Interfaces - Gotraining

Writes/Reader Interfaces - Standard Library

type Writer interface {
        Write(p []byte) (n int, err error)
}

The implementation of the Write method should attempt to write the entire length of the byte slice that is passed in.
If the entire slice could not be written, the number of bytes successfully written along with a non-nil error must be returned.
Otherwise, when completely successful, the returned n must equal len(p) and a nil error should be returned.
The Writer implementation must never modify the provided byte slice at any time.

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

The implementation should fill the provided byte slice with all the data that is immediately available, up to len(p) bytes.
If no data is immediately available, Read should block.
io.EOF is a special error value used to signal an end-of-file condition: no more data will follow.
When an error or EOF condition occurs, Reader implementations can choose either to return the error value immediately from that same Read call, or may wait and return n == 0 along with the error on the next Read call. Code using Readers should be able to handle both situations.
Anytime the Read method returns bytes, those bytes should be processed first before checking the error value for an EOF or other error value.
The implementation must never return a 0 byte read count with an error value of nil. Reads that result in no bytes read should always return an error.