reproduce tar exporter with socket error

Signed-off-by: Alex Couture-Beil <alex@earthly.dev>

client/client_test.go

@@ -113,6 +113,7 @@ func TestIntegration(t *testing.T) {
 		testCacheMountNoCache,
 		testExporterTargetExists,
 		testTarExporterWithSocket,
+		testTarExporterWithSocketCopy,
 		testTarExporterSymlink,
 		testMultipleRegistryCacheImportExport,
 		testSourceMap,
@@ -1653,6 +1654,48 @@ func testTarExporterWithSocket(t *testing.T, sb integration.Sandbox) {
 	require.NoError(t, err)
 }
 
+func testTarExporterWithSocketCopy(t *testing.T, sb integration.Sandbox) {
+	if os.Getenv("TEST_DOCKERD") == "1" {
+		t.Skip("tar exporter is temporarily broken on dockerd")
+	}
+
+	requiresLinux(t)
+	c, err := New(context.TODO(), sb.Address())
+	require.NoError(t, err)
+	defer c.Close()
+
+	alpine := llb.Image("docker.io/library/alpine:latest")
+	state := alpine.Run(llb.Args([]string{"sh", "-c", "nc -l -s local:/root/socket.sock & usleep 100000; kill %1"})).Root()
+
+	fa := llb.Copy(state, "/root", "/roo2",
+		&llb.CopyInfo{
+			FollowSymlinks:      true,
+			CopyDirContentsOnly: false, // !isDir
+			AttemptUnpack:       false,
+			CreateDestPath:      true,
+			AllowWildcard:       true,
+			AllowEmptyWildcard:  false,
+		})
+
+	alpine2 := alpine.File(fa)
+
+	def, err := alpine2.Marshal(context.TODO())
+	require.NoError(t, err)
+
+	_, err = c.Solve(context.TODO(), def, SolveOpt{
+		Exports: []ExportEntry{
+			{
+				Type:  ExporterTar,
+				Attrs: map[string]string{},
+				Output: func(m map[string]string) (io.WriteCloser, error) {
+					return nopWriteCloser{ioutil.Discard}, nil
+				},
+			},
+		},
+	}, nil)
+	require.NoError(t, err)
+}
+
 // moby/buildkit#1418
 func testTarExporterSymlink(t *testing.T, sb integration.Sandbox) {
 	requiresLinux(t)