docker1.9源码分析（一）：执行主函数以及命令行解析

主函数在docker/docker/docker.go中，首先是flag包处理参数，根据输入的参数执行相应的操作，之后

clientCli := client.NewDockerCli(stdin, stdout, stderr, clientFlags)

根据输入的clientFlags参数新建docker client

c := cli.New(clientCli, daemonCli)

建立命令行接口，其中cli是要执行的命令，根据参数可以是client，server，daemon端任意的命令

if err := c.Run(flag.Args()...); err != nil {
   if sterr, ok := err.(cli.StatusError); ok {
      if sterr.Status != "" {
         fmt.Fprintln(os.Stderr, sterr.Status)
         os.Exit(1)
      }
      os.Exit(sterr.StatusCode)
   }
   fmt.Fprintln(os.Stderr, err)
   os.Exit(1)
}

其中Run（）函数的实现在docker/cli/cli.go中，如下所示：

func (cli *Cli) Run(args ...string) error {
   if len(args) > 1 {
      command, err := cli.command(args[:2]...)
      switch err := err.(type) {
      case nil:
         return command(args[2:]...)
      case initErr:
         return err.error
      }
   }
   if len(args) > 0 {
      command, err := cli.command(args[0])
      switch err := err.(type) {
      case nil:
         return command(args[1:]...)
      case initErr:
         return err.error
      }
      cli.noSuchCommand(args[0])
   }
   return cli.CmdHelp()
}

其中command（）函数解析出具体要执行的命令，所以该函数执行用户输入的命令，然后根据解析出的函数名进入相应的Cmd执行，比如用户输入的是docker pull命令，那么就会执行docker/api/client/pull.go中的client.CmdPull函数，如下所示：

func (cli *DockerCli) CmdPull(args ...string) error {
   cmd := Cli.Subcmd("pull", []string{"NAME[:TAG|@DIGEST]"}, Cli.DockerCommands["pull"].Description, true)
   allTags := cmd.Bool([]string{"a", "-all-tags"}, false, "Download all tagged images in the repository")
   addTrustedFlags(cmd, true)
   cmd.Require(flag.Exact, 1)

   cmd.ParseFlags(args, true)
   remote := cmd.Arg(0)

   taglessRemote, tag := parsers.ParseRepositoryTag(remote)
   if tag == "" && !*allTags {
      tag = tags.DefaultTag  fmt.Fprintf(cli.out, "Using default tag: %s\n", tag)
   } else if tag != "" && *allTags {
      return fmt.Errorf("tag can't be used with --all-tags/-a")
   }

   ref := registry.ParseReference(tag)

   // Resolve the Repository name from fqn to RepositoryInfo
   repoInfo, err := registry.ParseRepositoryInfo(taglessRemote)
   if err != nil {
      return err
   }

   if isTrusted() && !ref.HasDigest() {
      // Check if tag is digest
      authConfig := registry.ResolveAuthConfig(cli.configFile, repoInfo.Index)
      return cli.trustedPull(repoInfo, ref, authConfig)
   }

   v := url.Values{}
   v.Set("fromImage", ref.ImageName(taglessRemote))

   _, _, err = cli.clientRequestAttemptLogin("POST", "/images/create?"+v.Encode(), nil, cli.out, repoInfo.Index, "pull")
   return err
}

首先是建立命令参数，之后是命令的解析

remote:镜像仓库全地址

taglessRemote：不带tag的的仓库地址

tag：tag值

repoInfo, err := registry.ParseRepositoryInfo(taglessRemote)

这一行代码将taglessRemote解析成一个RepositoryInfo，其实是将remoteName换成一种docker源码可以执行的表现形式，该结构体如下：

// RepositoryInfo describes a repository
type RepositoryInfo struct {
   // Index points to registry information
   Index *IndexInfo
   // RemoteName is the remote name of the repository, such as
   // "library/ubuntu-12.04-base"
   RemoteName string
   // LocalName is the local name of the repository, such as
   // "ubuntu-12.04-base"
   LocalName string
   // CanonicalName is the canonical name of the repository, such as
   // "docker.io/library/ubuntu-12.04-base"
   CanonicalName string
   // Official indicates whether the repository is considered official.
   // If the registry is official, and the normalized name does not
   // contain a '/' (e.g. "foo"), then it is considered an official repo.
   Official bool
}

其中，IndexInfo是镜像仓库主机的信息，"Name"是主机名，当为docker hub时，Official的值为true，私有仓库时值为false；RemoteName是在仓库中存储的值，LocalName是在本地节点中存储的名，CanonicalName是全名。