86 lines
2.2 KiB
Go
86 lines
2.2 KiB
Go
package context
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import (
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"sync"
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"github.com/docker/distribution/uuid"
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"golang.org/x/net/context"
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)
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// Context is a copy of Context from the golang.org/x/net/context package.
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type Context interface {
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context.Context
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}
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// instanceContext is a context that provides only an instance id. It is
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// provided as the main background context.
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type instanceContext struct {
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Context
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id string // id of context, logged as "instance.id"
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once sync.Once // once protect generation of the id
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}
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func (ic *instanceContext) Value(key interface{}) interface{} {
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if key == "instance.id" {
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ic.once.Do(func() {
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// We want to lazy initialize the UUID such that we don't
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// call a random generator from the package initialization
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// code. For various reasons random could not be available
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// https://github.com/docker/distribution/issues/782
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ic.id = uuid.Generate().String()
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})
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return ic.id
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}
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return ic.Context.Value(key)
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}
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var background = &instanceContext{
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Context: context.Background(),
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}
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// Background returns a non-nil, empty Context. The background context
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// provides a single key, "instance.id" that is globally unique to the
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// process.
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func Background() Context {
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return background
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}
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// WithValue returns a copy of parent in which the value associated with key is
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// val. Use context Values only for request-scoped data that transits processes
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// and APIs, not for passing optional parameters to functions.
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func WithValue(parent Context, key, val interface{}) Context {
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return context.WithValue(parent, key, val)
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}
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// stringMapContext is a simple context implementation that checks a map for a
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// key, falling back to a parent if not present.
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type stringMapContext struct {
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context.Context
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m map[string]interface{}
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}
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// WithValues returns a context that proxies lookups through a map. Only
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// supports string keys.
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func WithValues(ctx context.Context, m map[string]interface{}) context.Context {
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mo := make(map[string]interface{}, len(m)) // make our own copy.
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for k, v := range m {
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mo[k] = v
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}
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return stringMapContext{
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Context: ctx,
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m: mo,
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}
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}
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func (smc stringMapContext) Value(key interface{}) interface{} {
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if ks, ok := key.(string); ok {
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if v, ok := smc.m[ks]; ok {
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return v
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}
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}
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return smc.Context.Value(key)
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}
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