Allow unset --entrypoint in docker run or docker create

This fix tries to address the issue raised in #23498 to allow unset
`--entrypoint` in `docker run` or `docker create`.

This fix checks the flag `--entrypoint` and, in case `--entrypoint=` (`""`)
is passed, unset the Entrypoint during the container run.

Additional integration tests have been created to cover changes in this fix.

This fix fixes #23498.

Signed-off-by: Yong Tang <yong.tang.github@outlook.com>

daemon/create.go

@@ -240,6 +240,10 @@ func (daemon *Daemon) mergeAndVerifyConfig(config *containertypes.Config, img *i
 			return err
 		}
 	}
+	// Reset the Entrypoint if it is [""]
+	if len(config.Entrypoint) == 1 && config.Entrypoint[0] == "" {
+		config.Entrypoint = nil
+	}
 	if len(config.Entrypoint) == 0 && len(config.Cmd) == 0 {
 		return fmt.Errorf("No command specified")
 	}

integration-cli/docker_cli_create_test.go

@@ -478,3 +478,31 @@ func (s *DockerSuite) TestCreate64ByteHexID(c *check.C) {
 
 	dockerCmd(c, "create", imageID)
 }
+
+// Test case for #23498
+func (s *DockerSuite) TestCreateUnsetEntrypoint(c *check.C) {
+	testRequires(c, DaemonIsLinux)
+	name := "test-entrypoint"
+	dockerfile := `FROM busybox
+ADD entrypoint.sh /entrypoint.sh
+RUN chmod 755 /entrypoint.sh
+ENTRYPOINT ["/entrypoint.sh"]
+CMD echo foobar`
+
+	ctx, err := fakeContext(dockerfile, map[string]string{
+		"entrypoint.sh": `#!/bin/sh
+echo "I am an entrypoint"
+exec "$@"`,
+	})
+	c.Assert(err, check.IsNil)
+	defer ctx.Close()
+
+	_, err = buildImageFromContext(name, ctx, true)
+	c.Assert(err, check.IsNil)
+
+	out, _ := dockerCmd(c, "create", "--entrypoint=", name, "echo", "foo")
+	id := strings.TrimSpace(out)
+	c.Assert(id, check.Not(check.Equals), "")
+	out, _ = dockerCmd(c, "start", "-a", id)
+	c.Assert(strings.TrimSpace(out), check.Equals, "foo")
+}

integration-cli/docker_cli_run_test.go

@@ -4497,3 +4497,33 @@ func (s *DockerSuite) TestRunAddHostInHostMode(c *check.C) {
 	out, _ := dockerCmd(c, "run", "--add-host=extra:1.2.3.4", "--net=host", "busybox", "cat", "/etc/hosts")
 	c.Assert(out, checker.Contains, expectedOutput, check.Commentf("Expected '%s', but got %q", expectedOutput, out))
 }
+
+// Test case for #23498
+func (s *DockerSuite) TestRunUnsetEntrypoint(c *check.C) {
+	testRequires(c, DaemonIsLinux)
+	name := "test-entrypoint"
+	dockerfile := `FROM busybox
+ADD entrypoint.sh /entrypoint.sh
+RUN chmod 755 /entrypoint.sh
+ENTRYPOINT ["/entrypoint.sh"]
+CMD echo foobar`
+
+	ctx, err := fakeContext(dockerfile, map[string]string{
+		"entrypoint.sh": `#!/bin/sh
+echo "I am an entrypoint"
+exec "$@"`,
+	})
+	c.Assert(err, check.IsNil)
+	defer ctx.Close()
+
+	_, err = buildImageFromContext(name, ctx, true)
+	c.Assert(err, check.IsNil)
+
+	out, _ := dockerCmd(c, "run", "--entrypoint=", "-t", name, "echo", "foo")
+	c.Assert(strings.TrimSpace(out), check.Equals, "foo")
+
+	// CMD will be reset as well (the same as setting a custom entrypoint)
+	_, _, err = dockerCmdWithError("run", "--entrypoint=", "-t", name)
+	c.Assert(err, check.NotNil)
+	c.Assert(err.Error(), checker.Contains, "No command specified")
+}

runconfig/opts/parse.go

@@ -366,6 +366,9 @@ func Parse(flags *pflag.FlagSet, copts *ContainerOptions) (*container.Config, *c
 	}
 	if copts.flEntrypoint != "" {
 		entrypoint = strslice.StrSlice{copts.flEntrypoint}
+	} else if flags.Changed("entrypoint") {
+		// if `--entrypoint=` is parsed then Entrypoint is reset
+		entrypoint = []string{""}
 	}
 
 	ports, portBindings, err := nat.ParsePortSpecs(copts.flPublish.GetAll())