Windows: Go1.11: Use long path names in build context (TestBuildSymlinkBreakout)

Signed-off-by: John Howard <jhoward@microsoft.com>

integration-cli/docker_cli_build_test.go

@@ -24,6 +24,7 @@ import (
 	"github.com/docker/docker/internal/test/fakestorage"
 	"github.com/docker/docker/internal/testutil"
 	"github.com/docker/docker/pkg/archive"
+	"github.com/docker/docker/pkg/system"
 	"github.com/go-check/check"
 	"github.com/moby/buildkit/frontend/dockerfile/command"
 	"github.com/opencontainers/go-digest"
@@ -3601,6 +3602,11 @@ func (s *DockerSuite) TestBuildSymlinkBreakout(c *check.C) {
 	name := "testbuildsymlinkbreakout"
 	tmpdir, err := ioutil.TempDir("", name)
 	c.Assert(err, check.IsNil)
+
+	// See https://github.com/moby/moby/pull/37770 for reason for next line.
+	tmpdir, err = system.GetLongPathName(tmpdir)
+	c.Assert(err, check.IsNil)
+
 	defer os.RemoveAll(tmpdir)
 	ctx := filepath.Join(tmpdir, "context")
 	if err := os.MkdirAll(ctx, 0755); err != nil {

pkg/system/path_unix.go

@@ -0,0 +1,10 @@
+// +build !windows
+
+package system // import "github.com/docker/docker/pkg/system"
+
+// GetLongPathName converts Windows short pathnames to full pathnames.
+// For example C:\Users\ADMIN~1 --> C:\Users\Administrator.
+// It is a no-op on non-Windows platforms
+func GetLongPathName(path string) (string, error) {
+	return path, nil
+}

pkg/system/path_windows.go

@@ -0,0 +1,24 @@
+package system // import "github.com/docker/docker/pkg/system"
+
+import "syscall"
+
+// GetLongPathName converts Windows short pathnames to full pathnames.
+// For example C:\Users\ADMIN~1 --> C:\Users\Administrator.
+// It is a no-op on non-Windows platforms
+func GetLongPathName(path string) (string, error) {
+	// See https://groups.google.com/forum/#!topic/golang-dev/1tufzkruoTg
+	p := syscall.StringToUTF16(path)
+	b := p // GetLongPathName says we can reuse buffer
+	n, err := syscall.GetLongPathName(&p[0], &b[0], uint32(len(b)))
+	if err != nil {
+		return "", err
+	}
+	if n > uint32(len(b)) {
+		b = make([]uint16, n)
+		_, err = syscall.GetLongPathName(&p[0], &b[0], uint32(len(b)))
+		if err != nil {
+			return "", err
+		}
+	}
+	return syscall.UTF16ToString(b), nil
+}