new file mode 100644
--- /dev/null
+++ b/src/os/win32/ngx_wsasend.c
@@ -0,0 +1,183 @@
+
+/*
+ * Copyright (C) Igor Sysoev
+ */
+
+
+#include <ngx_config.h>
+#include <ngx_core.h>
+#include <ngx_event.h>
+
+
+ssize_t
+ngx_wsasend(ngx_connection_t *c, u_char *buf, size_t size)
+{
+    int           n;
+    u_long        sent;
+    ngx_err_t     err;
+    ngx_event_t  *wev;
+    WSABUF        wsabuf;
+
+    wev = c->write;
+
+    if (!wev->ready) {
+        return NGX_AGAIN;
+    }
+
+    /*
+     * WSABUF must be 4-byte aligned otherwise
+     * WSASend() will return undocumented WSAEINVAL error.
+     */
+
+    wsabuf.buf = (char *) buf;
+    wsabuf.len = size;
+
+    sent = 0;
+
+    n = WSASend(c->fd, &wsabuf, 1, &sent, 0, NULL, NULL);
+
+    ngx_log_debug4(NGX_LOG_DEBUG_EVENT, c->log, 0,
+                   "WSASend: fd:%d, %d, %ul of %uz", c->fd, n, sent, size);
+
+    if (n == 0) {
+        if (sent < size) {
+            wev->ready = 0;
+        }
+
+        c->sent += sent;
+
+        return sent;
+    }
+
+    err = ngx_socket_errno;
+
+    if (err == WSAEWOULDBLOCK) {
+        ngx_log_debug0(NGX_LOG_DEBUG_EVENT, c->log, err, "WSASend() not ready");
+        return NGX_AGAIN;
+    }
+
+    wev->error = 1;
+    ngx_connection_error(c, err, "WSASend() failed");
+
+    return NGX_ERROR;
+}
+
+
+ssize_t
+ngx_overlapped_wsasend(ngx_connection_t *c, u_char *buf, size_t size)
+{
+    int               n;
+    u_long            sent;
+    ngx_err_t         err;
+    ngx_event_t      *wev;
+    LPWSAOVERLAPPED   ovlp;
+    WSABUF            wsabuf;
+
+    wev = c->write;
+
+    if (!wev->ready) {
+        return NGX_AGAIN;
+    }
+
+    ngx_log_debug1(NGX_LOG_DEBUG_EVENT, c->log, 0,
+                   "wev->complete: %d", wev->complete);
+
+    if (!wev->complete) {
+
+        /* post the overlapped WSASend() */
+
+        /*
+         * WSABUFs must be 4-byte aligned otherwise
+         * WSASend() will return undocumented WSAEINVAL error.
+         */
+
+        wsabuf.buf = (char *) buf;
+        wsabuf.len = size;
+
+        sent = 0;
+
+        ovlp = (LPWSAOVERLAPPED) &c->write->ovlp;
+        ngx_memzero(ovlp, sizeof(WSAOVERLAPPED));
+
+        n = WSASend(c->fd, &wsabuf, 1, &sent, 0, ovlp, NULL);
+
+        ngx_log_debug4(NGX_LOG_DEBUG_EVENT, c->log, 0,
+                       "WSASend: fd:%d, %d, %ul of %uz", c->fd, n, sent, size);
+
+        wev->complete = 0;
+
+        if (n == 0) {
+            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 NGX_AGAIN;
+            }
+
+            if (sent < size) {
+                wev->ready = 0;
+            }
+
+            c->sent += sent;
+
+            return sent;
+        }
+
+        err = ngx_socket_errno;
+
+        if (err == WSA_IO_PENDING) {
+            ngx_log_debug0(NGX_LOG_DEBUG_EVENT, c->log, err,
+                           "WSASend() posted");
+            wev->active = 1;
+            return NGX_AGAIN;
+        }
+
+        wev->error = 1;
+        ngx_connection_error(c, err, "WSASend() failed");
+
+        return NGX_ERROR;
+    }
+
+    /* the overlapped WSASend() complete */
+
+    wev->complete = 0;
+    wev->active = 0;
+
+    if (ngx_event_flags & NGX_USE_IOCP_EVENT) {
+
+        if (wev->ovlp.error) {
+            ngx_connection_error(c, wev->ovlp.error, "WSASend() failed");
+            return NGX_ERROR;
+        }
+
+        sent = wev->available;
+
+    } else {
+        if (WSAGetOverlappedResult(c->fd, (LPWSAOVERLAPPED) &wev->ovlp,
+                                   &sent, 0, NULL)
+            == 0)
+        {
+            ngx_connection_error(c, ngx_socket_errno,
+                           "WSASend() or WSAGetOverlappedResult() failed");
+
+            return NGX_ERROR;
+        }
+    }
+
+    ngx_log_debug3(NGX_LOG_DEBUG_EVENT, c->log, 0,
+                   "WSAGetOverlappedResult: fd:%d, %ul of %uz",
+                   c->fd, sent, size);
+
+    if (sent < size) {
+        wev->ready = 0;
+    }
+
+    c->sent += sent;
+
+    return sent;
+}