Re-land "Extend the mDNS package with a native extension used on Mac OS"

src/pkg/mdns/mdns_extension_macos.cc

Index: src/pkg/mdns/mdns_extension_macos.cc
diff --git a/src/pkg/mdns/mdns_extension_macos.cc b/src/pkg/mdns/mdns_extension_macos.cc
new file mode 100644
index 0000000000000000000000000000000000000000..586f366ee073f60bac2a17eed6256de2a95e9f8a
--- /dev/null
+++ b/src/pkg/mdns/mdns_extension_macos.cc
@@ -0,0 +1,131 @@
+// Copyright (c) 2015, the Fletch project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE.md file.
+
+#if defined(FLETCH_TARGET_OS_MACOS)
+
+#include <errno.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <arpa/inet.h>
+#include <pthread.h>
+
+#include <dns_sd.h>
+
+#include "include/dart_api.h"
+#include "include/dart_native_api.h"
+
+#include "mdns_extension.h"
+
+// Context passed to the callback receiving the mDNS information.
+struct Context {
+  // The Dart port where the result should be delivered.
+  Dart_Port port;
+};
+
+// Print fatal error and exit.
+static void Fatal(const char *message) {
+  fprintf(stderr, "%s (errno %d)\n", message, errno);
+  exit(-1);
+}
+
+// Code running in the threads started for pumping the results.
+static void* ThreadFunction(void* data) {
+  DNSServiceRef ref = reinterpret_cast<DNSServiceRef>(data);
+
+  // Preocess results until an error occurs.
+  DNSServiceErrorType result = kDNSServiceErr_NoError;
+  while (result == kDNSServiceErr_NoError) {
+    result = DNSServiceProcessResult(ref);
+  }
+  // The expected error from deallocation the ref.
+  if (result != kDNSServiceErr_BadReference) {
+    fprintf(stderr, "Error from DNSServiceProcessResult: %d\n", result);
+  }
+
+  return NULL;
+}
+
+// Start a thread for receiving results from a specific DNSServiceRef.
+static int StartThread(DNSServiceRef ref) {
+  pthread_attr_t attr;
+  int result = pthread_attr_init(&attr);
+  if (result != 0) Fatal("Error from pthread_attr_init");
+
+  result = pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED);
+  if (result != 0) Fatal("Error from pthread_attr_setdetachstate");
+
+  pthread_t tid;
+  result = pthread_create(&tid, &attr, ThreadFunction, ref);
+  if (result != 0) Fatal("Error from pthread_create");
+
+  result = pthread_attr_destroy(&attr);
+  if (result != 0) Fatal("Error from pthread_attr_destroy");
+
+  return 0;
+}
+
+// Callback for results initiated by calling DNSServiceGetAddrInfo.
+static void GetAddrInfoCallback(DNSServiceRef ref,
+                                DNSServiceFlags flags,
+                                uint32_t interfaceIndex,
+                                DNSServiceErrorType errorCode,
+                                const char *hostname,
+                                const struct sockaddr *address,
+                                uint32_t ttl,
+                                void *context) {
+  if (address->sa_family == AF_INET) {
+    const struct sockaddr_in* address_in = (const struct sockaddr_in*)address;
+    const uint8_t* addr =
+        reinterpret_cast<const uint8_t*>(&address_in->sin_addr.s_addr);
+
+    struct Context* ctx = reinterpret_cast<struct Context*>(context);
+
+    // Build the response message.
+    Dart_CObject cobject_hostname;
+    cobject_hostname.type = Dart_CObject_kString;
+    cobject_hostname.value.as_string = const_cast<char*>(hostname);
+    Dart_CObject cobject_address;
+    cobject_address.type = Dart_CObject_kTypedData;
+    cobject_address.value.as_typed_data.length = 4;
+    cobject_address.value.as_typed_data.type = Dart_TypedData_kUint8;
+    cobject_address.value.as_typed_data.values = const_cast<uint8_t*>(addr);
+    Dart_CObject cobject_result;
+    cobject_result.type = Dart_CObject_kArray;
+    Dart_CObject* result_array[] = {&cobject_hostname, &cobject_address};
+    cobject_result.value.as_array.length = 2;
+    cobject_result.value.as_array.values = result_array;
+    Dart_PostCObject(ctx->port, &cobject_result);
+
+    // Result received, free allocated data and stop lookup.
+    free(ctx);
+    DNSServiceRefDeallocate(ref);
+  }
+}
+
+// Lookup request from Dart.
+void HandleLookup(Dart_Port port_id, char* hostname) {
+  DNSServiceRef ref;
+  DNSServiceErrorType result;
+  struct Context* context =
+      reinterpret_cast<struct Context*>(malloc(sizeof(struct Context)));
+  context->port = port_id;
+  result = DNSServiceGetAddrInfo(&ref,
+                                 0,
+                                 0,
+                                 kDNSServiceProtocol_IPv4,
+                                 hostname,
+                                 &GetAddrInfoCallback,
+                                 context);
+  if (result != kDNSServiceErr_NoError) {
+    fprintf(stderr, "Error from DNSServiceProcessResult: %d\n", result);
+  } else {
+    // Start a thread for retreiving the results.
+    // TODO(sgjesse): Add a timeout for killing the thread if there
+    // are no responses.
+    StartThread(ref);
+  }
+}
+
+#endif