Simplify and fix the c-ares TCP path on Windows

src/core/ext/filters/client_channel/resolver/dns/c_ares/grpc_ares_ev_driver_windows.cc

@@ -31,6 +31,9 @@
 #include "src/core/lib/gpr/string.h"
 #include "src/core/lib/gprpp/memory.h"
 #include "src/core/lib/iomgr/combiner.h"
+#include "src/core/lib/iomgr/iocp_windows.h"
+#include "src/core/lib/iomgr/sockaddr_utils.h"
+#include "src/core/lib/iomgr/sockaddr_windows.h"
 #include "src/core/lib/iomgr/socket_windows.h"
 #include "src/core/lib/iomgr/tcp_windows.h"
 #include "src/core/lib/slice/slice_internal.h"
@@ -50,6 +53,32 @@ struct iovec {
 
 namespace grpc_core {
 
+/* c-ares reads and takes action on the error codes of the
+ * "virtual socket operations" in this file, via the WSAGetLastError
+ * APIs. If code in this file wants to set a specific WSA error that
+ * c-ares should read, it must do so by calling SetWSAError() on the
+ * WSAErrorContext instance passed to it. A WSAErrorContext must only be
+ * instantiated at the top of the virtual socket function callstack. */
+class WSAErrorContext {
+ public:
+  explicit WSAErrorContext(){};
+
+  ~WSAErrorContext() {
+    if (error_ != 0) {
+      WSASetLastError(error_);
+    }
+  }
+
+  /* Disallow copy and assignment operators */
+  WSAErrorContext(const WSAErrorContext&) = delete;
+  WSAErrorContext& operator=(const WSAErrorContext&) = delete;
+
+  void SetWSAError(int error) { error_ = error; }
+
+ private:
+  int error_ = 0;
+};
+
 /* c-ares creates its own sockets and is meant to read them when readable and
  * write them when writeable. To fit this socket usage model into the grpc
  * windows poller (which gives notifications when attempted reads and writes are
@@ -68,11 +97,14 @@ class GrpcPolledFdWindows : public GrpcPolledFd {
     WRITE_WAITING_FOR_VERIFICATION_UPON_RETRY,
   };
 
-  GrpcPolledFdWindows(ares_socket_t as, grpc_combiner* combiner)
+  GrpcPolledFdWindows(ares_socket_t as, grpc_combiner* combiner,
+                      int address_family, int socket_type)
       : read_buf_(grpc_empty_slice()),
         write_buf_(grpc_empty_slice()),
-        write_state_(WRITE_IDLE),
+        tcp_write_state_(WRITE_IDLE),
-        gotten_into_driver_list_(false) {
+        gotten_into_driver_list_(false),
+        address_family_(address_family),
+        socket_type_(socket_type) {
     gpr_asprintf(&name_, "c-ares socket: %" PRIdPTR, as);
     winsocket_ = grpc_winsocket_create(as, name_);
     combiner_ = GRPC_COMBINER_REF(combiner, name_);
@@ -82,6 +114,16 @@ class GrpcPolledFdWindows : public GrpcPolledFd {
     GRPC_CLOSURE_INIT(&outer_write_closure_,
                       &GrpcPolledFdWindows::OnIocpWriteable, this,
                       grpc_combiner_scheduler(combiner_));
+    GRPC_CLOSURE_INIT(&on_tcp_connect_locked_,
+                      &GrpcPolledFdWindows::OnTcpConnectLocked, this,
+                      grpc_combiner_scheduler(combiner_));
+    GRPC_CLOSURE_INIT(&continue_register_for_on_readable_locked_,
+                      &GrpcPolledFdWindows::ContinueRegisterForOnReadableLocked,
+                      this, grpc_combiner_scheduler(combiner_));
+    GRPC_CLOSURE_INIT(
+        &continue_register_for_on_writeable_locked_,
+        &GrpcPolledFdWindows::ContinueRegisterForOnWriteableLocked, this,
+        grpc_combiner_scheduler(combiner_));
   }
 
   ~GrpcPolledFdWindows() {
@@ -111,6 +153,33 @@ class GrpcPolledFdWindows : public GrpcPolledFd {
     grpc_slice_unref_internal(read_buf_);
     GPR_ASSERT(!read_buf_has_data_);
     read_buf_ = GRPC_SLICE_MALLOC(4192);
+    if (connect_done_) {
+      GRPC_CLOSURE_SCHED(&continue_register_for_on_readable_locked_,
+                         GRPC_ERROR_NONE);
+    } else {
+      GPR_ASSERT(pending_continue_register_for_on_readable_locked_ == nullptr);
+      pending_continue_register_for_on_readable_locked_ =
+          &continue_register_for_on_readable_locked_;
+    }
+  }
+
+  static void ContinueRegisterForOnReadableLocked(void* arg,
+                                                  grpc_error* unused_error) {
+    GrpcPolledFdWindows* grpc_polled_fd =
+        static_cast<GrpcPolledFdWindows*>(arg);
+    grpc_polled_fd->InnerContinueRegisterForOnReadableLocked(GRPC_ERROR_NONE);
+  }
+
+  void InnerContinueRegisterForOnReadableLocked(grpc_error* unused_error) {
+    GRPC_CARES_TRACE_LOG(
+        "fd:|%s| InnerContinueRegisterForOnReadableLocked "
+        "wsa_connect_error_:%d",
+        GetName(), wsa_connect_error_);
+    GPR_ASSERT(connect_done_);
+    if (wsa_connect_error_ != 0) {
+      ScheduleAndNullReadClosure(GRPC_WSA_ERROR(wsa_connect_error_, "connect"));
+      return;
+    }
     WSABUF buffer;
     buffer.buf = (char*)GRPC_SLICE_START_PTR(read_buf_);
     buffer.len = GRPC_SLICE_LENGTH(read_buf_);
@@ -123,13 +192,14 @@ class GrpcPolledFdWindows : public GrpcPolledFd {
                     &winsocket_->read_info.overlapped, nullptr)) {
       int wsa_last_error = WSAGetLastError();
       char* msg = gpr_format_message(wsa_last_error);
-      grpc_error* error = GRPC_ERROR_CREATE_FROM_COPIED_STRING(msg);
       GRPC_CARES_TRACE_LOG(
-          "RegisterForOnReadableLocked: WSARecvFrom error:|%s|. fd:|%s|", msg,
+          "fd:|%s| RegisterForOnReadableLocked WSARecvFrom error code:|%d| "
-          GetName());
+          "msg:|%s|",
+          GetName(), wsa_last_error, msg);
       gpr_free(msg);
       if (wsa_last_error != WSA_IO_PENDING) {
-        ScheduleAndNullReadClosure(error);
+        ScheduleAndNullReadClosure(
+            GRPC_WSA_ERROR(wsa_last_error, "WSARecvFrom"));
         return;
       }
     }
@@ -137,25 +207,70 @@ class GrpcPolledFdWindows : public GrpcPolledFd {
   }
 
   void RegisterForOnWriteableLocked(grpc_closure* write_closure) override {
+    if (socket_type_ == SOCK_DGRAM) {
+      GRPC_CARES_TRACE_LOG("fd:|%s| RegisterForOnWriteableLocked called",
+                           GetName());
+    } else {
+      GPR_ASSERT(socket_type_ == SOCK_STREAM);
       GRPC_CARES_TRACE_LOG(
-        "RegisterForOnWriteableLocked. fd:|%s|. Current write state: %d",
+          "fd:|%s| RegisterForOnWriteableLocked called tcp_write_state_: %d",
-        GetName(), write_state_);
+          GetName(), tcp_write_state_);
+    }
     GPR_ASSERT(write_closure_ == nullptr);
     write_closure_ = write_closure;
-    switch (write_state_) {
+    if (connect_done_) {
+      GRPC_CLOSURE_SCHED(&continue_register_for_on_writeable_locked_,
+                         GRPC_ERROR_NONE);
+    } else {
+      GPR_ASSERT(pending_continue_register_for_on_writeable_locked_ == nullptr);
+      pending_continue_register_for_on_writeable_locked_ =
+          &continue_register_for_on_writeable_locked_;
+    }
+  }
+
+  static void ContinueRegisterForOnWriteableLocked(void* arg,
+                                                   grpc_error* unused_error) {
+    GrpcPolledFdWindows* grpc_polled_fd =
+        static_cast<GrpcPolledFdWindows*>(arg);
+    grpc_polled_fd->InnerContinueRegisterForOnWriteableLocked(GRPC_ERROR_NONE);
+  }
+
+  void InnerContinueRegisterForOnWriteableLocked(grpc_error* unused_error) {
+    GRPC_CARES_TRACE_LOG(
+        "fd:|%s| InnerContinueRegisterForOnWriteableLocked "
+        "wsa_connect_error_:%d",
+        GetName(), wsa_connect_error_);
+    GPR_ASSERT(connect_done_);
+    if (wsa_connect_error_ != 0) {
+      ScheduleAndNullWriteClosure(
+          GRPC_WSA_ERROR(wsa_connect_error_, "connect"));
+      return;
+    }
+    if (socket_type_ == SOCK_DGRAM) {
+      ScheduleAndNullWriteClosure(GRPC_ERROR_NONE);
+    } else {
+      GPR_ASSERT(socket_type_ == SOCK_STREAM);
+      int wsa_error_code = 0;
+      switch (tcp_write_state_) {
         case WRITE_IDLE:
           ScheduleAndNullWriteClosure(GRPC_ERROR_NONE);
           break;
         case WRITE_REQUESTED:
-        write_state_ = WRITE_PENDING;
+          tcp_write_state_ = WRITE_PENDING;
-        SendWriteBuf(nullptr, &winsocket_->write_info.overlapped);
+          if (SendWriteBuf(nullptr, &winsocket_->write_info.overlapped,
+                           &wsa_error_code) != 0) {
+            ScheduleAndNullWriteClosure(
+                GRPC_WSA_ERROR(wsa_error_code, "WSASend (overlapped)"));
+          } else {
             grpc_socket_notify_on_write(winsocket_, &outer_write_closure_);
+          }
           break;
         case WRITE_PENDING:
         case WRITE_WAITING_FOR_VERIFICATION_UPON_RETRY:
           abort();
       }
     }
+  }
 
   bool IsFdStillReadableLocked() override {
     return GRPC_SLICE_LENGTH(read_buf_) > 0;
@@ -171,13 +286,15 @@ class GrpcPolledFdWindows : public GrpcPolledFd {
 
   const char* GetName() override { return name_; }
 
-  ares_ssize_t RecvFrom(void* data, ares_socket_t data_len, int flags,
+  ares_ssize_t RecvFrom(WSAErrorContext* wsa_error_ctx, void* data,
+                        ares_socket_t data_len, int flags,
                         struct sockaddr* from, ares_socklen_t* from_len) {
     GRPC_CARES_TRACE_LOG(
-        "RecvFrom called on fd:|%s|. Current read buf length:|%d|", GetName(),
+        "fd:|%s| RecvFrom called read_buf_has_data:%d Current read buf "
-        GRPC_SLICE_LENGTH(read_buf_));
+        "length:|%d|",
+        GetName(), read_buf_has_data_, GRPC_SLICE_LENGTH(read_buf_));
     if (!read_buf_has_data_) {
-      WSASetLastError(WSAEWOULDBLOCK);
+      wsa_error_ctx->SetWSAError(WSAEWOULDBLOCK);
       return -1;
     }
     ares_ssize_t bytes_read = 0;
@@ -215,54 +332,99 @@ class GrpcPolledFdWindows : public GrpcPolledFd {
     return out;
   }
 
-  int SendWriteBuf(LPDWORD bytes_sent_ptr, LPWSAOVERLAPPED overlapped) {
+  int SendWriteBuf(LPDWORD bytes_sent_ptr, LPWSAOVERLAPPED overlapped,
+                   int* wsa_error_code) {
     WSABUF buf;
     buf.len = GRPC_SLICE_LENGTH(write_buf_);
     buf.buf = (char*)GRPC_SLICE_START_PTR(write_buf_);
     DWORD flags = 0;
     int out = WSASend(grpc_winsocket_wrapped_socket(winsocket_), &buf, 1,
                       bytes_sent_ptr, flags, overlapped, nullptr);
+    *wsa_error_code = WSAGetLastError();
     GRPC_CARES_TRACE_LOG(
-        "WSASend: name:%s. buf len:%d. bytes sent: %d. overlapped %p. return "
+        "fd:|%s| SendWriteBuf WSASend buf.len:%d *bytes_sent_ptr:%d "
-        "val: %d",
+        "overlapped:%p "
-        GetName(), buf.len, *bytes_sent_ptr, overlapped, out);
+        "return:%d *wsa_error_code:%d",
+        GetName(), buf.len, bytes_sent_ptr != nullptr ? *bytes_sent_ptr : 0,
+        overlapped, out, *wsa_error_code);
     return out;
   }
 
-  ares_ssize_t TrySendWriteBufSyncNonBlocking() {
+  ares_ssize_t SendV(WSAErrorContext* wsa_error_ctx, const struct iovec* iov,
-    GPR_ASSERT(write_state_ == WRITE_IDLE);
+                     int iov_count) {
+    GRPC_CARES_TRACE_LOG(
+        "fd:|%s| SendV called connect_done_:%d was_connect_error_:%d",
+        GetName(), connect_done_, wsa_connect_error_);
+    if (!connect_done_) {
+      wsa_error_ctx->SetWSAError(WSAEWOULDBLOCK);
+      return -1;
+    }
+    if (wsa_connect_error_ != 0) {
+      wsa_error_ctx->SetWSAError(wsa_connect_error_);
+      return -1;
+    }
+    switch (socket_type_) {
+      case SOCK_DGRAM:
+        return SendVUDP(wsa_error_ctx, iov, iov_count);
+      case SOCK_STREAM:
+        return SendVTCP(wsa_error_ctx, iov, iov_count);
+      default:
+        abort();
+    }
+  }
+
+  ares_ssize_t SendVUDP(WSAErrorContext* wsa_error_ctx, const struct iovec* iov,
+                        int iov_count) {
+    // c-ares doesn't handle retryable errors on writes of UDP sockets.
+    // Therefore, the sendv handler for UDP sockets must only attempt
+    // to write everything inline.
+    GRPC_CARES_TRACE_LOG("fd:|%s| SendVUDP called", GetName());
+    GPR_ASSERT(GRPC_SLICE_LENGTH(write_buf_) == 0);
+    grpc_slice_unref_internal(write_buf_);
+    write_buf_ = FlattenIovec(iov, iov_count);
     DWORD bytes_sent = 0;
-    if (SendWriteBuf(&bytes_sent, nullptr) != 0) {
+    int wsa_error_code = 0;
-      int wsa_last_error = WSAGetLastError();
+    if (SendWriteBuf(&bytes_sent, nullptr, &wsa_error_code) != 0) {
-      char* msg = gpr_format_message(wsa_last_error);
+      wsa_error_ctx->SetWSAError(wsa_error_code);
+      char* msg = gpr_format_message(wsa_error_code);
       GRPC_CARES_TRACE_LOG(
-          "TrySendWriteBufSyncNonBlocking: SendWriteBuf error:|%s|. fd:|%s|",
+          "fd:|%s| SendVUDP SendWriteBuf error code:%d msg:|%s|", GetName(),
-          msg, GetName());
+          wsa_error_code, msg);
       gpr_free(msg);
-      if (wsa_last_error == WSA_IO_PENDING) {
+      return -1;
-        WSASetLastError(WSAEWOULDBLOCK);
-        write_state_ = WRITE_REQUESTED;
-      }
     }
     write_buf_ = grpc_slice_sub_no_ref(write_buf_, bytes_sent,
                                        GRPC_SLICE_LENGTH(write_buf_));
     return bytes_sent;
   }
 
-  ares_ssize_t SendV(const struct iovec* iov, int iov_count) {
+  ares_ssize_t SendVTCP(WSAErrorContext* wsa_error_ctx, const struct iovec* iov,
-    GRPC_CARES_TRACE_LOG("SendV called on fd:|%s|. Current write state: %d",
+                        int iov_count) {
-                         GetName(), write_state_);
+    // The "sendv" handler on TCP sockets buffers up write
-    switch (write_state_) {
+    // requests and returns an artifical WSAEWOULDBLOCK. Writing that buffer out
+    // in the background, and making further send progress in general, will
+    // happen as long as c-ares continues to show interest in writeability on
+    // this fd.
+    GRPC_CARES_TRACE_LOG("fd:|%s| SendVTCP called tcp_write_state_:%d",
+                         GetName(), tcp_write_state_);
+    switch (tcp_write_state_) {
       case WRITE_IDLE:
+        tcp_write_state_ = WRITE_REQUESTED;
         GPR_ASSERT(GRPC_SLICE_LENGTH(write_buf_) == 0);
         grpc_slice_unref_internal(write_buf_);
         write_buf_ = FlattenIovec(iov, iov_count);
-        return TrySendWriteBufSyncNonBlocking();
+        wsa_error_ctx->SetWSAError(WSAEWOULDBLOCK);
+        return -1;
       case WRITE_REQUESTED:
       case WRITE_PENDING:
-        WSASetLastError(WSAEWOULDBLOCK);
+        wsa_error_ctx->SetWSAError(WSAEWOULDBLOCK);
         return -1;
       case WRITE_WAITING_FOR_VERIFICATION_UPON_RETRY:
+        // c-ares is retrying a send on data that we previously returned
+        // WSAEWOULDBLOCK for, but then subsequently wrote out in the
+        // background. Right now, we assume that c-ares is retrying the same
+        // send again. If c-ares still needs to send even more data, we'll get
+        // to it eventually.
         grpc_slice currently_attempted = FlattenIovec(iov, iov_count);
         GPR_ASSERT(GRPC_SLICE_LENGTH(currently_attempted) >=
                    GRPC_SLICE_LENGTH(write_buf_));
@@ -272,31 +434,159 @@ class GrpcPolledFdWindows : public GrpcPolledFd {
                      GRPC_SLICE_START_PTR(write_buf_)[i]);
           total_sent++;
         }
-        grpc_slice_unref_internal(write_buf_);
+        grpc_slice_unref_internal(currently_attempted);
-        write_buf_ =
+        tcp_write_state_ = WRITE_IDLE;
-            grpc_slice_sub_no_ref(currently_attempted, total_sent,
-                                  GRPC_SLICE_LENGTH(currently_attempted));
-        write_state_ = WRITE_IDLE;
-        total_sent += TrySendWriteBufSyncNonBlocking();
         return total_sent;
     }
     abort();
   }
 
-  int Connect(const struct sockaddr* target, ares_socklen_t target_len) {
+  static void OnTcpConnectLocked(void* arg, grpc_error* error) {
+    GrpcPolledFdWindows* grpc_polled_fd =
+        static_cast<GrpcPolledFdWindows*>(arg);
+    grpc_polled_fd->InnerOnTcpConnectLocked(error);
+  }
+
+  void InnerOnTcpConnectLocked(grpc_error* error) {
+    GRPC_CARES_TRACE_LOG(
+        "fd:%s InnerOnTcpConnectLocked error:|%s| "
+        "pending_register_for_readable:%" PRIdPTR
+        " pending_register_for_writeable:%" PRIdPTR,
+        GetName(), grpc_error_string(error),
+        pending_continue_register_for_on_readable_locked_,
+        pending_continue_register_for_on_writeable_locked_);
+    GPR_ASSERT(!connect_done_);
+    connect_done_ = true;
+    GPR_ASSERT(wsa_connect_error_ == 0);
+    if (error == GRPC_ERROR_NONE) {
+      DWORD transfered_bytes = 0;
+      DWORD flags;
+      BOOL wsa_success = WSAGetOverlappedResult(
+          grpc_winsocket_wrapped_socket(winsocket_),
+          &winsocket_->write_info.overlapped, &transfered_bytes, FALSE, &flags);
+      GPR_ASSERT(transfered_bytes == 0);
+      if (!wsa_success) {
+        wsa_connect_error_ = WSAGetLastError();
+        char* msg = gpr_format_message(wsa_connect_error_);
+        GRPC_CARES_TRACE_LOG(
+            "fd:%s InnerOnTcpConnectLocked WSA overlapped result code:%d "
+            "msg:|%s|",
+            GetName(), wsa_connect_error_, msg);
+        gpr_free(msg);
+      }
+    } else {
+      // Spoof up an error code that will cause any future c-ares operations on
+      // this fd to abort.
+      wsa_connect_error_ = WSA_OPERATION_ABORTED;
+    }
+    if (pending_continue_register_for_on_readable_locked_ != nullptr) {
+      GRPC_CLOSURE_SCHED(pending_continue_register_for_on_readable_locked_,
+                         GRPC_ERROR_NONE);
+    }
+    if (pending_continue_register_for_on_writeable_locked_ != nullptr) {
+      GRPC_CLOSURE_SCHED(pending_continue_register_for_on_writeable_locked_,
+                         GRPC_ERROR_NONE);
+    }
+  }
+
+  int Connect(WSAErrorContext* wsa_error_ctx, const struct sockaddr* target,
+              ares_socklen_t target_len) {
+    switch (socket_type_) {
+      case SOCK_DGRAM:
+        return ConnectUDP(wsa_error_ctx, target, target_len);
+      case SOCK_STREAM:
+        return ConnectTCP(wsa_error_ctx, target, target_len);
+      default:
+        abort();
+    }
+  }
+
+  int ConnectUDP(WSAErrorContext* wsa_error_ctx, const struct sockaddr* target,
+                 ares_socklen_t target_len) {
+    GRPC_CARES_TRACE_LOG("fd:%s ConnectUDP", GetName());
+    GPR_ASSERT(!connect_done_);
+    GPR_ASSERT(wsa_connect_error_ == 0);
     SOCKET s = grpc_winsocket_wrapped_socket(winsocket_);
-    GRPC_CARES_TRACE_LOG("Connect: fd:|%s|", GetName());
     int out =
         WSAConnect(s, target, target_len, nullptr, nullptr, nullptr, nullptr);
-    if (out != 0) {
+    wsa_connect_error_ = WSAGetLastError();
+    wsa_error_ctx->SetWSAError(wsa_connect_error_);
+    connect_done_ = true;
+    char* msg = gpr_format_message(wsa_connect_error_);
+    GRPC_CARES_TRACE_LOG("fd:%s WSAConnect error code:|%d| msg:|%s|", GetName(),
+                         wsa_connect_error_, msg);
+    gpr_free(msg);
+    // c-ares expects a posix-style connect API
+    return out == 0 ? 0 : -1;
+  }
+
+  int ConnectTCP(WSAErrorContext* wsa_error_ctx, const struct sockaddr* target,
+                 ares_socklen_t target_len) {
+    GRPC_CARES_TRACE_LOG("fd:%s ConnectTCP", GetName());
+    LPFN_CONNECTEX ConnectEx;
+    GUID guid = WSAID_CONNECTEX;
+    DWORD ioctl_num_bytes;
+    SOCKET s = grpc_winsocket_wrapped_socket(winsocket_);
+    if (WSAIoctl(s, SIO_GET_EXTENSION_FUNCTION_POINTER, &guid, sizeof(guid),
+                 &ConnectEx, sizeof(ConnectEx), &ioctl_num_bytes, nullptr,
+                 nullptr) != 0) {
       int wsa_last_error = WSAGetLastError();
+      wsa_error_ctx->SetWSAError(wsa_last_error);
       char* msg = gpr_format_message(wsa_last_error);
-      GRPC_CARES_TRACE_LOG("Connect error code:|%d|, msg:|%s|. fd:|%s|",
+      GRPC_CARES_TRACE_LOG(
-                           wsa_last_error, msg, GetName());
+          "fd:%s WSAIoctl(SIO_GET_EXTENSION_FUNCTION_POINTER) error code:%d "
+          "msg:|%s|",
+          GetName(), wsa_last_error, msg);
       gpr_free(msg);
-      // c-ares expects a posix-style connect API
+      connect_done_ = true;
+      wsa_connect_error_ = wsa_last_error;
+      return -1;
+    }
+    grpc_resolved_address wildcard4_addr;
+    grpc_resolved_address wildcard6_addr;
+    grpc_sockaddr_make_wildcards(0, &wildcard4_addr, &wildcard6_addr);
+    grpc_resolved_address* local_address = nullptr;
+    if (address_family_ == AF_INET) {
+      local_address = &wildcard4_addr;
+    } else {
+      local_address = &wildcard6_addr;
+    }
+    if (bind(s, (struct sockaddr*)local_address->addr,
+             (int)local_address->len) != 0) {
+      int wsa_last_error = WSAGetLastError();
+      wsa_error_ctx->SetWSAError(wsa_last_error);
+      char* msg = gpr_format_message(wsa_last_error);
+      GRPC_CARES_TRACE_LOG("fd:%s bind error code:%d msg:|%s|", GetName(),
+                           wsa_last_error, msg);
+      gpr_free(msg);
+      connect_done_ = true;
+      wsa_connect_error_ = wsa_last_error;
+      return -1;
+    }
+    int out = 0;
+    if (ConnectEx(s, target, target_len, nullptr, 0, nullptr,
+                  &winsocket_->write_info.overlapped) == 0) {
       out = -1;
+      int wsa_last_error = WSAGetLastError();
+      wsa_error_ctx->SetWSAError(wsa_last_error);
+      char* msg = gpr_format_message(wsa_last_error);
+      GRPC_CARES_TRACE_LOG("fd:%s ConnectEx error code:%d msg:|%s|", GetName(),
+                           wsa_last_error, msg);
+      gpr_free(msg);
+      if (wsa_last_error == WSA_IO_PENDING) {
+        // c-ares only understands WSAEINPROGRESS and EWOULDBLOCK error codes on
+        // connect, but an async connect on IOCP socket will give
+        // WSA_IO_PENDING, so we need to convert.
+        wsa_error_ctx->SetWSAError(WSAEWOULDBLOCK);
+      } else {
+        // By returning a non-retryable error to c-ares at this point,
+        // we're aborting the possibility of any future operations on this fd.
+        connect_done_ = true;
+        wsa_connect_error_ = wsa_last_error;
+        return -1;
       }
+    }
+    grpc_socket_notify_on_write(winsocket_, &on_tcp_connect_locked_);
     return out;
   }
 
@@ -319,12 +609,13 @@ class GrpcPolledFdWindows : public GrpcPolledFd {
          * in subsequent c-ares reads. */
         if (winsocket_->read_info.wsa_error != WSAEMSGSIZE) {
           GRPC_ERROR_UNREF(error);
-          char* msg = gpr_format_message(winsocket_->read_info.wsa_error);
+          error = GRPC_WSA_ERROR(winsocket_->read_info.wsa_error,
+                                 "OnIocpReadableInner");
           GRPC_CARES_TRACE_LOG(
-              "OnIocpReadableInner. winsocket error:|%s|. fd:|%s|", msg,
+              "fd:|%s| OnIocpReadableInner winsocket_->read_info.wsa_error "
-              GetName());
+              "code:|%d| msg:|%s|",
-          error = GRPC_ERROR_CREATE_FROM_COPIED_STRING(msg);
+              GetName(), winsocket_->read_info.wsa_error,
-          gpr_free(msg);
+              grpc_error_string(error));
         }
       }
     }
@@ -337,8 +628,8 @@ class GrpcPolledFdWindows : public GrpcPolledFd {
       read_buf_ = grpc_empty_slice();
     }
     GRPC_CARES_TRACE_LOG(
-        "OnIocpReadable finishing. read buf length now:|%d|. :fd:|%s|",
+        "fd:|%s| OnIocpReadable finishing. read buf length now:|%d|", GetName(),
-        GRPC_SLICE_LENGTH(read_buf_), GetName());
+        GRPC_SLICE_LENGTH(read_buf_));
     ScheduleAndNullReadClosure(error);
   }
 
@@ -349,22 +640,26 @@ class GrpcPolledFdWindows : public GrpcPolledFd {
 
   void OnIocpWriteableInner(grpc_error* error) {
     GRPC_CARES_TRACE_LOG("OnIocpWriteableInner. fd:|%s|", GetName());
+    GPR_ASSERT(socket_type_ == SOCK_STREAM);
     if (error == GRPC_ERROR_NONE) {
       if (winsocket_->write_info.wsa_error != 0) {
-        char* msg = gpr_format_message(winsocket_->write_info.wsa_error);
-        GRPC_CARES_TRACE_LOG(
-            "OnIocpWriteableInner. winsocket error:|%s|. fd:|%s|", msg,
-            GetName());
         GRPC_ERROR_UNREF(error);
-        error = GRPC_ERROR_CREATE_FROM_COPIED_STRING(msg);
+        error = GRPC_WSA_ERROR(winsocket_->write_info.wsa_error,
-        gpr_free(msg);
+                               "OnIocpWriteableInner");
+        GRPC_CARES_TRACE_LOG(
+            "fd:|%s| OnIocpWriteableInner. winsocket_->write_info.wsa_error "
+            "code:|%d| msg:|%s|",
+            GetName(), winsocket_->write_info.wsa_error,
+            grpc_error_string(error));
       }
     }
-    GPR_ASSERT(write_state_ == WRITE_PENDING);
+    GPR_ASSERT(tcp_write_state_ == WRITE_PENDING);
     if (error == GRPC_ERROR_NONE) {
-      write_state_ = WRITE_WAITING_FOR_VERIFICATION_UPON_RETRY;
+      tcp_write_state_ = WRITE_WAITING_FOR_VERIFICATION_UPON_RETRY;
       write_buf_ = grpc_slice_sub_no_ref(
           write_buf_, 0, winsocket_->write_info.bytes_transfered);
+      GRPC_CARES_TRACE_LOG("fd:|%s| OnIocpWriteableInner. bytes transferred:%d",
+                           GetName(), winsocket_->write_info.bytes_transfered);
     } else {
       grpc_slice_unref_internal(write_buf_);
       write_buf_ = grpc_empty_slice();
@@ -386,9 +681,22 @@ class GrpcPolledFdWindows : public GrpcPolledFd {
   grpc_closure outer_read_closure_;
   grpc_closure outer_write_closure_;
   grpc_winsocket* winsocket_;
-  WriteState write_state_;
+  // tcp_write_state_ is only used on TCP GrpcPolledFds
+  WriteState tcp_write_state_;
   char* name_ = nullptr;
   bool gotten_into_driver_list_;
+  int address_family_;
+  int socket_type_;
+  grpc_closure on_tcp_connect_locked_;
+  bool connect_done_ = false;
+  int wsa_connect_error_ = 0;
+  // We don't run register_for_{readable,writeable} logic until
+  // a socket is connected. In the interim, we queue readable/writeable
+  // registrations with the following state.
+  grpc_closure continue_register_for_on_readable_locked_;
+  grpc_closure continue_register_for_on_writeable_locked_;
+  grpc_closure* pending_continue_register_for_on_readable_locked_ = nullptr;
+  grpc_closure* pending_continue_register_for_on_writeable_locked_ = nullptr;
 };
 
 struct SockToPolledFdEntry {
@@ -454,39 +762,53 @@ class SockToPolledFdMap {
    * objects.
    */
   static ares_socket_t Socket(int af, int type, int protocol, void* user_data) {
+    if (type != SOCK_DGRAM && type != SOCK_STREAM) {
+      GRPC_CARES_TRACE_LOG("Socket called with invalid socket type:%d", type);
+      return INVALID_SOCKET;
+    }
     SockToPolledFdMap* map = static_cast<SockToPolledFdMap*>(user_data);
     SOCKET s = WSASocket(af, type, protocol, nullptr, 0,
                          grpc_get_default_wsa_socket_flags());
     if (s == INVALID_SOCKET) {
+      GRPC_CARES_TRACE_LOG(
+          "WSASocket failed with params af:%d type:%d protocol:%d", af, type,
+          protocol);
       return s;
     }
     grpc_tcp_set_non_block(s);
     GrpcPolledFdWindows* polled_fd =
-        New<GrpcPolledFdWindows>(s, map->combiner_);
+        New<GrpcPolledFdWindows>(s, map->combiner_, af, type);
+    GRPC_CARES_TRACE_LOG(
+        "fd:|%s| created with params af:%d type:%d protocol:%d",
+        polled_fd->GetName(), af, type, protocol);
     map->AddNewSocket(s, polled_fd);
     return s;
   }
 
   static int Connect(ares_socket_t as, const struct sockaddr* target,
                      ares_socklen_t target_len, void* user_data) {
+    WSAErrorContext wsa_error_ctx;
     SockToPolledFdMap* map = static_cast<SockToPolledFdMap*>(user_data);
     GrpcPolledFdWindows* polled_fd = map->LookupPolledFd(as);
-    return polled_fd->Connect(target, target_len);
+    return polled_fd->Connect(&wsa_error_ctx, target, target_len);
   }
 
   static ares_ssize_t SendV(ares_socket_t as, const struct iovec* iov,
                             int iovec_count, void* user_data) {
+    WSAErrorContext wsa_error_ctx;
     SockToPolledFdMap* map = static_cast<SockToPolledFdMap*>(user_data);
     GrpcPolledFdWindows* polled_fd = map->LookupPolledFd(as);
-    return polled_fd->SendV(iov, iovec_count);
+    return polled_fd->SendV(&wsa_error_ctx, iov, iovec_count);
   }
 
   static ares_ssize_t RecvFrom(ares_socket_t as, void* data, size_t data_len,
                                int flags, struct sockaddr* from,
                                ares_socklen_t* from_len, void* user_data) {
+    WSAErrorContext wsa_error_ctx;
     SockToPolledFdMap* map = static_cast<SockToPolledFdMap*>(user_data);
     GrpcPolledFdWindows* polled_fd = map->LookupPolledFd(as);
-    return polled_fd->RecvFrom(data, data_len, flags, from, from_len);
+    return polled_fd->RecvFrom(&wsa_error_ctx, data, data_len, flags, from,
+                               from_len);
   }
 
   static int CloseSocket(SOCKET s, void* user_data) {