Cannot use (type []byte) as type io.Reader

Question

I don't understand the error, this is my main.go that I execute in the machine "A":

package main

import (
    "fmt"
    "net"
    "os"
    "github.com/mistifyio/go-zfs"
)

func main() {
    // Listen for incoming connections.
    l, err := net.Listen("tcp", "192.168.99.5:9977")
    if err != nil ...
    // Close the listener when the application closes.
    defer l.Close()
    fmt.Println("Listening on " + CONN_HOST + ":" + CONN_PORT)
    for {
        // Listen for an incoming connection.
        conn, err := l.Accept()
        if err != nil ...

        //Handle connections in a new goroutine.
        go handleRequest(conn)
    }
}

// Handles incoming requests.
func handleRequest(conn net.Conn) {
    // Make a buffer to hold incoming data.
    buff := make([]byte, 1024)
    // Read the incoming connection into the buffer.
    _, err := conn.Read(buff)
    if err != nil {
        fmt.Printf("Error reading: %s.\n", err.Error())
    }
    // ReceiveSnapshot
    ds, err := zfs.ReceiveSnapshot(buff, "tank/replication")
    if err != nil {
        fmt.Printf("Error receiving: %s.\n", err.Error())
    }
    fmt.Printf("%s... done!\n", ds)
    // Send a response back to person contacting us.
    conn.Write([]byte("Received!"))
    // Close the connection when you're done with it.
    conn.Close()
}

Now, I show you the function ReceiveSnapshot from github.com/mistifyio/go-zfs/zfs.go:

type command struct {
    Command string
    Stdin   io.Reader
    Stdout  io.Writer
}

func ReceiveSnapshot(input io.Reader, name string) (*Dataset, error) {
    c := command{Command: "zfs", Stdin: input}
    _, err := c.Run("receive", name)
    if err != nil {
        return nil, err
    }
    return GetDataset(name)
}

I have seen in golang pkg the doc of io.Reader:

type Reader interface {
        Read(p []byte) (n int, err error)
}

Why do I receive the error...

• cannot use buff (type []byte) as type io.Reader in argument to zfs.ReceiveSnapshot: []byte does not implement io.Reader (missing Read method)

...when I make go install ?

Answer 1

I think you are missing a step in your logic when you think that []byte would be equivalent to Reader just because the Reader's Read method receives a []byte as a parameter.

Let me try to clarify:

Your ReceiveSnapshot function expects a Reader as a parameter:

ReceiveSnapshot( input io.Reader ...

In order for a type to fulfil the Reader interface, that type should itself implement this function:

Read(p []byte) (n int, err error)

Note that the type should implement that function in order to be a Reader.

[]byte does not implement a Read function. It is just a coincidence that the argument to Read happens to be a []byte.

In order for this to work, you need to send ReceiveSnapshot a proper Reader.

Luckily for you, having a []byte and wanting to Read for it is a common situation so the API provides an easy way to do this:

https://golang.org/pkg/bytes/#NewReader

You just need to send bytes.NewReader(buff) to your ReceiveSnapshot function instead of just buff.