SUBSCRIBE initiates a subscription to a track. The associated parameters determine the range and mechanism of object delivery; the Location Filter (see Section 3.3.1) selects which Objects are sent, and a FILL_PARAMETERS parameter (see Section 9.20.16) additionally retrieves the fill range on a fill fetch stream (see Section 3.4).
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 6.4.2.1.
-
Track Namespace: Identifies the namespace of the track as defined in (Section 8.7).
-
Track Name: Identifies the track name as defined in (Section 2.4.1).
-
Parameters: The parameters are defined in Section 9.20.
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.