httpx/circuitbreaker/breaker_test.go

package circuitbreaker

import (
	"errors"
	"io"
	"net/http"
	"strings"
	"testing"
	"time"

	"git.codelab.vc/pkg/httpx/internal/clock"
	"git.codelab.vc/pkg/httpx/middleware"
)

func mockTransport(fn func(*http.Request) (*http.Response, error)) http.RoundTripper {
	return middleware.RoundTripperFunc(fn)
}

func okResponse() *http.Response {
	return &http.Response{
		StatusCode: http.StatusOK,
		Body:       io.NopCloser(strings.NewReader("")),
		Header:     make(http.Header),
	}
}

func errResponse(code int) *http.Response {
	return &http.Response{
		StatusCode: code,
		Body:       io.NopCloser(strings.NewReader("")),
		Header:     make(http.Header),
	}
}

func TestBreaker_StartsInClosedState(t *testing.T) {
	b := NewBreaker()
	if s := b.State(); s != StateClosed {
		t.Fatalf("state = %v, want %v", s, StateClosed)
	}
}

func TestBreaker_TransitionsToOpenAfterThreshold(t *testing.T) {
	const threshold = 3
	b := NewBreaker(
		WithFailureThreshold(threshold),
		WithOpenDuration(time.Hour), // long duration so it stays open
	)

	for i := 0; i < threshold; i++ {
		done, err := b.Allow()
		if err != nil {
			t.Fatalf("iteration %d: Allow returned error: %v", i, err)
		}
		done(false)
	}

	if s := b.State(); s != StateOpen {
		t.Fatalf("state = %v, want %v", s, StateOpen)
	}
}

func TestBreaker_OpenRejectsRequests(t *testing.T) {
	b := NewBreaker(
		WithFailureThreshold(1),
		WithOpenDuration(time.Hour),
	)

	// Trip the breaker.
	done, err := b.Allow()
	if err != nil {
		t.Fatalf("Allow returned error: %v", err)
	}
	done(false)

	// Subsequent requests should be rejected.
	_, err = b.Allow()
	if !errors.Is(err, ErrCircuitOpen) {
		t.Fatalf("err = %v, want %v", err, ErrCircuitOpen)
	}
}

func TestBreaker_TransitionsToHalfOpenAfterDuration(t *testing.T) {
	const openDuration = 50 * time.Millisecond
	clk := clock.Mock(time.Now())
	b := NewBreaker(
		WithFailureThreshold(1),
		WithOpenDuration(openDuration),
		withClock(clk),
	)

	// Trip the breaker.
	done, err := b.Allow()
	if err != nil {
		t.Fatal(err)
	}
	done(false)

	if s := b.State(); s != StateOpen {
		t.Fatalf("state = %v, want %v", s, StateOpen)
	}

	// Advance past the open duration.
	clk.Advance(openDuration + time.Millisecond)

	if s := b.State(); s != StateHalfOpen {
		t.Fatalf("state = %v, want %v", s, StateHalfOpen)
	}
}

func TestBreaker_HalfOpenToClosedOnSuccess(t *testing.T) {
	const openDuration = 50 * time.Millisecond
	clk := clock.Mock(time.Now())
	b := NewBreaker(
		WithFailureThreshold(1),
		WithOpenDuration(openDuration),
		withClock(clk),
	)

	// Trip the breaker.
	done, err := b.Allow()
	if err != nil {
		t.Fatal(err)
	}
	done(false)

	// Advance into half-open.
	clk.Advance(openDuration + time.Millisecond)

	// A successful request in half-open should close the breaker.
	done, err = b.Allow()
	if err != nil {
		t.Fatalf("Allow in half-open returned error: %v", err)
	}
	done(true)

	if s := b.State(); s != StateClosed {
		t.Fatalf("state = %v, want %v", s, StateClosed)
	}
}

func TestBreaker_HalfOpenToOpenOnFailure(t *testing.T) {
	const openDuration = 50 * time.Millisecond
	clk := clock.Mock(time.Now())
	b := NewBreaker(
		WithFailureThreshold(1),
		WithOpenDuration(openDuration),
		withClock(clk),
	)

	// Trip the breaker.
	done, err := b.Allow()
	if err != nil {
		t.Fatal(err)
	}
	done(false)

	// Advance into half-open.
	clk.Advance(openDuration + time.Millisecond)

	// A failed request in half-open should re-open the breaker.
	done, err = b.Allow()
	if err != nil {
		t.Fatalf("Allow in half-open returned error: %v", err)
	}
	done(false)

	if s := b.State(); s != StateOpen {
		t.Fatalf("state = %v, want %v", s, StateOpen)
	}
}

func TestTransport_PerHostBreakers(t *testing.T) {
	const threshold = 2

	base := mockTransport(func(req *http.Request) (*http.Response, error) {
		if req.URL.Host == "failing.example.com" {
			return errResponse(http.StatusInternalServerError), nil
		}
		return okResponse(), nil
	})

	rt := Transport(
		WithFailureThreshold(threshold),
		WithOpenDuration(time.Hour),
	)(base)

	t.Run("failing host trips breaker", func(t *testing.T) {
		for i := 0; i < threshold; i++ {
			req, err := http.NewRequest(http.MethodGet, "https://failing.example.com/test", nil)
			if err != nil {
				t.Fatal(err)
			}
			resp, err := rt.RoundTrip(req)
			if err != nil {
				t.Fatalf("iteration %d: unexpected error: %v", i, err)
			}
			resp.Body.Close()
		}

		// Next request to failing host should be rejected.
		req, err := http.NewRequest(http.MethodGet, "https://failing.example.com/test", nil)
		if err != nil {
			t.Fatal(err)
		}
		_, err = rt.RoundTrip(req)
		if !errors.Is(err, ErrCircuitOpen) {
			t.Fatalf("err = %v, want %v", err, ErrCircuitOpen)
		}
	})

	t.Run("healthy host is unaffected", func(t *testing.T) {
		req, err := http.NewRequest(http.MethodGet, "https://healthy.example.com/test", nil)
		if err != nil {
			t.Fatal(err)
		}
		resp, err := rt.RoundTrip(req)
		if err != nil {
			t.Fatalf("unexpected error: %v", err)
		}
		resp.Body.Close()
		if resp.StatusCode != http.StatusOK {
			t.Errorf("status = %d, want %d", resp.StatusCode, http.StatusOK)
		}
	})
}

func TestTransport_SuccessResetsFailures(t *testing.T) {
	callCount := 0
	base := mockTransport(func(req *http.Request) (*http.Response, error) {
		callCount++
		// Fail on odd calls, succeed on even.
		if callCount%2 == 1 {
			return errResponse(http.StatusInternalServerError), nil
		}
		return okResponse(), nil
	})

	rt := Transport(
		WithFailureThreshold(3),
		WithOpenDuration(time.Hour),
	)(base)

	// Alternate fail/success — should never trip because successes reset the
	// consecutive failure counter.
	for i := 0; i < 10; i++ {
		req, err := http.NewRequest(http.MethodGet, "https://host.example.com/test", nil)
		if err != nil {
			t.Fatal(err)
		}
		resp, err := rt.RoundTrip(req)
		if err != nil {
			t.Fatalf("iteration %d: unexpected error (circuit should not be open): %v", i, err)
		}
		resp.Body.Close()
	}
}