From c70a0a93374eae11f20b90aec539b0c190eb6faa Mon Sep 17 00:00:00 2001
From: Matthias Kruk <m@m10k.eu>
Date: Sat, 17 Sep 2022 14:22:07 +0900
Subject: [PATCH] include/ipc: Add "topic" field to pubsub IPC messages

Messages that were sent with ipc_endpoint_publish() don't contain
information about the topic that they were published on, making it
impossible for the receiver to determine what topic a message was
published on if they are subscribed to more than one topic.

This commit adds a new field "topic" to IPC messages and modifies
ipc_endpoint_publish() so that it sets the field appropriately. This
further adds the function ipc_msg_get_topic() that may be used to
determine the topic an IPC message was published on.
---
 include/ipc.sh               | 26 +++++++++++++++++++++++---
 spec/ipc_message.schema.json |  5 +++++
 2 files changed, 28 insertions(+), 3 deletions(-)

diff --git a/include/ipc.sh b/include/ipc.sh
index 46605ed..79b5bd0 100644
--- a/include/ipc.sh
+++ b/include/ipc.sh
@@ -1,7 +1,7 @@
 #!/bin/bash
 
 # ipc.sh - Toolbox module for message-based IPC
-# Copyright (C) 2021 Matthias Kruk
+# Copyright (C) 2021-2022 Matthias Kruk
 #
 # This program is free software: you can redistribute it and/or modify
 # it under the terms of the GNU General Public License as published by
@@ -279,6 +279,11 @@ _ipc_msg_new() {
 	local source="$1"
 	local destination="$2"
 	local data="$3"
+	local topic="$4"
+
+	# For non-pubsub messages, the topic will be unset. This will
+	# cause the topic not to show up in the JSON object because
+	# json_object() skips empty fields.
 
 	local encoded_data
 	local timestamp
@@ -299,6 +304,7 @@ _ipc_msg_new() {
 				     "destination" "$destination"   \
 				     "user"        "$USER"          \
 				     "timestamp"   "$timestamp"     \
+	                             "topic"       "$topic"         \
 				     "data"        "$encoded_data"); then
 		log_error "Could not make message"
 
@@ -406,6 +412,19 @@ ipc_msg_get_data() {
 	return 0
 }
 
+ipc_msg_get_topic() {
+	local msg="$1"
+
+	local topic
+
+	if ! topic=$(_ipc_msg_get "$msg" "topic"); then
+		return 1
+	fi
+
+	echo "$topic"
+	return 0
+}
+
 ipc_msg_get_signature() {
 	local msg="$1"
 
@@ -560,10 +579,11 @@ ipc_endpoint_send() {
 	local source="$1"
 	local destination="$2"
 	local data="$3"
+	local topic="$4"
 
 	local msg
 
-	if ! msg=$(_ipc_msg_new "$source" "$destination" "$data"); then
+	if ! msg=$(_ipc_msg_new "$source" "$destination" "$data" "$topic"); then
 		return 1
 	fi
 
@@ -706,7 +726,7 @@ ipc_endpoint_publish() {
 	fi
 
 	while read -r subscriber; do
-		ipc_endpoint_send "$endpoint" "$subscriber" "$message"
+		ipc_endpoint_send "$endpoint" "$subscriber" "$message" "$topic"
 	done < <(_ipc_endpoint_topic_get_subscribers "$topic")
 
 	return 0
diff --git a/spec/ipc_message.schema.json b/spec/ipc_message.schema.json
index 06379d6..1ee8f2c 100644
--- a/spec/ipc_message.schema.json
+++ b/spec/ipc_message.schema.json
@@ -21,6 +21,11 @@
 	    "type": "string"
 	},
 
+	"topic": {
+	    "description": "The topic that the message was published on",
+	    "type": "string"
+	},
+
 	"timestamp": {
 	    "description": "The UNIX timestamp when the message was sent",
 	    "type": "integer"
-- 
2.47.3