diff --git a/mio/lib/http-fil.c b/mio/lib/http-fil.c
index 9cbb323..8a582b1 100644
--- a/mio/lib/http-fil.c
+++ b/mio/lib/http-fil.c
@@ -370,15 +370,8 @@ static int file_client_on_write (mio_dev_sck_t* sck, mio_iolen_t wrlen, void* wr
 		MIO_ASSERT (mio, file_state->num_pending_writes_to_client > 0);
 		file_state->num_pending_writes_to_client--;
 
-#if 0
-XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
-		if (file_state->peer && file_state->num_pending_writes_to_client == FILE_STATE_PENDING_IO_THRESHOLD)
-		{
-			if (!(file_state->over & FILE_STATE_OVER_READ_FROM_PEER) &&
-			    mio_dev_pro_read(file_state->peer, MIO_DEV_PRO_OUT, 1) <= -1) goto oops;
-		}
-#endif
-		file_state_send_contents_to_client (file_state);
+		if (file_state->req_method == MIO_HTTP_GET)
+			file_state_send_contents_to_client (file_state);
 
 		if ((file_state->over & FILE_STATE_OVER_READ_FROM_PEER) && file_state->num_pending_writes_to_client <= 0)
 		{
@@ -598,6 +591,7 @@ static int open_peer (file_state_t* file_state, const mio_bch_t* actual_file)
 	switch (file_state->req_method)
 	{
 		case MIO_HTTP_GET:
+		case MIO_HTTP_HEAD:
 			if (access(actual_file, R_OK) == -1)
 			{
 				file_state_send_final_status_to_client (file_state, ERRNO_TO_STATUS_CODE(errno), 1); /* 404 not found 403 Forbidden */
@@ -613,6 +607,7 @@ static int open_peer (file_state_t* file_state, const mio_bch_t* actual_file)
 
 			return 0;
 
+#if 0
 		case MIO_HTTP_PUT:
 		case MIO_HTTP_POST:
 /* TOOD: this is destructive. jump to default if not allowed by flags... */
@@ -633,6 +628,7 @@ static int open_peer (file_state_t* file_state, const mio_bch_t* actual_file)
 				return -1;
 			}
 			return 0;
+#endif
 
 #if 0
 		case MIO_HTTP_DELETE:
@@ -654,6 +650,8 @@ static MIO_INLINE void fadvise_on_peer (file_state_t* file_state)
 
 int mio_svc_htts_dofile (mio_svc_htts_t* htts, mio_dev_sck_t* csck, mio_htre_t* req, const mio_bch_t* docroot, const mio_bch_t* file)
 {
+/* TODO: ETag, Last-Modified... */
+
 	mio_t* mio = htts->mio;
 	mio_svc_htts_cli_t* cli = mio_dev_sck_getxtn(csck);
 	file_state_t* file_state = MIO_NULL;
@@ -708,23 +706,10 @@ int mio_svc_htts_dofile (mio_svc_htts_t* htts, mio_dev_sck_t* csck, mio_htre_t*
 
 	if (req->flags & MIO_HTRE_ATTR_EXPECT100)
 	{
-/* TODO: check method. if GET, file contents can be transmitted without 100 continue ... */
 		if (mio_comp_http_version_numbers(&req->version, 1, 1) >= 0 && 
-		   (file_state->req_content_length_unlimited || file_state->req_content_length > 0)) 
+		   (file_state->req_content_length_unlimited || file_state->req_content_length > 0) &&
+		   (file_state->req_method != MIO_HTTP_GET && file_state->req_method != MIO_HTTP_HEAD))  
 		{
-			/* 
-			 * Don't send 100 Continue if http verions is lower than 1.1
-			 * [RFC7231] 
-			 *  A server that receives a 100-continue expectation in an HTTP/1.0
-			 *  request MUST ignore that expectation.
-			 *
-			 * Don't send 100 Continue if expected content lenth is 0. 
-			 * [RFC7231]
-			 *  A server MAY omit sending a 100 (Continue) response if it has
-			 *  already received some or all of the message body for the
-			 *  corresponding request, or if the framing indicates that there is
-			 *  no message body.
-			 */
 			mio_bch_t msgbuf[64];
 			mio_oow_t msglen;
 
@@ -788,6 +773,11 @@ int mio_svc_htts_dofile (mio_svc_htts_t* htts, mio_dev_sck_t* csck, mio_htre_t*
 		if (file_state_send_header_to_client(file_state, 200, 0) <= -1 ||
 		    file_state_send_contents_to_client(file_state) <= -1) goto oops;
 	}
+	else if (file_state->req_method == MIO_HTTP_HEAD)
+	{
+		if (file_state_send_header_to_client(file_state, 200, 0) <= -1) goto oops;
+		file_state_mark_over (file_state, FILE_STATE_OVER_READ_FROM_PEER | FILE_STATE_OVER_WRITE_TO_PEER);
+	}
 
 	/* TODO: store current input watching state and use it when destroying the file_state data */
 	if (mio_dev_sck_read(csck, !(file_state->over & FILE_STATE_OVER_READ_FROM_CLIENT)) <= -1) goto oops;
diff --git a/mio/lib/http-svr.c b/mio/lib/http-svr.c
index 063e0e1..7058e01 100644
--- a/mio/lib/http-svr.c
+++ b/mio/lib/http-svr.c
@@ -153,7 +153,6 @@ static int listener_on_read (mio_dev_sck_t* sck, const void* buf, mio_iolen_t le
 
 	if ((x = mio_htrd_feed(cli->htrd, buf, len, &rem)) <= -1) 
 	{
-printf ("** HTTS - client htrd feed failure socket(%p) - %d\n", sck, x);
 		goto oops;
 	}
 
@@ -172,7 +171,6 @@ printf ("** HTTS - client htrd feed failure socket(%p) - %d\n", sck, x);
 	return 0;
 
 oops:
-printf ("HALTING CLIENT SOCKEXXT %p\n", sck);
 	mio_dev_sck_halt (sck);
 	return 0;
 }
diff --git a/mio/lib/http-thr.c b/mio/lib/http-thr.c
index fec2109..9d41cb7 100644
--- a/mio/lib/http-thr.c
+++ b/mio/lib/http-thr.c
@@ -879,7 +879,7 @@ int mio_svc_htts_dothr (mio_svc_htts_t* htts, mio_dev_sck_t* csck, mio_htre_t* r
 	MIO_SVC_HTTS_RSRC_ATTACH (thr_state, cli->rsrc);
 
 	thr_state->peer = mio_dev_thr_make(mio, MIO_SIZEOF(*thr_peer), &mi);
-	if (MIO_UNLIKELY(!thr_state->peer)) goto oops;
+	if (MIO_UNLIKELY(!thr_state->peer)) { printf ("dev thr make failure. \n"); goto oops; }
 
 	tfs = MIO_NULL; /* mark that tfs is delegated to the thread */
 
diff --git a/mio/lib/mio.c b/mio/lib/mio.c
index c8d13bd..32fbe43 100644
--- a/mio/lib/mio.c
+++ b/mio/lib/mio.c
@@ -1231,14 +1231,130 @@ static void on_write_timeout (mio_t* mio, const mio_ntime_t* now, mio_tmrjob_t*
 	if (x <= -1) mio_dev_halt (dev);
 }
 
+static MIO_INLINE int __enqueue_completed_write (mio_dev_t* dev, mio_iolen_t len, void* wrctx, const mio_devaddr_t* dstaddr)
+{
+	mio_t* mio = dev->mio;
+	mio_cwq_t* cwq;
+	mio_oow_t cwq_extra_aligned, cwqfl_index;
+
+	cwq_extra_aligned = (dstaddr? dstaddr->len: 0);
+	cwq_extra_aligned = MIO_ALIGN_POW2(cwq_extra_aligned, MIO_CWQFL_ALIGN);
+	cwqfl_index = cwq_extra_aligned / MIO_CWQFL_SIZE;
+
+	if (cwqfl_index < MIO_COUNTOF(mio->cwqfl) && mio->cwqfl[cwqfl_index])
+	{
+		/* take an available cwq object from the free cwq list */
+		cwq = dev->mio->cwqfl[cwqfl_index];
+		dev->mio->cwqfl[cwqfl_index] = cwq->q_next;
+	}
+	else
+	{
+		cwq = (mio_cwq_t*)mio_allocmem(mio, MIO_SIZEOF(*cwq) + cwq_extra_aligned);
+		if (MIO_UNLIKELY(!cwq)) return -1;
+	}
+
+	MIO_MEMSET (cwq, 0, MIO_SIZEOF(*cwq));
+	cwq->dev = dev;
+	cwq->ctx = wrctx;
+	if (dstaddr)
+	{
+		cwq->dstaddr.ptr = (mio_uint8_t*)(cwq + 1);
+		cwq->dstaddr.len = dstaddr->len;
+		MIO_MEMCPY (cwq->dstaddr.ptr, dstaddr->ptr, dstaddr->len);
+	}
+	else
+	{
+		cwq->dstaddr.len = 0;
+	}
+
+	cwq->olen = len;
+
+	MIO_CWQ_ENQ (&dev->mio->cwq, cwq);
+	dev->cw_count++; /* increment the number of complete write operations */
+	return 0;
+}
+
+static MIO_INLINE int __enqueue_pending_write (mio_dev_t* dev, mio_iolen_t olen, mio_iolen_t urem, mio_iovec_t* iov, mio_iolen_t iov_cnt, mio_iolen_t iov_index, const mio_ntime_t* tmout, void* wrctx, const mio_devaddr_t* dstaddr)
+{
+	mio_t* mio = dev->mio;
+	mio_wq_t* q;
+	mio_iolen_t i, j;
+
+	if (dev->dev_cap & MIO_DEV_CAP_OUT_UNQUEUEABLE)
+	{
+		/* writing queuing is not requested. so return failure */
+		mio_seterrbfmt (mio, MIO_ENOCAPA, "device incapable of queuing");
+		return -1;
+	}
+
+	/* queue the remaining data*/
+	q = (mio_wq_t*)mio_allocmem(mio, MIO_SIZEOF(*q) + (dstaddr? dstaddr->len: 0) + urem);
+	if (MIO_UNLIKELY(!q)) return -1;
+
+	q->tmridx = MIO_TMRIDX_INVALID;
+	q->dev = dev;
+	q->ctx = wrctx;
+
+	if (dstaddr)
+	{
+		q->dstaddr.ptr = (mio_uint8_t*)(q + 1);
+		q->dstaddr.len = dstaddr->len;
+		MIO_MEMCPY (q->dstaddr.ptr, dstaddr->ptr, dstaddr->len);
+	}
+	else
+	{
+		q->dstaddr.len = 0;
+	}
+
+	q->ptr = (mio_uint8_t*)(q + 1) + q->dstaddr.len;
+	q->len = urem;
+	q->olen = olen; /* original length to use when invoking on_write() */
+	for (i = iov_index, j = 0; i < iov_cnt; i++)
+	{
+		MIO_MEMCPY (&q->ptr[j], iov[i].iov_ptr, iov[i].iov_len);
+		j += iov[i].iov_len;
+	}
+
+	if (tmout && MIO_IS_POS_NTIME(tmout))
+	{
+		mio_tmrjob_t tmrjob;
+
+		MIO_MEMSET (&tmrjob, 0, MIO_SIZEOF(tmrjob));
+		tmrjob.ctx = q;
+		mio_gettime (mio, &tmrjob.when);
+		MIO_ADD_NTIME (&tmrjob.when, &tmrjob.when, tmout);
+		tmrjob.handler = on_write_timeout;
+		tmrjob.idxptr = &q->tmridx;
+
+		q->tmridx = mio_instmrjob(mio, &tmrjob);
+		if (q->tmridx == MIO_TMRIDX_INVALID) 
+		{
+			mio_freemem (mio, q);
+			return -1;
+		}
+	}
+
+	MIO_WQ_ENQ (&dev->wq, q);
+	if (!(dev->dev_cap & MIO_DEV_CAP_OUT_WATCHED))
+	{
+		/* if output is not being watched, arrange to do so */
+		if (mio_dev_watch(dev, MIO_DEV_WATCH_RENEW, MIO_DEV_EVENT_IN) <= -1)
+		{
+			unlink_wq (mio, q);
+			mio_freemem (mio, q);
+			return -1;
+		}
+	}
+
+	return 0; /* request pused to a write queue. */
+}
+
 static int __dev_write (mio_dev_t* dev, const void* data, mio_iolen_t len, const mio_ntime_t* tmout, void* wrctx, const mio_devaddr_t* dstaddr)
 {
 	mio_t* mio = dev->mio;
 	const mio_uint8_t* uptr;
 	mio_iolen_t urem, ulen;
-	mio_wq_t* q;
-	mio_cwq_t* cwq;
-	mio_oow_t cwq_extra_aligned, cwqfl_index;
+	mio_iovec_t iov;
 	int x;
 
 	if (dev->dev_cap & MIO_DEV_CAP_OUT_CLOSED)
@@ -1317,120 +1433,22 @@ static int __dev_write (mio_dev_t* dev, const void* data, mio_iolen_t len, const
 		goto enqueue_completed_write;
 	}
 
-	return 1; /* written immediately and called on_write callback */
+	return 1; /* written immediately and called on_write callback. but this line will never be reached */
 
 enqueue_data:
-	if (dev->dev_cap & MIO_DEV_CAP_OUT_UNQUEUEABLE)
-	{
-		/* writing queuing is not requested. so return failure */
-		mio_seterrbfmt (mio, MIO_ENOCAPA, "device incapable of queuing");
-		return -1;
-	}
-
-	/* queue the remaining data*/
-	q = (mio_wq_t*)mio_allocmem(mio, MIO_SIZEOF(*q) + (dstaddr? dstaddr->len: 0) + urem);
-	if (!q) return -1;
-
-	q->tmridx = MIO_TMRIDX_INVALID;
-	q->dev = dev;
-	q->ctx = wrctx;
-
-	if (dstaddr)
-	{
-		q->dstaddr.ptr = (mio_uint8_t*)(q + 1);
-		q->dstaddr.len = dstaddr->len;
-		MIO_MEMCPY (q->dstaddr.ptr, dstaddr->ptr, dstaddr->len);
-	}
-	else
-	{
-		q->dstaddr.len = 0;
-	}
-
-	q->ptr = (mio_uint8_t*)(q + 1) + q->dstaddr.len;
-	q->len = urem;
-	q->olen = len;
-	MIO_MEMCPY (q->ptr, uptr, urem);
-
-	if (tmout && MIO_IS_POS_NTIME(tmout))
-	{
-		mio_tmrjob_t tmrjob;
-
-		MIO_MEMSET (&tmrjob, 0, MIO_SIZEOF(tmrjob));
-		tmrjob.ctx = q;
-		mio_gettime (mio, &tmrjob.when);
-		MIO_ADD_NTIME (&tmrjob.when, &tmrjob.when, tmout);
-		tmrjob.handler = on_write_timeout;
-		tmrjob.idxptr = &q->tmridx;
-
-		q->tmridx = mio_instmrjob(mio, &tmrjob);
-		if (q->tmridx == MIO_TMRIDX_INVALID) 
-		{
-			mio_freemem (mio, q);
-			return -1;
-		}
-	}
-
-	MIO_WQ_ENQ (&dev->wq, q);
-	if (!(dev->dev_cap & MIO_DEV_CAP_OUT_WATCHED))
-	{
-		/* if output is not being watched, arrange to do so */
-		if (mio_dev_watch(dev, MIO_DEV_WATCH_RENEW, MIO_DEV_EVENT_IN) <= -1)
-		{
-			unlink_wq (mio, q);
-			mio_freemem (mio, q);
-			return -1;
-		}
-	}
-
-	return 0; /* request pused to a write queue. */
+	iov.iov_ptr = (void*)uptr;
+	iov.iov_len = urem;
+	return __enqueue_pending_write(dev, len, urem, &iov, 1, 0, tmout, wrctx, dstaddr);
 
 enqueue_completed_write:
-	/* queue the remaining data*/
-	cwq_extra_aligned = (dstaddr? dstaddr->len: 0);
-	cwq_extra_aligned = MIO_ALIGN_POW2(cwq_extra_aligned, MIO_CWQFL_ALIGN);
-	cwqfl_index = cwq_extra_aligned / MIO_CWQFL_SIZE;
-
-	if (cwqfl_index < MIO_COUNTOF(mio->cwqfl) && mio->cwqfl[cwqfl_index])
-	{
-		/* take an available cwq object from the free cwq list */
-		cwq = dev->mio->cwqfl[cwqfl_index];
-		dev->mio->cwqfl[cwqfl_index] = cwq->q_next;
-	}
-	else
-	{
-		cwq = (mio_cwq_t*)mio_allocmem(mio, MIO_SIZEOF(*cwq) + cwq_extra_aligned);
-		if (MIO_UNLIKELY(!cwq)) return -1;
-	}
-
-	MIO_MEMSET (cwq, 0, MIO_SIZEOF(*cwq));
-	cwq->dev = dev;
-	cwq->ctx = wrctx;
-	if (dstaddr)
-	{
-		cwq->dstaddr.ptr = (mio_uint8_t*)(cwq + 1);
-		cwq->dstaddr.len = dstaddr->len;
-		MIO_MEMCPY (cwq->dstaddr.ptr, dstaddr->ptr, dstaddr->len);
-	}
-	else
-	{
-		cwq->dstaddr.len = 0;
-	}
-
-	cwq->olen = len;
-
-	MIO_CWQ_ENQ (&dev->mio->cwq, cwq);
-	dev->cw_count++; /* increment the number of complete write operations */
-	return 0;
+	return __enqueue_completed_write(dev, len, wrctx, dstaddr);
 }
 
 static int __dev_writev (mio_dev_t* dev, mio_iovec_t* iov, mio_iolen_t iovcnt, const mio_ntime_t* tmout, void* wrctx, const mio_devaddr_t* dstaddr)
 {
 	mio_t* mio = dev->mio;
 	mio_iolen_t urem, len;
-	mio_iolen_t index = 0, i, j;
-	mio_wq_t* q;
-	mio_cwq_t* cwq;
-	mio_oow_t cwq_extra_aligned, cwqfl_index;
+	mio_iolen_t index = 0, i;
 	int x;
 
 	if (dev->dev_cap & MIO_DEV_CAP_OUT_CLOSED)
@@ -1522,117 +1540,41 @@ static int __dev_writev (mio_dev_t* dev, mio_iovec_t* iov, mio_iolen_t iovcnt, c
 		goto enqueue_completed_write;
 	}
 
-	return 1; /* written immediately and called on_write callback */
+	return 1; /* written immediately and called on_write callback. but this line will never be reached */
 
 enqueue_data:
-	if (dev->dev_cap & MIO_DEV_CAP_OUT_UNQUEUEABLE)
+	return __enqueue_pending_write(dev, len, urem, iov, iovcnt, index, tmout, wrctx, dstaddr);
+
+enqueue_completed_write:
+	return __enqueue_completed_write(dev, len, wrctx, dstaddr);
+}
+
+static int __dev_sendfile (mio_dev_t* dev, mio_syshnd_t in_fd, mio_uintmax_t offset, mio_iolen_t len, const mio_ntime_t* tmout, void* wrctx, const mio_devaddr_t* dstaddr)
+{
+	mio_t* mio = dev->mio;
+
+	if (dev->dev_cap & MIO_DEV_CAP_OUT_CLOSED)
 	{
-		/* writing queuing is not requested. so return failure */
-		mio_seterrbfmt (mio, MIO_ENOCAPA, "device incapable of queuing");
+		mio_seterrbfmt (mio, MIO_ENOCAPA, "unable to write to closed device");
 		return -1;
 	}
 
-	/* queue the remaining data*/
-	q = (mio_wq_t*)mio_allocmem(mio, MIO_SIZEOF(*q) + (dstaddr? dstaddr->len: 0) + urem);
-	if (MIO_UNLIKELY(!q)) return -1;
-
-	q->tmridx = MIO_TMRIDX_INVALID;
-	q->dev = dev;
-	q->ctx = wrctx;
-
-	if (dstaddr)
+	if (!MIO_WQ_IS_EMPTY(&dev->wq)) 
 	{
-		q->dstaddr.ptr = (mio_uint8_t*)(q + 1);
-		q->dstaddr.len = dstaddr->len;
-		MIO_MEMCPY (q->dstaddr.ptr, dstaddr->ptr, dstaddr->len);
-	}
-	else
-	{
-		q->dstaddr.len = 0;
+		/* if the writing queue is not empty, enqueue this request immediately */
+		goto enqueue_data;
 	}
 
-	q->ptr = (mio_uint8_t*)(q + 1) + q->dstaddr.len;
-	q->len = urem;
-	q->olen = len; /* original length to use when invoking on_write() */
-	for (i = index, j = 0; i < iovcnt; i++)
-	{
-		MIO_MEMCPY (&q->ptr[j], iov[i].iov_ptr, iov[i].iov_len);
-		j += iov[i].iov_len;
-	}
+	return 1; 
 
-	if (tmout && MIO_IS_POS_NTIME(tmout))
-	{
-		mio_tmrjob_t tmrjob;
-
-		MIO_MEMSET (&tmrjob, 0, MIO_SIZEOF(tmrjob));
-		tmrjob.ctx = q;
-		mio_gettime (mio, &tmrjob.when);
-		MIO_ADD_NTIME (&tmrjob.when, &tmrjob.when, tmout);
-		tmrjob.handler = on_write_timeout;
-		tmrjob.idxptr = &q->tmridx;
-
-		q->tmridx = mio_instmrjob(mio, &tmrjob);
-		if (q->tmridx == MIO_TMRIDX_INVALID) 
-		{
-			mio_freemem (mio, q);
-			return -1;
-		}
-	}
-
-	MIO_WQ_ENQ (&dev->wq, q);
-	if (!(dev->dev_cap & MIO_DEV_CAP_OUT_WATCHED))
-	{
-		/* if output is not being watched, arrange to do so */
-		if (mio_dev_watch(dev, MIO_DEV_WATCH_RENEW, MIO_DEV_EVENT_IN) <= -1)
-		{
-			unlink_wq (mio, q);
-			mio_freemem (mio, q);
-			return -1;
-		}
-	}
-
-	return 0; /* request pused to a write queue. */
+enqueue_data:
+	/*return __enqueue_pending_write(dev, len, urem, iov, iovcnt, index, tmout, wrctx, dstaddr);*/
 
 enqueue_completed_write:
-	/* queue the remaining data*/
-	cwq_extra_aligned = (dstaddr? dstaddr->len: 0);
-	cwq_extra_aligned = MIO_ALIGN_POW2(cwq_extra_aligned, MIO_CWQFL_ALIGN);
-	cwqfl_index = cwq_extra_aligned / MIO_CWQFL_SIZE;
-
-	if (cwqfl_index < MIO_COUNTOF(mio->cwqfl) && mio->cwqfl[cwqfl_index])
-	{
-		/* take an available cwq object from the free cwq list */
-		cwq = dev->mio->cwqfl[cwqfl_index];
-		dev->mio->cwqfl[cwqfl_index] = cwq->q_next;
-	}
-	else
-	{
-		cwq = (mio_cwq_t*)mio_allocmem(mio, MIO_SIZEOF(*cwq) + cwq_extra_aligned);
-		if (!cwq) return -1;
-	}
-
-	MIO_MEMSET (cwq, 0, MIO_SIZEOF(*cwq));
-	cwq->dev = dev;
-	cwq->ctx = wrctx;
-	if (dstaddr)
-	{
-		cwq->dstaddr.ptr = (mio_uint8_t*)(cwq + 1);
-		cwq->dstaddr.len = dstaddr->len;
-		MIO_MEMCPY (cwq->dstaddr.ptr, dstaddr->ptr, dstaddr->len);
-	}
-	else
-	{
-		cwq->dstaddr.len = 0;
-	}
-
-	cwq->olen = len;
-
-	MIO_CWQ_ENQ (&dev->mio->cwq, cwq);
-	dev->cw_count++; /* increment the number of complete write operations */
+	/*return __enqueue_completed_write(dev, len, wrctx, dstaddr);*/
 	return 0;
 }
 
-
 int mio_dev_write (mio_dev_t* dev, const void* data, mio_iolen_t len, void* wrctx, const mio_devaddr_t* dstaddr)
 {
 	return __dev_write(dev, data, len, MIO_NULL, wrctx, dstaddr);