proxy: ensure Client fields are 64-bit aligned

proxy/client.go

@@ -39,6 +39,11 @@ type CertSource interface {
 // localhost port and tunneling them securely over a TLS connection to a remote
 // database instance defined by its PlanetScale unique branch identifier.
 type Client struct {
+	// connectionsCounter is used to enforce the optional maxConnections limit
+	// NOTE: don't move this field, as we need to make sure the fields are
+	// 64-bit aligned
+	connectionsCounter uint64
+
 	remoteAddr     string
 	localAddr      string
 	instance       string
@@ -47,9 +52,6 @@ type Client struct {
 
 	log *zap.Logger
 
-	// connectionsCounter is used to enforce the optional maxConnections limit
-	connectionsCounter uint64
-
 	// configCache contains the TLS certificate chache for each indiviual
 	// database
 	configCache *tlsCache

proxy/client_test.go

@@ -11,6 +11,7 @@ import (
 	"net"
 	"path/filepath"
 	"testing"
+	"unsafe"
 
 	qt "github.com/frankban/quicktest"
 	"go.uber.org/zap/zaptest"
@@ -182,6 +183,17 @@ func TestClient_run(t *testing.T) {
 	<-done
 }
 
+func TestClient_SyncAtomicAlignment(t *testing.T) {
+	c := qt.New(t)
+
+	// copied from: https://github.com/GoogleCloudPlatform/cloudsql-proxy/blob/302d5d87ac52d8b814625f7b27344fd9ba6a0348/proxy/proxy/client_test.go#L290
+	// The sync/atomic pkg has a bug that requires the developer to guarantee
+	// 64-bit alignment when using 64-bit functions on 32-bit systems.
+	client := &Client{} //nolint: staticcheck
+	offset := unsafe.Offsetof(client.connectionsCounter)
+	c.Assert(int(offset%64), qt.Equals, 0, qt.Commentf("Client.connectionsCounter is not aligned"))
+}
+
 type testCert struct {
 	serverCfg  *tls.Config
 	clientCert tls.Certificate