cotainerd源码阅读——创建使用unix domain socket的grpc server

创建grpc server

cmd\containerd\command\main.go

// App returns a *cli.App instance.
func App() *cli.App {
    app := cli.NewApp()
    app.Name = "containerd"
    ......
    app.Action = func(cliContext *cli.Context) error {
        ......
        // setup the main grpc endpoint
        l, err := sys.GetLocalListener(config.GRPC.Address, config.GRPC.UID, config.GRPC.GID)
        if err != nil {
            return fmt.Errorf("failed to get listener for main endpoint: %w", err)
        }
        serve(ctx, l, server.ServeGRPC)
        ......
    }
    return app
}

NewApp creates a new cli Application with some reasonable defaults for Name, Usage, Version and Action.

 

创建unix domain socket

pkg\sys\socket_unix.go

// CreateUnixSocket creates a unix socket and returns the listener
func CreateUnixSocket(path string) (net.Listener, error) {
    // BSDs have a 104 limit
    if len(path) > 104 {
        return nil, fmt.Errorf("%q: unix socket path too long (> 104)", path)
    }
    if err := os.MkdirAll(filepath.Dir(path), 0660); err != nil {
        return nil, err
    }
    if err := unix.Unlink(path); err != nil && !os.IsNotExist(err) {
        return nil, err
    }
    return net.Listen("unix", path)
}

// GetLocalListener returns a listener out of a unix socket.
func GetLocalListener(path string, uid, gid int) (net.Listener, error) {
    // Ensure parent directory is created
    if err := mkdirAs(filepath.Dir(path), uid, gid); err != nil {
        return nil, err
    }

    l, err := CreateUnixSocket(path)
    if err != nil {
        return l, fmt.Errorf("failed to create unix socket on %s: %w", path, err)
    }

    if err := os.Chmod(path, 0660); err != nil {
        l.Close()
        return nil, err
    }

    if err := os.Chown(path, uid, gid); err != nil {
        l.Close()
        return nil, err
    }

    return l, nil
}

 

使用defaultConfig获取默认配置

cmd\containerd\command\config.go

func defaultConfig() *srvconfig.Config {
    return platformAgnosticDefaultConfig()
}

func platformAgnosticDefaultConfig() *srvconfig.Config {
    return &srvconfig.Config{
        Version: version.ConfigVersion,
        Root:    defaults.DefaultRootDir,
        State:   defaults.DefaultStateDir,
        GRPC: srvconfig.GRPCConfig{
            Address:        defaults.DefaultAddress,
            MaxRecvMsgSize: defaults.DefaultMaxRecvMsgSize,
            MaxSendMsgSize: defaults.DefaultMaxSendMsgSize,
        },
        DisabledPlugins:  []string{},
        RequiredPlugins:  []string{},
        StreamProcessors: streamProcessors(),
    }
}

defaults.DefaultAddress 在defaults包下有多个系统（linux、windows、freebsd等）的定义，那编译的时候是怎么识别使用哪个系统的配置？答案是根据系统类型或指定的GOOS，来选择对应系统结尾的文件的进行编译的。例如：如果是linux，则选择以linux结尾的defaults_linux.go文件进行编译；如果是windows，则选择以windows结尾的default_windows.go文件进行编译。

 

unix domain socket地址

defaults\defaults_linux.go

const (
    // DefaultAddress is the default unix socket address
    DefaultAddress = "/run/containerd/containerd.sock"
)