ContextWithSpan return a new `context.Context` that holds a reference to the span.

FromIncomingContext extract trace info from span.

HeaderExtractor extract trace info from span.

HeaderInjector inject trace info to span.

MetadataInjector inject trace info to span.

SetGlobalTracer set global trace instance.

SpanFromContext return the span attached to current context.

StartSpanFromContext start a span from current context.

TraceID return trace id as string.