What are the known types of contexts in Go?

In Go, the standard context package provides several functions for creating contexts:

• context.Background(): Returns a non-nil, empty context, which is typically used as the root context for incoming requests or main functions. It is never canceled, has no deadline, and carries no values.

• context.TODO(): Returns a non-nil, empty context. It is used when you are unsure about which context to use or when the code is not yet updated to accept a context. Like Background(), it is never canceled, has no deadline, and carries no values. It serves as a temporary placeholder.

• context.WithCancel(parent Context): Returns a derived context that can be canceled with the returned cancel function. Canceling this context releases resources associated with it and its children.

  // Creating a cancellable context
  ctx, cancel := context.WithCancel(context.Background())
  defer cancel() // Cancel the context upon function exit
  
  // Using ctx...
  

• context.WithDeadline(parent Context, deadline time.Time): Returns a derived context that will be automatically canceled at the specified deadline. It also returns a cancel function that can be called earlier to cancel.

  // Creating a context with a deadline
  deadline := time.Now().Add(5 * time.Second)
  ctx, cancel := context.WithDeadline(context.Background(), deadline)
  defer cancel()
  
  // Using ctx...
  

• context.WithTimeout(parent Context, timeout time.Duration): Similar to WithDeadline, but takes a duration. It returns a derived context that will be automatically canceled after the specified timeout.

  // Creating a context with a timeout
  ctx, cancel := context.WithTimeout(context.Background(), 2*time.Second)
  defer cancel()
  
  // Using ctx...
  

• context.WithValue(parent Context, key, val any): Returns a derived context that carries the specified key/value pair. It is used for passing request-specific data through the API.

  // Creating a context with a value
  type userIDKey string
  ctx := context.WithValue(context.Background(), userIDKey("user_id"), 123)
  
  // Retrieving the value from the context
  if userID, ok := ctx.Value(userIDKey("user_id")).(int); ok {
      // use userID
  }
  

These functions allow building a hierarchy of contexts, where child contexts inherit properties from parent contexts and can be canceled independently or when the parent is canceled.