From 4d03f397dfc352a958344dcd9454a4d904242d34 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Juhani=20Krekel=C3=A4?= <juhani@krekelä.fi>
Date: Sun, 7 Jul 2019 19:37:51 +0300
Subject: [PATCH] Handle communicating message IDs

---
 ethermess.c | 128 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 128 insertions(+)

diff --git a/ethermess.c b/ethermess.c
index 04beaae..954955c 100644
--- a/ethermess.c
+++ b/ethermess.c
@@ -24,6 +24,8 @@
 #define EMT_SPEAK_VERSION 0
 #define EMT_STATUS_REQUEST 1
 #define EMT_STATUS 2
+#define EMT_MSGID_REQUEST 3
+#define EMT_MSGID 4
 
 #define EMS_AVAILABLE 0
 #define EMS_UNAVAILABLE 1
@@ -39,6 +41,45 @@ unsigned char own_status = EMS_AVAILABLE;
 unsigned char own_nick[256] = {'n', 'o', 'r', 't', 't', 'i'};
 unsigned char own_nick_length = 6;
 
+bool own_message_queued = false;
+unsigned char own_message_destination_mac[6];
+unsigned char own_message[1500 - 2 - 2 - 2];
+size_t own_message_length = 0;
+
+struct msgid_cache_entry {
+	unsigned char other_mac[6];
+	bool know_send;
+	bool know_receive;
+	uint16_t next_send;
+	uint16_t next_receive;
+};
+
+struct msgid_cache_entry msgid_cache[256];
+ssize_t msgid_cache_fill = 0;
+unsigned char next_slot = 0;
+
+ssize_t msgid_cache_lookup(const unsigned char mac[6]) {
+	for (ssize_t i = 0; i < msgid_cache_fill; i++) {
+		if (memcmp(msgid_cache[i].other_mac, mac, 6) == 0) {
+			// Found it
+			return i;
+		}
+	}
+
+	// Did not find it
+	return -1;
+}
+
+ssize_t msgid_cache_add(const unsigned char mac[6]) {
+	ssize_t index = next_slot++;
+
+	memcpy(msgid_cache[index].other_mac, mac, sizeof(msgid_cache[index].other_mac));
+	msgid_cache[index].know_send = false;
+	msgid_cache[index].know_receive = false;
+
+	return index;
+}
+
 char hexify(int nybble) {
 	assert(0 <= nybble && nybble <= 16);
 	return "0123456789abcdef"[nybble];
@@ -129,6 +170,44 @@ void send_status(const unsigned char destination[6]) {
 	send_frame(frame, sizeof(frame));
 }
 
+void send_msgid_request(const unsigned char destination[6]) {
+	unsigned char frame[14 + 2];
+
+	write_headers(frame, destination, EMT_MSGID_REQUEST);
+
+	send_frame(frame, sizeof(frame));
+}
+
+void send_msgid(const unsigned char destination[6]) {
+	unsigned char frame[14 + 2 + 2];
+
+	write_headers(frame, destination, EMT_MSGID);
+
+	// Look up destination in the ID cache
+	ssize_t cache_index = msgid_cache_lookup(destination);
+	if (cache_index == -1) {
+		// Not in the cache
+		// Create a new entry
+		cache_index = msgid_cache_add(destination);
+	}
+
+	if (!msgid_cache[cache_index].know_receive) {
+		// We don't have receive ID stored in the cache
+		// In that case, start from 0
+		// TODO: Make it random instead
+		msgid_cache[cache_index].next_receive = 0;
+		msgid_cache[cache_index].know_receive = true;
+	}
+
+	// Message ID of next message we're waiting to receive
+	uint16_t msgid = msgid_cache[cache_index].next_receive;
+
+	frame[16] = msgid >> 8;
+	frame[17] = msgid & 0xff;
+
+	send_frame(frame, sizeof(frame));
+}
+
 void read_command(void) {
 	int cmd = getchar();
 	if (cmd == EOF) {
@@ -139,6 +218,8 @@ void read_command(void) {
 		running = false;
 	} else if (cmd == 's') {
 		send_status_request(broadcast_mac);
+	} else if (cmd == 'i') {
+		send_msgid_request(broadcast_mac);
 	} else if (cmd == '\n') {
 		// Ignore
 	} else {
@@ -172,6 +253,8 @@ void handle_status(const unsigned char source_mac[6], const unsigned char *data,
 	unsigned char nick[256];
 	memcpy(nick, &data[2], nick_length);
 
+	// TODO: check that nick is valid utf-8 with no control chars
+
 	char mac[18];
 	format_mac(source_mac, mac);
 
@@ -205,6 +288,38 @@ void handle_status(const unsigned char source_mac[6], const unsigned char *data,
 	}
 }
 
+void handle_msgid(const unsigned char source_mac[6], const unsigned char *data, size_t data_length) {
+	if (data_length < 2) {
+		// Too short
+		fprintf(stderr, "Data too short: %zu\n", data_length); // debg
+		return;
+	}
+
+	uint16_t msgid = data[0] << 8 | data[1];
+
+	ssize_t cache_index = msgid_cache_lookup(source_mac);
+	if (cache_index == -1) {
+		// Not in the cache, so add it there
+		cache_index = msgid_cache_add(source_mac);
+	}
+
+	msgid_cache[cache_index].next_send = msgid;
+	msgid_cache[cache_index].know_send = true;
+
+	char mac[18];
+	format_mac(source_mac, mac);
+
+	errno = 0;
+	if (printf("%s awaits message ID %" PRIu16 "\n", mac, msgid_cache[cache_index].next_send) == 0) {
+		err(1, "printf");
+	}
+
+	errno = 0;
+	if (fflush(stdout) == EOF) {
+		err(1, "fflush");
+	}
+}
+
 void process_frame(void) {
 	unsigned char frame[1518]; // Largest a 802.3 frame can be without FCS
 
@@ -261,9 +376,19 @@ void process_frame(void) {
 			handle_status(source_mac, &frame[16], packet_length - 16);
 			break;
 
+		case EMT_MSGID_REQUEST:
+			send_msgid(source_mac);
+			break;
+
+		case EMT_MSGID:
+			handle_msgid(source_mac, &frame[16], packet_length - 16);
+			break;
+
 		default:
 			fprintf(stderr, "Ignoring packet of type %i\n", packet_type);
 	}
+
+	// TODO: Check that padding, if any, is all zeroes
 }
 
 void eventloop(void) {
@@ -367,6 +492,9 @@ int main(int argc, char **argv) {
 	format_mac(own_mac, own_mac_str);
 	fprintf(stderr, "%s\n", own_mac_str);
 
+	// Initialize the message id cache
+	memset(msgid_cache, 0, sizeof(msgid_cache));
+
 	// Request status from everyone, so that we can get an idea of who is on the network
 	send_status_request(broadcast_mac);