Recover #

// Go makes it possible to _recover_ from a panic, by
// using the `recover` built-in function. A `recover` can
// stop a `panic` from aborting the program and let it
// continue with execution instead.

// An example of where this can be useful: a server
// wouldn't want to crash if one of the client connections
// exhibits a critical error. Instead, the server would
// want to close that connection and continue serving
// other clients. In fact, this is what Go's `net/http`
// does by default for HTTP servers.

package main

import "fmt"

// This function panics.
func mayPanic() {
	panic("a problem")
}

func main() {
	// `recover` must be called within a deferred function.
	// When the enclosing function panics, the defer will
	// activate and a `recover` call within it will catch
	// the panic.
	defer func() {
		if r := recover(); r != nil {
			// The return value of `recover` is the error raised in
			// the call to `panic`.
			fmt.Println("Recovered. Error:\n", r)
		}
	}()

	mayPanic()

	// This code will not run, because `mayPanic` panics.
	// The execution of `main` stops at the point of the
	// panic and resumes in the deferred closure.
	fmt.Println("After mayPanic()")
}

$ go run recover.go
Recovered. Error:
 a problem