inhies · October 21, 2016 17:09 · Oct 21, 2016
diff --git a/topic.go b/topic.go
@@ -0,0 +1,132 @@
+package main
+
+import (
+	"log"
+	"strings"
+)
+
+type check struct {
+	Sub, Topic  string
+	ShouldMatch bool
+}
+
+func main() {
+	tests := []check{
+		{"myhome/groundfloor/+/temperature", "myhome/groundfloor/livingroom/temperature", true},
+		{"myhome/groundfloor/+/temperature", "myhome/groundfloor/kitchen/temperature", true},
+		{"myhome/groundfloor/+/temperature", "myhome/groundfloor/kitchen/brightness", false},
+		{"myhome/groundfloor/+/temperature", "myhome/firstfloor/kitchen/temperature", false},
+		{"myhome/groundfloor/+/temperature", "myhome/groundfloor/kitchen/fridge/temperature", false},
+
+		{"myhome/groundfloor/#", "myhome/groundfloor/livingroom/temperature", true},
+		{"myhome/groundfloor/#", "myhome/groundfloor/kitchen/temperature", true},
+		{"myhome/groundfloor/#", "myhome/groundfloor/kitchen/brightness", true},
+		{"myhome/groundfloor/#", "myhome/firstfloor/kitchen/temperature", false},
+
+		{"a/b/c/d", "a/b/c/d", true},
+		{"+/b/c/d", "a/b/c/d", true},
+		{"a/+/c/d", "a/b/c/d", true},
+		{"a/+/+/d", "a/b/c/d", true},
+		{"+/+/+/+", "a/b/c/d", true},
+
+		{"a/b/c", "a/b/c/d", false},
+		{"b/+/c/d", "a/b/c/d", false},
+		{"+/+/+", "a/b/c/d", false},
+
+		{"#", "a/b/c/d", true},
+		{"a/#", "a/b/c/d", true},
+		{"a/b/#", "a/b/c/d", true},
+		{"a/b/c/#", "a/b/c/d", true},
+		{"+/b/c/#", "a/b/c/d", true},
+
+		{"a/+/topic", "a//topic", true},
+		{"+/a/topic", "/a/topic", true},
+		{"#", "/a/topic", true},
+		{"a/topic/+", "a/topic/", true},
+
+		{"a/topic/#", "a/topic/", true},
+
+		{"sport/tennis/player1/#", "sport/tennis/player1", true},
+		{"sport/tennis/player1/#", "sport/tennis/player1/ranking", true},
+		{"sport/tennis/player1/#", "sport/tennis/player1/score/wimbledon", true},
+
+		{"sport/#", "sport/tennis/player1", true},
+		{"sport/tennis/#", "sport/tennis/player1", true},
+		{"sport/tennis#", "sport/tennis/player1", false},
+		{"sport/tennis/#/ranking", "sport/tennis/player1", false},
+
+		{"sport/tennis/+", "sport/tennis/player1", true},
+		{"sport/tennis/+", "sport/tennis/player1/ranking", false},
+		{"sport/+", "sport", false},
+		{"sport/+", "sport/", true},
+
+		{"+/+", "/finance", true},
+		{"/+", "/finance", true},
+		{"+", "/finance", false},
+	}
+
+	for i, v := range tests {
+		if CheckTopic(v.Sub, v.Topic) != v.ShouldMatch {
+			log.Fatalf("Failed on %v: %v", i, v)
+		}
+	}
+}
+
+// CheckTopic returns true if a message topic satisfies
+// a message subscription.
+func CheckTopic(sub, topic string) bool {
+	s := strings.Split(sub, "/")
+	t := strings.Split(topic, "/")
+
+	// Check for leading '$' first, becuase we don't want to accidentally
+	// match it using a wildcard later. '$' topics are reserved for the
+	// broker to use and is not for clients.
+	if (sub[0] == '$' && topic[0] != '$') ||
+		(topic[0] == '$' && sub[0] != '$') {
+		return false
+	}
+
+	// Work through the subscription section by section and see if it matches the
+	// topic exatly or via wildcards.
+	for i := 0; i < len(s) && i < len(t); i++ {
+		switch s[i] {
+		case "+":
+			//Single wildcard, dont need to compare
+			continue
+		case "#":
+			if i < len(s)-1 {
+				// Invalid, # is not the last character
+				return false
+			}
+			// Everything after this doesn't matter
+			return true
+		default:
+			if s[i] != t[i] {
+				// This section of the topic and subscription
+				// dont match, so the topic is not a match for
+				// the subscription
+				return false
+
+			}
+		}
+	}
+
+	// If we made it this far, everything has matched so far
+	if len(s) == len(t) {
+		// Topic and subscription both have the same amount of sections
+		// and they all matched so return true.
+		return true
+	} else {
+		// the topic and subscription have a mismatch in the number of
+		// sections, but if the last character is this wildcard, then
+		// everything will match
+		if s[len(s)-1] == "#" {
+			return true
+		}
+
+		// Either the topic or subscription is longer than the other
+		// and the wildcard is not on the end, so they are not a match
+		return false
+	}
+
+}
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