Propagate request context behaviour to gin context methods implementing stdlib context.Context interface.

It makes possible to correctly cancel handlers when request cancelled (connection closed, etc.)
Try to extract value from request context when it was not found in gin context

Signed-off-by: Vladimir Stolyarov <xakep6666@gmail.com>

context.go

@@ -984,45 +984,3 @@ func (c *Context) NegotiateFormat(offered ...string) string {
 func (c *Context) SetAccepted(formats ...string) {
 	c.Accepted = formats
 }
-
-/************************************/
-/***** GOLANG.ORG/X/NET/CONTEXT *****/
-/************************************/
-
-// Deadline returns the time when work done on behalf of this context
-// should be canceled. Deadline returns ok==false when no deadline is
-// set. Successive calls to Deadline return the same results.
-func (c *Context) Deadline() (deadline time.Time, ok bool) {
-	return
-}
-
-// Done returns a channel that's closed when work done on behalf of this
-// context should be canceled. Done may return nil if this context can
-// never be canceled. Successive calls to Done return the same value.
-func (c *Context) Done() <-chan struct{} {
-	return nil
-}
-
-// Err returns a non-nil error value after Done is closed,
-// successive calls to Err return the same error.
-// If Done is not yet closed, Err returns nil.
-// If Done is closed, Err returns a non-nil error explaining why:
-// Canceled if the context was canceled
-// or DeadlineExceeded if the context's deadline passed.
-func (c *Context) Err() error {
-	return nil
-}
-
-// Value returns the value associated with this context for key, or nil
-// if no value is associated with key. Successive calls to Value with
-// the same key returns the same result.
-func (c *Context) Value(key interface{}) interface{} {
-	if key == 0 {
-		return c.Request
-	}
-	if keyAsString, ok := key.(string); ok {
-		val, _ := c.Get(keyAsString)
-		return val
-	}
-	return nil
-}

context_17.go

@@ -8,6 +8,7 @@ package gin
 
 import (
 	"github.com/gin-gonic/gin/render"
+	"time"
 )
 
 // PureJSON serializes the given struct as JSON into the response body.
@@ -15,3 +16,47 @@ import (
 func (c *Context) PureJSON(code int, obj interface{}) {
 	c.Render(code, render.PureJSON{Data: obj})
 }
+
+/*****************************************/
+/***** STDLIB CONTEXT IMPLEMENTATION *****/
+/*****************************************/
+
+// Deadline returns the time when work done on behalf of this context
+// should be canceled. Deadline returns ok==false when no deadline is
+// set. Successive calls to Deadline return the same results.
+func (c *Context) Deadline() (deadline time.Time, ok bool) {
+	return c.Request.Context().Deadline()
+}
+
+// Done returns a channel that's closed when work done on behalf of this
+// context should be canceled. Done may return nil if this context can
+// never be canceled. Successive calls to Done return the same value.
+func (c *Context) Done() <-chan struct{} {
+	return c.Request.Context().Done()
+}
+
+// Err returns a non-nil error value after Done is closed,
+// successive calls to Err return the same error.
+// If Done is not yet closed, Err returns nil.
+// If Done is closed, Err returns a non-nil error explaining why:
+// Canceled if the context was canceled
+// or DeadlineExceeded if the context's deadline passed.
+func (c *Context) Err() error {
+	return c.Request.Context().Err()
+}
+
+// Value returns the value associated with this context for key, or nil
+// if no value is associated with key. Successive calls to Value with
+// the same key returns the same result.
+func (c *Context) Value(key interface{}) interface{} {
+	if key == 0 {
+		return c.Request
+	}
+	if keyAsString, ok := key.(string); ok {
+		val, exists := c.Get(keyAsString)
+		if exists {
+			return val
+		}
+	}
+	return c.Request.Context().Value(key)
+}

context_pre17.go

@@ -0,0 +1,51 @@
+// Copyright 2018 Gin Core Team.  All rights reserved.
+// Use of this source code is governed by a MIT style
+// license that can be found in the LICENSE file.
+
+// +build !go1.7
+
+package gin
+
+import "time"
+
+/************************************/
+/***** GOLANG.ORG/X/NET/CONTEXT *****/
+/************************************/
+
+// Deadline returns the time when work done on behalf of this context
+// should be canceled. Deadline returns ok==false when no deadline is
+// set. Successive calls to Deadline return the same results.
+func (c *Context) Deadline() (deadline time.Time, ok bool) {
+	return
+}
+
+// Done returns a channel that's closed when work done on behalf of this
+// context should be canceled. Done may return nil if this context can
+// never be canceled. Successive calls to Done return the same value.
+func (c *Context) Done() <-chan struct{} {
+	return nil
+}
+
+// Err returns a non-nil error value after Done is closed,
+// successive calls to Err return the same error.
+// If Done is not yet closed, Err returns nil.
+// If Done is closed, Err returns a non-nil error explaining why:
+// Canceled if the context was canceled
+// or DeadlineExceeded if the context's deadline passed.
+func (c *Context) Err() error {
+	return nil
+}
+
+// Value returns the value associated with this context for key, or nil
+// if no value is associated with key. Successive calls to Value with
+// the same key returns the same result.
+func (c *Context) Value(key interface{}) interface{} {
+	if key == 0 {
+		return c.Request
+	}
+	if keyAsString, ok := key.(string); ok {
+		val, _ := c.Get(keyAsString)
+		return val
+	}
+	return nil
+}