An implementation of failpoints for golang. Please read design.md for a deeper understanding.

Failpoints are special comments that include a failpoint variable declaration and some trigger code,

func someFunc() string {
	// gofail: var SomeFuncString string
	// // this is called when the failpoint is triggered
	// return SomeFuncString
	return "default"
}

Building with failpoints will translate gofail comments in place to code that accesses the gofail runtime.

Call gofail in the directory with failpoints to generate gofail runtime bindings, then build as usual,

gofail enable
go build cmd/

The translated code looks something like,

func someFunc() string {
        if vSomeFuncString, __fpErr := __fp_SomeFuncString.Acquire(); __fpErr == nil { SomeFuncString, __fpTypeOK := vSomeFuncString.(string); if !__fpTypeOK { goto __badTypeSomeFuncString}
		// this is called when the failpoint is triggered
		return SomeFuncString; __badTypeSomeFuncString: __fp_SomeFuncString.BadType(vSomeFuncString, "string"); };
        return "default"
}

To disable failpoints and revert to the original code,

gofail disable

After building with failpoints enabled, the program's failpoints can be activated so they may trigger when evaluated.

From the command line, trigger the failpoint to set SomeFuncString to hello,

GOFAIL_FAILPOINTS='my/package/path/SomeFuncString=return("hello")' ./cmd

Multiple failpoints are set by using ';' for a delimiter,

GOFAIL_FAILPOINTS='failpoint1=return("hello");failpoint2=sleep(10)' ./cmd

First, enable the HTTP server from the command line,

GOFAIL_HTTP="127.0.0.1:1234" ./cmd

Activate a failpoint with curl,

$ curl http://127.0.0.1:1234/my/package/path/SomeFuncString -XPUT -d'return("hello")'

List the failpoints,

$ curl http://127.0.0.1:1234/
my/package/path/SomeFuncString=return("hello")

Deactivate a failpoint,

$ curl http://127.0.0.1:1234/my/package/path/SomeFuncString -XDELETE

From a unit test,

import (
	"testing"

	gofail "go.etcd.io/gofail/runtime"
)

func TestWhatever(t *testing.T) {
	gofail.Enable("my/package/path/SomeFuncString", `return("hello")`)
	defer gofail.Disable("my/package/path/SomeFuncString")
	...
}