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Make InstanceQueryOptions public to allow for custom predicates #77

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Make InstanceQueryOptions public to allow for custom predicates #77

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824e92f
Make InstanceQueryOptions public to allow for custom predicates
tmarshall98 Nov 15, 2021
2814244
Make InstanceQueryOptions.Predicate and Intn public.
tmarshall98 Nov 15, 2021
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62 changes: 31 additions & 31 deletions net.go
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Original file line number Diff line number Diff line change
Expand Up @@ -129,26 +129,26 @@ func instanceCount(apps []*Application) int {
return count
}

type instanceQueryOptions struct {
// predicate guides filtering, indicating whether to retain an instance when it returns true or
type InstanceQueryOptions struct {
// Predicate guides filtering, indicating whether to retain an instance when it returns true or
// drop it when it returns false.
predicate func(*Instance) bool
// intn behaves like the rand.Rand.Intn function, aiding in randomizing the order of the result
Predicate func(*Instance) bool
// Intn behaves like the rand.Rand.Intn function, aiding in randomizing the order of the result
// sequence when non-nil.
intn func(int) int
Intn func(int) int
}

// InstanceQueryOption is a customization supplied to instance query functions like
// GetInstancesByVIPAddress to tailor the set of instances returned.
type InstanceQueryOption func(*instanceQueryOptions) error
type InstanceQueryOption func(*InstanceQueryOptions) error

func retainIfStatusIs(status StatusType, o *instanceQueryOptions) {
if prev := o.predicate; prev != nil {
o.predicate = func(instance *Instance) bool {
func retainIfStatusIs(status StatusType, o *InstanceQueryOptions) {
if prev := o.Predicate; prev != nil {
o.Predicate = func(instance *Instance) bool {
return prev(instance) || instance.Status == status
}
} else {
o.predicate = func(instance *Instance) bool {
o.Predicate = func(instance *Instance) bool {
return instance.Status == status
}
}
Expand All @@ -158,7 +158,7 @@ func retainIfStatusIs(status StatusType, o *instanceQueryOptions) {
//
// Supplying multiple options produced by this function applies their logical disjunction.
func WithStatus(status StatusType) InstanceQueryOption {
return func(o *instanceQueryOptions) error {
return func(o *InstanceQueryOptions) error {
if len(status) == 0 {
return errors.New("invalid instance status")
}
Expand All @@ -171,23 +171,23 @@ func WithStatus(status StatusType) InstanceQueryOption {
//
// Combining this function with the options produced by WithStatus applies their logical
// disjunction.
func ThatAreUp(o *instanceQueryOptions) error {
func ThatAreUp(o *InstanceQueryOptions) error {
retainIfStatusIs(UP, o)
return nil
}

// Shuffled requests randomizing the order of the sequence of instances returned, using the default
// shared rand.Source.
func Shuffled(o *instanceQueryOptions) error {
o.intn = rand.Intn
func Shuffled(o *InstanceQueryOptions) error {
o.Intn = rand.Intn
return nil
}

// ShuffledWith requests randomizing the order of the sequence of instances returned, using the
// supplied source of random numbers.
func ShuffledWith(r *rand.Rand) InstanceQueryOption {
return func(o *instanceQueryOptions) error {
o.intn = r.Intn
return func(o *InstanceQueryOptions) error {
o.Intn = r.Intn
return nil
}
}
Expand All @@ -208,14 +208,14 @@ func shuffleInstances(instances []*Instance, intn func(int) int) {
}

// filterInstances returns a filtered subset of the supplied sequence of instances, retaining only those
// instances for which the supplied predicate function returns true. It returns the retained instances in
// instances for which the supplied Predicate function returns true. It returns the retained instances in
// the same order the occurred in the input sequence. Note that the returned slice may share storage with
// the input sequence.
//
// The filtering algorithm is arguably baroque, in the interest of efficiency: namely, eliminating
// allocation and copying when we can avoid it. We only need to allocate and copy elements of the
// input sequence when the result sequence contains at least two nonadjacent subsequences of the
// input sequence. That is, if the predicate is, say, retaining only instances with status "UP", we
// input sequence. That is, if the Predicate is, say, retaining only instances with status "UP", we
// can avoid copying elements and instead return a subsequence of the input sequence in the
// following cases (where "U" indicates an instance with status "UP", "d" with status "DOWN"):
//
Expand Down Expand Up @@ -265,7 +265,7 @@ func shuffleInstances(instances []*Instance, intn func(int) int) {
// Continue collecting any remaining retained elements into the array.
// Return the populated subsequence of the array.
//
// The algorithm evaluates the predicate exactly once for each element of the input sequence.
// The algorithm evaluates the Predicate exactly once for each element of the input sequence.
func filterInstances(instances []*Instance, pred func(*Instance) bool) []*Instance {
for firstBegin, instance := range instances {
if !pred(instance) {
Expand Down Expand Up @@ -315,7 +315,7 @@ func filterInstancesInApps(apps []*Application, pred func(*Instance) bool) []*In
}
}

func (e *EurekaConnection) getInstancesByVIPAddress(addr string, secure bool, opts instanceQueryOptions) ([]*Instance, error) {
func (e *EurekaConnection) getInstancesByVIPAddress(addr string, secure bool, opts InstanceQueryOptions) ([]*Instance, error) {
var slug string
if secure {
slug = EurekaURLSlugs["InstancesBySecureVIPAddress"]
Expand Down Expand Up @@ -344,7 +344,7 @@ func (e *EurekaConnection) getInstancesByVIPAddress(addr string, secure bool, op
return nil, err
}
var instances []*Instance
if pred := opts.predicate; pred != nil {
if pred := opts.Predicate; pred != nil {
instances = filterInstancesInApps(r.Applications, pred)
} else {
switch len(r.Applications) {
Expand All @@ -359,25 +359,25 @@ func (e *EurekaConnection) getInstancesByVIPAddress(addr string, secure bool, op
}
}
}
if intn := opts.intn; intn != nil {
if intn := opts.Intn; intn != nil {
shuffleInstances(instances, intn)
}
return instances, nil
}

func mergeInstanceQueryOptions(defaults instanceQueryOptions, opts []InstanceQueryOption) (instanceQueryOptions, error) {
func mergeInstanceQueryOptions(defaults InstanceQueryOptions, opts []InstanceQueryOption) (InstanceQueryOptions, error) {
for _, o := range opts {
if o != nil {
if err := o(&defaults); err != nil {
return instanceQueryOptions{}, err
return InstanceQueryOptions{}, err
}
}
}
return defaults, nil
}

func collectInstanceQueryOptions(opts []InstanceQueryOption) (instanceQueryOptions, error) {
return mergeInstanceQueryOptions(instanceQueryOptions{}, opts)
func collectInstanceQueryOptions(opts []InstanceQueryOption) (InstanceQueryOptions, error) {
return mergeInstanceQueryOptions(InstanceQueryOptions{}, opts)
}

// GetInstancesByVIPAddress returns the set of instances registered with the given VIP address,
Expand Down Expand Up @@ -435,7 +435,7 @@ func scheduleInstanceUpdates(d time.Duration, produce func() ([]*Instance, error
return c
}

func (e *EurekaConnection) scheduleVIPAddressUpdates(addr string, secure bool, await bool, done <-chan struct{}, opts instanceQueryOptions) <-chan InstanceSetUpdate {
func (e *EurekaConnection) scheduleVIPAddressUpdates(addr string, secure bool, await bool, done <-chan struct{}, opts InstanceQueryOptions) <-chan InstanceSetUpdate {
produce := func() ([]*Instance, error) {
return e.getInstancesByVIPAddress(addr, secure, opts)
}
Expand Down Expand Up @@ -467,8 +467,8 @@ func (e *EurekaConnection) makeInstanceProducerForApp(name string, opts []Instan
if err != nil {
return nil, err
}
predicate := options.predicate
intn := options.intn
predicate := options.Predicate
intn := options.Intn
return func() ([]*Instance, error) {
app, err := e.GetApp(name)
if err != nil {
Expand Down Expand Up @@ -520,7 +520,7 @@ func (e *EurekaConnection) newInstanceSetSourceFor(produce func() ([]*Instance,
}
// NB: If an application contained no instances, such that it either lacked the "instance" field
// entirely or had it present but with a "null" value, or none of the present instances
// satisfied the filtering predicate, then it's possible that the slice returned by
// satisfied the filtering Predicate, then it's possible that the slice returned by
// getInstancesByVIPAddress (or similar) will be nil. Make it possible to discern when we've
// received at least one update in Latest by never storing a nil value for a successful update.
if await {
Expand Down Expand Up @@ -549,7 +549,7 @@ func (e *EurekaConnection) newInstanceSetSourceFor(produce func() ([]*Instance,
return s
}

func (e *EurekaConnection) newInstanceSetSourceForVIPAddress(addr string, secure bool, await bool, opts instanceQueryOptions) *InstanceSetSource {
func (e *EurekaConnection) newInstanceSetSourceForVIPAddress(addr string, secure bool, await bool, opts InstanceQueryOptions) *InstanceSetSource {
produce := func() ([]*Instance, error) {
return e.getInstancesByVIPAddress(addr, secure, opts)
}
Expand Down
35 changes: 18 additions & 17 deletions net_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -10,16 +10,16 @@ import (
)

func instancePredicateFrom(t *testing.T, opts ...InstanceQueryOption) func(*Instance) bool {
var mergedOptions instanceQueryOptions
var mergedOptions InstanceQueryOptions
for _, o := range opts {
if err := o(&mergedOptions); err != nil {
t.Fatal(err)
}
}
if pred := mergedOptions.predicate; pred != nil {
if pred := mergedOptions.Predicate; pred != nil {
return pred
}
t.Fatal("no predicate available")
t.Fatal("no Predicate available")
panic("unreachable")
}

Expand All @@ -42,22 +42,22 @@ func (s *countingSource) Reset() {
}

func TestInstanceQueryOptions(t *testing.T) {
Convey("A status predicate", t, func() {
Convey("A status Predicate", t, func() {
Convey("mandates a nonempty status", func() {
var opts instanceQueryOptions
var opts InstanceQueryOptions
err := WithStatus("")(&opts)
So(err, ShouldNotBeNil)
So(opts.predicate, ShouldBeNil)
So(opts.Predicate, ShouldBeNil)
})
matchesStatus := func(pred func(*Instance) bool, status StatusType) bool {
return pred(&Instance{Status: status})
}
Convey("matches a single status", func() {
var opts instanceQueryOptions
var opts InstanceQueryOptions
desiredStatus := UNKNOWN
err := WithStatus(desiredStatus)(&opts)
So(err, ShouldBeNil)
pred := opts.predicate
pred := opts.Predicate
So(pred, ShouldNotBeNil)
So(matchesStatus(pred, desiredStatus), ShouldBeTrue)
for _, status := range []StatusType{UP, DOWN, STARTING, OUTOFSERVICE} {
Expand All @@ -66,13 +66,13 @@ func TestInstanceQueryOptions(t *testing.T) {
}
})
Convey("matches a set of states", func() {
var opts instanceQueryOptions
var opts InstanceQueryOptions
desiredStates := []StatusType{DOWN, OUTOFSERVICE}
for _, status := range desiredStates {
err := WithStatus(status)(&opts)
So(err, ShouldBeNil)
}
pred := opts.predicate
pred := opts.Predicate
So(pred, ShouldNotBeNil)
for _, status := range desiredStates {
So(matchesStatus(pred, status), ShouldBeTrue)
Expand All @@ -85,27 +85,27 @@ func TestInstanceQueryOptions(t *testing.T) {
})
Convey("A shuffling directive", t, func() {
Convey("using the global Rand instance", func() {
var opts instanceQueryOptions
var opts InstanceQueryOptions
err := Shuffled(&opts)
So(err, ShouldBeNil)
So(opts.intn, ShouldNotBeNil)
So(opts.intn(1), ShouldEqual, 0)
So(opts.Intn, ShouldNotBeNil)
So(opts.Intn(1), ShouldEqual, 0)
})
Convey("using a specific Rand instance", func() {
source := countingSource{}
var opts instanceQueryOptions
var opts InstanceQueryOptions
err := ShuffledWith(rand.New(&source))(&opts)
So(err, ShouldBeNil)
So(opts.intn, ShouldNotBeNil)
So(opts.Intn, ShouldNotBeNil)
So(source.callCount, ShouldEqual, 0)
So(opts.intn(2), ShouldEqual, 0)
So(opts.Intn(2), ShouldEqual, 0)
So(source.callCount, ShouldEqual, 1)
})
})
}

func TestFilterInstancesInApps(t *testing.T) {
Convey("A predicate should preserve only those instances", t, func() {
Convey("A Predicate should preserve only those instances", t, func() {
Convey("with status UP", func() {
areUp := instancePredicateFrom(t, ThatAreUp)
Convey("from an empty set of applications", func() {
Expand Down Expand Up @@ -213,6 +213,7 @@ func TestFilterInstancesInApps(t *testing.T) {
})
})
}

// Preclude compiler optimization eliding the filter procedure.
var filterBenchmarkResult []*Instance

Expand Down