Package flag

type Flags ¶

Flags provides the ability to create and communicate feature flags.

type Flags uint64

Flags is a bitset

const (
    Debug Flags = 1 << 0

    // SamplingSet and Sampled handle Sampled tribool logic for interop with
    // instrumenting libraries / propagation channels not using a separate Sampled
    // header and potentially encoding this in flags.
    //
    // When we receive a flag we do this:
    // 1. Sampled bit is set => true
    // 2. Sampled bit is not set => inspect SamplingSet bit.
    // 2a. SamplingSet bit is set => false
    // 2b. SamplingSet bit is not set => null
    // Note on 2b.: depending on the propagator having a separate Sampled header
    // we either assume Sampling is false or unknown. In the latter case we will
    // run our sampler even though we are not the root of the trace.
    //
    // When propagating to a downstream service we will always be explicit and
    // will provide a set SamplingSet bit in case of our binary propagator either
    SamplingSet Flags = 1 << 1
    Sampled     Flags = 1 << 2
    // When set, we can ignore the value of the parentId. This is used for binary
    // fixed width transports or transports like proto3 that return a default
    // value if a value has not been set (thus not enabling you to distinguish
    // between the value being set to the default or not set at all).
    //
    // While many zipkin systems re-use a trace id as the root span id, we know
    // that some don't. With this flag, we can tell for sure if the span is root
    // as opposed to the convention trace id == span id == parent id.
    IsRoot Flags = 1 << 3
)