dap: use container fs requests to get a more accurate state for the file system

The container filesystem request API that has been added to buildkit
allows a container created through the `NewContainer` API to also access
the filesystems. This is useful when an error occurs because it allows
us to grab the mutable state of the mounts used during the actual build
rather than the input version copies which don't contain any files that
were added as part of the failed command.

This gives us a more accurate view of the filesystem that was previously
only accessible through using `exec` and `ls`/`cat` commands that may
not always exist.

Signed-off-by: Jonathan A. Sternberg <jonathan.sternberg@docker.com>

build/invoke.go

@@ -11,6 +11,7 @@ import (
 	gateway "github.com/moby/buildkit/frontend/gateway/client"
 	"github.com/pkg/errors"
 	"github.com/sirupsen/logrus"
+	"github.com/tonistiigi/fsutil/types"
 )
 
 type InvokeConfig struct {
@@ -145,6 +146,18 @@ func (c *Container) Exec(ctx context.Context, cfg *InvokeConfig, stdin io.ReadCl
 	return err
 }
 
+func (c *Container) ReadFile(ctx context.Context, req gateway.ReadContainerRequest) ([]byte, error) {
+	return c.container.ReadFile(ctx, req)
+}
+
+func (c *Container) ReadDir(ctx context.Context, req gateway.ReadDirContainerRequest) ([]*types.Stat, error) {
+	return c.container.ReadDir(ctx, req)
+}
+
+func (c *Container) StatFile(ctx context.Context, req gateway.StatContainerRequest) (*types.Stat, error) {
+	return c.container.StatFile(ctx, req)
+}
+
 func exec(ctx context.Context, resultCtx *ResultHandle, cfg *InvokeConfig, ctr gateway.Container, stdin io.ReadCloser, stdout io.WriteCloser, stderr io.WriteCloser) error {
 	processCfg, err := resultCtx.getProcessConfig(cfg, stdin, stdout, stderr)
 	if err != nil {