SUBSCRIBE initiates a subscription to a track. The associated parameters determine the range and mechanism of object delivery; the Location Filter (see Section 5.1.2) selects which Objects are sent, and a FILL_PARAMETERS parameter (see Section 10.2.15) additionally retrieves the fill range on a fill fetch stream (see Section 5.1.3).
The format of SUBSCRIBE is as follows:
SUBSCRIBE Message {
Type (vi64) = 0x3,
Length (16),
Request ID (vi64),
Track Namespace (..),
Track Name Length (vi64),
Track Name (..),
Number of Parameters (vi64),
Parameters (..) ...
}
-
Request ID: See Section 10.1.
-
Track Namespace: Identifies the namespace of the track as defined in (Section 2.4.1).
-
Track Name: Identifies the track name as defined in (Section 2.4.1).
-
Parameters: The parameters are defined in Section 10.2.
On successful subscription, the publisher MUST reply with a SUBSCRIBE_OK, allowing the subscriber to determine the start group/object when not explicitly specified, and start sending objects.