fault package - github.com/lingrino/go-fault - Go Packages (original) (raw)

Package fault provides standard http middleware for fault injection in go.

Basics

Use the fault package to inject faults into the http request path of your service. Faults work by modifying and/or delaying your service's http responses. Place the Fault middleware high enough in the chain that it can act quickly, but after any other middlewares that should complete before fault injection (auth, redirects, etc...).

The type and severity of injected faults is controlled by options passed to NewFault(Injector, Options). NewFault must be passed an Injector, which is an interface that holds the actual fault injection code in Injector.Handler. The Fault wraps Injector.Handler in another Fault.Handler that applies generic Fault logic (such as what % of requests to run the Injector on) to the Injector.

Make sure you use the NewFault() and NewTypeInjector() constructors to create valid Faults and Injectors.

Injectors

There are three main Injectors provided by the fault package:

fault.RejectInjector fault.ErrorInjector fault.SlowInjector

RejectInjector

Use fault.RejectInjector to immediately return an empty response. For example, a curl for a rejected response will produce:

$ curl https://github.com curl: (52) Empty reply from server

ErrorInjector

Use fault.ErrorInjector to immediately return a valid http status code of your choosing along with the standard HTTP response body for that code. For example, you can return a 200, 301, 418, 500, or any other valid status code to test how your clients respond to different statuses. Pass the WithStatusText() option to customize the response text.

SlowInjector

Use fault.SlowInjector to wait a configured time.Duration before proceeding with the request. For example, you can use the SlowInjector to add a 10ms delay to your requests.

RandomInjector

Use fault.RandomInjector to randomly choose one of the above faults to inject. Pass a list of Injector to fault.NewRandomInjector and when RandomInjector is evaluated it will randomly run one of the injectors that you passed.

Combining Faults

It is easy to combine any of the Injectors into a chained action. There are two ways you might want to combine Injectors.

First, you can create separate Faults for each Injector that are sequential but independent of each other. For example, you can chain Faults such that 1% of requests will return a 500 error and another 1% of requests will be rejected.

Second, you might want to combine Faults such that 1% of requests will be slowed for 10ms and then rejected. You want these Faults to depend on each other. For this use the special ChainInjector, which consolidates any number of Injectors into a single Injector that runs each of the provided Injectors sequentially. When you add the ChainInjector to a Fault the entire chain will always execute together.

Allowing And Blocking Paths

The NewFault() constructor has WithPathBlocklist() and WithPathAllowlist() options. Any path you include in the PathBlocklist will never have faults run against it. With PathAllowlist, if you provide a non-empty list then faults will not be run against any paths except those specified in PathAllowlist. The PathBlocklist take priority over the PathAllowlist, a path in both lists will never have a fault run against it. The paths that you include must match exactly the path in req.URL.Path, including leading and trailing slashes.

Simmilarly, you may also use WithHeaderBlocklist() and WithHeaderAllowlist() to block or allow faults based on a map of header keys to values. These lists behave in the same way as the path allowlists and blocklists except that they operate on headers. Header equality is determined using http.Header.Get(key) which automatically canonicalizes your keys and does not support multi-value headers. Keep these limitations in mind when working with header allowlists and blocklists.

Specifying very large lists of paths or headers may cause memory or performance issues. If you're running into these problems you should instead consider using your http router to enable the middleware on only a subset of your routes.

Custom Injectors

The fault package provides an Injector interface and you can satisfy that interface to provide your own Injector. Use custom injectors to add additional logic to the package-provided injectors or to create your own completely new Injector that can still be managed by a Fault.

Reporter

The package provides a Reporter interface that can be added to Faults and Injectors using the WithReporter option. A Reporter will receive events when the state of the Injector changes. For example, Reporter.Report(InjectorName, StateStarted) is run at the beginning of all Injectors. The Reporter is meant to be provided by the consumer of the package and integrate with services like stats and logging. The default Reporter throws away all events.

Random Seeds

By default all randomness is seeded with defaultRandSeed(1), the same default as math/rand. This helps you reproduce any errors you see when running an Injector. If you prefer, you can also customize the seed passing WithRandSeed() to NewFault and NewRandomInjector.

Custom Injector Functions

Some Injectors support customizing the functions they use to run their injections. You can take advantage of these options to add your own logic to an existing Injector instead of creating your own. For example, modify the SlowInjector function to slow in a rancom distribution instead of for a fixed duration. Be careful when you use these options that your return values fall within the same range of values expected by the default functions to avoid panics or other undesirable begavior.

Customize the function a Fault uses to determine participation (default: rand.Float32) by passing WithRandFloat32Func() to NewFault().

Customize the function a RandomInjector uses to choose which injector to run (default: rand.Intn) by passing WithRandIntFunc() to NewRandomInjector().

Customize the function a SlowInjector uses to wait (default: time.Sleep) by passing WithSlowFunc() to NewSlowInjector().

Configuration

Configuration for the fault package is done through options passed to NewFault and NewInjector. Once a Fault is created its enabled state and participation percentage can be updated with SetEnabled() and SetParticipation(). There is no other way to manage configuration for the package. It is up to the user of the fault package to manage how the options are generated. Common options are feature flags, environment variables, or code changes in deploys.

Example is a package-level documentation example.

// Wait one millisecond then continue si, _ := fault.NewSlowInjector(time.Millisecond)

// Return a 500 ei, _ := fault.NewErrorInjector(http.StatusInternalServerError)

// Chain slow and error injectors together ci, _ := fault.NewChainInjector([]fault.Injector{si, ei})

// Run our fault injection 100% of the time f, _ := fault.NewFault(ci, fault.WithEnabled(true), fault.WithParticipation(1.0), fault.WithPathBlocklist([]string{"/ping", "/health"}), )

// mainHandler responds 200/OK var mainHandler = http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) { http.Error(w, "OK", http.StatusOK) })

// Insert our middleware before the mainHandler handlerChain := f.Handler((mainHandler))

// Create dummy request and response records req, _ := http.NewRequestWithContext(context.Background(), "GET", "/", nil) rr := httptest.NewRecorder()

// Run our request handlerChain.ServeHTTP(rr, req)

// Verify the correct response fmt.Println(rr.Code) fmt.Println(rr.Body.String())

Output:

500 Internal Server Error

This section is empty.

This section is empty.

type ChainInjector struct {

}

ChainInjector combines many Injectors into a single Injector that runs them in order.

func NewChainInjector(is []Injector, opts ...ChainInjectorOption) (*ChainInjector, error)

NewChainInjector combines many Injectors into a single Injector that runs them in order.

ExampleNewChainInjector shows how to create a new ChainInjector.

si, err := fault.NewSlowInjector(time.Minute) fmt.Print(err) ri, err := fault.NewRejectInjector() fmt.Print(err)

_, err = fault.NewChainInjector([]fault.Injector{si, ri})

fmt.Print(err)

Output:

func (*ChainInjector) Handler

Handler executes ChainInjector.middlewares in order and then returns.

type ChainInjectorOption interface {

}

ChainInjectorOption configures a ChainInjector.

type ErrorInjector struct {

}

ErrorInjector responds with an http status code and message.

NewErrorInjector returns an ErrorInjector that reponds with a status code.

ExampleNewErrorInjector shows how to create a new ErrorInjector.

_, err := fault.NewErrorInjector(http.StatusInternalServerError)

fmt.Print(err)

Output:

func (*ErrorInjector) Handler

Handler responds with the configured status code and text.

type ErrorInjectorOption interface {

}

ErrorInjectorOption configures an ErrorInjector.

WithStatusText sets custom status text to write.

Fault combines an Injector with options on when to use that Injector.

func NewFault(i Injector, opts ...Option) (*Fault, error)

NewFault sets/validates the Injector and Options and returns a usable Fault.

ExampleNewFault shows how to create a new Fault.

ei, err := fault.NewErrorInjector(http.StatusInternalServerError) fmt.Print(err)

_, err = fault.NewFault(ei, fault.WithEnabled(true), fault.WithParticipation(0.25), )

fmt.Print(err)

Output:

ExampleNewFault_allowlist shows how to create a new Fault with a path/header allowlist.

ei, err := fault.NewErrorInjector(http.StatusInternalServerError) fmt.Print(err)

_, err = fault.NewFault(ei, fault.WithEnabled(true), fault.WithParticipation(0.25), fault.WithPathAllowlist([]string{"/injecthere", "/andhere"}), fault.WithHeaderAllowlist(map[string]string{"allow": "this header"}), )

fmt.Print(err)

Output:

ExampleNewFault_blocklist shows how to create a new Fault with a path/header blocklist.

ei, err := fault.NewErrorInjector(http.StatusInternalServerError) fmt.Print(err)

_, err = fault.NewFault(ei, fault.WithEnabled(true), fault.WithParticipation(0.25), fault.WithPathBlocklist([]string{"/ping", "/health"}), fault.WithHeaderBlocklist(map[string]string{"block": "this header"}), )

fmt.Print(err)

Output:

func (*Fault) Handler

Handler determines if the Injector should execute and runs it if so.

func (f *Fault) SetEnabled(o enabledOption) error

SetEnabled updates the enabled state of the Fault.

func (f *Fault) SetParticipation(o participationOption) error

SetParticipation updates the participation percentage of the Fault.

Injector are added to Faults and run as middleware in a request.

InjectorState represents the states an injector can be in.

const (

StateStarted [InjectorState](#InjectorState) = [iota](/builtin#iota) + 1

StateFinished

StateSkipped

)

type NoopReporter struct{}

NoopReporter is a reporter that does nothing.

func NewNoopReporter() *NoopReporter

NewNoopReporter returns a new NoopReporter.

type Option interface {

}

Option configures a Fault.

func WithEnabled(e bool) Option

WithEnabled sets if the Fault should evaluate.

WithHeaderAllowlist is, if set, a map of header keys to values of the only headers that the Injector will run against.

WithHeaderBlocklist is a map of header keys to values that the Injector will not run against.

WithParticipation sets the percent of requests that run the Injector. 0.0 <= p <= 1.0.

func WithPathAllowlist(allowlist []string) Option

WithPathAllowlist is, if set, a list of the only paths that the Injector will run against.

func WithPathBlocklist(blocklist []string) Option

WithPathBlocklist is a list of paths that the Injector will not run against.

func WithRandFloat32Func

func WithRandFloat32Func(f func() float32) Option

WithRandFloat32Func sets the function that will be used to randomly get our float value. Default rand.Float32. Always returns a float32 between [0.0,1.0) to avoid errors.

type RandSeedOption

type RandSeedOption interface { Option RandomInjectorOption }

RandSeedOption configures things that can set a random seed.

func WithRandSeed

WithRandSeed sets the rand.Rand seed for this struct.

type RandomInjector

type RandomInjector struct {

}

RandomInjector combines many Injectors into a single Injector that runs one randomly.

func NewRandomInjector

func NewRandomInjector(is []Injector, opts ...RandomInjectorOption) (*RandomInjector, error)

NewRandomInjector combines many Injectors into a single Injector that runs one randomly.

ExampleNewChainInjector shows how to create a new RandomInjector.

si, err := fault.NewSlowInjector(time.Minute) fmt.Print(err) ri, err := fault.NewRejectInjector() fmt.Print(err)

_, err = fault.NewRandomInjector([]fault.Injector{si, ri})

fmt.Print(err)

Output:

func (*RandomInjector) Handler

Handler executes a random Injector from RandomInjector.middlewares.

type RandomInjectorOption

type RandomInjectorOption interface {

}

RandomInjectorOption configures a RandomInjector.

func WithRandIntFunc

WithRandIntFunc sets the function that will be used to randomly get an int. Default rand.Intn. Always returns an integer between [0,n) to avoid panics.

type RejectInjector struct {

}

RejectInjector sends back an empty response.

func NewRejectInjector(opts ...RejectInjectorOption) (*RejectInjector, error)

NewRejectInjector returns a RejectInjector.

ExampleNewRejectInjector shows how to create a new RejectInjector.

_, err := fault.NewRejectInjector()

fmt.Print(err)

Output:

func (*RejectInjector) Handler

Handler rejects the request, returning an empty response.

type RejectInjectorOption interface {

}

RejectInjectorOption configures a RejectInjector.

type Reporter interface { Report(name string, state InjectorState) }

Reporter receives events from faults to use for logging, stats, and other custom reporting.

type ReporterOption interface { RejectInjectorOption ErrorInjectorOption SlowInjectorOption }

ReporterOption configures structs that accept a Reporter.

func WithReporter(r Reporter) ReporterOption

WithReporter sets the Reporter.

type SlowInjector struct {

}

SlowInjector waits and then continues the request.

NewSlowInjector returns a SlowInjector.

ExampleNewSlowInjector shows how to create a new SlowInjector.

_, err := fault.NewSlowInjector(time.Second * 10)

fmt.Print(err)

Output:

func (*SlowInjector) Handler

Handler runs i.slowF to wait the set duration and then continues.

type SlowInjectorOption interface {

}

SlowInjectorOption configures a SlowInjector.

WithSlowFunc sets the function that will be used to wait the time.Duration.