Test the eviction, source cache, upstream and transform metrics
The tests check the metrics on a variant hit, on misses that fetch or use the cached source, on a failed fetch, and on both kinds of eviction. A source whose cached file is gone must count as a source cache miss. A transform waiting for a processing slot must count as in progress. The tests fail until the metrics exist. Model: opus-5-5
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package imageproxy
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import (
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"os"
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"testing"
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"time"
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"sneak.berlin/go/pixa/internal/imageprocessor"
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"sneak.berlin/go/pixa/internal/imagerequest"
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)
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// metricValues holds the source cache, upstream fetch and transform metrics
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// of a proxy and its cache. A histogram is given by its count of
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// observations.
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type metricValues struct {
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sourceCacheHits uint64
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sourceCacheMisses uint64
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fetchDurations uint64
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fetchErrors uint64
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transformDuration uint64
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inProgress float64
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}
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// readMetricValues reads the metrics of svc and its cache that
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// metricValues holds from their metrics registry.
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func readMetricValues(t *testing.T, svc *testProxy) metricValues {
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t.Helper()
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families, err := svc.registry.Gather()
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if err != nil {
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t.Fatalf("failed to gather the metrics: %v", err)
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}
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var values metricValues
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for _, family := range families {
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metric := family.GetMetric()[0]
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switch family.GetName() {
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case "pixa_source_cache_hits_total":
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values.sourceCacheHits = uint64(metric.GetCounter().GetValue())
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case "pixa_source_cache_misses_total":
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values.sourceCacheMisses = uint64(metric.GetCounter().GetValue())
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case "pixa_upstream_fetch_duration_seconds":
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values.fetchDurations = metric.GetHistogram().GetSampleCount()
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case "pixa_upstream_fetch_errors_total":
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values.fetchErrors = uint64(metric.GetCounter().GetValue())
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case "pixa_transform_duration_seconds":
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values.transformDuration = metric.GetHistogram().GetSampleCount()
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case "pixa_transforms_in_progress":
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values.inProgress = metric.GetGauge().GetValue()
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}
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}
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return values
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}
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// TestProxy_Get_CountsSourceCacheFetchesAndTransforms walks Get through a
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// miss that fetches the source, a hit, a miss that uses the cached source
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// and a miss whose source is not found upstream, checking the source cache,
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// upstream fetch and transform metrics after each.
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func TestProxy_Get_CountsSourceCacheFetchesAndTransforms(t *testing.T) {
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t.Parallel()
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svc, fixtures := setupTestProxy(t)
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// want is source cache hits, source cache misses, fetch durations
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// observed, fetch errors, transform durations observed, transforms in
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// progress.
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steps := []struct {
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name string
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path string
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size int
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wantErr bool
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want metricValues
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}{
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{"miss that fetches the source", testPathPhoto, 50, false,
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metricValues{0, 1, 1, 0, 1, 0}},
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{"hit", testPathPhoto, 50, false,
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metricValues{0, 1, 1, 0, 1, 0}},
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{"miss that uses the cached source", testPathPhoto, 25, false,
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metricValues{1, 1, 1, 0, 2, 0}},
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{"miss whose source is not found", "/images/absent.jpg", 50, true,
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metricValues{1, 2, 1, 1, 2, 0}},
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}
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for _, step := range steps {
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resp, err := svc.Get(t.Context(), &imagerequest.Request{
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Source: imagerequest.Source{
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Host: fixtures.GoodHost,
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Path: step.path,
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},
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Transform: imagerequest.Transform{
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Size: imagerequest.Size{Width: step.size, Height: step.size},
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Format: imagerequest.FormatJPEG,
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Quality: 85,
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FitMode: imagerequest.FitCover,
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},
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})
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if (err != nil) != step.wantErr {
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t.Fatalf("%s: Get() error = %v, want error %t", step.name, err, step.wantErr)
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}
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if err == nil {
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_ = resp.Content.Close()
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}
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got := readMetricValues(t, svc)
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t.Logf("after the %s: metrics = %+v", step.name, got)
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if got != step.want {
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t.Fatalf("after the %s: metrics = %+v, want %+v", step.name, got, step.want)
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}
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}
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}
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// TestProxy_Get_CountsMissingSourceFileAsSourceCacheMiss deletes the file of
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// a cached source but keeps its row. A request for a second variant of that
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// source must fetch the source again, and count a source cache miss, not a
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// hit.
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func TestProxy_Get_CountsMissingSourceFileAsSourceCacheMiss(t *testing.T) {
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t.Parallel()
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svc, fixtures := setupTestProxy(t)
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// A first request caches the photo as a source.
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resp, err := svc.Get(t.Context(), widthOnlyRequest(fixtures, 50))
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if err != nil {
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t.Fatalf("first Get() error = %v", err)
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}
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_ = resp.Content.Close()
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source := widthOnlyRequest(fixtures, 50).Source
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err = os.Remove(sourceFilePath(svc, source.Key()))
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if err != nil {
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t.Fatalf("failed to delete the cached source file: %v", err)
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}
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before := readMetricValues(t, svc)
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resp, err = svc.Get(t.Context(), widthOnlyRequest(fixtures, 25))
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if err != nil {
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t.Fatalf("Get() of a second variant error = %v", err)
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}
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_ = resp.Content.Close()
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after := readMetricValues(t, svc)
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t.Logf("before the second variant: metrics = %+v; after: %+v", before, after)
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if after.sourceCacheHits != before.sourceCacheHits ||
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after.sourceCacheMisses != before.sourceCacheMisses+1 {
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t.Errorf("source cache hits went from %d to %d and misses from %d to %d, "+
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"want no new hit and one more miss", before.sourceCacheHits,
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after.sourceCacheHits, before.sourceCacheMisses, after.sourceCacheMisses)
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}
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}
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// TestProxy_Get_CountsTransformWaitingForSlotAsInProgress holds the only
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// processing slot and starts a request that must transform the photo. While
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// the request waits for the slot, pixa_transforms_in_progress must be 1; once
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// the request returns, 0.
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func TestProxy_Get_CountsTransformWaitingForSlotAsInProgress(t *testing.T) {
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t.Parallel()
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svc, fixtures := setupTestProxy(t)
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svc.processor = imageprocessor.New(
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imageprocessor.Params{MaxInputBytes: 50 << 20, MaxConcurrentProcessing: 1},
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)
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release := holdProcessingSlot(t, svc.processor)
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result := startGet(t.Context(), svc, widthOnlyRequest(fixtures, 50))
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// The request fetches the photo first, then waits for the slot.
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deadline := time.Now().Add(5 * time.Second)
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for readMetricValues(t, svc).inProgress != 1 && time.Now().Before(deadline) {
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time.Sleep(10 * time.Millisecond)
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}
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waiting := readMetricValues(t, svc).inProgress
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t.Logf("while the request waits for the slot: transforms in progress = %v",
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waiting)
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select {
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case got := <-result:
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t.Fatalf("Get() returned while the only processing slot was held, "+
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"error = %v", got.err)
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default:
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}
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if waiting != 1 {
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t.Fatalf("transforms in progress = %v while the request waits for the "+
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"slot, want 1", waiting)
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}
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release()
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got := <-result
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if got.err != nil {
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t.Fatalf("Get() error = %v", got.err)
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}
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returned := readMetricValues(t, svc).inProgress
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t.Logf("once the request returned: transforms in progress = %v", returned)
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if returned != 0 {
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t.Errorf("transforms in progress = %v once the request returned, want 0",
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returned)
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}
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}
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