ctxutil

package module
Version: v1.0.0 Latest Latest
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Published: Aug 2, 2019 License: Apache-2.0 Imports: 4 Imported by: 0

README

ctxutil

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Package ctxutil is a collection of functions for contexts.

Functions

func Interrupt

func Interrupt() context.Context

Interrupt is a convenience function for catching SIGINT on a background context.

Example:
func main() {
	ctx := ctxutil.Interrupt()
	// use ctx...
}
func WithSignal

func WithSignal(parent context.Context, sigWhiteList ...os.Signal) context.Context

WithSignal returns a context which is done when an OS signal is sent. parent is a parent context to wrap. sigWhiteList is a list of signals to listen on. According to the signal.Notify behavior, an empty list will listen to any OS signal. If an OS signal closed this context, ErrSignal will be returned in the Err() method of the returned context.

This method creates the signal channel and invokes a goroutine.

Example
func main() {
	// Create a context which will be cancelled on SIGINT.
	ctx := ctxutil.WithSignal(context.Background(), os.Interrupt)
	// use ctx...
}
func WithValues

func WithValues(ctx, values context.Context) context.Context

WithValues composes values from multiple contexts. It returns a context that exposes the deadline and cancel of ctx, and combined values from ctx and values. A value in ctx context overrides a value with the same key in values context.

Consider the following standard HTTP Go server stack:

  1. Middlewares that extract user credentials and request id from the
headers and inject them to the `http.Request` context as values.
  1. The http.Handler launches an asynchronous goroutine task which
needs those values from the context.
  1. After launching the asynchronous task the handler returns 202 to
the client, the goroutine continues to run in background.

Problem Statement:

  • The async task can't use the request context - it is cancelled
as the `http.Handler` returns.
  • There is no way to use the context values in the async task.
  • Specially if those values are used automatically with client
`http.Roundtripper` (extract the request id from the context
and inject it to http headers in a following request.)

The suggested function ctx := ctxutil.WithValues(ctx, values) does the following:

  1. When ctx.Value() is called, the key is searched in the
original `ctx` and if not found it searches in `values`.
  1. When Done()/Deadline()/Err() are called, it is uses
original `ctx`'s state.
Example

This is how an http.Handler should run a goroutine that need values from the context.

func handle(w http.ResponseWriter, r *http.Request) {
	// [ do something ... ]

	// Create async task context that enables it run for 1 minute, for example
	asyncCtx, asyncCancel = ctxutil.WithTimeout(context.Background(), time.Minute)
	// Use values from the request context
	asyncCtx = ctxutil.WithValues(asyncCtx, r.Context())
	// Run the async task with it's context
	go func() {
		defer asyncCancel()
		asyncTask(asyncCtx)
	}()
}

Created by goreadme

Documentation

Overview

Package ctxutil is a collection of functions for contexts.

Index

Constants

This section is empty.

Variables

This section is empty.

Functions

func Interrupt

func Interrupt() context.Context

Interrupt is a convenience function for catching SIGINT on a background context.

### Example:

func main() {
	ctx := ctxutil.Interrupt()
	// use ctx...
}

func WithSignal

func WithSignal(parent context.Context, sigWhiteList ...os.Signal) context.Context

WithSignal returns a context which is done when an OS signal is sent. parent is a parent context to wrap. sigWhiteList is a list of signals to listen on. According to the signal.Notify behavior, an empty list will listen to any OS signal. If an OS signal closed this context, ErrSignal will be returned in the Err() method of the returned context.

This method creates the signal channel and invokes a goroutine.

### Example

func main() {
	// Create a context which will be cancelled on SIGINT.
	ctx := ctxutil.WithSignal(context.Background(), os.Interrupt)
	// use ctx...
}

func WithValues

func WithValues(ctx, values context.Context) context.Context

WithValues composes values from multiple contexts. It returns a context that exposes the deadline and cancel of `ctx`, and combined values from `ctx` and `values`. A value in `ctx` context overrides a value with the same key in `values` context.

Consider the following standard HTTP Go server stack:

1. Middlewares that extract user credentials and request id from the

headers and inject them to the `http.Request` context as values.

2. The `http.Handler` launches an asynchronous goroutine task which

needs those values from the context.

3. After launching the asynchronous task the handler returns 202 to

the client, the goroutine continues to run in background.

Problem Statement: * The async task can't use the request context - it is cancelled

as the `http.Handler` returns.

* There is no way to use the context values in the async task. * Specially if those values are used automatically with client

`http.Roundtripper` (extract the request id from the context
and inject it to http headers in a following request.)

The suggested function `ctx := ctxutil.WithValues(ctx, values)` does the following:

1. When `ctx.Value()` is called, the key is searched in the

original `ctx` and if not found it searches in `values`.

2. When `Done()`/`Deadline()`/`Err()` are called, it is uses

original `ctx`'s state.

### Example

This is how an `http.Handler` should run a goroutine that need values from the context.

func handle(w http.ResponseWriter, r *http.Request) {
	// [ do something ... ]

	// Create async task context that enables it run for 1 minute, for example
	asyncCtx, asyncCancel = ctxutil.WithTimeout(context.Background(), time.Minute)
	// Use values from the request context
	asyncCtx = ctxutil.WithValues(asyncCtx, r.Context())
	// Run the async task with it's context
	go func() {
		defer asyncCancel()
		asyncTask(asyncCtx)
	}()
}

Types

type ErrSignal

type ErrSignal struct {
	Signal os.Signal
}

ErrSignal is returned when a signal is received. The Signal field will contain the received signal.

func (ErrSignal) Error

func (e ErrSignal) Error() string

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