方法中的Golang无效接收者类型

问题描述：

I'm trying to make a simple package to send SSH commands to a server.

I have the following code:

type Connection *ssh.Client

func Connect(addr, user, password string) (conn Connection, err error) {
    sshConfig := &ssh.ClientConfig{
        User: user,
        Auth: []ssh.AuthMethod{
            ssh.Password(password),
        },
        HostKeyCallback: ssh.HostKeyCallback(func(hostname string, remote net.Addr, key ssh.PublicKey) error { return nil }),
    }

    conn, err = ssh.Dial("tcp", addr, sshConfig)
    return
}

func (conn Connection) SendCommand() ([]byte, error) {
    session, err := (*ssh.Client)(conn).NewSession()
    // ...
}

My problem is on the two lines func (conn Connection) SendCommand() ([]byte, error) and session, err := (*ssh.Client)(conn).NewSession().

I can't figure out how to use the methods available for *ssh.Client from my overlaying Connection type.

I understand that I need to do some conversion, and using ssh.Client(*conn).NewSession() would work, but it copies the values of the *ssh.Client which doesn't seem to be the right method.

What should do to access the methods available for a *ssh.Client when working with my custom type Connection *ssh.Client type?

答

You can't declare a new type with a pointer TypeSpec. Also declaring a new type is used specifically to remove the entire method set, so you won't have any of the original methods from the *ssh.Client.

What you want is to use composition by embedding the *ssh.Client in your own struct type:

type Connection struct {
    *ssh.Client
}

func Connect(addr, user, password string) (*Connection, error) {
    sshConfig := &ssh.ClientConfig{
        User: user,
        Auth: []ssh.AuthMethod{
            ssh.Password(password),
        },
        HostKeyCallback: ssh.HostKeyCallback(func(hostname string, remote net.Addr, key ssh.PublicKey) error { return nil }),
    }

    conn, err = ssh.Dial("tcp", addr, sshConfig)
    if err != nil {
        return nil, err
    }

    return &Connection{conn}, nil
}

func (conn *Connection) SendCommand() ([]byte, error) {
    session, err := conn.NewSession()
    // ...
}

答

This is the best I can come up with:

type Connection ssh.Client

func (conn *Connection) SendCommand() ([]byte, error) {
    (*ssh.Client)(conn).NewSession()

Note that I've changed the type to not be a pointer type (but then I've made a pointer receiver for SendCommand). I'm not sure there's any way to create a function with a pointer type as a receiver.

方法中的Golang无效接收者类型

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