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>

context/context.go

@@ -1,21 +1,16 @@
 package context
 
 import (
+	"context"
 	"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
+	context.Context
 	id   string    // id of context, logged as "instance.id"
 	once sync.Once // once protect generation of the id
 }
@@ -42,17 +37,10 @@ var background = &instanceContext{
 // 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 {
+func Background() context.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/http.go

@@ -1,6 +1,7 @@
 package context
 
 import (
+	"context"
 	"errors"
 	"net"
 	"net/http"
@@ -68,7 +69,7 @@ func RemoteIP(r *http.Request) string {
 // is available at "http.request". Other common attributes are available under
 // the prefix "http.request.". If a request is already present on the context,
 // this method will panic.
-func WithRequest(ctx Context, r *http.Request) Context {
+func WithRequest(ctx context.Context, r *http.Request) context.Context {
 	if ctx.Value("http.request") != nil {
 		// NOTE(stevvooe): This needs to be considered a programming error. It
 		// is unlikely that we'd want to have more than one request in
@@ -87,7 +88,7 @@ func WithRequest(ctx Context, r *http.Request) Context {
 // GetRequest returns the http request in the given context. Returns
 // ErrNoRequestContext if the context does not have an http request associated
 // with it.
-func GetRequest(ctx Context) (*http.Request, error) {
+func GetRequest(ctx context.Context) (*http.Request, error) {
 	if r, ok := ctx.Value("http.request").(*http.Request); r != nil && ok {
 		return r, nil
 	}
@@ -96,13 +97,13 @@ func GetRequest(ctx Context) (*http.Request, error) {
 
 // GetRequestID attempts to resolve the current request id, if possible. An
 // error is return if it is not available on the context.
-func GetRequestID(ctx Context) string {
+func GetRequestID(ctx context.Context) string {
 	return GetStringValue(ctx, "http.request.id")
 }
 
 // WithResponseWriter returns a new context and response writer that makes
 // interesting response statistics available within the context.
-func WithResponseWriter(ctx Context, w http.ResponseWriter) (Context, http.ResponseWriter) {
+func WithResponseWriter(ctx context.Context, w http.ResponseWriter) (context.Context, http.ResponseWriter) {
 	if closeNotifier, ok := w.(http.CloseNotifier); ok {
 		irwCN := &instrumentedResponseWriterCN{
 			instrumentedResponseWriter: instrumentedResponseWriter{
@@ -125,7 +126,7 @@ func WithResponseWriter(ctx Context, w http.ResponseWriter) (Context, http.Respo
 // GetResponseWriter returns the http.ResponseWriter from the provided
 // context. If not present, ErrNoResponseWriterContext is returned. The
 // returned instance provides instrumentation in the context.
-func GetResponseWriter(ctx Context) (http.ResponseWriter, error) {
+func GetResponseWriter(ctx context.Context) (http.ResponseWriter, error) {
 	v := ctx.Value("http.response")
 
 	rw, ok := v.(http.ResponseWriter)
@@ -145,7 +146,7 @@ var getVarsFromRequest = mux.Vars
 // example, if looking for the variable "name", it can be accessed as
 // "vars.name". Implementations that are accessing values need not know that
 // the underlying context is implemented with gorilla/mux vars.
-func WithVars(ctx Context, r *http.Request) Context {
+func WithVars(ctx context.Context, r *http.Request) context.Context {
 	return &muxVarsContext{
 		Context: ctx,
 		vars:    getVarsFromRequest(r),
@@ -155,7 +156,7 @@ func WithVars(ctx Context, r *http.Request) Context {
 // GetRequestLogger returns a logger that contains fields from the request in
 // the current context. If the request is not available in the context, no
 // fields will display. Request loggers can safely be pushed onto the context.
-func GetRequestLogger(ctx Context) Logger {
+func GetRequestLogger(ctx context.Context) Logger {
 	return GetLogger(ctx,
 		"http.request.id",
 		"http.request.method",
@@ -171,7 +172,7 @@ func GetRequestLogger(ctx Context) Logger {
 // Because the values are read at call time, pushing a logger returned from
 // this function on the context will lead to missing or invalid data. Only
 // call this at the end of a request, after the response has been written.
-func GetResponseLogger(ctx Context) Logger {
+func GetResponseLogger(ctx context.Context) Logger {
 	l := getLogrusLogger(ctx,
 		"http.response.written",
 		"http.response.status",
@@ -188,7 +189,7 @@ func GetResponseLogger(ctx Context) Logger {
 
 // httpRequestContext makes information about a request available to context.
 type httpRequestContext struct {
-	Context
+	context.Context
 
 	startedAt time.Time
 	id        string
@@ -247,7 +248,7 @@ fallback:
 }
 
 type muxVarsContext struct {
-	Context
+	context.Context
 	vars map[string]string
 }
 
@@ -282,7 +283,7 @@ type instrumentedResponseWriterCN struct {
 // implemented by the parent ResponseWriter.
 type instrumentedResponseWriter struct {
 	http.ResponseWriter
-	Context
+	context.Context
 
 	mu      sync.Mutex
 	status  int

context/logger.go

@@ -1,10 +1,11 @@
 package context
 
 import (
+	"context"
 	"fmt"
+	"runtime"
 
 	"github.com/sirupsen/logrus"
-	"runtime"
 )
 
 // Logger provides a leveled-logging interface.
@@ -40,22 +41,24 @@ type Logger interface {
 	Warnln(args ...interface{})
 }
 
+type loggerKey struct{}
+
 // WithLogger creates a new context with provided logger.
-func WithLogger(ctx Context, logger Logger) Context {
-	return WithValue(ctx, "logger", logger)
+func WithLogger(ctx context.Context, logger Logger) context.Context {
+	return context.WithValue(ctx, loggerKey{}, logger)
 }
 
 // GetLoggerWithField returns a logger instance with the specified field key
 // and value without affecting the context. Extra specified keys will be
 // resolved from the context.
-func GetLoggerWithField(ctx Context, key, value interface{}, keys ...interface{}) Logger {
+func GetLoggerWithField(ctx context.Context, key, value interface{}, keys ...interface{}) Logger {
 	return getLogrusLogger(ctx, keys...).WithField(fmt.Sprint(key), value)
 }
 
 // GetLoggerWithFields returns a logger instance with the specified fields
 // without affecting the context. Extra specified keys will be resolved from
 // the context.
-func GetLoggerWithFields(ctx Context, fields map[interface{}]interface{}, keys ...interface{}) Logger {
+func GetLoggerWithFields(ctx context.Context, fields map[interface{}]interface{}, keys ...interface{}) Logger {
 	// must convert from interface{} -> interface{} to string -> interface{} for logrus.
 	lfields := make(logrus.Fields, len(fields))
 	for key, value := range fields {
@@ -71,7 +74,7 @@ func GetLoggerWithFields(ctx Context, fields map[interface{}]interface{}, keys .
 // argument passed to GetLogger will be passed to fmt.Sprint when expanded as
 // a logging key field. If context keys are integer constants, for example,
 // its recommended that a String method is implemented.
-func GetLogger(ctx Context, keys ...interface{}) Logger {
+func GetLogger(ctx context.Context, keys ...interface{}) Logger {
 	return getLogrusLogger(ctx, keys...)
 }
 
@@ -79,11 +82,11 @@ func GetLogger(ctx Context, keys ...interface{}) Logger {
 // are provided, they will be resolved on the context and included in the
 // logger. Only use this function if specific logrus functionality is
 // required.
-func getLogrusLogger(ctx Context, keys ...interface{}) *logrus.Entry {
+func getLogrusLogger(ctx context.Context, keys ...interface{}) *logrus.Entry {
 	var logger *logrus.Entry
 
 	// Get a logger, if it is present.
-	loggerInterface := ctx.Value("logger")
+	loggerInterface := ctx.Value(loggerKey{})
 	if loggerInterface != nil {
 		if lgr, ok := loggerInterface.(*logrus.Entry); ok {
 			logger = lgr

context/trace.go

@@ -1,6 +1,7 @@
 package context
 
 import (
+	"context"
 	"runtime"
 	"time"
 
@@ -36,7 +37,7 @@ import (
 //
 // Notice that the function name is automatically resolved, along with the
 // package and a trace id is emitted that can be linked with parent ids.
-func WithTrace(ctx Context) (Context, func(format string, a ...interface{})) {
+func WithTrace(ctx context.Context) (context.Context, func(format string, a ...interface{})) {
 	if ctx == nil {
 		ctx = Background()
 	}
@@ -69,7 +70,7 @@ func WithTrace(ctx Context) (Context, func(format string, a ...interface{})) {
 // also provides fast lookup for the various attributes that are available on
 // the trace.
 type traced struct {
-	Context
+	context.Context
 	id     string
 	parent string
 	start  time.Time

context/trace_test.go

@@ -1,6 +1,7 @@
 package context
 
 import (
+	"context"
 	"runtime"
 	"testing"
 	"time"
@@ -35,7 +36,7 @@ func TestWithTrace(t *testing.T) {
 	ctx, done := WithTrace(Background())
 	defer done("this will be emitted at end of test")
 
-	checkContextForValues(t, ctx, append(base, valueTestCase{
+	checkContextForValues(ctx, t, append(base, valueTestCase{
 		key:      "trace.func",
 		expected: f.Name(),
 	}))
@@ -48,7 +49,7 @@ func TestWithTrace(t *testing.T) {
 		ctx, done := WithTrace(ctx)
 		defer done("this should be subordinate to the other trace")
 		time.Sleep(time.Second)
-		checkContextForValues(t, ctx, append(base, valueTestCase{
+		checkContextForValues(ctx, t, append(base, valueTestCase{
 			key:      "trace.func",
 			expected: f.Name(),
 		}, valueTestCase{
@@ -67,8 +68,7 @@ type valueTestCase struct {
 	notnilorempty bool // just check not empty/not nil
 }
 
-func checkContextForValues(t *testing.T, ctx Context, values []valueTestCase) {
-
+func checkContextForValues(ctx context.Context, t *testing.T, values []valueTestCase) {
 	for _, testcase := range values {
 		v := ctx.Value(testcase.key)
 		if testcase.notnilorempty {

context/util.go

@@ -1,13 +1,14 @@
 package context
 
 import (
+	"context"
 	"time"
 )
 
 // Since looks up key, which should be a time.Time, and returns the duration
 // since that time. If the key is not found, the value returned will be zero.
 // This is helpful when inferring metrics related to context execution times.
-func Since(ctx Context, key interface{}) time.Duration {
+func Since(ctx context.Context, key interface{}) time.Duration {
 	if startedAt, ok := ctx.Value(key).(time.Time); ok {
 		return time.Since(startedAt)
 	}
@@ -16,7 +17,7 @@ func Since(ctx Context, key interface{}) time.Duration {
 
 // GetStringValue returns a string value from the context. The empty string
 // will be returned if not found.
-func GetStringValue(ctx Context, key interface{}) (value string) {
+func GetStringValue(ctx context.Context, key interface{}) (value string) {
 	if valuev, ok := ctx.Value(key).(string); ok {
 		value = valuev
 	}

context/version.go

@@ -1,16 +1,22 @@
 package context
 
+import "context"
+
+type versionKey struct{}
+
+func (versionKey) String() string { return "version" }
+
 // WithVersion stores the application version in the context. The new context
 // gets a logger to ensure log messages are marked with the application
 // version.
-func WithVersion(ctx Context, version string) Context {
-	ctx = WithValue(ctx, "version", version)
+func WithVersion(ctx context.Context, version string) context.Context {
+	ctx = context.WithValue(ctx, versionKey{}, version)
 	// push a new logger onto the stack
-	return WithLogger(ctx, GetLogger(ctx, "version"))
+	return WithLogger(ctx, GetLogger(ctx, versionKey{}))
 }
 
 // GetVersion returns the application version from the context. An empty
 // string may returned if the version was not set on the context.
-func GetVersion(ctx Context) string {
-	return GetStringValue(ctx, "version")
+func GetVersion(ctx context.Context) string {
+	return GetStringValue(ctx, versionKey{})
 }