Extract extracts tracing information from carrier with given format.

Inject injects tracing information into carrier with given format.

StartClientSpan starts the client span with given context, service and operation names.

StartServerSpan starts the server span with given context, carrier, service and operation names.

GrpcFormat means grpc carrier format.

HttpFormat means http carrier format.

ErrInvalidCarrier indicates an error that the carrier is invalid.

A Span is a calling span that connects caller and callee.