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package context
import (
"sync"
"github.com/docker/distribution/uuid"
"golang.org/x/net/context"
)
// Context is a copy of Context from the golang.org/x/net/context package.
type Context interface {
context.Context
}
// instanceContext is a context that provides only an instance id. It is
// provided as the main background context.
type instanceContext struct {
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/docker/distribution/issues/782
ic.id = uuid.Generate().String()
})
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 {
return background
}
// WithValue returns a copy of parent in which the value associated with key is
// val. Use context Values only for request-scoped data that transits processes
// and APIs, not for passing optional parameters to functions.
func WithValue(parent Context, key, val interface{}) Context {
return context.WithValue(parent, key, val)
}
// 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)
}
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