When using NSS, only schedule transport socket reads when the transport buffer is empty.

net/base/nss_memio.h

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 // Written in NSPR style to also be suitable for adding to the NSS demo suite
 
 #ifndef __MEMIO_H
 #define __MEMIO_H
 
 #include <stddef.h>
 
@@ skipping 32 matching lines @@
 void memio_SetPeerName(PRFileDesc *fd, const PRNetAddr *peername);
 
 /* Return a private pointer needed by the following
  * four functions.  (We could have passed a PRFileDesc to
  * them, but that would be slower.  Better for the caller
  * to grab the pointer once and cache it.
  * This may be a premature optimization.)
  */
 memio_Private *memio_GetSecret(PRFileDesc *fd);
 
+/* Ask memio how many bytes were requested by a higher layer during the last
+ * read request that could not be satisfied (due to the buffer being empty).
+ * Returns 0 if there was no unsatisfied read request.
+ */
+int memio_GetReadRequest(memio_Private *secret);

[wtc, 2012/12/20 02:41:22]

The specification of this function is not very clear unless
I look at its implementation in the .c file.

All we need is a boolean function that tells us whether a
read was requested by a higher layer when the buffer was
empty.

[Ryan Sleevi, 2012/12/20 02:55:58]

While yes, we only need a bool, I typed it as an int both to match the OpenSSL
implementation and to allow for the 'proper' behaviour from the point of view of
a generic socket API, which would be to have the transport only read 'as much'
data as requested.

+
 /* Ask memio where to put bytes from the network, and how many it can handle.
  * Returns bytes available to write, or 0 if none available.
  * Puts current buffer position into *buf.
  */
 int memio_GetReadParams(memio_Private *secret, char **buf);
 
 /* Tell memio how many bytes were read from the network.
  * If bytes_read is 0, causes EOF to be reported to
  * NSS after it reads the last byte from the circular buffer.
  * If bytes_read is < 0, it is treated as an NSPR error code.
@@ skipping 17 matching lines @@
  * map from Unix errors to NSPR error codes.
  * On EWOULDBLOCK or the equivalent, don't call this function.
  */
 void memio_PutWriteResult(memio_Private *secret, int bytes_written);
 
 #ifdef __cplusplus
 }
 #endif
 
 #endif