Update workhorse zipartifacts test to ensure minimum number of range requests

zipartifacts uses a http-client based ReaderAt implementation that fetches parts of a remote zip
file by using Range headers. We don't have direct control of the ranges that will be requested, so
this test ensures that changes to the underlying zip reader won't negatively affect performance by
making more range requests than expected.

workhorse/internal/zipartifacts/open_archive_test.go

@@ -2,56 +2,124 @@ package zipartifacts
 
 import (
 	"archive/zip"
+	"bytes"
 	"context"
 	"fmt"
-	"io/ioutil"
+	"io"
 	"net/http"
 	"net/http/httptest"
 	"os"
 	"path/filepath"
+	"runtime"
+	"strings"
 	"testing"
 
 	"github.com/stretchr/testify/require"
 )
 
-func TestOpenHTTPArchive(t *testing.T) {
-	const (
-		zipFile   = "test.zip"
-		entryName = "hello.txt"
-		contents  = "world"
-		testRoot  = "testdata/public"
-	)
-
-	require.NoError(t, os.MkdirAll(testRoot, 0755))
-	f, err := os.Create(filepath.Join(testRoot, zipFile))
-	require.NoError(t, err, "create file")
+func createArchive(t *testing.T, dir string) (map[string][]byte, int64) {
+	f, err := os.Create(filepath.Join(dir, "test.zip"))
+	require.NoError(t, err)
 	defer f.Close()
-
 	zw := zip.NewWriter(f)
+
+	entries := make(map[string][]byte)
+	for _, size := range []int{0, 32 * 1024, 128 * 1024, 5 * 1024 * 1024} {
+		entryName := fmt.Sprintf("file_%d", size)
+		entries[entryName] = bytes.Repeat([]byte{'z'}, size)
+
 		w, err := zw.Create(entryName)
-	require.NoError(t, err, "create zip entry")
-	_, err = fmt.Fprint(w, contents)
-	require.NoError(t, err, "write zip entry contents")
-	require.NoError(t, zw.Close(), "close zip writer")
-	require.NoError(t, f.Close(), "close file")
+		require.NoError(t, err)
+
+		_, err = w.Write(entries[entryName])
+		require.NoError(t, err)
+	}
+
+	require.NoError(t, zw.Close())
+	fi, err := f.Stat()
+	require.NoError(t, err)
+	require.NoError(t, f.Close())
+
+	return entries, fi.Size()
+}
 
-	srv := httptest.NewServer(http.FileServer(http.Dir(testRoot)))
+func TestOpenHTTPArchive(t *testing.T) {
+	dir := t.TempDir()
+	entries, _ := createArchive(t, dir)
+
+	srv := httptest.NewServer(http.FileServer(http.Dir(dir)))
 	defer srv.Close()
 
-	zr, err := OpenArchive(context.Background(), srv.URL+"/"+zipFile)
-	require.NoError(t, err, "call OpenArchive")
-	require.Len(t, zr.File, 1)
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+
+	zr, err := OpenArchive(ctx, srv.URL+"/test.zip")
+	require.NoError(t, err)
+	require.Len(t, zr.File, len(entries))
+
+	for _, zf := range zr.File {
+		entry, ok := entries[zf.Name]
+		require.True(t, ok)
 
-	zf := zr.File[0]
-	require.Equal(t, entryName, zf.Name, "zip entry name")
+		r, err := zf.Open()
+		require.NoError(t, err)
 
-	entry, err := zf.Open()
-	require.NoError(t, err, "get zip entry reader")
-	defer entry.Close()
+		contents, err := io.ReadAll(r)
+		require.NoError(t, err)
+		require.Equal(t, entry, contents)
 
-	actualContents, err := ioutil.ReadAll(entry)
-	require.NoError(t, err, "read zip entry contents")
-	require.Equal(t, contents, string(actualContents), "compare zip entry contents")
+		require.NoError(t, r.Close())
+	}
+}
+
+func TestMinimalRangeRequests(t *testing.T) {
+	if strings.HasPrefix(runtime.Version(), "go1.17") {
+		t.Skipf("skipped for go1.17: https://gitlab.com/gitlab-org/gitlab/-/issues/340778")
+	}
+
+	dir := t.TempDir()
+	entries, archiveSize := createArchive(t, dir)
+
+	mux := http.NewServeMux()
+
+	var ranges []string
+	mux.HandleFunc("/", func(rw http.ResponseWriter, r *http.Request) {
+		rangeHdr := r.Header.Get("Range")
+		if rangeHdr == "" {
+			rw.Header().Add("Content-Length", fmt.Sprintf("%d", archiveSize))
+			return
+		}
+
+		ranges = append(ranges, rangeHdr)
+		http.FileServer(http.Dir(dir)).ServeHTTP(rw, r)
+	})
+
+	srv := httptest.NewServer(mux)
+	defer srv.Close()
+
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+
+	zr, err := OpenArchive(ctx, srv.URL+"/test.zip")
+	require.NoError(t, err)
+	require.Len(t, zr.File, len(entries))
+
+	require.Len(t, ranges, 2, "range requests should be minimal")
+	require.NotContains(t, ranges, "bytes=0-", "range request should not request from zero")
+
+	for _, zf := range zr.File {
+		r, err := zf.Open()
+		require.NoError(t, err)
+
+		_, err = io.Copy(io.Discard, r)
+		require.NoError(t, err)
+
+		require.NoError(t, r.Close())
+	}
+
+	// ensure minimal requests: https://gitlab.com/gitlab-org/gitlab/-/issues/340778
+	require.Len(t, ranges, 3, "range requests should be minimal")
+	require.Contains(t, ranges, "bytes=0-")
 }
 
 func TestOpenHTTPArchiveNotSendingAcceptEncodingHeader(t *testing.T) {
@@ -64,5 +132,8 @@ func TestOpenHTTPArchiveNotSendingAcceptEncodingHeader(t *testing.T) {
 	srv := httptest.NewServer(http.HandlerFunc(requestHandler))
 	defer srv.Close()
 
-	OpenArchive(context.Background(), srv.URL)
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+
+	OpenArchive(ctx, srv.URL)
 }