context: remove definition of Context

Back in the before time, the best practices surrounding usage of Context
weren't quite worked out. We defined our own type to make usage easier.
As this packaged was used elsewhere, it make it more and more
challenging to integrate with the forked `Context` type. Now that it is
available in the standard library, we can just use that one directly.

To make usage more consistent, we now use `dcontext` when referring to
the distribution context package.

Signed-off-by: Stephen J Day <stephen.day@docker.com>

registry/proxy/scheduler/scheduler.go

@@ -1,12 +1,13 @@
 package scheduler
 
 import (
+	"context"
 	"encoding/json"
 	"fmt"
 	"sync"
 	"time"
 
-	"github.com/docker/distribution/context"
+	dcontext "github.com/docker/distribution/context"
 	"github.com/docker/distribution/reference"
 	"github.com/docker/distribution/registry/storage/driver"
 )
@@ -120,7 +121,7 @@ func (ttles *TTLExpirationScheduler) Start() error {
 		return fmt.Errorf("Scheduler already started")
 	}
 
-	context.GetLogger(ttles.ctx).Infof("Starting cached object TTL expiration scheduler...")
+	dcontext.GetLogger(ttles.ctx).Infof("Starting cached object TTL expiration scheduler...")
 	ttles.stopped = false
 
 	// Start timer for each deserialized entry
@@ -142,7 +143,7 @@ func (ttles *TTLExpirationScheduler) Start() error {
 
 				err := ttles.writeState()
 				if err != nil {
-					context.GetLogger(ttles.ctx).Errorf("Error writing scheduler state: %s", err)
+					dcontext.GetLogger(ttles.ctx).Errorf("Error writing scheduler state: %s", err)
 				} else {
 					ttles.indexDirty = false
 				}
@@ -163,7 +164,7 @@ func (ttles *TTLExpirationScheduler) add(r reference.Reference, ttl time.Duratio
 		Expiry:    time.Now().Add(ttl),
 		EntryType: eType,
 	}
-	context.GetLogger(ttles.ctx).Infof("Adding new scheduler entry for %s with ttl=%s", entry.Key, entry.Expiry.Sub(time.Now()))
+	dcontext.GetLogger(ttles.ctx).Infof("Adding new scheduler entry for %s with ttl=%s", entry.Key, entry.Expiry.Sub(time.Now()))
 	if oldEntry, present := ttles.entries[entry.Key]; present && oldEntry.timer != nil {
 		oldEntry.timer.Stop()
 	}
@@ -193,10 +194,10 @@ func (ttles *TTLExpirationScheduler) startTimer(entry *schedulerEntry, ttl time.
 		ref, err := reference.Parse(entry.Key)
 		if err == nil {
 			if err := f(ref); err != nil {
-				context.GetLogger(ttles.ctx).Errorf("Scheduler error returned from OnExpire(%s): %s", entry.Key, err)
+				dcontext.GetLogger(ttles.ctx).Errorf("Scheduler error returned from OnExpire(%s): %s", entry.Key, err)
 			}
 		} else {
-			context.GetLogger(ttles.ctx).Errorf("Error unpacking reference: %s", err)
+			dcontext.GetLogger(ttles.ctx).Errorf("Error unpacking reference: %s", err)
 		}
 
 		delete(ttles.entries, entry.Key)
@@ -210,7 +211,7 @@ func (ttles *TTLExpirationScheduler) Stop() {
 	defer ttles.Unlock()
 
 	if err := ttles.writeState(); err != nil {
-		context.GetLogger(ttles.ctx).Errorf("Error writing scheduler state: %s", err)
+		dcontext.GetLogger(ttles.ctx).Errorf("Error writing scheduler state: %s", err)
 	}
 
 	for _, entry := range ttles.entries {