Propagate request context behaviour to gin context methods implementi…

…ng 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 <[email protected]>

context.go

@@ -985,22 +985,22 @@ func (c *Context) SetAccepted(formats ...string) {
 	c.Accepted = formats
 }
 
-/************************************/
-/***** GOLANG.ORG/X/NET/CONTEXT *****/
-/************************************/
+/*****************************************/
+/***** 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
+	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 nil
+	return c.Request.Context().Done()
 }
 
 // Err returns a non-nil error value after Done is closed,
@@ -1010,7 +1010,7 @@ func (c *Context) Done() <-chan struct{} {
 // Canceled if the context was canceled
 // or DeadlineExceeded if the context's deadline passed.
 func (c *Context) Err() error {
-	return nil
+	return c.Request.Context().Err()
 }
 
 // Value returns the value associated with this context for key, or nil
@@ -1021,8 +1021,10 @@ func (c *Context) Value(key interface{}) interface{} {
 		return c.Request
 	}
 	if keyAsString, ok := key.(string); ok {
-		val, _ := c.Get(keyAsString)
-		return val
+		val, exists := c.Get(keyAsString)
+		if exists {
+			return val
+		}
 	}
-	return nil
+	return c.Request.Context().Value(key)
 }