bufferevent_openssl.c

/*
 * Copyright (c) 2009-2012 Niels Provos and Nick Mathewson
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. The name of the author may not be used to endorse or promote products
 *    derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

// Get rid of OSX 10.7 and greater deprecation warnings.
#if defined(__APPLE__) && defined(__clang__)
#pragma clang diagnostic ignored "-Wdeprecated-declarations"
#endif

#include "event2/event-config.h"
#include "evconfig-private.h"

#include <sys/types.h>

#ifdef EVENT__HAVE_SYS_TIME_H
#include <sys/time.h>
#endif

#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#ifdef EVENT__HAVE_STDARG_H
#include <stdarg.h>
#endif
#ifdef EVENT__HAVE_UNISTD_H
#include <unistd.h>
#endif

#ifdef _WIN32
#include <winsock2.h>
#endif

#include "event2/bufferevent.h"
#include "event2/bufferevent_struct.h"
#include "event2/bufferevent_ssl.h"
#include "event2/buffer.h"
#include "event2/event.h"

#include "mm-internal.h"
#include "bufferevent-internal.h"
#include "log-internal.h"

#include <openssl/bio.h>
#include <openssl/ssl.h>
#include <openssl/err.h>
#include "openssl-compat.h"

/*
 * Define an OpenSSL bio that targets a bufferevent.
 */

/* --------------------
   A BIO is an OpenSSL abstraction that handles reading and writing data.  The
   library will happily speak SSL over anything that implements a BIO
   interface.

   Here we define a BIO implementation that directs its output to a
   bufferevent.  We'll want to use this only when none of OpenSSL's built-in
   IO mechanisms work for us.
   -------------------- */

/* every BIO type needs its own integer type value. */
#define BIO_TYPE_LIBEVENT 57
/* ???? Arguably, we should set BIO_TYPE_FILTER or BIO_TYPE_SOURCE_SINK on
 * this. */

#if 0
static void
print_err(int val)
{
	int err;
	printf("Error was %d\n", val);

	while ((err = ERR_get_error())) {
		const char *msg = (const char*)ERR_reason_error_string(err);
		const char *lib = (const char*)ERR_lib_error_string(err);
		const char *func = (const char*)ERR_func_error_string(err);

		printf("%s in %s %s\n", msg, lib, func);
	}
}
#else
#define print_err(v) ((void)0)
#endif

/* Called to initialize a new BIO */
static int
bio_bufferevent_new(BIO *b)
{
	BIO_set_init(b, 0);
	BIO_set_data(b, NULL); /* We'll be putting the bufferevent in this field.*/
	return 1;
}

/* Called to uninitialize the BIO. */
static int
bio_bufferevent_free(BIO *b)
{
	if (!b)
		return 0;
	if (BIO_get_shutdown(b)) {
		if (BIO_get_init(b) && BIO_get_data(b))
			bufferevent_free(BIO_get_data(b));
		BIO_free(b);
	}
	return 1;
}

/* Called to extract data from the BIO. */
static int
bio_bufferevent_read(BIO *b, char *out, int outlen)
{
	int r = 0;
	struct evbuffer *input;

	BIO_clear_retry_flags(b);

	if (!out)
		return 0;
	if (!BIO_get_data(b))
		return -1;

	input = bufferevent_get_input(BIO_get_data(b));
	if (evbuffer_get_length(input) == 0) {
		/* If there's no data to read, say so. */
		BIO_set_retry_read(b);
		return -1;
	} else {
		r = evbuffer_remove(input, out, outlen);
	}

	return r;
}

/* Called to write data info the BIO */
static int
bio_bufferevent_write(BIO *b, const char *in, int inlen)
{
	struct bufferevent *bufev = BIO_get_data(b);
	struct evbuffer *output;
	size_t outlen;

	BIO_clear_retry_flags(b);

	if (!BIO_get_data(b))
		return -1;

	output = bufferevent_get_output(bufev);
	outlen = evbuffer_get_length(output);

	/* Copy only as much data onto the output buffer as can fit under the
	 * high-water mark. */
	if (bufev->wm_write.high && bufev->wm_write.high <= (outlen+inlen)) {
		if (bufev->wm_write.high <= outlen) {
			/* If no data can fit, we'll need to retry later. */
			BIO_set_retry_write(b);
			return -1;
		}
		inlen = bufev->wm_write.high - outlen;
	}

	EVUTIL_ASSERT(inlen > 0);
	evbuffer_add(output, in, inlen);
	return inlen;
}

/* Called to handle various requests */
static long
bio_bufferevent_ctrl(BIO *b, int cmd, long num, void *ptr)
{
	struct bufferevent *bufev = BIO_get_data(b);
	long ret = 1;

	switch (cmd) {
	case BIO_CTRL_GET_CLOSE:
		ret = BIO_get_shutdown(b);
		break;
	case BIO_CTRL_SET_CLOSE:
		BIO_set_shutdown(b, (int)num);
		break;
	case BIO_CTRL_PENDING:
		ret = evbuffer_get_length(bufferevent_get_input(bufev)) != 0;
		break;
	case BIO_CTRL_WPENDING:
		ret = evbuffer_get_length(bufferevent_get_output(bufev)) != 0;
		break;
	/* XXXX These two are given a special-case treatment because
	 * of cargo-cultism.  I should come up with a better reason. */
	case BIO_CTRL_DUP:
	case BIO_CTRL_FLUSH:
		ret = 1;
		break;
	default:
		ret = 0;
		break;
	}
	return ret;
}

/* Called to write a string to the BIO */
static int
bio_bufferevent_puts(BIO *b, const char *s)
{
	return bio_bufferevent_write(b, s, strlen(s));
}

/* Method table for the bufferevent BIO */
static BIO_METHOD *methods_bufferevent;

/* Return the method table for the bufferevents BIO */
static BIO_METHOD *
BIO_s_bufferevent(void)
{
	if (methods_bufferevent == NULL) {
		methods_bufferevent = BIO_meth_new(BIO_TYPE_LIBEVENT, "bufferevent");
		if (methods_bufferevent == NULL)
			return NULL;
		BIO_meth_set_write(methods_bufferevent, bio_bufferevent_write);
		BIO_meth_set_read(methods_bufferevent, bio_bufferevent_read);
		BIO_meth_set_puts(methods_bufferevent, bio_bufferevent_puts);
		BIO_meth_set_ctrl(methods_bufferevent, bio_bufferevent_ctrl);
		BIO_meth_set_create(methods_bufferevent, bio_bufferevent_new);
		BIO_meth_set_destroy(methods_bufferevent, bio_bufferevent_free);
	}
	return methods_bufferevent;
}

/* Create a new BIO to wrap communication around a bufferevent.  If close_flag
 * is true, the bufferevent will be freed when the BIO is closed. */
static BIO *
BIO_new_bufferevent(struct bufferevent *bufferevent, int close_flag)
{
	BIO *result;
	if (!bufferevent)
		return NULL;
	if (!(result = BIO_new(BIO_s_bufferevent())))
		return NULL;
	BIO_set_init(result, 1);
	BIO_set_data(result, bufferevent);
	BIO_set_shutdown(result, close_flag ? 1 : 0);
	return result;
}

/* --------------------
   Now, here's the OpenSSL-based implementation of bufferevent.

   The implementation comes in two flavors: one that connects its SSL object
   to an underlying bufferevent using a BIO_bufferevent, and one that has the
   SSL object connect to a socket directly.  The latter should generally be
   faster, except on Windows, where your best bet is using a
   bufferevent_async.

   (OpenSSL supports many other BIO types, too.  But we can't use any unless
   we have a good way to get notified when they become readable/writable.)
   -------------------- */

struct bio_data_counts {
	unsigned long n_written;
	unsigned long n_read;
};

struct bufferevent_openssl {
	/* Shared fields with common bufferevent implementation code.
	   If we were set up with an underlying bufferevent, we use the
	   events here as timers only.  If we have an SSL, then we use
	   the events as socket events.
	 */
	struct bufferevent_private bev;
	/* An underlying bufferevent that we're directing our output to.
	   If it's NULL, then we're connected to an fd, not an evbuffer. */
	struct bufferevent *underlying;
	/* The SSL object doing our encryption. */
	SSL *ssl;

	/* A callback that's invoked when data arrives on our outbuf so we
	   know to write data to the SSL. */
	struct evbuffer_cb_entry *outbuf_cb;

	/* A count of how much data the bios have read/written total.  Used
	   for rate-limiting. */
	struct bio_data_counts counts;

	/* If this value is greater than 0, then the last SSL_write blocked,
	 * and we need to try it again with this many bytes. */
	ev_ssize_t last_write;

#define NUM_ERRORS 3
	ev_uint32_t errors[NUM_ERRORS];

	/* When we next get available space, we should say "read" instead of
	   "write". This can happen if there's a renegotiation during a read
	   operation. */
	unsigned read_blocked_on_write : 1;
	/* When we next get data, we should say "write" instead of "read". */
	unsigned write_blocked_on_read : 1;
	/* Treat TCP close before SSL close on SSL >= v3 as clean EOF. */
	unsigned allow_dirty_shutdown : 1;
	/* XXX */
	unsigned n_errors : 2;

	/* Are we currently connecting, accepting, or doing IO? */
	unsigned state : 2;
	/* If we reset fd, we sould reset state too */
	unsigned old_state : 2;
};

static int be_openssl_enable(struct bufferevent *, short);
static int be_openssl_disable(struct bufferevent *, short);
static void be_openssl_unlink(struct bufferevent *);
static void be_openssl_destruct(struct bufferevent *);
static int be_openssl_adj_timeouts(struct bufferevent *);
static int be_openssl_flush(struct bufferevent *bufev,
    short iotype, enum bufferevent_flush_mode mode);
static int be_openssl_ctrl(struct bufferevent *, enum bufferevent_ctrl_op, union bufferevent_ctrl_data *);

const struct bufferevent_ops bufferevent_ops_openssl = {
	"ssl",
	evutil_offsetof(struct bufferevent_openssl, bev.bev),
	be_openssl_enable,
	be_openssl_disable,
	be_openssl_unlink,
	be_openssl_destruct,
	be_openssl_adj_timeouts,
	be_openssl_flush,
	be_openssl_ctrl,
};

/* Given a bufferevent, return a pointer to the bufferevent_openssl that
 * contains it, if any. */
static inline struct bufferevent_openssl *
upcast(struct bufferevent *bev)
{
	struct bufferevent_openssl *bev_o;
	if (bev->be_ops != &bufferevent_ops_openssl)
		return NULL;
	bev_o = (void*)( ((char*)bev) -
			 evutil_offsetof(struct bufferevent_openssl, bev.bev));
	EVUTIL_ASSERT(bev_o->bev.bev.be_ops == &bufferevent_ops_openssl);
	return bev_o;
}

static inline void
put_error(struct bufferevent_openssl *bev_ssl, unsigned long err)
{
	if (bev_ssl->n_errors == NUM_ERRORS)
		return;
	/* The error type according to openssl is "unsigned long", but
	   openssl never uses more than 32 bits of it.  It _can't_ use more
	   than 32 bits of it, since it needs to report errors on systems
	   where long is only 32 bits.
	 */
	bev_ssl->errors[bev_ssl->n_errors++] = (ev_uint32_t) err;
}

/* Have the base communications channel (either the underlying bufferevent or
 * ev_read and ev_write) start reading.  Take the read-blocked-on-write flag
 * into account. */
static int
start_reading(struct bufferevent_openssl *bev_ssl)
{
	if (bev_ssl->underlying) {
		bufferevent_unsuspend_read_(bev_ssl->underlying,
		    BEV_SUSPEND_FILT_READ);
		return 0;
	} else {
		struct bufferevent *bev = &bev_ssl->bev.bev;
		int r;
		r = bufferevent_add_event_(&bev->ev_read, &bev->timeout_read);
		if (r == 0 && bev_ssl->read_blocked_on_write)
			r = bufferevent_add_event_(&bev->ev_write,
			    &bev->timeout_write);
		return r;
	}
}

/* Have the base communications channel (either the underlying bufferevent or
 * ev_read and ev_write) start writing.  Take the write-blocked-on-read flag
 * into account. */
static int
start_writing(struct bufferevent_openssl *bev_ssl)
{
	int r = 0;
	if (bev_ssl->underlying) {
		if (bev_ssl->write_blocked_on_read) {
			bufferevent_unsuspend_read_(bev_ssl->underlying,
			    BEV_SUSPEND_FILT_READ);
		}
	} else {
		struct bufferevent *bev = &bev_ssl->bev.bev;
		r = bufferevent_add_event_(&bev->ev_write, &bev->timeout_write);
		if (!r && bev_ssl->write_blocked_on_read)
			r = bufferevent_add_event_(&bev->ev_read,
			    &bev->timeout_read);
	}
	return r;
}

static void
stop_reading(struct bufferevent_openssl *bev_ssl)
{
	if (bev_ssl->write_blocked_on_read)
		return;
	if (bev_ssl->underlying) {
		bufferevent_suspend_read_(bev_ssl->underlying,
		    BEV_SUSPEND_FILT_READ);
	} else {
		struct bufferevent *bev = &bev_ssl->bev.bev;
		event_del(&bev->ev_read);
	}
}

static void
stop_writing(struct bufferevent_openssl *bev_ssl)
{
	if (bev_ssl->read_blocked_on_write)
		return;
	if (bev_ssl->underlying) {
		bufferevent_unsuspend_read_(bev_ssl->underlying,
		    BEV_SUSPEND_FILT_READ);
	} else {
		struct bufferevent *bev = &bev_ssl->bev.bev;
		event_del(&bev->ev_write);
	}
}

static int
set_rbow(struct bufferevent_openssl *bev_ssl)
{
	if (!bev_ssl->underlying)
		stop_reading(bev_ssl);
	bev_ssl->read_blocked_on_write = 1;
	return start_writing(bev_ssl);
}

static int
set_wbor(struct bufferevent_openssl *bev_ssl)
{
	if (!bev_ssl->underlying)
		stop_writing(bev_ssl);
	bev_ssl->write_blocked_on_read = 1;
	return start_reading(bev_ssl);
}

static int
clear_rbow(struct bufferevent_openssl *bev_ssl)
{
	struct bufferevent *bev = &bev_ssl->bev.bev;
	int r = 0;
	bev_ssl->read_blocked_on_write = 0;
	if (!(bev->enabled & EV_WRITE))
		stop_writing(bev_ssl);
	if (bev->enabled & EV_READ)
		r = start_reading(bev_ssl);
	return r;
}


static int
clear_wbor(struct bufferevent_openssl *bev_ssl)
{
	struct bufferevent *bev = &bev_ssl->bev.bev;
	int r = 0;
	bev_ssl->write_blocked_on_read = 0;
	if (!(bev->enabled & EV_READ))
		stop_reading(bev_ssl);
	if (bev->enabled & EV_WRITE)
		r = start_writing(bev_ssl);
	return r;
}

static void
conn_closed(struct bufferevent_openssl *bev_ssl, int when, int errcode, int ret)
{
	int event = BEV_EVENT_ERROR;
	int dirty_shutdown = 0;
	unsigned long err;

	switch (errcode) {
	case SSL_ERROR_ZERO_RETURN:
		/* Possibly a clean shutdown. */
		if (SSL_get_shutdown(bev_ssl->ssl) & SSL_RECEIVED_SHUTDOWN)
			event = BEV_EVENT_EOF;
		else
			dirty_shutdown = 1;
		break;
	case SSL_ERROR_SYSCALL:
		/* IO error; possibly a dirty shutdown. */
		if ((ret == 0 || ret == -1) && ERR_peek_error() == 0)
			dirty_shutdown = 1;
		break;
	case SSL_ERROR_SSL:
		/* Protocol error. */
		break;
	case SSL_ERROR_WANT_X509_LOOKUP:
		/* XXXX handle this. */
		break;
	case SSL_ERROR_NONE:
	case SSL_ERROR_WANT_READ:
	case SSL_ERROR_WANT_WRITE:
	case SSL_ERROR_WANT_CONNECT:
	case SSL_ERROR_WANT_ACCEPT:
	default:
		/* should be impossible; treat as normal error. */
		event_warnx("BUG: Unexpected OpenSSL error code %d", errcode);
		break;
	}

	while ((err = ERR_get_error())) {
		put_error(bev_ssl, err);
	}

	if (dirty_shutdown && bev_ssl->allow_dirty_shutdown)
		event = BEV_EVENT_EOF;

	stop_reading(bev_ssl);
	stop_writing(bev_ssl);

	/* when is BEV_EVENT_{READING|WRITING} */
	event = when | event;
	bufferevent_run_eventcb_(&bev_ssl->bev.bev, event, 0);
}

static void
init_bio_counts(struct bufferevent_openssl *bev_ssl)
{
	BIO *rbio, *wbio;

	wbio = SSL_get_wbio(bev_ssl->ssl);
	bev_ssl->counts.n_written = wbio ? BIO_number_written(wbio) : 0;
	rbio = SSL_get_rbio(bev_ssl->ssl);
	bev_ssl->counts.n_read = rbio ? BIO_number_read(rbio) : 0;
}

static inline void
decrement_buckets(struct bufferevent_openssl *bev_ssl)
{
	unsigned long num_w = BIO_number_written(SSL_get_wbio(bev_ssl->ssl));
	unsigned long num_r = BIO_number_read(SSL_get_rbio(bev_ssl->ssl));
	/* These next two subtractions can wrap around. That's okay. */
	unsigned long w = num_w - bev_ssl->counts.n_written;
	unsigned long r = num_r - bev_ssl->counts.n_read;
	if (w)
		bufferevent_decrement_write_buckets_(&bev_ssl->bev, w);
	if (r)
		bufferevent_decrement_read_buckets_(&bev_ssl->bev, r);
	bev_ssl->counts.n_written = num_w;
	bev_ssl->counts.n_read = num_r;
}

#define OP_MADE_PROGRESS 1
#define OP_BLOCKED 2
#define OP_ERR 4

/* Return a bitmask of OP_MADE_PROGRESS (if we read anything); OP_BLOCKED (if
   we're now blocked); and OP_ERR (if an error occurred). */
static int
do_read(struct bufferevent_openssl *bev_ssl, int n_to_read) {
	/* Requires lock */
	struct bufferevent *bev = &bev_ssl->bev.bev;
	struct evbuffer *input = bev->input;
	int r, n, i, n_used = 0, atmost;
	struct evbuffer_iovec space[2];
	int result = 0;

	if (bev_ssl->bev.read_suspended)
		return 0;

	atmost = bufferevent_get_read_max_(&bev_ssl->bev);
	if (n_to_read > atmost)
		n_to_read = atmost;

	n = evbuffer_reserve_space(input, n_to_read, space, 2);
	if (n < 0)
		return OP_ERR;

	for (i=0; i<n; ++i) {
		if (bev_ssl->bev.read_suspended)
			break;
		ERR_clear_error();
		r = SSL_read(bev_ssl->ssl, space[i].iov_base, space[i].iov_len);
		if (r>0) {
			result |= OP_MADE_PROGRESS;
			if (bev_ssl->read_blocked_on_write)
				if (clear_rbow(bev_ssl) < 0)
					return OP_ERR | result;
			++n_used;
			space[i].iov_len = r;
			decrement_buckets(bev_ssl);
		} else {
			int err = SSL_get_error(bev_ssl->ssl, r);
			print_err(err);
			switch (err) {
			case SSL_ERROR_WANT_READ:
				/* Can't read until underlying has more data. */
				if (bev_ssl->read_blocked_on_write)
					if (clear_rbow(bev_ssl) < 0)
						return OP_ERR | result;
				break;
			case SSL_ERROR_WANT_WRITE:
				/* This read operation requires a write, and the
				 * underlying is full */
				if (!bev_ssl->read_blocked_on_write)
					if (set_rbow(bev_ssl) < 0)
						return OP_ERR | result;
				break;
			default:
				conn_closed(bev_ssl, BEV_EVENT_READING, err, r);
				break;
			}
			result |= OP_BLOCKED;
			break; /* out of the loop */
		}
	}

	if (n_used) {
		evbuffer_commit_space(input, space, n_used);
		if (bev_ssl->underlying)
			BEV_RESET_GENERIC_READ_TIMEOUT(bev);
	}

	return result;
}

/* Return a bitmask of OP_MADE_PROGRESS (if we wrote anything); OP_BLOCKED (if
   we're now blocked); and OP_ERR (if an error occurred). */
static int
do_write(struct bufferevent_openssl *bev_ssl, int atmost)
{
	int i, r, n, n_written = 0;
	struct bufferevent *bev = &bev_ssl->bev.bev;
	struct evbuffer *output = bev->output;
	struct evbuffer_iovec space[8];
	int result = 0;

	if (bev_ssl->last_write > 0)
		atmost = bev_ssl->last_write;
	else
		atmost = bufferevent_get_write_max_(&bev_ssl->bev);

	n = evbuffer_peek(output, atmost, NULL, space, 8);
	if (n < 0)
		return OP_ERR | result;

	if (n > 8)
		n = 8;
	for (i=0; i < n; ++i) {
		if (bev_ssl->bev.write_suspended)
			break;

		/* SSL_write will (reasonably) return 0 if we tell it to
		   send 0 data.  Skip this case so we don't interpret the
		   result as an error */
		if (space[i].iov_len == 0)
			continue;

		ERR_clear_error();
		r = SSL_write(bev_ssl->ssl, space[i].iov_base,
		    space[i].iov_len);
		if (r > 0) {
			result |= OP_MADE_PROGRESS;
			if (bev_ssl->write_blocked_on_read)
				if (clear_wbor(bev_ssl) < 0)
					return OP_ERR | result;
			n_written += r;
			bev_ssl->last_write = -1;
			decrement_buckets(bev_ssl);
		} else {
			int err = SSL_get_error(bev_ssl->ssl, r);
			print_err(err);
			switch (err) {
			case SSL_ERROR_WANT_WRITE:
				/* Can't read until underlying has more data. */
				if (bev_ssl->write_blocked_on_read)
					if (clear_wbor(bev_ssl) < 0)
						return OP_ERR | result;
				bev_ssl->last_write = space[i].iov_len;
				break;
			case SSL_ERROR_WANT_READ:
				/* This read operation requires a write, and the
				 * underlying is full */
				if (!bev_ssl->write_blocked_on_read)
					if (set_wbor(bev_ssl) < 0)
						return OP_ERR | result;
				bev_ssl->last_write = space[i].iov_len;
				break;
			default:
				conn_closed(bev_ssl, BEV_EVENT_WRITING, err, r);
				bev_ssl->last_write = -1;
				break;
			}
			result |= OP_BLOCKED;
			break;
		}
	}
	if (n_written) {
		evbuffer_drain(output, n_written);
		if (bev_ssl->underlying)
			BEV_RESET_GENERIC_WRITE_TIMEOUT(bev);

		bufferevent_trigger_nolock_(bev, EV_WRITE, BEV_OPT_DEFER_CALLBACKS);
	}
	return result;
}

#define WRITE_FRAME 15000

#define READ_DEFAULT 4096

/* Try to figure out how many bytes to read; return 0 if we shouldn't be
 * reading. */
static int
bytes_to_read(struct bufferevent_openssl *bev)
{
	struct evbuffer *input = bev->bev.bev.input;
	struct event_watermark *wm = &bev->bev.bev.wm_read;
	int result = READ_DEFAULT;
	ev_ssize_t limit;
	/* XXX 99% of this is generic code that nearly all bufferevents will
	 * want. */

	if (bev->write_blocked_on_read) {
		return 0;
	}

	if (! (bev->bev.bev.enabled & EV_READ)) {
		return 0;
	}

	if (bev->bev.read_suspended) {
		return 0;
	}

	if (wm->high) {
		if (evbuffer_get_length(input) >= wm->high) {
			return 0;
		}

		result = wm->high - evbuffer_get_length(input);
	} else {
		result = READ_DEFAULT;
	}

	/* Respect the rate limit */
	limit = bufferevent_get_read_max_(&bev->bev);
	if (result > limit) {
		result = limit;
	}

	return result;
}


/* Things look readable.  If write is blocked on read, write till it isn't.
 * Read from the underlying buffer until we block or we hit our high-water
 * mark.
 */
static void
consider_reading(struct bufferevent_openssl *bev_ssl)
{
	int r;
	int n_to_read;
	int all_result_flags = 0;

	while (bev_ssl->write_blocked_on_read) {
		r = do_write(bev_ssl, WRITE_FRAME);
		if (r & (OP_BLOCKED|OP_ERR))
			break;
	}
	if (bev_ssl->write_blocked_on_read)
		return;

	n_to_read = bytes_to_read(bev_ssl);

	while (n_to_read) {
		r = do_read(bev_ssl, n_to_read);
		all_result_flags |= r;

		if (r & (OP_BLOCKED|OP_ERR))
			break;

		if (bev_ssl->bev.read_suspended)
			break;
        
		/* Read all pending data.  This won't hit the network
		 * again, and will (most importantly) put us in a state
		 * where we don't need to read anything else until the
		 * socket is readable again.  It'll potentially make us
		 * overrun our read high-watermark (somewhat
		 * regrettable).  The damage to the rate-limit has
		 * already been done, since OpenSSL went and read a
		 * whole SSL record anyway. */
		n_to_read = SSL_pending(bev_ssl->ssl);

		/* XXX This if statement is actually a bad bug, added to avoid
		 * XXX a worse bug.
		 *
		 * The bad bug: It can potentially cause resource unfairness
		 * by reading too much data from the underlying bufferevent;
		 * it can potentially cause read looping if the underlying
		 * bufferevent is a bufferevent_pair and deferred callbacks
		 * aren't used.
		 *
		 * The worse bug: If we didn't do this, then we would
		 * potentially not read any more from bev_ssl->underlying
		 * until more data arrived there, which could lead to us
		 * waiting forever.
		 */
		if (!n_to_read && bev_ssl->underlying)
			n_to_read = bytes_to_read(bev_ssl);
	}

	if (all_result_flags & OP_MADE_PROGRESS) {
		struct bufferevent *bev = &bev_ssl->bev.bev;

		bufferevent_trigger_nolock_(bev, EV_READ, 0);
	}

	if (!bev_ssl->underlying) {
		/* Should be redundant, but let's avoid busy-looping */
		if (bev_ssl->bev.read_suspended ||
		    !(bev_ssl->bev.bev.enabled & EV_READ)) {
			event_del(&bev_ssl->bev.bev.ev_read);
		}
	}
}

static void
consider_writing(struct bufferevent_openssl *bev_ssl)
{
	int r;
	struct evbuffer *output = bev_ssl->bev.bev.output;
	struct evbuffer *target = NULL;
	struct event_watermark *wm = NULL;

	while (bev_ssl->read_blocked_on_write) {
		r = do_read(bev_ssl, 1024); /* XXXX 1024 is a hack */
		if (r & OP_MADE_PROGRESS) {
			struct bufferevent *bev = &bev_ssl->bev.bev;

			bufferevent_trigger_nolock_(bev, EV_READ, 0);
		}
		if (r & (OP_ERR|OP_BLOCKED))
			break;
	}
	if (bev_ssl->read_blocked_on_write)
		return;
	if (bev_ssl->underlying) {
		target = bev_ssl->underlying->output;
		wm = &bev_ssl->underlying->wm_write;
	}
	while ((bev_ssl->bev.bev.enabled & EV_WRITE) &&
	    (! bev_ssl->bev.write_suspended) &&
	    evbuffer_get_length(output) &&
	    (!target || (! wm->high || evbuffer_get_length(target) < wm->high))) {
		int n_to_write;
		if (wm && wm->high)
			n_to_write = wm->high - evbuffer_get_length(target);
		else
			n_to_write = WRITE_FRAME;
		r = do_write(bev_ssl, n_to_write);
		if (r & (OP_BLOCKED|OP_ERR))
			break;
	}

	if (!bev_ssl->underlying) {
		if (evbuffer_get_length(output) == 0) {
			event_del(&bev_ssl->bev.bev.ev_write);
		} else if (bev_ssl->bev.write_suspended ||
		    !(bev_ssl->bev.bev.enabled & EV_WRITE)) {
			/* Should be redundant, but let's avoid busy-looping */
			event_del(&bev_ssl->bev.bev.ev_write);
		}
	}
}

static void
be_openssl_readcb(struct bufferevent *bev_base, void *ctx)
{
	struct bufferevent_openssl *bev_ssl = ctx;
	consider_reading(bev_ssl);
}

static void
be_openssl_writecb(struct bufferevent *bev_base, void *ctx)
{
	struct bufferevent_openssl *bev_ssl = ctx;
	consider_writing(bev_ssl);
}

static void
be_openssl_eventcb(struct bufferevent *bev_base, short what, void *ctx)
{
	struct bufferevent_openssl *bev_ssl = ctx;
	int event = 0;

	if (what & BEV_EVENT_EOF) {
		if (bev_ssl->allow_dirty_shutdown)
			event = BEV_EVENT_EOF;
		else
			event = BEV_EVENT_ERROR;
	} else if (what & BEV_EVENT_TIMEOUT) {
		/* We sure didn't set this.  Propagate it to the user. */
		event = what;
	} else if (what & BEV_EVENT_ERROR) {
		/* An error occurred on the connection.  Propagate it to the user. */
		event = what;
	} else if (what & BEV_EVENT_CONNECTED) {
		/* Ignore it.  We're saying SSL_connect() already, which will
		   eat it. */
	}
	if (event)
		bufferevent_run_eventcb_(&bev_ssl->bev.bev, event, 0);
}

static void
be_openssl_readeventcb(evutil_socket_t fd, short what, void *ptr)
{
	struct bufferevent_openssl *bev_ssl = ptr;
	bufferevent_incref_and_lock_(&bev_ssl->bev.bev);
	if (what == EV_TIMEOUT) {
		bufferevent_run_eventcb_(&bev_ssl->bev.bev,
		    BEV_EVENT_TIMEOUT|BEV_EVENT_READING, 0);
	} else {
		consider_reading(bev_ssl);
	}
	bufferevent_decref_and_unlock_(&bev_ssl->bev.bev);
}

static void
be_openssl_writeeventcb(evutil_socket_t fd, short what, void *ptr)
{
	struct bufferevent_openssl *bev_ssl = ptr;
	bufferevent_incref_and_lock_(&bev_ssl->bev.bev);
	if (what == EV_TIMEOUT) {
		bufferevent_run_eventcb_(&bev_ssl->bev.bev,
		    BEV_EVENT_TIMEOUT|BEV_EVENT_WRITING, 0);
	} else {
		consider_writing(bev_ssl);
	}
	bufferevent_decref_and_unlock_(&bev_ssl->bev.bev);
}

static int
be_openssl_auto_fd(struct bufferevent_openssl *bev_ssl, int fd)
{
	if (!bev_ssl->underlying) {
		struct bufferevent *bev = &bev_ssl->bev.bev;
		if (event_initialized(&bev->ev_read) && fd < 0) {
			fd = event_get_fd(&bev->ev_read);
		}
	}
	return fd;
}

static int
set_open_callbacks(struct bufferevent_openssl *bev_ssl, evutil_socket_t fd)
{
	if (bev_ssl->underlying) {
		bufferevent_setcb(bev_ssl->underlying,
		    be_openssl_readcb, be_openssl_writecb, be_openssl_eventcb,
		    bev_ssl);
		return 0;
	} else {
		struct bufferevent *bev = &bev_ssl->bev.bev;
		int rpending=0, wpending=0, r1=0, r2=0;

		if (event_initialized(&bev->ev_read)) {
			rpending = event_pending(&bev->ev_read, EV_READ, NULL);
			wpending = event_pending(&bev->ev_write, EV_WRITE, NULL);

			event_del(&bev->ev_read);
			event_del(&bev->ev_write);
		}

		event_assign(&bev->ev_read, bev->ev_base, fd,
		    EV_READ|EV_PERSIST|EV_FINALIZE,
		    be_openssl_readeventcb, bev_ssl);
		event_assign(&bev->ev_write, bev->ev_base, fd,
		    EV_WRITE|EV_PERSIST|EV_FINALIZE,
		    be_openssl_writeeventcb, bev_ssl);

		if (rpending)
			r1 = bufferevent_add_event_(&bev->ev_read, &bev->timeout_read);
		if (wpending)
			r2 = bufferevent_add_event_(&bev->ev_write, &bev->timeout_write);

		return (r1<0 || r2<0) ? -1 : 0;
	}
}

static int
do_handshake(struct bufferevent_openssl *bev_ssl)
{
	int r;

	switch (bev_ssl->state) {
	default:
	case BUFFEREVENT_SSL_OPEN:
		EVUTIL_ASSERT(0);
		return -1;
	case BUFFEREVENT_SSL_CONNECTING:
	case BUFFEREVENT_SSL_ACCEPTING:
		ERR_clear_error();
		r = SSL_do_handshake(bev_ssl->ssl);
		break;
	}
	decrement_buckets(bev_ssl);

	if (r==1) {
		int fd = event_get_fd(&bev_ssl->bev.bev.ev_read);
		/* We're done! */
		bev_ssl->state = BUFFEREVENT_SSL_OPEN;
		set_open_callbacks(bev_ssl, fd); /* XXXX handle failure */
		/* Call do_read and do_write as needed */
		bufferevent_enable(&bev_ssl->bev.bev, bev_ssl->bev.bev.enabled);
		bufferevent_run_eventcb_(&bev_ssl->bev.bev,
		    BEV_EVENT_CONNECTED, 0);
		return 1;
	} else {
		int err = SSL_get_error(bev_ssl->ssl, r);
		print_err(err);
		switch (err) {
		case SSL_ERROR_WANT_WRITE:
			stop_reading(bev_ssl);
			return start_writing(bev_ssl);
		case SSL_ERROR_WANT_READ:
			stop_writing(bev_ssl);
			return start_reading(bev_ssl);
		default:
			conn_closed(bev_ssl, BEV_EVENT_READING, err, r);
			return -1;
		}
	}
}

static void
be_openssl_handshakecb(struct bufferevent *bev_base, void *ctx)
{
	struct bufferevent_openssl *bev_ssl = ctx;
	do_handshake(bev_ssl);/* XXX handle failure */
}

static void
be_openssl_handshakeeventcb(evutil_socket_t fd, short what, void *ptr)
{
	struct bufferevent_openssl *bev_ssl = ptr;

	bufferevent_incref_and_lock_(&bev_ssl->bev.bev);
	if (what & EV_TIMEOUT) {
		bufferevent_run_eventcb_(&bev_ssl->bev.bev, BEV_EVENT_TIMEOUT, 0);
	} else
		do_handshake(bev_ssl);/* XXX handle failure */
	bufferevent_decref_and_unlock_(&bev_ssl->bev.bev);
}

static int
set_handshake_callbacks(struct bufferevent_openssl *bev_ssl, evutil_socket_t fd)
{
	if (bev_ssl->underlying) {
		bufferevent_setcb(bev_ssl->underlying,
		    be_openssl_handshakecb, be_openssl_handshakecb,
		    be_openssl_eventcb,
		    bev_ssl);

		if (fd < 0)
			return 0;

		if (bufferevent_setfd(bev_ssl->underlying, fd))
			return 1;

		return do_handshake(bev_ssl);
	} else {
		struct bufferevent *bev = &bev_ssl->bev.bev;

		if (event_initialized(&bev->ev_read)) {
			event_del(&bev->ev_read);
			event_del(&bev->ev_write);
		}

		event_assign(&bev->ev_read, bev->ev_base, fd,
		    EV_READ|EV_PERSIST|EV_FINALIZE,
		    be_openssl_handshakeeventcb, bev_ssl);
		event_assign(&bev->ev_write, bev->ev_base, fd,
		    EV_WRITE|EV_PERSIST|EV_FINALIZE,
		    be_openssl_handshakeeventcb, bev_ssl);
		if (fd >= 0)
			bufferevent_enable(bev, bev->enabled);
		return 0;
	}
}

int
bufferevent_ssl_renegotiate(struct bufferevent *bev)
{
	struct bufferevent_openssl *bev_ssl = upcast(bev);
	if (!bev_ssl)
		return -1;
	if (SSL_renegotiate(bev_ssl->ssl) < 0)
		return -1;
	bev_ssl->state = BUFFEREVENT_SSL_CONNECTING;
	if (set_handshake_callbacks(bev_ssl, be_openssl_auto_fd(bev_ssl, -1)) < 0)
		return -1;
	if (!bev_ssl->underlying)
		return do_handshake(bev_ssl);
	return 0;
}

static void
be_openssl_outbuf_cb(struct evbuffer *buf,
    const struct evbuffer_cb_info *cbinfo, void *arg)
{
	struct bufferevent_openssl *bev_ssl = arg;
	int r = 0;
	/* XXX need to hold a reference here. */

	if (cbinfo->n_added && bev_ssl->state == BUFFEREVENT_SSL_OPEN) {
		if (cbinfo->orig_size == 0)
			r = bufferevent_add_event_(&bev_ssl->bev.bev.ev_write,
			    &bev_ssl->bev.bev.timeout_write);

		if (bev_ssl->underlying)
			consider_writing(bev_ssl);
	}
	/* XXX Handle r < 0 */
	(void)r;
}


static int
be_openssl_enable(struct bufferevent *bev, short events)
{
	struct bufferevent_openssl *bev_ssl = upcast(bev);
	int r1 = 0, r2 = 0;

	if (events & EV_READ)
		r1 = start_reading(bev_ssl);
	if (events & EV_WRITE)
		r2 = start_writing(bev_ssl);

	if (bev_ssl->underlying) {
		if (events & EV_READ)
			BEV_RESET_GENERIC_READ_TIMEOUT(bev);
		if (events & EV_WRITE)
			BEV_RESET_GENERIC_WRITE_TIMEOUT(bev);

		if (events & EV_READ)
			consider_reading(bev_ssl);
		if (events & EV_WRITE)
			consider_writing(bev_ssl);
	}
	return (r1 < 0 || r2 < 0) ? -1 : 0;
}

static int
be_openssl_disable(struct bufferevent *bev, short events)
{
	struct bufferevent_openssl *bev_ssl = upcast(bev);

	if (events & EV_READ)
		stop_reading(bev_ssl);
	if (events & EV_WRITE)
		stop_writing(bev_ssl);

	if (bev_ssl->underlying) {
		if (events & EV_READ)
			BEV_DEL_GENERIC_READ_TIMEOUT(bev);
		if (events & EV_WRITE)
			BEV_DEL_GENERIC_WRITE_TIMEOUT(bev);
	}
	return 0;
}

static void
be_openssl_unlink(struct bufferevent *bev)
{
	struct bufferevent_openssl *bev_ssl = upcast(bev);

	if (bev_ssl->bev.options & BEV_OPT_CLOSE_ON_FREE) {
		if (bev_ssl->underlying) {
			if (BEV_UPCAST(bev_ssl->underlying)->refcnt < 2) {
				event_warnx("BEV_OPT_CLOSE_ON_FREE set on an "
				    "bufferevent with too few references");
			} else {
				bufferevent_free(bev_ssl->underlying);
				/* We still have a reference to it, via our
				 * BIO. So we don't drop this. */
				// bev_ssl->underlying = NULL;
			}
		}
	} else {
		if (bev_ssl->underlying) {
			if (bev_ssl->underlying->errorcb == be_openssl_eventcb)
				bufferevent_setcb(bev_ssl->underlying,
				    NULL,NULL,NULL,NULL);
			bufferevent_unsuspend_read_(bev_ssl->underlying,
			    BEV_SUSPEND_FILT_READ);
		}
	}
}

static void
be_openssl_destruct(struct bufferevent *bev)
{
	struct bufferevent_openssl *bev_ssl = upcast(bev);

	if (bev_ssl->bev.options & BEV_OPT_CLOSE_ON_FREE) {
		if (! bev_ssl->underlying) {
			evutil_socket_t fd = -1;
			BIO *bio = SSL_get_wbio(bev_ssl->ssl);
			if (bio)
				fd = BIO_get_fd(bio, NULL);
			if (fd >= 0)
				evutil_closesocket(fd);
		}
		SSL_free(bev_ssl->ssl);
	}
}

static int
be_openssl_adj_timeouts(struct bufferevent *bev)
{
	struct bufferevent_openssl *bev_ssl = upcast(bev);

	if (bev_ssl->underlying) {
		return bufferevent_generic_adj_timeouts_(bev);
	} else {
		return bufferevent_generic_adj_existing_timeouts_(bev);
	}
}

static int
be_openssl_flush(struct bufferevent *bufev,
    short iotype, enum bufferevent_flush_mode mode)
{
	/* XXXX Implement this. */
	return 0;
}

static int
be_openssl_set_fd(struct bufferevent_openssl *bev_ssl,
    enum bufferevent_ssl_state state, int fd)
{
	bev_ssl->state = state;

	switch (state) {
	case BUFFEREVENT_SSL_ACCEPTING:
		SSL_set_accept_state(bev_ssl->ssl);
		if (set_handshake_callbacks(bev_ssl, fd) < 0)
			return -1;
		break;
	case BUFFEREVENT_SSL_CONNECTING:
		SSL_set_connect_state(bev_ssl->ssl);
		if (set_handshake_callbacks(bev_ssl, fd) < 0)
			return -1;
		break;
	case BUFFEREVENT_SSL_OPEN:
		if (set_open_callbacks(bev_ssl, fd) < 0)
			return -1;
		break;
	default:
		return -1;
	}

	return 0;
}

static int
be_openssl_ctrl(struct bufferevent *bev,
    enum bufferevent_ctrl_op op, union bufferevent_ctrl_data *data)
{
	struct bufferevent_openssl *bev_ssl = upcast(bev);
	switch (op) {
	case BEV_CTRL_SET_FD:
		if (!bev_ssl->underlying) {
			BIO *bio;
			bio = BIO_new_socket(data->fd, 0);
			SSL_set_bio(bev_ssl->ssl, bio, bio);
		} else {
			BIO *bio;
			if (!(bio = BIO_new_bufferevent(bev_ssl->underlying, 0)))
				return -1;
			SSL_set_bio(bev_ssl->ssl, bio, bio);
		}

		return be_openssl_set_fd(bev_ssl, bev_ssl->old_state, data->fd);
	case BEV_CTRL_GET_FD:
		if (bev_ssl->underlying) {
			data->fd = event_get_fd(&bev_ssl->underlying->ev_read);
		} else {
			data->fd = event_get_fd(&bev->ev_read);
		}
		return 0;
	case BEV_CTRL_GET_UNDERLYING:
		data->ptr = bev_ssl->underlying;
		return 0;
	case BEV_CTRL_CANCEL_ALL:
	default:
		return -1;
	}
}

SSL *
bufferevent_openssl_get_ssl(struct bufferevent *bufev)
{
	struct bufferevent_openssl *bev_ssl = upcast(bufev);
	if (!bev_ssl)
		return NULL;
	return bev_ssl->ssl;
}

static struct bufferevent *
bufferevent_openssl_new_impl(struct event_base *base,
    struct bufferevent *underlying,
    evutil_socket_t fd,
    SSL *ssl,
    enum bufferevent_ssl_state state,
    int options)
{
	struct bufferevent_openssl *bev_ssl = NULL;
	struct bufferevent_private *bev_p = NULL;
	int tmp_options = options & ~BEV_OPT_THREADSAFE;

	if (underlying != NULL && fd >= 0)
		return NULL; /* Only one can be set. */

	if (!(bev_ssl = mm_calloc(1, sizeof(struct bufferevent_openssl))))
		goto err;

	bev_p = &bev_ssl->bev;

	if (bufferevent_init_common_(bev_p, base,
		&bufferevent_ops_openssl, tmp_options) < 0)
		goto err;

	/* Don't explode if we decide to realloc a chunk we're writing from in
	 * the output buffer. */
	SSL_set_mode(ssl, SSL_MODE_ACCEPT_MOVING_WRITE_BUFFER);

	bev_ssl->underlying = underlying;
	bev_ssl->ssl = ssl;

	bev_ssl->outbuf_cb = evbuffer_add_cb(bev_p->bev.output,
	    be_openssl_outbuf_cb, bev_ssl);

	if (options & BEV_OPT_THREADSAFE)
		bufferevent_enable_locking_(&bev_ssl->bev.bev, NULL);

	if (underlying) {
		bufferevent_init_generic_timeout_cbs_(&bev_ssl->bev.bev);
		bufferevent_incref_(underlying);
	}

	bev_ssl->old_state = state;
	bev_ssl->last_write = -1;

	init_bio_counts(bev_ssl);

	fd = be_openssl_auto_fd(bev_ssl, fd);
	if (be_openssl_set_fd(bev_ssl, state, fd))
		goto err;

	if (underlying) {
		bufferevent_setwatermark(underlying, EV_READ, 0, 0);
		bufferevent_enable(underlying, EV_READ|EV_WRITE);
		if (state == BUFFEREVENT_SSL_OPEN)
			bufferevent_suspend_read_(underlying,
			    BEV_SUSPEND_FILT_READ);
	}

	return &bev_ssl->bev.bev;
err:
	if (bev_ssl)
		bufferevent_free(&bev_ssl->bev.bev);
	return NULL;
}

struct bufferevent *
bufferevent_openssl_filter_new(struct event_base *base,
    struct bufferevent *underlying,
    SSL *ssl,
    enum bufferevent_ssl_state state,
    int options)
{
	/* We don't tell the BIO to close the bufferevent; we do it ourselves
	 * on be_openssl_destruct */
	int close_flag = 0; /* options & BEV_OPT_CLOSE_ON_FREE; */
	BIO *bio;
	if (!underlying)
		return NULL;
	if (!(bio = BIO_new_bufferevent(underlying, close_flag)))
		return NULL;

	SSL_set_bio(ssl, bio, bio);

	return bufferevent_openssl_new_impl(
		base, underlying, -1, ssl, state, options);
}

struct bufferevent *
bufferevent_openssl_socket_new(struct event_base *base,
    evutil_socket_t fd,
    SSL *ssl,
    enum bufferevent_ssl_state state,
    int options)
{
	/* Does the SSL already have an fd? */
	BIO *bio = SSL_get_wbio(ssl);
	long have_fd = -1;

	if (bio)
		have_fd = BIO_get_fd(bio, NULL);

	if (have_fd >= 0) {
		/* The SSL is already configured with an fd. */
		if (fd < 0) {
			/* We should learn the fd from the SSL. */
			fd = (evutil_socket_t) have_fd;
		} else if (have_fd == (long)fd) {
			/* We already know the fd from the SSL; do nothing */
		} else {
			/* We specified an fd different from that of the SSL.
			   This is probably an error on our part.  Fail. */
			return NULL;
		}
		(void) BIO_set_close(bio, 0);
	} else {
		/* The SSL isn't configured with a BIO with an fd. */
		if (fd >= 0) {
			/* ... and we have an fd we want to use. */
			bio = BIO_new_socket(fd, 0);
			SSL_set_bio(ssl, bio, bio);
		} else {
			/* Leave the fd unset. */
		}
	}

	return bufferevent_openssl_new_impl(
		base, NULL, fd, ssl, state, options);
}

int
bufferevent_openssl_get_allow_dirty_shutdown(struct bufferevent *bev)
{
	int allow_dirty_shutdown = -1;
	struct bufferevent_openssl *bev_ssl;
	BEV_LOCK(bev);
	bev_ssl = upcast(bev);
	if (bev_ssl)
		allow_dirty_shutdown = bev_ssl->allow_dirty_shutdown;
	BEV_UNLOCK(bev);
	return allow_dirty_shutdown;
}

void
bufferevent_openssl_set_allow_dirty_shutdown(struct bufferevent *bev,
    int allow_dirty_shutdown)
{
	struct bufferevent_openssl *bev_ssl;
	BEV_LOCK(bev);
	bev_ssl = upcast(bev);
	if (bev_ssl)
		bev_ssl->allow_dirty_shutdown = !!allow_dirty_shutdown;
	BEV_UNLOCK(bev);
}

unsigned long
bufferevent_get_openssl_error(struct bufferevent *bev)
{
	unsigned long err = 0;
	struct bufferevent_openssl *bev_ssl;
	BEV_LOCK(bev);
	bev_ssl = upcast(bev);
	if (bev_ssl && bev_ssl->n_errors) {
		err = bev_ssl->errors[--bev_ssl->n_errors];
	}
	BEV_UNLOCK(bev);
	return err;
}