From e3c12afced98c1fa7493907416dace65fb83319b Mon Sep 17 00:00:00 2001
From: Al Cutter <al@google.com>
Date: Fri, 5 Sep 2025 18:32:41 +0100
Subject: [PATCH] Detect emulated spanner and apply workaround

---
 storage/gcp/antispam/gcp.go      | 23 +++++++++++++++++++++++
 storage/gcp/antispam/gcp_test.go | 13 -------------
 2 files changed, 23 insertions(+), 13 deletions(-)

diff --git a/storage/gcp/antispam/gcp.go b/storage/gcp/antispam/gcp.go
index 3727427fe..7c6fd15bd 100644
--- a/storage/gcp/antispam/gcp.go
+++ b/storage/gcp/antispam/gcp.go
@@ -19,10 +19,15 @@
 package gcp
 
 import (
+	"bytes"
+	"compress/gzip"
 	"context"
+	"encoding/base64"
 	"errors"
 	"fmt"
+	"io"
 	"iter"
+	"os"
 	"sync/atomic"
 	"time"
 
@@ -191,6 +196,17 @@ func (d *AntispamStorage) Follower(b func([]byte) ([][]byte, error)) tessera.Fol
 	// does not support BatchWrite :(
 	f.updateIndex = f.batchUpdateIndex
 
+	if r := os.Getenv("SPANNER_EMULATOR_HOST"); r != "" {
+		const warn = `H4sIAAAAAAAAA83VwRGAIAwEwH+qoFwrsEAr8eEDPZO7gxkcGV6G7IAJ2tr8iDp07Fs6J7BnImcK5J3EmHVIT2Dvp2YTVJMu/y1+X+jiFQ84LtK9mLHr0aqh+K15PwkWRDaPrcbU5WdMKILtCDMF5hSgQEdJlw/36D7eRYqPfsVNVBcMsNH2QQKq/p957Yr8RfWIE22t7L7ABwAA`
+		r, _ := base64.StdEncoding.DecodeString(warn)
+		gzr, _ := gzip.NewReader(bytes.NewReader([]byte(r)))
+		w, _ := io.ReadAll(gzr)
+		klog.Warningf("%s\nWarning: you're running under the Spanner emulator - this is not a supported environment!\n\n", string(w))
+
+		// Hack in a workaround for spannertest not supporting BatchWrites
+		f.updateIndex = emulatorWorkaroundUpdateIndexTx
+	}
+
 	return f
 }
 
@@ -460,3 +476,10 @@ func createAndPrepareTables(ctx context.Context, spannerDB string, ddl []string,
 	}
 	return nil
 }
+
+// emulatorWorkaroundUpdateIndexTx is a workaround for spannertest not supporting BatchWrites.
+// We use this func as a replacement for follower's updateIndex hook, and simply commit the index
+// updates inline with the larger transaction.
+func emulatorWorkaroundUpdateIndexTx(_ context.Context, txn *spanner.ReadWriteTransaction, ms []*spanner.Mutation) error {
+	return txn.BufferWrite(ms)
+}
diff --git a/storage/gcp/antispam/gcp_test.go b/storage/gcp/antispam/gcp_test.go
index e7b66f777..29853c25d 100644
--- a/storage/gcp/antispam/gcp_test.go
+++ b/storage/gcp/antispam/gcp_test.go
@@ -15,13 +15,11 @@
 package gcp
 
 import (
-	"context"
 	"crypto/sha256"
 	"os"
 	"testing"
 	"time"
 
-	"cloud.google.com/go/spanner"
 	"cloud.google.com/go/spanner/spannertest"
 	"github.com/transparency-dev/tessera"
 	"github.com/transparency-dev/tessera/api"
@@ -78,8 +76,6 @@ func TestAntispamStorage(t *testing.T) {
 			}()
 
 			f := as.Follower(testBundleHasher)
-			// Hack in a workaround for spannertest not supporting BatchWrites
-			f.(*follower).updateIndex = updateIndexTx
 
 			go f.Follow(t.Context(), fl.LogReader)
 
@@ -168,8 +164,6 @@ func TestAntispamPushbackRecovers(t *testing.T) {
 			}()
 
 			f := as.Follower(testBundleHasher)
-			// Hack in a workaround for spannertest not supporting BatchWrites
-			f.(*follower).updateIndex = updateIndexTx
 
 			entryIndex := make(map[string]uint64)
 			a := tessera.NewPublicationAwaiter(t.Context(), fl.LogReader.ReadCheckpoint, 100*time.Millisecond)
@@ -249,10 +243,3 @@ func testBundleHasher(b []byte) ([][]byte, error) {
 	}
 	return r, err
 }
-
-// updateIndexTx is a workaround for spannertest not supporting BatchWrites.
-// We use this func as a replacement for follower's updateIndex hook, and simply commit the index
-// updates inline with the larger transaction.
-func updateIndexTx(_ context.Context, txn *spanner.ReadWriteTransaction, ms []*spanner.Mutation) error {
-	return txn.BufferWrite(ms)
-}