Prefer mmap to sendfile unless a DRAINS_TO_FD flag is set. Allows add_file to work with SSL.

The sendfile() implementation for evbuffer_add_file is potentially more
efficient, but it has a problem: you can only use it to send bytes over
a socket using sendfile().  If you are writing bytes via SSL_send() or
via a filter, or if you need to be able to inspect your buffer, it
doesn't work.

As an easy fix, this patch disables the sendfile-based implementation of
evbuffer_add_file on an evbuffer unless the user sets a new
EVBUFFER_FLAG_DRAINS_TO_FD flag on that evbuffer, indicating that the
evbuffer will not be inspected, but only written out via
evbuffer_write(), evbuffer_write_atmost(), or drained with stuff like
evbuffer_drain() or evbuffer_add_buffer().  This flag is off by
default, except for evbuffers used for output on bufferevent_socket.

In the future, it could be interesting to make a best-effort file
segment implementation that tries to send via sendfile, but mmaps on
demand.  That's too much complexity for a stable release series, though.

1 files changed, 2 insertions, 0 deletions

diff --git a/evbuffer-internal.h b/evbuffer-internal.h
index 5879f874..89139602 100644
--- a/evbuffer-internal.h
+++ b/evbuffer-internal.h
@@ -129,6 +129,8 @@ struct evbuffer {
 	/** True iff this buffer is set up for overlapped IO. */
 	unsigned is_overlapped : 1;
 #endif
+	/** Zero or more EVBUFFER_FLAG_* bits */
+	ev_uint32_t flags;
 
 	/** Used to implement deferred callbacks. */
 	struct deferred_cb_queue *cb_queue;