From 9d1cde47a22d3f43e07a807d6dd183d3f768137d Mon Sep 17 00:00:00 2001
From: Mattias Andrée <maandree@kth.se>
Date: Tue, 24 Oct 2017 18:36:51 +0200
Subject: Add contol messages for flood control
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Signed-off-by: Mattias Andrée <maandree@kth.se>
---
 README  | 59 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 sbusd.c | 43 ++++++++++++++++++++++++++++++++++++++++++-
 test.c  |  1 +
 3 files changed, 102 insertions(+), 1 deletion(-)

diff --git a/README b/README
index eef3a3d..2fe8419 100644
--- a/README
+++ b/README
@@ -133,3 +133,62 @@ Secret messages:
 		B: Send B's credentials with routing key private to A.
 		A: Send a random message with routing key private to B.
 		B: Send back the message with routing key private to A.
+
+Flood control:
+	The following control messages can be sent to the server to
+	choose the server behaviour when messages cannot be delivered
+	without blocking. All control messages are optional and server
+	may choose to ignore them at any time, even if previously
+	honoured. Most recently sent control message that precedence.
+
+	^CMSG blocking/soft/queue\(\x00.*\)*$
+
+		Delivering is preferable, the server should queue up
+		message that cannot be sent.
+
+	^CMSG blocking/soft/discard\(\x00.*\)*$
+
+		Delivering is unimportant, the server should discard
+		message that cannot be sent.
+
+	^CMSG blocking/soft/block\(\x00.*\)*$
+
+		Delivering is important, the server may block communication
+		to guarantee that messages are delivered.
+
+	^CMSG blocking/soft/error\(\x00.*\)*$
+
+		The server may treat a client as misbehaving if message
+		cannot be sent.
+
+	^CMSG blocking/hard/discard\(\x00.*\)*$
+
+		If the server has queued up too many message it should
+		start discarding new message instead of queuing them.
+
+	^CMSG blocking/hard/block\(\x00.*\)*$
+
+		If the server has queued up too many message it should
+		start blocking communication until it can start queuing
+		messages again.
+
+	^CMSG blocking/hard/error\(\x00.*\)*$
+
+		If the server has queued up too many message it should
+		start treating clients that are blocking as misbehaving.
+
+	^CMSG order/queue\(\x00.*\)*$
+
+		If the client is blocking it is preferable that messages
+		are sent in order.
+
+	^CMSG order/stack\(\x00.*\)*$
+
+		If the client is blocking it is preferable that messages
+		are sent in reverse order.
+
+	^CMSG order/random\(\x00.*\)*$
+
+		If the client is blocking it is preferable that messages
+		are sent in such order that memory is freed up as fast
+		as possible.
diff --git a/sbusd.c b/sbusd.c
index 6a4e717..e2f3005 100644
--- a/sbusd.c
+++ b/sbusd.c
@@ -24,8 +24,26 @@
 #define STYPE_MAX(T) (long long int)((1ULL << (8 * sizeof(T) - 1)) - 1)
 #define eprintf(...) (weprintf(__VA_ARGS__), exit(1))
 
+enum blocking_mode {
+	BLOCKING_QUEUE,
+	BLOCKING_DISCARD,
+	BLOCKING_BLOCK,
+	BLOCKING_ERROR
+};
+
+enum order {
+	ORDER_QUEUE = 0,
+	ORDER_STACK = 1,
+	ORDER_RANDOM_QUEUE = 2,
+	ORDER_RANDOM_STACK = 3,
+};
+#define ORDER_RANDOM 2
+
 struct client {
 	int fd;
+	enum blocking_mode soft_blocking_mode;
+	enum blocking_mode hard_blocking_mode;
+	enum order order;
 	char **subs;
 	size_t nsubs;
 	size_t subs_siz;
@@ -84,6 +102,9 @@ add_client(int fd)
 	if (!cl)
 		return NULL;
 	cl->fd = fd;
+	cl->soft_blocking_mode = BLOCKING_QUEUE;
+	cl->hard_blocking_mode = BLOCKING_DISCARD;
+	cl->order = ORDER_RANDOM_QUEUE;
 	cl->subs = NULL;
 	cl->nsubs = 0;
 	cl->subs_siz = 0;
@@ -266,7 +287,7 @@ remove_subscription(struct client *cl, const char *key)
 static int
 send_packet(struct client *cl, const char *buf, size_t n)
 {
-	/* TODO queue instead of block */
+	/* TODO honour cl->soft_blocking_mode, cl->hard_blocking_mode, and cl->order */
 	return -(send(cl->fd, buf, n, 0) < 0);
 }
 
@@ -275,6 +296,26 @@ handle_cmsg(struct client *cl, const char *msg, size_t n)
 {
 	if (!strcmp(msg, "CMSG !/cred/prefix")) {
 		n = sizeof("CMSG !/cred/prefix");
+	} else if (!strcmp(msg, "CMSG blocking/soft/queue")) {
+		cl->soft_blocking_mode = BLOCKING_QUEUE;
+	} else if (!strcmp(msg, "CMSG blocking/soft/discard")) {
+		cl->soft_blocking_mode = BLOCKING_DISCARD;
+	} else if (!strcmp(msg, "CMSG blocking/soft/block")) {
+		cl->soft_blocking_mode = BLOCKING_BLOCK;
+	} else if (!strcmp(msg, "CMSG blocking/soft/error")) {
+		cl->soft_blocking_mode = BLOCKING_ERROR;
+	} else if (!strcmp(msg, "CMSG blocking/hard/discard")) {
+		cl->hard_blocking_mode = BLOCKING_DISCARD;
+	} else if (!strcmp(msg, "CMSG blocking/hard/block")) {
+		cl->hard_blocking_mode = BLOCKING_BLOCK;
+	} else if (!strcmp(msg, "CMSG blocking/hard/error")) {
+		cl->hard_blocking_mode = BLOCKING_ERROR;
+	} else if (!strcmp(msg, "CMSG order/queue")) {
+		cl->order = ORDER_QUEUE;
+	} else if (!strcmp(msg, "CMSG order/stack")) {
+		cl->order = ORDER_STACK;
+	} else if (!strcmp(msg, "CMSG order/random")) {
+		cl->order |= ORDER_RANDOM;
 	} else {
 		return;
 	}
diff --git a/test.c b/test.c
index c2ba2a8..daaec35 100644
--- a/test.c
+++ b/test.c
@@ -355,3 +355,4 @@ main(void)
 
 /* TODO untested sbusd flags: -p[/dev/null] (-f) -u */
 /* TODO test credentials */
+/* TODO test CMSG server */
-- 
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