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The correct method for transferring data from an io.Reader to a destination bytes.Buffer in Golang without any intermediate steps is to use the Copy() function from the io package.

Here is an example code snippet:

package main

import (
    "bytes"
    "io"
    "os"
)

func main() {
    // Open a file to read
    file, err := os.Open("example.txt")
    if err != nil {
        panic(err)
    }
    defer file.Close()

    // Create a bytes.Buffer to write to
    buffer := bytes.Buffer{}

    // Copy the contents of the file to the buffer
    _, err = io.Copy(&buffer, file)
    if err != nil {
        panic(err)
    }

    // Print the contents of the buffer
    println(buffer.String())
}

In this code, we open a file to read, then create a bytes.Buffer to write to. We use the io.Copy() function to transfer the contents of the file to the buffer. Finally, we print the contents of the buffer to verify that the data was transferred correctly.