package dcontext import ( "context" "sync" "github.com/google/uuid" ) // instanceContext is a context that provides only an instance id. It is // provided as the main background context. type instanceContext struct { context.Context id string // id of context, logged as "instance.id" once sync.Once // once protect generation of the id } func (ic *instanceContext) Value(key interface{}) interface{} { if key == "instance.id" { ic.once.Do(func() { // We want to lazy initialize the UUID such that we don't // call a random generator from the package initialization // code. For various reasons random could not be available // https://github.com/distribution/distribution/issues/782 ic.id = uuid.NewString() }) return ic.id } return ic.Context.Value(key) } var background = &instanceContext{ Context: context.Background(), } // Background returns a non-nil, empty Context. The background context // provides a single key, "instance.id" that is globally unique to the // process. func Background() context.Context { return background } // stringMapContext is a simple context implementation that checks a map for a // key, falling back to a parent if not present. type stringMapContext struct { context.Context m map[string]interface{} } // WithValues returns a context that proxies lookups through a map. Only // supports string keys. func WithValues(ctx context.Context, m map[string]interface{}) context.Context { mo := make(map[string]interface{}, len(m)) // make our own copy. for k, v := range m { mo[k] = v } return stringMapContext{ Context: ctx, m: mo, } } func (smc stringMapContext) Value(key interface{}) interface{} { if ks, ok := key.(string); ok { if v, ok := smc.m[ks]; ok { return v } } return smc.Context.Value(key) }