Add multiple results and timeout handling to the Mac OS mDNS native extension

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
index 329596d99b6d251b606a906cf7648033cf6fe8c6..90751c9797114e3470dcc5c87f135f7094c97526 100644
--- a/src/pkg/mdns/mdns_extension_macos.cc
+++ b/src/pkg/mdns/mdns_extension_macos.cc
@@ -10,6 +10,7 @@
 #include <string.h>
 #include <arpa/inet.h>
 #include <pthread.h>
+#include <sys/time.h>
 
 #include <dns_sd.h>
 
@@ -18,8 +19,15 @@
 
 #include "mdns_extension.h"
 
+// Constants.
+static uint32_t kUsecsInSecs = 1000000;
+static uint32_t kMillisecsInUsecs = 1000;
+
 // Context passed to the callback receiving the mDNS information.
 struct Context {
+  DNSServiceRef ref;
+  // The timeout waiting for results.
+  int timeout;
   // The Dart port where the result should be delivered.
   Dart_Port port;
 };
@@ -30,25 +38,66 @@ static void Fatal(const char *message) {
   exit(-1);
 }
 
+int64_t timeval_to_usec(const struct timeval* tv) {
+  return( (int64_t)tv->tv_sec * kUsecsInSecs + tv->tv_usec ) ;
+}
+
+struct timeval* usec_to_timeval(int64_t usec, struct timeval* tv) {
+  tv->tv_sec = usec / kUsecsInSecs;
+  tv->tv_usec = usec % kUsecsInSecs;
+  return tv;
+}
+
+// Free allocated resources associated with a context.
+static void FreeContext(Context* ctx) {
+  DNSServiceRefDeallocate(ctx->ref);
+  free(ctx);
+}
+
 // 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);
+  Context* ctx = reinterpret_cast<Context*>(data);
+
+  // Determint the end-time for responses to this request. Timeout from Dart
+  // is in milliseconds.
+  struct timeval time;
+  if (gettimeofday(&time, NULL) == -1) {
+    FreeContext(ctx);
+    return NULL;
   }
-  // The expected error from deallocation the ref.
-  if (result != kDNSServiceErr_BadReference) {
-    fprintf(stderr, "Error from DNSServiceProcessResult: %d\n", result);
+  int64_t end_time = timeval_to_usec(&time) + ctx->timeout * kMillisecsInUsecs;
+
+  // Setup single file descriptor for select.
+  int fd = DNSServiceRefSockFD(ctx->ref);
+  fd_set readfds;
+  FD_ZERO(&readfds);
+  FD_SET(fd, &readfds);
+  while (true) {
+    struct timeval timeout;
+    int64_t timeout_usec = end_time - timeval_to_usec(&time);
+    if (timeout_usec <= 0) break;
+    usec_to_timeval(timeout_usec, &timeout);
+    int rc = select(fd + 1, &readfds, NULL, NULL, &timeout);
+    if (rc == -1 && errno  == EINTR) continue;
+
+    // Terminate the loop if timeout or error.
+    if (rc <= 0) break;
+
+    // Process the result which is ready.
+    DNSServiceErrorType result = kDNSServiceErr_NoError;
+    result = DNSServiceProcessResult(ctx->ref);

[wibling, 2015/11/10 14:44:56]

NIT: Merge the two above lines into one.

[Søren Gjesse, 2015/11/10 15:30:05]

Done.

+    if (result != kDNSServiceErr_NoError) break;
+
+    // Prepare new timeout.
+    if (gettimeofday(&time, NULL) == -1) break;
   }
 
+  FreeContext(ctx);
   return NULL;
 }
 
 // Start a thread for receiving results from a specific DNSServiceRef.
-static int StartThread(DNSServiceRef ref) {
+static int StartThread(Context* ctx) {
   pthread_attr_t attr;
   int result = pthread_attr_init(&attr);
   if (result != 0) Fatal("Error from pthread_attr_init");
@@ -57,7 +106,7 @@ static int StartThread(DNSServiceRef ref) {
   if (result != 0) Fatal("Error from pthread_attr_setdetachstate");
 
   pthread_t tid;
-  result = pthread_create(&tid, &attr, ThreadFunction, ref);
+  result = pthread_create(&tid, &attr, ThreadFunction, ctx);
   if (result != 0) Fatal("Error from pthread_create");
 
   result = pthread_attr_destroy(&attr);
@@ -113,19 +162,14 @@ static void QueryRecordCallback(DNSServiceRef ref,
   cobject_result.value.as_array.length = 4;
   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, int type, char* fullname) {
+void HandleLookup(Dart_Port port_id, int type, char* fullname, int timeout) {
   DNSServiceRef ref;
   DNSServiceErrorType result;
   struct Context* context =
       reinterpret_cast<struct Context*>(malloc(sizeof(struct Context)));
-  context->port = port_id;
   result = DNSServiceQueryRecord(&ref,
                                  0,
                                  0,
@@ -137,10 +181,11 @@ void HandleLookup(Dart_Port port_id, int type, char* fullname) {
   if (result != kDNSServiceErr_NoError) {
     fprintf(stderr, "Error from DNSServiceQueryRecord: %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);
+    // Start a thread for pumping the results.
+    context->ref = ref;
+    context->timeout = timeout;
+    context->port = port_id;
+    StartThread(context);
   }
 }