[Nbd] [PATCH v2 2/6] server: Fix botched strlen computation of error message

[Eric Blake <eblake@...696...>]

Commit 3b80382 tried to make it easy for the server to send an
error message whose length was determined by strlen(), but ended
up sending a length of UINT32_MAX, causing clients to either
hang up (reply too large) or wait for nearly 4G of data that was
never coming.

Signed-off-by: Eric Blake <eblake@...696...>
---
 nbd-server.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/nbd-server.c b/nbd-server.c
index 25c335b..d0c6fa6 100644
--- a/nbd-server.c
+++ b/nbd-server.c
@@ -1321,11 +1321,12 @@ static void send_reply(CLIENT* client, uint32_t opt, uint32_t reply_type, ssize_
 		htonl(reply_type),
 		htonl(datasize),
 	};
+	if(datasize < 0) {
+		datasize = strlen((char*)data);
+		header.datasize = htonl(datasize);
+	}
 	socket_write(client, &header, sizeof(header));
 	if(datasize != 0) {
-		if(datasize < 0) {
-			datasize = strlen((char*)data);
-		}
 		socket_write(client, data, datasize);
 	}
 }
-- 
2.7.4