Add test for copying entire container rootfs

CID=$(docker create alpine)
docker cp $CID:/ out

Signed-off-by: Brian Goff <cpuguy83@gmail.com>
Signed-off-by: Tibor Vass <tibor@docker.com>
(cherry picked from commit 6db9f1c3d6)
Signed-off-by: Tibor Vass <tibor@docker.com>

integration/container/copy_test.go

@@ -1,13 +1,20 @@
 package container // import "github.com/docker/docker/integration/container"
 
 import (
+	"archive/tar"
 	"context"
+	"encoding/json"
 	"fmt"
+	"io"
+	"io/ioutil"
+	"os"
 	"testing"
 
 	"github.com/docker/docker/api/types"
 	"github.com/docker/docker/client"
 	"github.com/docker/docker/integration/internal/container"
+	"github.com/docker/docker/internal/test/fakecontext"
+	"github.com/docker/docker/pkg/jsonmessage"
 	"gotest.tools/assert"
 	is "gotest.tools/assert/cmp"
 	"gotest.tools/skip"
@@ -64,3 +71,78 @@ func TestCopyToContainerPathIsNotDir(t *testing.T) {
 	err := apiclient.CopyToContainer(ctx, cid, "/etc/passwd/", nil, types.CopyToContainerOptions{})
 	assert.Assert(t, is.ErrorContains(err, "not a directory"))
 }
+
+func TestCopyFromContainerRoot(t *testing.T) {
+	skip.If(t, testEnv.DaemonInfo.OSType == "windows")
+	defer setupTest(t)()
+
+	ctx := context.Background()
+	apiClient := testEnv.APIClient()
+
+	dir, err := ioutil.TempDir("", t.Name())
+	assert.NilError(t, err)
+	defer os.RemoveAll(dir)
+
+	buildCtx := fakecontext.New(t, dir, fakecontext.WithFile("foo", "hello"), fakecontext.WithFile("baz", "world"), fakecontext.WithDockerfile(`
+		FROM scratch
+		COPY foo /foo
+		COPY baz /bar/baz
+		CMD /fake
+	`))
+	defer buildCtx.Close()
+
+	resp, err := apiClient.ImageBuild(ctx, buildCtx.AsTarReader(t), types.ImageBuildOptions{})
+	assert.NilError(t, err)
+	defer resp.Body.Close()
+
+	var imageID string
+	err = jsonmessage.DisplayJSONMessagesStream(resp.Body, ioutil.Discard, 0, false, func(msg jsonmessage.JSONMessage) {
+		var r types.BuildResult
+		assert.NilError(t, json.Unmarshal(*msg.Aux, &r))
+		imageID = r.ID
+	})
+	assert.NilError(t, err)
+	assert.Assert(t, imageID != "")
+
+	cid := container.Create(ctx, t, apiClient, container.WithImage(imageID))
+
+	rdr, _, err := apiClient.CopyFromContainer(ctx, cid, "/")
+	assert.NilError(t, err)
+	defer rdr.Close()
+
+	tr := tar.NewReader(rdr)
+	expect := map[string]string{
+		"/foo":     "hello",
+		"/bar/baz": "world",
+	}
+	found := make(map[string]bool, 2)
+	var numFound int
+	for {
+		h, err := tr.Next()
+		if err == io.EOF {
+			break
+		}
+		assert.NilError(t, err)
+
+		expected, exists := expect[h.Name]
+		if !exists {
+			// this archive will have extra stuff in it since we are copying from root
+			// and docker adds a bunch of stuff
+			continue
+		}
+
+		numFound++
+		found[h.Name] = true
+
+		buf, err := ioutil.ReadAll(tr)
+		assert.NilError(t, err)
+		assert.Check(t, is.Equal(string(buf), expected))
+
+		if numFound == len(expect) {
+			break
+		}
+	}
+
+	assert.Check(t, found["/foo"], "/foo file not found in archive")
+	assert.Check(t, found["/bar/baz"], "/bar/baz file not found in archive")
+}