Pass correct prefix to restrict file listing in S3 object storage

We had unit tests in place, but our fake storage implementation
did not handle prefix restrictions in its fake `ListObjects()` method.
Fixed the fake storage, so now we’ll detect this problem in unit tests.

#33

cmd/qrank-builder/pageentities.go

@@ -197,7 +197,7 @@ func buildSitePageEntities(site WikiSite, ctx context.Context, dumps string, s3
 func storedPageEntities(ctx context.Context, s3 S3) (map[string][]string, error) {
 	re := regexp.MustCompile(`^page_entities/([a-z0-9_\-]+)-(\d{8})-page_entities.zst$`)
 	result := make(map[string][]string, 1000)
-	opts := minio.ListObjectsOptions{Prefix: "pageviews/"}
+	opts := minio.ListObjectsOptions{Prefix: "page_entities/"}
 	for obj := range s3.ListObjects(ctx, "qrank", opts) {
 		if obj.Err != nil {
 			return nil, obj.Err

cmd/qrank-builder/s3_test.go

@@ -7,6 +7,7 @@ import (
 	"context"
 	"fmt"
 	"os"
+	"strings"
 
 	"github.com/minio/minio-go/v7"
 )
@@ -26,9 +27,12 @@ func (s3 *FakeS3) ListObjects(ctx context.Context, bucketName string, opts minio
 	ch := make(chan minio.ObjectInfo, 2)
 	go func() {
 		defer close(ch)
+		prefix := opts.Prefix
 		if bucketName == "qrank" {
 			for key, _ := range s3.data {
-				ch <- minio.ObjectInfo{Key: key}
+				if strings.HasPrefix(key, prefix) {
+					ch <- minio.ObjectInfo{Key: key}
+				}
 			}
 		}
 	}()