build: raise maximum size limit for dockerfile and fix size check

Raise the maximum size limit for the dockerfile and correct the size
check. The size check was intended to use the size attribute from the
file stat, but the original gogo version confused the `Size()`
method (which returned the size of the proto message) with the `Size`
attribute (which was named `Size_`).

During the conversion, we noticed the mistake but kept the incorrect
behavior for the sake of keeping the conversion simple.

This also raises the maximum limit because 512 kB is likely a bit too
conservative. The limit has been raised to 2 MB and the limit has been
included in the error message.

Signed-off-by: Jonathan A. Sternberg <[email protected]>

build/url.go

@@ -7,13 +7,15 @@ import (
 
 	"github.com/docker/buildx/driver"
 	"github.com/docker/buildx/util/progress"
+	"github.com/docker/go-units"
 	"github.com/moby/buildkit/client"
 	"github.com/moby/buildkit/client/llb"
 	gwclient "github.com/moby/buildkit/frontend/gateway/client"
 	"github.com/pkg/errors"
-	"google.golang.org/protobuf/proto"
 )
 
+const maxDockerfileSize = 2 * 1024 * 1024 // 2 MB
+
 func createTempDockerfileFromURL(ctx context.Context, d *driver.DriverHandle, url string, pw progress.Writer) (string, error) {
 	c, err := driver.Boot(ctx, ctx, d, pw)
 	if err != nil {
@@ -44,8 +46,8 @@ func createTempDockerfileFromURL(ctx context.Context, d *driver.DriverHandle, ur
 		if err != nil {
 			return nil, err
 		}
-		if proto.Size(stat) > 512*1024 {
-			return nil, errors.Errorf("Dockerfile %s bigger than allowed max size", url)
+		if stat.Size > maxDockerfileSize {
+			return nil, errors.Errorf("Dockerfile %s bigger than allowed max size (%s)", url, units.HumanSize(maxDockerfileSize))
 		}
 
 		dt, err := ref.ReadFile(ctx, gwclient.ReadRequest{