diff --git a/src/Tiny_httpd.ml b/src/Tiny_httpd.ml
index e06f5b15..53726469 100644
--- a/src/Tiny_httpd.ml
+++ b/src/Tiny_httpd.ml
@@ -84,7 +84,9 @@ module Byte_stream = struct
 
   let rec iter f (self:t) : unit =
     let s, i, len = self.bs_fill_buf () in
-    if len > 0 then (
+    if len=0 then (
+      self.bs_close();
+    ) else (
       f s i len;
       self.bs_consume len;
       (iter [@tailcall]) f self
@@ -98,13 +100,15 @@ module Byte_stream = struct
     let len =
       ref (
         match len with
-        | Some n -> min n (Bytes.length s- i)
-        | None -> Bytes.length s- i
+        | Some n ->
+          if n > Bytes.length s -i then invalid_arg "Byte_stream.of_bytes";
+          n
+        | None -> Bytes.length s - i
       )
     in
     let i = ref i in
     { bs_fill_buf=(fun () -> s, !i, !len);
-      bs_close=(fun () -> ());
+      bs_close=(fun () -> len := 0);
       bs_consume=(fun n -> assert (n<= !len); i := !i + n; len := !len - n);
     }
 
@@ -121,20 +125,17 @@ module Byte_stream = struct
       close_in_noerr ic;
       raise e
 
-  (* Read as much as possible into [buf]. *)
-  let read_into_buf (self:t) (buf:Buf_.t) : int =
-    let s, i, len = self.bs_fill_buf () in
-    if len > 0 then (
-      Buf_.add_bytes buf s i len;
-      self.bs_consume len;
-    );
-    len
-
   let read_all ?(buf=Buf_.create()) (self:t) : string =
     let continue = ref true in
     while !continue do
-      let n_rd = read_into_buf self buf in
-      if n_rd = 0 then (
+      let s, i, len = self.bs_fill_buf () in
+      _debug (fun k->k "read-all: got i=%d, len=%d, bufsize %d" i len (Buf_.size buf));
+      if len > 0 then (
+        Buf_.add_bytes buf s i len;
+        self.bs_consume len;
+      );
+      assert (len >= 0);
+      if len = 0 then (
         continue := false
       )
     done;
@@ -145,24 +146,24 @@ module Byte_stream = struct
     assert (Bytes.length bytes >= n);
     let offset = ref 0 in
     while !offset < n do
-      let n_read =
-        let s, i, len = self.bs_fill_buf () in
-        let n_read = min len (n- !offset) in
-        Bytes.blit s i bytes !offset n_read;
-        offset := !offset + n_read;
-        self.bs_consume n_read;
-        n_read
-      in
+      let s, i, len = self.bs_fill_buf () in
+      let n_read = min len (n- !offset) in
+      Bytes.blit s i bytes !offset n_read;
+      offset := !offset + n_read;
+      self.bs_consume n_read;
       if n_read=0 then too_short();
     done
 
-  (* read a line into the buffer *)
+  (* read a line into the buffer, after clearing it. *)
   let read_line_into (self:t) ~buf : unit =
     Buf_.clear buf;
     let continue = ref true in
     while !continue do
       let s, i, len = self.bs_fill_buf () in
-      if len=0 then continue := false;
+      if len=0 then (
+        continue := false;
+        if Buf_.size buf = 0 then raise End_of_file;
+      );
       let j = ref i in
       while !j < i+len && Bytes.get s !j <> '\n' do
         incr j
@@ -178,6 +179,56 @@ module Byte_stream = struct
       )
     done
 
+  (* new stream with maximum size [max_size].
+     @param close_rec if true, closing this will also close the input stream
+     @param too_big called with read size if the max size is reached *)
+  let limit_size_to ~close_rec ~max_size ~too_big (self:t) : t =
+    let size = ref 0 in
+    let continue = ref true in
+    { bs_fill_buf =
+        (fun () ->
+          if !continue then self.bs_fill_buf() else Bytes.empty, 0, 0);
+      bs_close=(fun () ->
+          if close_rec then self.bs_close ());
+      bs_consume = (fun n ->
+          size := !size + n;
+          if !size > max_size then (
+            continue := false;
+            too_big !size
+          ) else (
+            self.bs_consume n
+          ));
+    }
+
+  (* read exactly [size] bytes from the stream *)
+  let read_exactly ~close_rec ~size ~too_short (self:t) : t =
+    if size=0 then (
+      empty
+    ) else (
+      let size = ref size in
+      { bs_fill_buf = (fun () ->
+            (* must not block on [self] if we're done *)
+            if !size = 0 then Bytes.empty, 0, 0
+            else (
+              let buf, i, len = self.bs_fill_buf () in
+              let len = min len !size in
+              if len = 0 && !size > 0 then (
+                too_short !size;
+              );
+              buf, i, len
+            )
+          );
+        bs_close=(fun () ->
+            (* close underlying stream if [close_rec] *)
+            if close_rec then self.bs_close();
+            size := 0);
+        bs_consume = (fun n ->
+            let n = min n !size in
+            size := !size - n;
+            self.bs_consume n);
+      }
+    )
+
   let read_line ?(buf=Buf_.create()) self : string =
     read_line_into self ~buf;
     Buf_.contents buf
@@ -306,6 +357,7 @@ module Request = struct
 
   (* decode a "chunked" stream into a normal stream *)
   let read_stream_chunked_ ?(buf=Buf_.create()) (bs:byte_stream) : byte_stream =
+    _debug (fun k->k "body: start reading chunked stream...");
     let read_next_chunk_len () : int =
       let line = Byte_stream.read_line ~buf bs in
       (* parse chunk length, ignore extensions *)
@@ -318,7 +370,7 @@ module Request = struct
       chunk_size
     in
     let refill = ref true in
-    let bytes = Bytes.make 4096  ' ' in
+    let bytes = Bytes.make (16 * 4096)  ' ' in
     let offset = ref 0 in
     let len = ref 0 in
     let chunk_size = ref 0 in
@@ -354,46 +406,24 @@ module Request = struct
 
   let limit_body_size_ ~max_size (bs:byte_stream) : byte_stream =
     _debug (fun k->k "limit size of body to max-size=%d" max_size);
-    let size = ref 0 in
-    { bs_fill_buf = bs.bs_fill_buf;
-      bs_close=bs.bs_close;
-      bs_consume = (fun n ->
-          size := !size + n;
-          if !size > max_size then (
-            (* read too much *)
-            bad_reqf 413
-              "body size was supposed to be %d, but at least %d bytes received"
-              max_size !size
-          );
-          bs.bs_consume n);
-    }
+    Byte_stream.limit_size_to ~max_size ~close_rec:true bs
+      ~too_big:(fun size ->
+          (* read too much *)
+          bad_reqf 413
+            "body size was supposed to be %d, but at least %d bytes received"
+            max_size size
+        )
 
   let limit_body_size ~max_size (req:byte_stream t) : byte_stream t =
     { req with body=limit_body_size_ ~max_size req.body }
 
   (* read exactly [size] bytes from the stream *)
   let read_exactly ~size (bs:byte_stream) : byte_stream =
-    if size=0 then (
-      Byte_stream.empty
-    ) else (
-      let size = ref size in
-      { bs_fill_buf = (fun () ->
-            let buf, i, len = bs.bs_fill_buf () in
-            let len = min len !size in
-            if len = 0 && !size > 0 then (
-              bad_reqf 400 "body is too short"
-            );
-            buf, i, len
-          );
-        bs_close=(fun () ->
-            (* do not close underlying stream *)
-            size := 0);
-        bs_consume = (fun n ->
-            let n = min n !size in
-            size := !size - n;
-            bs.bs_consume n);
-      }
-    )
+    _debug (fun k->k "body: must read exactly %d bytes" size);
+    Byte_stream.read_exactly bs ~close_rec:false
+      ~size ~too_short:(fun size ->
+          bad_reqf 400 "body is too short by %d bytes" size
+        )
 
   (* parse request, but not body (yet) *)
   let parse_req_start ~buf (bs:byte_stream) : unit t option resp_result =
diff --git a/src/bin/http_of_dir.ml b/src/bin/http_of_dir.ml
index 30642f10..f2558ccf 100644
--- a/src/bin/http_of_dir.ml
+++ b/src/bin/http_of_dir.ml
@@ -141,6 +141,7 @@ let serve ~config (dir:string) : _ result =
          S.Byte_stream.to_chan oc req.S.Request.body;
          flush oc;
          close_out oc;
+         S._debug (fun k->k "done uploading");
          S.Response.make_raw ~code:201 "upload successful"
       )
   ) else (