go-fault: github.com/github/go-fault Index | Examples | Files

package fault

import "github.com/github/go-fault"

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

All configuration for the fault package is done through options passed to NewFault and NewInjector. 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.

Code:

// 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.NewRequest("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

Index

Examples

Package Files

doc.go fault.go injector.go injector_chain.go injector_error.go injector_random.go injector_reject.go injector_slow.go reporter.go

Variables

var (
    // ErrNilInjector when a nil Injector is passed.
    ErrNilInjector = errors.New("injector cannot be nil")
    // ErrInvalidPercent when a percent is outside of [0.0,1.0).
    ErrInvalidPercent = errors.New("percent must be 0.0 <= percent <= 1.0")
)
var (
    // ErrInvalidHTTPCode when an invalid status code is provided.
    ErrInvalidHTTPCode = errors.New("not a valid http status code")
)

type ChainInjector Uses

type ChainInjector struct {
    // contains filtered or unexported fields
}

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

func NewChainInjector Uses

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.

Code:

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:

<nil><nil><nil>

func (*ChainInjector) Handler Uses

func (i *ChainInjector) Handler(next http.Handler) http.Handler

Handler executes ChainInjector.middlewares in order and then returns.

type ChainInjectorOption Uses

type ChainInjectorOption interface {
    // contains filtered or unexported methods
}

ChainInjectorOption configures a ChainInjector.

type ErrorInjector Uses

type ErrorInjector struct {
    // contains filtered or unexported fields
}

ErrorInjector responds with an http status code and message.

func NewErrorInjector Uses

func NewErrorInjector(code int, opts ...ErrorInjectorOption) (*ErrorInjector, error)

NewErrorInjector returns an ErrorInjector that reponds with a status code.

ExampleNewErrorInjector shows how to create a new ErrorInjector.

Code:

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

fmt.Print(err)

Output:

<nil>

func (*ErrorInjector) Handler Uses

func (i *ErrorInjector) Handler(next http.Handler) http.Handler

Handler responds with the configured status code and text.

type ErrorInjectorOption Uses

type ErrorInjectorOption interface {
    // contains filtered or unexported methods
}

ErrorInjectorOption configures an ErrorInjector.

func WithStatusText Uses

func WithStatusText(t string) ErrorInjectorOption

WithStatusText sets custom status text to write.

type Fault Uses

type Fault struct {
    // contains filtered or unexported fields
}

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

func NewFault Uses

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.

Code:

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

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

fmt.Print(err)

Output:

<nil><nil>

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

Code:

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:

<nil><nil>

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

Code:

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:

<nil><nil>

func (*Fault) Handler Uses

func (f *Fault) Handler(next http.Handler) http.Handler

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

type Injector Uses

type Injector interface {
    Handler(next http.Handler) http.Handler
}

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

type InjectorState Uses

type InjectorState int

InjectorState represents the states an injector can be in.

const (
    // StateStarted when an Injector has started.
    StateStarted InjectorState = iota + 1
    // StateFinished when an Injector has finished.
    StateFinished
    // StateSkipped when an Injector is skipped.
    StateSkipped
)

type NoopReporter Uses

type NoopReporter struct{}

NoopReporter is a reporter that does nothing.

func NewNoopReporter Uses

func NewNoopReporter() *NoopReporter

NewNoopReporter returns a new NoopReporter.

func (*NoopReporter) Report Uses

func (r *NoopReporter) Report(name string, state InjectorState)

Report does nothing.

type Option Uses

type Option interface {
    // contains filtered or unexported methods
}

Option configures a Fault.

func WithEnabled Uses

func WithEnabled(e bool) Option

WithEnabled sets if the Fault should evaluate.

func WithHeaderAllowlist Uses

func WithHeaderAllowlist(allowlist map[string]string) Option

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

func WithHeaderBlocklist Uses

func WithHeaderBlocklist(blocklist map[string]string) Option

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

func WithParticipation Uses

func WithParticipation(p float32) Option

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

func WithPathAllowlist Uses

func WithPathAllowlist(allowlist []string) Option

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

func WithPathBlocklist Uses

func WithPathBlocklist(blocklist []string) Option

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

func WithRandFloat32Func Uses

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 Uses

type RandSeedOption interface {
    Option
    RandomInjectorOption
}

RandSeedOption configures things that can set a random seed.

func WithRandSeed Uses

func WithRandSeed(s int64) RandSeedOption

WithRandSeed sets the rand.Rand seed for this struct.

type RandomInjector Uses

type RandomInjector struct {
    // contains filtered or unexported fields
}

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

func NewRandomInjector Uses

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.

Code:

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:

<nil><nil><nil>

func (*RandomInjector) Handler Uses

func (i *RandomInjector) Handler(next http.Handler) http.Handler

Handler executes a random Injector from RandomInjector.middlewares.

type RandomInjectorOption Uses

type RandomInjectorOption interface {
    // contains filtered or unexported methods
}

RandomInjectorOption configures a RandomInjector.

func WithRandIntFunc Uses

func WithRandIntFunc(f func(int) int) RandomInjectorOption

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 Uses

type RejectInjector struct {
    // contains filtered or unexported fields
}

RejectInjector sends back an empty response.

func NewRejectInjector Uses

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

NewRejectInjector returns a RejectInjector.

ExampleNewRejectInjector shows how to create a new RejectInjector.

Code:

_, err := fault.NewRejectInjector()

fmt.Print(err)

Output:

<nil>

func (*RejectInjector) Handler Uses

func (i *RejectInjector) Handler(next http.Handler) http.Handler

Handler rejects the request, returning an empty response.

type RejectInjectorOption Uses

type RejectInjectorOption interface {
    // contains filtered or unexported methods
}

RejectInjectorOption configures a RejectInjector.

type Reporter Uses

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

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

type ReporterOption Uses

type ReporterOption interface {
    RejectInjectorOption
    ErrorInjectorOption
    SlowInjectorOption
}

ReporterOption configures structs that accept a Reporter.

func WithReporter Uses

func WithReporter(r Reporter) ReporterOption

WithReporter sets the Reporter.

type SlowInjector Uses

type SlowInjector struct {
    // contains filtered or unexported fields
}

SlowInjector waits and then continues the request.

func NewSlowInjector Uses

func NewSlowInjector(d time.Duration, opts ...SlowInjectorOption) (*SlowInjector, error)

NewSlowInjector returns a SlowInjector.

ExampleNewSlowInjector shows how to create a new SlowInjector.

Code:

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

fmt.Print(err)

Output:

<nil>

func (*SlowInjector) Handler Uses

func (i *SlowInjector) Handler(next http.Handler) http.Handler

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

type SlowInjectorOption Uses

type SlowInjectorOption interface {
    // contains filtered or unexported methods
}

SlowInjectorOption configures a SlowInjector.

func WithSlowFunc Uses

func WithSlowFunc(f func(t time.Duration)) SlowInjectorOption

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

Package fault imports 6 packages (graph). Updated 2020-07-04. Refresh now. Tools for package owners.