Sequence Number

Apache Thrift built sequence numbers into every protocol exchange to allow for clients that may submit multiple outstanding requests on a single transport connection. This is typically done by asynchronous clients.

The following rules apply to sequence numbers:

1. A sequence number is a signed 32-bit integer. Negative values are allowed.
2. Sequence numbers MUST be unique across all outstanding requests on a given transport connection. There is no requirement for unique numbers between different transport connections even if they are from the same client.
3. A server MUST reply to a client with the same sequence number that was used in the request. This includes any exception-based reply.
4. A client MAY use sequence numbers if it needs them for proper operation.
5. A client SHOULD set the sequence number to zero if it does not rely on them.
6. Wrapped protocols (such as THeaderProtocol) SHOULD use the same sequence number on the wrapping as is used on the payload protocol.

Servers will not inspect or make any logic choices based on the sequence number sent by the client. The server's only job is to process the request and reply with the same sequence number.