// getContextFromReader will read the contents of the given reader as either a
// Dockerfile or tar archive to be extracted to a temporary directory used as
// the context directory. Returns the absolute path to the temporary context
// directory, the relative path of the dockerfile in that context directory,
// and a non-nil error on success.
func getContextFromReader(r io.Reader, dockerfileName string) (absContextDir, relDockerfile string, err error) {
	buf := bufio.NewReader(r)

	magic, err := buf.Peek(archive.HeaderSize)
	if err != nil && err != io.EOF {
		return "", "", fmt.Errorf("failed to peek context header from STDIN: %v", err)
	}

	if absContextDir, err = ioutil.TempDir("", "docker-build-context-"); err != nil {
		return "", "", fmt.Errorf("unbale to create temporary context directory: %v", err)
	}

	defer func(d string) {
		if err != nil {
			os.RemoveAll(d)
		}
	}(absContextDir)

	if !archive.IsArchive(magic) { // Input should be read as a Dockerfile.
		// -f option has no meaning when we're reading it from stdin,
		// so just use our default Dockerfile name
		relDockerfile = api.DefaultDockerfileName

		return absContextDir, relDockerfile, writeToFile(buf, filepath.Join(absContextDir, relDockerfile))
	}

	if err := archive.Untar(buf, absContextDir, nil); err != nil {
		return "", "", fmt.Errorf("unable to extract stdin to temporary context directory: %v", err)
	}

	return getDockerfileRelPath(absContextDir, dockerfileName)
}

// getContextFromReader will read the contents of the given reader as either a
// Dockerfile or tar archive. Returns a tar archive used as a context and a
// path to the Dockerfile inside the tar.
func getContextFromReader(r io.ReadCloser, dockerfileName string) (out io.ReadCloser, relDockerfile string, err error) {
	buf := bufio.NewReader(r)

	magic, err := buf.Peek(archive.HeaderSize)
	if err != nil && err != io.EOF {
		return nil, "", fmt.Errorf("failed to peek context header from STDIN: %v", err)
	}

	if archive.IsArchive(magic) {
		return ioutils.NewReadCloserWrapper(buf, func() error { return r.Close() }), dockerfileName, nil
	}

	// Input should be read as a Dockerfile.
	tmpDir, err := ioutil.TempDir("", "docker-build-context-")
	if err != nil {
		return nil, "", fmt.Errorf("unbale to create temporary context directory: %v", err)
	}

	f, err := os.Create(filepath.Join(tmpDir, api.DefaultDockerfileName))
	if err != nil {
		return nil, "", err
	}
	_, err = io.Copy(f, buf)
	if err != nil {
		f.Close()
		return nil, "", err
	}

	if err := f.Close(); err != nil {
		return nil, "", err
	}
	if err := r.Close(); err != nil {
		return nil, "", err
	}

	tar, err := archive.Tar(tmpDir, archive.Uncompressed)
	if err != nil {
		return nil, "", err
	}

	return ioutils.NewReadCloserWrapper(tar, func() error {
		err := tar.Close()
		os.RemoveAll(tmpDir)
		return err
	}), api.DefaultDockerfileName, nil

}

// CmdBuild builds a new image from the source code at a given path.
//
// If '-' is provided instead of a path or URL, Docker will build an image from either a Dockerfile or tar archive read from STDIN.
//
// Usage: docker build [OPTIONS] PATH | URL | -
func (cli *DockerCli) CmdBuild(args ...string) error {
	cmd := cli.Subcmd("build", "PATH | URL | -", "Build a new image from the source code at PATH", true)
	tag := cmd.String([]string{"t", "-tag"}, "", "Repository name (and optionally a tag) for the image")
	suppressOutput := cmd.Bool([]string{"q", "-quiet"}, false, "Suppress the verbose output generated by the containers")
	noCache := cmd.Bool([]string{"#no-cache", "-no-cache"}, false, "Do not use cache when building the image")
	rm := cmd.Bool([]string{"#rm", "-rm"}, true, "Remove intermediate containers after a successful build")
	forceRm := cmd.Bool([]string{"-force-rm"}, false, "Always remove intermediate containers")
	pull := cmd.Bool([]string{"-pull"}, false, "Always attempt to pull a newer version of the image")
	dockerfileName := cmd.String([]string{"f", "-file"}, "", "Name of the Dockerfile (Default is 'PATH/Dockerfile')")
	flMemoryString := cmd.String([]string{"m", "-memory"}, "", "Memory limit")
	flMemorySwap := cmd.String([]string{"-memory-swap"}, "", "Total memory (memory + swap), '-1' to disable swap")
	flCPUShares := cmd.Int64([]string{"c", "-cpu-shares"}, 0, "CPU shares (relative weight)")
	flCpuQuota := cmd.Int64([]string{"-cpu-quota"}, 0, "Limit the CPU CFS (Completely Fair Scheduler) quota")
	flCPUSetCpus := cmd.String([]string{"-cpuset-cpus"}, "", "CPUs in which to allow execution (0-3, 0,1)")
	flCPUSetMems := cmd.String([]string{"-cpuset-mems"}, "", "MEMs in which to allow execution (0-3, 0,1)")
	flCgroupParent := cmd.String([]string{"-cgroup-parent"}, "", "Optional parent cgroup for the container")

	cmd.Require(flag.Exact, 1)
	cmd.ParseFlags(args, true)

	var (
		context  archive.Archive
		isRemote bool
		err      error
	)

	_, err = exec.LookPath("git")
	hasGit := err == nil
	if cmd.Arg(0) == "-" {
		// As a special case, 'docker build -' will build from either an empty context with the
		// contents of stdin as a Dockerfile, or a tar-ed context from stdin.
		buf := bufio.NewReader(cli.in)
		magic, err := buf.Peek(tarHeaderSize)
		if err != nil && err != io.EOF {
			return fmt.Errorf("failed to peek context header from STDIN: %v", err)
		}
		if !archive.IsArchive(magic) {
			dockerfile, err := ioutil.ReadAll(buf)
			if err != nil {
				return fmt.Errorf("failed to read Dockerfile from STDIN: %v", err)
			}

			// -f option has no meaning when we're reading it from stdin,
			// so just use our default Dockerfile name
			*dockerfileName = api.DefaultDockerfileName
			context, err = archive.Generate(*dockerfileName, string(dockerfile))
		} else {
			context = ioutil.NopCloser(buf)
		}
	} else if urlutil.IsURL(cmd.Arg(0)) && (!urlutil.IsGitURL(cmd.Arg(0)) || !hasGit) {
		isRemote = true
	} else {
		root := cmd.Arg(0)
		if urlutil.IsGitURL(root) {
			root, err = utils.GitClone(root)
			if err != nil {
				return err
			}
			defer os.RemoveAll(root)
		}
		if _, err := os.Stat(root); err != nil {
			return err
		}

		absRoot, err := filepath.Abs(root)
		if err != nil {
			return err
		}

		filename := *dockerfileName // path to Dockerfile

		if *dockerfileName == "" {
			// No -f/--file was specified so use the default
			*dockerfileName = api.DefaultDockerfileName
			filename = filepath.Join(absRoot, *dockerfileName)

			// Just to be nice ;-) look for 'dockerfile' too but only
			// use it if we found it, otherwise ignore this check
			if _, err = os.Lstat(filename); os.IsNotExist(err) {
				tmpFN := path.Join(absRoot, strings.ToLower(*dockerfileName))
				if _, err = os.Lstat(tmpFN); err == nil {
					*dockerfileName = strings.ToLower(*dockerfileName)
					filename = tmpFN
				}
			}
		}

		origDockerfile := *dockerfileName // used for error msg
		if filename, err = filepath.Abs(filename); err != nil {
			return err
		}

		// Verify that 'filename' is within the build context
		filename, err = symlink.FollowSymlinkInScope(filename, absRoot)
		if err != nil {
//.........这里部分代码省略.........