] + select({
+        "@platforms//os:macos": [],
+        "@platforms//os:linux": [
+            "@avahi",
+        ],
+        })
 )
 
 #

pkg/vere/io/ames.c

@@ -1,6 +1,7 @@
 /// @file
 
 #include "vere.h"
+#include "mdns.h"
 
 #include "noun.h"
 #include "ur.h"
@@ -2083,6 +2084,50 @@ _ames_recv_cb(uv_udp_t*        wax_u,
   }
 }
 
+static void
+_mdns_dear_bail(u3_ovum* egg_u, u3_noun lud)
+{
+  u3z(lud);
+  u3_ovum_free(egg_u);
+}
+
+/* _ames_put_dear(): send lane to arvo after hearing mdns response
+*/
+static void
+_ames_put_dear(c3_c* ship, c3_w s_addr, c3_s port, void* context)
+{
+  u3_ames* sam_u = (u3_ames*)context;
+
+  u3_lane lan;
+  lan.pip_w = ntohl(s_addr);
+  lan.por_s = ntohs(port);
+
+  u3_noun whu = u3dc("slaw", c3__p, u3i_string(ship));
+
+  if (u3_nul == whu) {
+    u3l_log("ames: strange ship from mdns: %s", ship);
+    return;
+  }
+
+  u3_noun our = u3i_chubs(2, sam_u->pir_u->who_d);
+  if (our == u3t(whu)) {
+    u3z(whu);
+    u3z(our);
+    return;
+  }
+
+  u3z(our);
+
+  u3_noun wir = u3nc(c3__ames, u3_nul);
+  u3_noun cad = u3nt(c3__dear, u3k(u3t(whu)), u3nc(c3n, u3_ames_encode_lane(lan)));
+
+  u3_auto_peer(
+               u3_auto_plan(&sam_u->car_u,
+                            u3_ovum_init(0, c3__a, wir, cad)),
+               0, 0, _mdns_dear_bail);
+  u3z(whu);
+}
+
 /* _ames_io_start(): initialize ames I/O.
 */
 static void
@@ -2147,6 +2192,15 @@ _ames_io_start(u3_ames* sam_u)
     u3l_log("ames: live on %d (localhost only)", sam_u->pir_u->por_s);
   }
 
+  {
+    u3_noun our = u3dc("scot", 'p', u3k(who));
+    char* our_s = u3r_string(our);
+    u3z(our);
+
+    mdns_init(por_s, our_s, _ames_put_dear, (void *)sam_u);
+    c3_free(our_s);
+  }
+
   uv_udp_recv_start(&sam_u->wax_u, _ames_alloc, _ames_recv_cb);
 
   sam_u->car_u.liv_o = c3y;

pkg/vere/mdns.c

@@ -0,0 +1,210 @@
+/// @file
+
+#include "vere.h"
+#include "mdns.h"
+#include "dns_sd.h"
+
+typedef struct _mdns_payload {
+  mdns_cb*      cb;
+  DNSServiceRef sref;
+  char          who[58];
+  uint16_t      port;
+  uv_poll_t     poll;
+  void*         context;
+} mdns_payload;
+
+static void close_cb(uv_handle_t* poll) {
+  mdns_payload* payload = (mdns_payload*)poll->data;
+  DNSServiceRefDeallocate(payload->sref);
+  c3_free(payload);
+}
+
+static void getaddrinfo_cb(uv_getaddrinfo_t* req, int status, struct addrinfo* res) {
+  mdns_payload* payload = (mdns_payload*)req->data;
+
+  if (status < 0) {
+    u3l_log("mdns: getaddrinfo error: %s", uv_strerror(status));
+  } else {
+    struct sockaddr_in* addr = (struct sockaddr_in*)res->ai_addr;
+    payload->cb(payload->who, addr->sin_addr.s_addr, payload->port, payload->context);
+  }
+
+  payload->poll.data = payload;
+  uv_close((uv_handle_t*)&payload->poll, close_cb);
+  c3_free(req);
+  uv_freeaddrinfo(res);
+}
+
+static void resolve_cb(DNSServiceRef sref,
+                       DNSServiceFlags f,
+                       uint32_t interface,
+                       DNSServiceErrorType err,
+                       const char *name,
+                       const char *host,
+                       uint16_t port,
+                       uint16_t tl,
+                       const unsigned char *t,
+                       void *context)
+{
+  mdns_payload* payload = (mdns_payload*)context;
+
+  uv_poll_stop(&payload->poll);
+
+  if (err != kDNSServiceErr_NoError) {
+    u3l_log("mdns: dns resolve error %d", err);
+    payload->poll.data = payload;
+    uv_close((uv_handle_t*)&payload->poll, close_cb);
+    return;
+  }
+
+  payload->sref = sref;
+  payload->port = port;
+
+  int i;
+  payload->who[0] = '~';
+  for (i = 0; name[i] != '\0' && name[i] != '.' && i < 58; ++i)
+  {
+    payload->who[i+1] = name[i];
+  }
+
+  struct addrinfo hints;
+  memset(&hints, 0, sizeof(hints));
+  hints.ai_family = AF_INET; // Request only IPv4 addresses
+  hints.ai_socktype = SOCK_STREAM; // TCP socket
+
+  uv_getaddrinfo_t* req = (uv_getaddrinfo_t*)c3_malloc(sizeof(uv_getaddrinfo_t));
+  req->data = (void*)payload;
+
+  uv_loop_t* loop = uv_default_loop();
+
+  int error = uv_getaddrinfo(loop, req, getaddrinfo_cb, host, NULL, &hints);
+
+  if (error < 0) {
+    u3l_log("mdns: getaddrinfo error: %s\n", uv_strerror(error));
+    payload->poll.data = payload;
+    uv_close((uv_handle_t*)&payload->poll, close_cb);
+    c3_free(req);
+  }
+}
+
+static void poll_cb(uv_poll_t* handle, int status, int events) {
+  DNSServiceRef sref = (DNSServiceRef) handle->data;
+  int err = DNSServiceProcessResult(sref);
+}
+
+static void init_sref_poll(DNSServiceRef sref, mdns_payload* payload) {
+  int fd = DNSServiceRefSockFD(sref);
+  uv_loop_t* loop = uv_default_loop();
+  payload->poll.data = (void*)sref;
+  uv_poll_init(loop, &payload->poll, fd);
+  uv_poll_start(&payload->poll, UV_READABLE, poll_cb);
+}
+
+static void browse_cb(DNSServiceRef s,
+                      DNSServiceFlags f,
+                      uint32_t interface,
+                      DNSServiceErrorType err,
+                      const char* name,
+                      const char* type,
+                      const char* domain,
+                      void* context)
+{
+  if (err != kDNSServiceErr_NoError) {
+    u3l_log("mdns: service browse error %i", err);
+    return;
+  }
+
+  if (f & kDNSServiceFlagsAdd) {	// Add
+    // we are leaking payload because we don't know when we are done
+    // browsing, luckily we only browse once
+    mdns_payload* payload = (mdns_payload*)context;
+    mdns_payload* payload_copy = c3_malloc(sizeof *payload_copy);
+
+    // copy to prevent asynchronous thrashing of payload
+    memcpy(payload_copy, payload, sizeof(mdns_payload));
+
+
+    DNSServiceErrorType err =
+      DNSServiceResolve(&payload_copy->sref, 0, interface,
+                        name, type, domain, resolve_cb,
+                        (void*)payload_copy);
+
+    init_sref_poll(payload_copy->sref, payload_copy);
+
+    if (err != kDNSServiceErr_NoError) {
+      u3l_log("mdns: dns service resolve error %i", err);
+      payload_copy->poll.data = payload_copy;
+      uv_close((uv_handle_t*)&payload_copy->poll, close_cb);
+    }
+  }
+}
+
+static void register_close_cb(uv_handle_t* poll) {
+  // not freeing sref with DNSServiceRefDeallocate since that
+  // deregisters us from mdns
+  mdns_payload* payload = (mdns_payload*)poll->data;
+  c3_free(payload);
+}
+
+
+static void register_cb(DNSServiceRef sref,
+                        DNSServiceFlags f,
+                        DNSServiceErrorType err,
+                        const char* name,
+                        const char* type,
+                        const char* domain,
+                        void* context)
+{
+  mdns_payload* payload = (mdns_payload*)context;
+
+  if (err != kDNSServiceErr_NoError) {
+    u3l_log("mdns: service register error %i", err);
+  } else {
+    u3l_log("mdns: %s registered on all interfaces", name);
+  }
+  uv_poll_stop(&payload->poll);
+  uv_close((uv_handle_t*)&payload->poll, register_close_cb);
+}
+
+void mdns_init(uint16_t port, char* our, mdns_cb* cb, void* context)
+{
+  #if defined(U3_OS_linux)
+  setenv("AVAHI_COMPAT_NOWARN", "1", 0);
+  setenv("DBUS_SYSTEM_BUS_ADDRESS", "unix:path=/var/run/dbus/system_bus_socket", 0);
+  #   endif
+
+  mdns_payload* register_payload = (mdns_payload*)c3_malloc(sizeof(mdns_payload));
+
+  DNSServiceRef sref;
+  DNSServiceErrorType err;
+  char* our_no_sig = our + 1; // certain url parsers don't like the ~
+  err = DNSServiceRegister(&sref, 0, 0, our_no_sig, "_ames._udp",
+                           NULL, NULL, htons(port), 0, NULL, register_cb, (void*)register_payload);
+
+  if (err != kDNSServiceErr_NoError) {
+    u3l_log("mdns: service register error %i", err);
+    DNSServiceRefDeallocate(sref);
+    return;
+  }
+
+  init_sref_poll(sref, register_payload);
+
+  mdns_payload* browse_payload = (mdns_payload*)c3_malloc(sizeof(mdns_payload));
+
+  browse_payload->cb = cb;
+  browse_payload->context = context;
+
+  DNSServiceErrorType dnserr;
+  DNSServiceRef sref2;
+
+  dnserr = DNSServiceBrowse(&sref2, 0, 0, "_ames._udp", NULL, browse_cb, (void *)browse_payload);
+
+  if (dnserr != kDNSServiceErr_NoError) {
+    u3l_log("mdns: service browse error %i", dnserr);
+    DNSServiceRefDeallocate(sref2);
+    return;
+  }
+
+  init_sref_poll(sref2, browse_payload);
+
+}

pkg/vere/mdns.h

@@ -0,0 +1,5 @@
+#include "noun.h"
+
+typedef void mdns_cb(c3_c* ship, c3_w s_addr, c3_s port, void* context);
+
+void mdns_init(uint16_t port, char* our, mdns_cb* cb, void* context);