From 83057033caaf4f0c08679adee2badbe206e943b7 Mon Sep 17 00:00:00 2001
From: Rusty Russell <rusty@rustcorp.com.au>
Date: Tue, 25 Jan 2011 10:59:15 +1030
Subject: [PATCH] lca2011: fix client disconnect during answer (poorly).

We seek an oracle or a client when we need one, and unset when we
are destroyed.  This can cause crossed answers; better would be to
actually move the questions/answers around.
---
 ccan/oserver/oserver.c | 77 +++++++++++++++++++++++++-----------------
 1 file changed, 46 insertions(+), 31 deletions(-)

diff --git a/ccan/oserver/oserver.c b/ccan/oserver/oserver.c
index 2d4cac4..c293dd5 100644
--- a/ccan/oserver/oserver.c
+++ b/ccan/oserver/oserver.c
@@ -20,11 +20,9 @@
 enum state {
 	SENDING_GREETING,
 	RECEIVING_USER_QUESTION,
-	AWAITING_A_SUBCLIENT,
 	SENDING_OTHER_QUESTION_PREFIX,
 	SENDING_OTHER_QUESTION,
 	RECEIVING_OTHER_ANSWER,
-	AWAITING_OUR_ORACLE,
 	SENDING_ANSWER_PREFIX,
 	SENDING_ANSWER,
 	FINISHED
@@ -33,11 +31,9 @@ enum state {
 static uint16_t state_flag_map[] = {
 	[SENDING_GREETING]		= TEVENT_FD_WRITE,
 	[RECEIVING_USER_QUESTION]	= TEVENT_FD_READ,
-	[AWAITING_A_SUBCLIENT]		= 0,
 	[SENDING_OTHER_QUESTION_PREFIX] = TEVENT_FD_WRITE,
 	[SENDING_OTHER_QUESTION]	= TEVENT_FD_WRITE,
 	[RECEIVING_OTHER_ANSWER]	= TEVENT_FD_READ,
-	[AWAITING_OUR_ORACLE]		= 0,
 	[SENDING_ANSWER_PREFIX]		= TEVENT_FD_WRITE,
 	[SENDING_ANSWER]		= TEVENT_FD_WRITE,
 	[FINISHED]			= 0
@@ -153,6 +149,11 @@ static bool get_oracle(struct client *me)
 	return false;
 }
 
+static void wakeup(struct client *c)
+{
+	tevent_fd_set_flags(c->fde, state_flag_map[c->state]);
+}
+
 static void service_client(struct tevent_context *ev,
 			   struct tevent_fd *fde, uint16_t flags, void *_c)
 {
@@ -168,50 +169,36 @@ static void service_client(struct tevent_context *ev,
 		len = read_string(c->fd, &c->question);
 		if (len <= 0)
 			goto fail;
-		if (input_finished(c->question)) {
-			/* Look for someone to be oracle to. */
-			if (get_subclient(c)) {
-				set_state(c, SENDING_OTHER_QUESTION_PREFIX);
-			} else {
-				/* We sit here until someone find_oracles us */
-				set_state(c, AWAITING_A_SUBCLIENT);
-			}
-
-			/* Look for an oracle for ourselves. */
-			if (get_oracle(c)) {
-				assert(c->oracle->state
-				       == AWAITING_A_SUBCLIENT);
-				set_state(c->oracle,
-					  SENDING_OTHER_QUESTION_PREFIX);
-			}
-		}
+		if (input_finished(c->question))
+			set_state(c, SENDING_OTHER_QUESTION_PREFIX);
 		break;
 	case SENDING_OTHER_QUESTION_PREFIX:
+		if (!c->subclient)
+			goto need_subclient;
 		if (!send_string(c, "While the Oracle ponders,"
 				 " please answer the following question:\n"))
 			goto fail;
 		break;
 	case SENDING_OTHER_QUESTION:
+		if (!c->subclient)
+			goto need_subclient;
 		if (!send_string(c, c->subclient->question))
 			goto fail;
 		break;
 	case RECEIVING_OTHER_ANSWER:
+		if (!c->subclient)
+			goto need_subclient;
 		len = read_string(c->fd, &c->subclient->answer);
 		if (len <= 0)
 			goto fail;
 		if (input_finished(c->subclient->answer)) {
-			/* Did our oracle answer for us already? */
-			if (input_finished(c->answer))
-				set_state(c, SENDING_ANSWER_PREFIX);
-			else
-				set_state(c, AWAITING_OUR_ORACLE);
-
-			/* If they were waiting for an answer, move them. */
-			if (c->subclient->state == AWAITING_OUR_ORACLE)
-				set_state(c->subclient, SENDING_ANSWER_PREFIX);
+			set_state(c, SENDING_ANSWER_PREFIX);
+			wakeup(c->subclient);
 		}
 		break;
 	case SENDING_ANSWER_PREFIX:
+		if (!input_finished(c->answer))
+			goto need_answer;
 		if (!send_string(c, "The Oracle spake thus:\n"))
 			goto fail;
 		break;
@@ -225,15 +212,43 @@ static void service_client(struct tevent_context *ev,
 
 	if (c->state != FINISHED)
 		return;
-
 fail:
 	talloc_free(c);
+	return;
+
+need_subclient:
+	if (!get_subclient(c)) {
+		/* We can't get one: go to sleep until someone find_oracle() */
+		tevent_fd_set_flags(c->fde, 0);
+	} else
+		/* In case they are waiting... */
+		wakeup(c->subclient);
+	return;
+
+need_answer:
+	/* If we don't have an oracle and find one, that's OK. */
+	if (!c->oracle && get_oracle(c)) {
+		/* In case they are waiting... */
+		wakeup(c->oracle);
+		return;
+	}
+
+	/* Either our oracle is not finished, or we don't have one: sleep. */
+	tevent_fd_set_flags(c->fde, 0);
 }
 
 static int cleanup_client(struct client *client)
 {
 	unsigned int i;
 
+	/* We were an oracle? */
+	if (client->subclient)
+		client->subclient->oracle = NULL;
+
+	/* We had an oracle? */
+	if (client->oracle)
+		client->oracle->subclient = NULL;
+
 	for (i = 0; i < ARRAY_SIZE(client->oserver->clients); i++) {
 		if (client->oserver->clients[i] == client) {
 			client->oserver->clients[i] = NULL;
-- 
2.39.2