From 804a1e69f2e34fe55ffa76c1ac4b8ce928011497 Mon Sep 17 00:00:00 2001
From: Matt Johnston <matt@ucc.asn.au>
Date: Wed, 20 Mar 2013 22:31:07 +0800
Subject: [PATCH] use an empty writebuf rather than a NULL one

---
 circbuffer.c     |  4 +++-
 common-channel.c | 19 +++++++------------
 2 files changed, 10 insertions(+), 13 deletions(-)

diff --git a/circbuffer.c b/circbuffer.c
index 7953737..55c4422 100644
--- a/circbuffer.c
+++ b/circbuffer.c
@@ -37,7 +37,9 @@ circbuffer * cbuf_new(unsigned int size) {
 	}
 
 	cbuf = (circbuffer*)m_malloc(sizeof(circbuffer));
-	cbuf->data = (unsigned char*)m_malloc(size);
+	if (size > 0) {
+		cbuf->data = (unsigned char*)m_malloc(size);
+	}
 	cbuf->used = 0;
 	cbuf->readpos = 0;
 	cbuf->writepos = 0;
diff --git a/common-channel.c b/common-channel.c
index be68266..9328a2e 100644
--- a/common-channel.c
+++ b/common-channel.c
@@ -95,7 +95,8 @@ void chancleanup() {
 static void
 chan_initwritebuf(struct Channel *channel)
 {
-	dropbear_assert(channel->writebuf == NULL && channel->recvwindow == 0);
+	dropbear_assert(channel->writebuf->size == 0 && channel->recvwindow == 0);
+	cbuf_free(channel->writebuf);
 	channel->writebuf = cbuf_new(opts.recv_window);
 	channel->recvwindow = opts.recv_window;
 }
@@ -159,7 +160,7 @@ static struct Channel* newchannel(unsigned int remotechan,
 	newchan->await_open = 0;
 	newchan->flushing = 0;
 
-	newchan->writebuf = NULL;
+	newchan->writebuf = cbuf_new(0); /* resized later by chan_initwritebuf */
 	newchan->recvwindow = 0;
 
 	newchan->extrabuf = NULL; /* The user code can set it up */
@@ -233,7 +234,6 @@ void channelio(fd_set *readfds, fd_set *writefds) {
 				continue; /* Important not to use the channel after
 							 check_in_progress(), as it may be NULL */
 			}
-			dropbear_assert(channel->writebuf);
 			writechannel(channel, channel->writefd, channel->writebuf);
 		}
 		
@@ -259,9 +259,7 @@ void channelio(fd_set *readfds, fd_set *writefds) {
  * stderr of a channel's endpoint. */
 static unsigned int write_pending(struct Channel * channel) {
 
-	if (channel->writefd >= 0 
-			&& channel->writebuf 
-			&& cbuf_getused(channel->writebuf) > 0) {
+	if (channel->writefd >= 0 && cbuf_getused(channel->writebuf) > 0) {
 		return 1;
 	} else if (channel->errfd >= 0 && channel->extrabuf && 
 			cbuf_getused(channel->extrabuf) > 0) {
@@ -452,8 +450,7 @@ static void writechannel(struct Channel* channel, int fd, circbuffer *cbuf) {
 	}
 
 	dropbear_assert(channel->recvwindow <= opts.recv_window);
-	dropbear_assert(channel->writebuf == NULL ||
-			channel->recvwindow <= cbuf_getavail(channel->writebuf));
+	dropbear_assert(channel->recvwindow <= cbuf_getavail(channel->writebuf));
 	dropbear_assert(channel->extrabuf == NULL ||
 			channel->recvwindow <= cbuf_getavail(channel->extrabuf));
 	
@@ -546,10 +543,8 @@ static void remove_channel(struct Channel * channel) {
 	TRACE(("enter remove_channel"))
 	TRACE(("channel index is %d", channel->index))
 
-	if (channel->writebuf) {
-		cbuf_free(channel->writebuf);
-		channel->writebuf = NULL;
-	}
+	cbuf_free(channel->writebuf);
+	channel->writebuf = NULL;
 
 	if (channel->extrabuf) {
 		cbuf_free(channel->extrabuf);