Wildcard Characters in Topic Subscriptions

When the * and > characters are used in Solace Message Format (SMF) topic subscriptions, they function as wildcards, which affect the topic matches that may occur.

The * and > characters don't have any special meaning when they are used in published topics. They are treated as literal characters - not as wildcards - and don't affect topic matches. However, to avoid confusion, Solace does not recommend using * and > as literal characters in published topics.

Using the * Wildcard

The * wildcard functions in the following ways:

1. When * appears by itself at a level within a topic subscription (as in, animals/*/cats, or animals/domestic/*), it indicates a wildcard match at that level.

   A * wildcard at the end of a topic subscription performs a wildcard match only at that level.

   Example: animals/domestic/* matches the topics animals/domestic/cats and animals/domestic/dogs, but it doesn't match the topic animals/domestic/dogs/beagles.

2. When * is preceded by a topic prefix at a level within a topic subscription (as in, animals/red*/wild), it indicates a "prefix and 0 or more” match at that level.

   Example: animals/red*/wild matches both the topics animals/red/wild and animals/reddish/wild.

3. The * may be used at multiple levels within a topic subscription, with or without topic prefixes.

   Example: animals/*/cats/* is valid and matches the topics animals/domestic/cats/persian and animals/wild/cats/leopard, but doesn't match the topic animals/domestic/cats/persian/grey, nor does it match the topic animals/domestic/dogs/beagles.

4. Use of * in an arbitrary location within a level, and not covered by the previous rules, is treated as a literal character; general sub-string matching is not supported.

   Example: The * in topic subscriptions animals/*bro and animals/br*wn is treated as a literal *, not a wildcard.

Using the > Wildcard

The > wildcard functions in the following ways:

1. When > appears by itself at the last level of a topic subscription (as in, animals/domestic/>), it provides a “one or more” wildcard match for any topics with an identical prefix to the subscription.

   Example: animals/domestic/> doesn't match the topic animals/domestic, but it does match the topics animals/domestic/cats, animals/domestic/dogs, animals/domestic/dogs/beagles, and animals/domestic/dogs/beagles/long-eared.

2. A > that appears anywhere other than by itself at the last level of a topic subscription in the string is treated as the > character rather than a wildcard.

   Example: animals> and animals/domestic> are literal subscriptions and don't match animals/domestic/dogs/beagles.

3. The > and * characters can be used together within a topic subscription.

   Example: animals/*/cats/> matches the topics animals/domestic/cats/persian, animals/wild/cats/leopard, and animals/domestic/cats/persian/grey, but it doesn't match the topic animals/domestic/dogs/beagles.

Wildcard Restrictions

Wildcards have the following restrictions:

• Event brokers automatically create topic subscriptions beginning with the prefix #P2P for each client, which enables messages to be sent directly to that client (for example, in request/reply scenarios). Therefore, to ensure that wildcards cannot be used to receive messages that are intended for the inboxes of other clients, the * or > wildcards never match the string #P2P, regardless of where the wildcard or #P2P string is located within the topic subscription string.

• Messages published to topics that begin with a $ character are never matched by standalone wildcards (*/... or >) at the first level of a topic subscription. This ensures that system and event log messages beginning with a $ character aren't included in topic subscriptions for which they weren't intended.

Wildcard Examples

The following table provides examples of topic subscription matches when using wildcards.

Wildcard Subject	Matches Messages With Subjects Like:	Does Not Match Messages With Subjects Like:
animals/domestic/*	animals/domestic/cats animals/domestic/dogs	animals/domestic/dogs/beagles
animals/*/cats/*	animals/domestic/cats/persian animals/wild/cats/leopard	animals/domestic/cats/persian/grey animals/domestic/dogs/beagles
animals/domestic/dog*	animals/domestic/dog animals/domestic/doggy	animals/domestic/dog/beagle animals/domestic/cat
animals/domestic/>	animals/domestic/cats animals/domestic/dogs/beagles	animals animals/domestic animals/Domestic
animals/*/cats/>	animals/domestic/cats/tabby/grey animals/wild/cats/leopard	animals/domestic/dogs/beagles
my/test/*	my/test/topic	My/Test/Topic my/test