From 607b7ab6922ccfcb02d1d51f33d0d11139db6c32 Mon Sep 17 00:00:00 2001
From: Christine Dodrill <xe@tailscale.com>
Date: Fri, 4 Jun 2021 15:27:03 -0400
Subject: [PATCH] tstest/integration/vms: aggressively re-verify shasums
 (#2050)

I've run into a couple issues where the tests time out while a VM image
is being downloaded, making the cache poisoned for the next run. This
moves the hash checking into its own function and calls it much sooner
in the testing chain. If the hash check fails, the OS is redownloaded.

Signed-off-by: Christine Dodrill <xe@tailscale.com>
---
 tstest/integration/vms/vms_test.go | 50 +++++++++++++++++++++---------
 1 file changed, 35 insertions(+), 15 deletions(-)

diff --git a/tstest/integration/vms/vms_test.go b/tstest/integration/vms/vms_test.go
index 16a2a1dda..bdbdc758c 100644
--- a/tstest/integration/vms/vms_test.go
+++ b/tstest/integration/vms/vms_test.go
@@ -10,6 +10,7 @@ import (
 	"context"
 	"crypto/sha256"
 	"encoding/hex"
+	"errors"
 	"flag"
 	"fmt"
 	"io"
@@ -94,6 +95,19 @@ func fetchDistro(t *testing.T, resultDistro Distro) {
 	qcowPath := filepath.Join(cdir, "qcow2", resultDistro.sha256sum)
 
 	_, err = os.Stat(qcowPath)
+	if err == nil {
+		hash := checkCachedImageHash(t, resultDistro, cdir)
+		if hash != resultDistro.sha256sum {
+			t.Logf("hash for %s (%s) doesn't match expected %s, re-downloading", resultDistro.name, qcowPath, resultDistro.sha256sum)
+		}
+
+		if err := os.Remove(qcowPath); err != nil {
+			t.Fatalf("can't delete wrong cached image: %v", err)
+		}
+
+		err = errors.New("some fake non-nil error to force a redownload")
+	}
+
 	if err != nil {
 		t.Logf("downloading distro image %s to %s", resultDistro.url, qcowPath)
 		fout, err := os.Create(qcowPath)
@@ -121,27 +135,33 @@ func fetchDistro(t *testing.T, resultDistro Distro) {
 			t.Fatalf("can't close fout: %v", err)
 		}
 
-		fin, err := os.Open(qcowPath)
-		if err != nil {
-			t.Fatal(err)
-		}
-
-		hasher := sha256.New()
-		if _, err := io.Copy(hasher, fin); err != nil {
-			t.Fatal(err)
-		}
-		hash := hex.EncodeToString(hasher.Sum(nil))
+		hash := checkCachedImageHash(t, resultDistro, cdir)
 
 		if hash != resultDistro.sha256sum {
-			t.Logf("got:  %q", hash)
-			t.Logf("want: %q", resultDistro.sha256sum)
-			t.Fatal("hash mismatch, someone is doing something nasty")
+			t.Fatalf("hash mismatch, want: %s, got: %s", resultDistro.sha256sum, hash)
 		}
-
-		t.Logf("hash check passed (%s)", resultDistro.sha256sum)
 	}
 }
 
+func checkCachedImageHash(t *testing.T, d Distro, cacheDir string) (gotHash string) {
+	t.Helper()
+
+	qcowPath := filepath.Join(cacheDir, "qcow2", d.sha256sum)
+
+	fin, err := os.Open(qcowPath)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	hasher := sha256.New()
+	if _, err := io.Copy(hasher, fin); err != nil {
+		t.Fatal(err)
+	}
+	gotHash = hex.EncodeToString(hasher.Sum(nil))
+
+	return
+}
+
 // run runs a command or fails the test.
 func run(t *testing.T, dir, prog string, args ...string) {
 	t.Helper()