async_req: check for errors when monitoring socket for readability

Add an option to wait_for_read_send(), so that the request, upon
calling back, report whether the socket actually contains data
or is in EOF/error state. EOF is signalled via the EPIPE error.

This is useful for clients which do not expect data to arrive but
wait for readability to detect a closed socket (i.e. they do not
intend to actually read the socket when it's readable). Actual data
arrival would indicate a bug in this case, so the check can
be used to print an error message.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=11397

Signed-off-by: Uri Simchoni <urisimchoni@gmail.com>
Reviewed-by: Jeremy Allison <jra@samba.org>
Reviewed-by: Volker Lendecke <vl@samba.org>

2 files changed, 44 insertions, 5 deletions

diff --git a/lib/async_req/async_sock.c b/lib/async_req/async_sock.c
index d2cda1572db..bc3780c9199 100644
--- a/lib/async_req/async_sock.c
+++ b/lib/async_req/async_sock.c
@@ -534,6 +534,8 @@ ssize_t read_packet_recv(struct tevent_req *req, TALLOC_CTX *mem_ctx,
 
 struct wait_for_read_state {
 	struct tevent_fd *fde;
+	int fd;
+	bool check_errors;
 };
 
 static void wait_for_read_cleanup(struct tevent_req *req,
@@ -544,8 +546,8 @@ static void wait_for_read_done(struct tevent_context *ev,
 			       void *private_data);
 
 struct tevent_req *wait_for_read_send(TALLOC_CTX *mem_ctx,
-				      struct tevent_context *ev,
-				      int fd)
+				      struct tevent_context *ev, int fd,
+				      bool check_errors)
 {
 	struct tevent_req *req;
 	struct wait_for_read_state *state;
@@ -562,6 +564,9 @@ struct tevent_req *wait_for_read_send(TALLOC_CTX *mem_ctx,
 	if (tevent_req_nomem(state->fde, req)) {
 		return tevent_req_post(req, ev);
 	}
+
+	state->fd = fd;
+	state->check_errors = check_errors;
 	return req;
 }
 
@@ -581,10 +586,44 @@ static void wait_for_read_done(struct tevent_context *ev,
 {
 	struct tevent_req *req = talloc_get_type_abort(
 		private_data, struct tevent_req);
+	struct wait_for_read_state *state =
+	    tevent_req_data(req, struct wait_for_read_state);
+	ssize_t nread;
+	char c;
 
-	if (flags & TEVENT_FD_READ) {
+	if ((flags & TEVENT_FD_READ) == 0) {
+		return;
+	}
+
+	if (!state->check_errors) {
 		tevent_req_done(req);
+		return;
 	}
+
+	nread = recv(state->fd, &c, 1, MSG_PEEK);
+
+	if (nread == 0) {
+		tevent_req_error(req, EPIPE);
+		return;
+	}
+
+	if ((nread == -1) && (errno == EINTR)) {
+		/* come back later */
+		return;
+	}
+
+	if ((nread == -1) && (errno == ENOTSOCK)) {
+		/* Ignore this specific error on pipes */
+		tevent_req_done(req);
+		return;
+	}
+
+	if (nread == -1) {
+		tevent_req_error(req, errno);
+		return;
+	}
+
+	tevent_req_done(req);
 }
 
 bool wait_for_read_recv(struct tevent_req *req, int *perr)
diff --git a/lib/async_req/async_sock.h b/lib/async_req/async_sock.h
index 1b76fabed53..abbf822228d 100644
--- a/lib/async_req/async_sock.h
+++ b/lib/async_req/async_sock.h
@@ -53,8 +53,8 @@ ssize_t read_packet_recv(struct tevent_req *req, TALLOC_CTX *mem_ctx,
 			 uint8_t **pbuf, int *perrno);
 
 struct tevent_req *wait_for_read_send(TALLOC_CTX *mem_ctx,
-				      struct tevent_context *ev,
-				      int fd);
+				      struct tevent_context *ev, int fd,
+				      bool check_errors);
 bool wait_for_read_recv(struct tevent_req *req, int *perr);
 
 #endif