[wpiutil] Add mDNS resolver and announcer (#3733)

wpiutil/src/main/native/linux/MulticastServiceResolver.cpp

@@ -0,0 +1,148 @@
+// Copyright (c) FIRST and other WPILib contributors.
+// Open Source Software; you can modify and/or share it under the terms of
+// the WPILib BSD license file in the root directory of this project.
+
+#include "wpi/MulticastServiceResolver.h"
+
+#include "AvahiClient.h"
+#include "wpi/SmallString.h"
+#include "wpi/mutex.h"
+
+using namespace wpi;
+
+struct MulticastServiceResolver::Impl {
+  AvahiFunctionTable& table = AvahiFunctionTable::Get();
+  std::shared_ptr<AvahiThread> thread = AvahiThread::Get();
+  AvahiClient* client;
+  AvahiServiceBrowser* browser;
+  std::string serviceType;
+  MulticastServiceResolver* resolver;
+
+  void onFound(ServiceData&& data) {
+    resolver->eventQueue.push(std::move(data));
+    resolver->event.Set();
+  }
+};
+
+MulticastServiceResolver::MulticastServiceResolver(
+    std::string_view serviceType) {
+  pImpl = std::make_unique<Impl>();
+  pImpl->serviceType = serviceType;
+  pImpl->resolver = this;
+}
+
+MulticastServiceResolver::~MulticastServiceResolver() noexcept {
+  Stop();
+}
+
+bool MulticastServiceResolver::HasImplementation() const {
+  return pImpl->table.IsValid();
+}
+
+static void ResolveCallback(AvahiServiceResolver* r, AvahiIfIndex interface,
+                            AvahiProtocol protocol, AvahiResolverEvent event,
+                            const char* name, const char* type,
+                            const char* domain, const char* host_name,
+                            const AvahiAddress* address, uint16_t port,
+                            AvahiStringList* txt, AvahiLookupResultFlags flags,
+                            void* userdata) {
+  MulticastServiceResolver::Impl* impl =
+      reinterpret_cast<MulticastServiceResolver::Impl*>(userdata);
+
+  if (event == AVAHI_RESOLVER_FOUND) {
+    if (address->proto == AVAHI_PROTO_INET) {
+      AvahiStringList* strLst = txt;
+      MulticastServiceResolver::ServiceData data;
+      while (strLst != nullptr) {
+        std::string_view value{reinterpret_cast<const char*>(strLst->text),
+                               strLst->size};
+        strLst = strLst->next;
+        size_t splitIndex = value.find('=');
+        if (splitIndex == value.npos) {
+          // Todo make this just do key
+          continue;
+        }
+        std::string_view key = value.substr(0, splitIndex);
+        value = value.substr(splitIndex + 1, value.size() - splitIndex - 1);
+        data.txt.emplace_back(std::pair<std::string, std::string>{key, value});
+      }
+      wpi::SmallString<256> outputHostName;
+      char label[256];
+      do {
+        impl->table.unescape_label(&host_name, label, sizeof(label));
+        if (label[0] == '\0') {
+          break;
+        }
+        outputHostName.append(label);
+        outputHostName.append(".");
+      } while (true);
+
+      data.ipv4Address = address->data.ipv4.address;
+      data.port = port;
+      data.serviceName = name;
+      data.hostName = outputHostName.string();
+
+      impl->onFound(std::move(data));
+    }
+  }
+
+  impl->table.service_resolver_free(r);
+}
+
+static void BrowseCallback(AvahiServiceBrowser* b, AvahiIfIndex interface,
+                           AvahiProtocol protocol, AvahiBrowserEvent event,
+                           const char* name, const char* type,
+                           const char* domain, AvahiLookupResultFlags flags,
+                           void* userdata) {
+  MulticastServiceResolver::Impl* impl =
+      reinterpret_cast<MulticastServiceResolver::Impl*>(userdata);
+
+  if (event == AVAHI_BROWSER_NEW) {
+    impl->table.service_resolver_new(
+        impl->table.service_browser_get_client(b), interface, protocol, name,
+        type, domain, AVAHI_PROTO_UNSPEC, AVAHI_LOOKUP_USE_MULTICAST,
+        ResolveCallback, userdata);
+  }
+}
+
+static void ClientCallback(AvahiClient* client, AvahiClientState state,
+                           void* userdata) {
+  MulticastServiceResolver::Impl* impl =
+      reinterpret_cast<MulticastServiceResolver::Impl*>(userdata);
+
+  if (state == AVAHI_CLIENT_S_RUNNING) {
+    impl->browser = impl->table.service_browser_new(
+        client, AVAHI_IF_UNSPEC, AVAHI_PROTO_UNSPEC, impl->serviceType.c_str(),
+        "local", AvahiLookupFlags::AVAHI_LOOKUP_USE_MULTICAST, BrowseCallback,
+        userdata);
+  }
+}
+
+void MulticastServiceResolver::Start() {
+  if (!pImpl->table.IsValid()) {
+    return;
+  }
+  std::scoped_lock lock{*pImpl->thread};
+  if (pImpl->client) {
+    return;
+  }
+
+  pImpl->client =
+      pImpl->table.client_new(pImpl->thread->GetPoll(), AVAHI_CLIENT_NO_FAIL,
+                              ClientCallback, pImpl.get(), nullptr);
+}
+
+void MulticastServiceResolver::Stop() {
+  if (!pImpl->table.IsValid()) {
+    return;
+  }
+  std::scoped_lock lock{*pImpl->thread};
+  if (pImpl->client) {
+    if (pImpl->browser) {
+      pImpl->table.service_browser_free(pImpl->browser);
+      pImpl->browser = nullptr;
+    }
+    pImpl->table.client_free(pImpl->client);
+    pImpl->client = nullptr;
+  }
+}