--- a/src/os/win32/ngx_wsasend_chain.c
+++ b/src/os/win32/ngx_wsasend_chain.c
@@ -6,6 +6,249 @@
 
 ngx_chain_t *ngx_wsasend_chain(ngx_connection_t *c, ngx_chain_t *in)
 {
+    int           rc;
+    char         *prev;
+    size_t        size, sent;
+    LPWSABUF      wsabuf;
+    ngx_err_t     err;
+    ngx_event_t  *wev;
+    ngx_array_t   wsabufs;
+    ngx_chain_t  *cl;
+
+    wev = c->write;
+
+    if (!wev->ready) {
+        return in;
+    }
+
+    /*
+     * WSABUFs must be 4-byte aligned otherwise
+     * WSASend() will return undocumented WSAEINVAL error.
+     */
+
+    ngx_init_array(wsabufs, c->pool, 10, sizeof(WSABUF), NGX_CHAIN_ERROR);
+
+    prev = NULL;
+    wsabuf = NULL;
+
+    /* create the WSABUF and coalesce the neighbouring bufs */
+
+    for (cl = in; cl; cl = cl->next) {
+
+        if (prev == cl->hunk->pos) {
+            wsabuf->len += cl->hunk->last - cl->hunk->pos;
+            prev = cl->hunk->last;
+
+        } else {
+            ngx_test_null(wsabuf, ngx_push_array(&wsabufs), NGX_CHAIN_ERROR);
+            wsabuf->buf = cl->hunk->pos;
+            wsabuf->len = cl->hunk->last - cl->hunk->pos;
+            prev = cl->hunk->last;
+        }
+    }
+
+    rc = WSASend(c->fd, wsabufs.elts, wsabufs.nelts, &sent, 0, NULL, NULL);
+
+    if (rc == -1) {
+        err = ngx_errno;
+
+        if (err == WSAEWOULDBLOCK) {
+            ngx_log_error(NGX_LOG_INFO, c->log, err, "WSASend() EAGAIN");
+            wev->ready = 0;
+            return in;
+
+        } else {
+            wev->error = 1;
+            ngx_log_error(NGX_LOG_CRIT, c->log, err, "WSASend() failed");
+            return NGX_CHAIN_ERROR;
+        }
+    }
+
+#if (NGX_DEBUG_WRITE_CHAIN)
+    ngx_log_debug(c->log, "WSASend(): %d" _ sent);
+#endif
+
+    c->sent += sent;
+
+    for (cl = in; cl && sent > 0; cl = cl->next) {
+
+        size = cl->hunk->last - cl->hunk->pos;
+
+        if (sent >= size) {
+            sent -= size;
+
+            if (cl->hunk->type & NGX_HUNK_IN_MEMORY) {
+                cl->hunk->pos = cl->hunk->last;
+            }
+
+            continue;
+        }
+
+        if (cl->hunk->type & NGX_HUNK_IN_MEMORY) {
+            cl->hunk->pos += sent;
+        }
+
+        break;
+    }
+
+    if (cl) {
+        wev->ready = 0;
+    }
+
+    return cl;
+}
+
+
+ngx_chain_t *ngx_overlapped_wsasend_chain(ngx_connection_t *c, ngx_chain_t *in)
+{
+    int               rc;
+    char             *prev;
+    size_t            size, sent;
+    LPWSABUF          wsabuf;
+    ngx_err_t         err;
+    ngx_event_t      *wev;
+    ngx_array_t       wsabufs;
+    ngx_chain_t      *cl;
+    LPWSAOVERLAPPED   ovlp;
+
+    wev = c->write;
+
+    if (!wev->ready) {
+        return in;
+    }
+
+    if (!wev->complete) {
+
+        /* post the overlapped WSASend() */
+ 
+        /*
+         * WSABUFs must be 4-byte aligned otherwise
+         * WSASend() will return undocumented WSAEINVAL error.
+         */
+
+        ngx_init_array(wsabufs, c->pool, 10, sizeof(WSABUF), NGX_CHAIN_ERROR);
+
+        prev = NULL;
+        wsabuf = NULL;
+ 
+        /* create the WSABUF and coalesce the neighbouring bufs */
+
+        for (cl = in; cl; cl = cl->next) {
+
+            if (prev == cl->hunk->pos) {
+                wsabuf->len += cl->hunk->last - cl->hunk->pos;
+                prev = cl->hunk->last;
+ 
+            } else {
+                ngx_test_null(wsabuf, ngx_push_array(&wsabufs),
+                              NGX_CHAIN_ERROR);
+                wsabuf->buf = cl->hunk->pos;
+                wsabuf->len = cl->hunk->last - cl->hunk->pos;
+                prev = cl->hunk->last;
+            }
+        }
+
+        ovlp = (LPWSAOVERLAPPED) &c->write->ovlp;
+        ngx_memzero(ovlp, sizeof(WSAOVERLAPPED));
+ 
+        rc = WSASend(c->fd, wsabufs.elts, wsabufs.nelts, &sent, 0, ovlp, NULL);
+
+        wev->complete = 0;
+
+        if (rc == -1) {
+            err = ngx_errno;
+
+            if (err == WSA_IO_PENDING) {
+                wev->active = 1;
+                return in;
+
+            } else {
+                wev->error = 1;
+                ngx_log_error(NGX_LOG_CRIT, c->log, err, "WSASend() failed");
+                return NGX_CHAIN_ERROR;
+            }
+ 
+        } else if (ngx_event_flags & NGX_USE_IOCP_EVENT) {
+
+             /*
+              * if a socket was bound with I/O completion port then
+              * GetQueuedCompletionStatus() would anyway return its status
+              * despite that WSASend() was already complete
+              */
+
+            wev->active = 1;
+            return in;
+        }
+
+    } else {
+
+        /* the overlapped WSASend() complete */
+
+        wev->complete = 0;
+        wev->active = 0;
+
+        if (ngx_event_flags & NGX_USE_IOCP_EVENT) {
+            if (wev->ovlp.error) {
+                ngx_log_error(NGX_LOG_ERR, c->log, wev->ovlp.error,
+                              "WSASend() failed");
+                return NGX_CHAIN_ERROR;
+            }
+
+            sent = wev->available;
+
+        } else {
+            if (WSAGetOverlappedResult(c->fd, (LPWSAOVERLAPPED) &wev->ovlp,
+                                       &sent, 0, NULL) == 0) {
+                ngx_log_error(NGX_LOG_CRIT, c->log, ngx_socket_errno,
+                             "WSASend() or WSAGetOverlappedResult() failed");
+    
+                return NGX_CHAIN_ERROR;
+            }
+        }
+    }
+
+#if (NGX_DEBUG_WRITE_CHAIN)
+    ngx_log_debug(c->log, "WSASend(): %d" _ sent);
+#endif
+
+    c->sent += sent;
+
+    for (cl = in; cl && sent > 0; cl = cl->next) {
+
+        size = cl->hunk->last - cl->hunk->pos;
+
+        if (sent >= size) {
+            sent -= size;
+
+            if (cl->hunk->type & NGX_HUNK_IN_MEMORY) {
+                cl->hunk->pos = cl->hunk->last;
+            }
+
+            continue;
+        }
+
+        if (cl->hunk->type & NGX_HUNK_IN_MEMORY) {
+            cl->hunk->pos += sent;
+        }
+
+        break;
+    }
+
+    if (cl) {
+        wev->ready = 0;
+
+    } else {
+        wev->ready = 1;
+    }
+
+    return cl;
+}
+
+
+#if 0
+
+ngx_chain_t *ngx_wsasend_chain(ngx_connection_t *c, ngx_chain_t *in)
+{
     int               rc;
     char             *prev;
     size_t            size, sent;
@@ -175,7 +418,7 @@ non-block
         break;
     }
 
-    ngx_destroy_array(&wsabufs);
-
     return ce;
 }
+
+#endif