0. demo details:

For each demo, start server and then run client:

go run demo1/server/server1.go

go run demo1/client/client1.go

• Demo1: go http client wants to wait for server response with timeout
• Demo2: go http client wants to cancel request when some event happens on client (like press enter)
• Demo3: curl http client cancel request with ctrl+c and go http server terminate request processing
• CtxDemo: four different demos, just exhibits different behaviour of different type of context

1. context api:

type Context interface {
	Deadline() (deadline time.Time, ok bool)
	Done() <-chan struct{}
	Value(key interface{}) interface{}
}

func WithCancel(parent Context) (ctx Context, cancel CancelFunc)
func WithDeadline(parent Context, d time.Time) (Context, CancelFunc)
func WithTimeout(parent Context, timeout time.Duration) (Context, CancelFunc)

2. context usage:

context use to pass ..

deadlines 
cancelation signals 
request-scoped values 

.. across API boundaries to all the goroutines involved in handling a request.

• Background is typically used in main, init, and tests
• WithCancel is also useful for canceling redundant requests when using multiple replicas
• WithTimeout is useful for setting a deadline on requests to backend servers

3. references:

• https://github.com/campoy/justforfunc/tree/master/09-context
• https://blog.golang.org/context
• https://www.youtube.com/watch?v=LSzR0VEraWw
• https://golang.org/pkg/context/