Standard Library I/O

Go's input and output (I/O) system is primarily built on two simple but powerful interfaces: io.Reader and io.Writer. These interfaces allow you to abstract away the source of data—whether it's a file, a network socket, or a simple memory buffer—and write generic, reusable code.

1. The Core Interfaces

I. io.Reader

Any type that can be read from implements this interface.

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

II. io.Writer

Any type that can be written to implements this interface.

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

2. Using bufio for Efficiency

Reading data one byte at a time is inefficient because each call to the operating system has overhead. The bufio package provides a buffered layer that reads large chunks of data into memory at once.

file, _ := os.Open("large_file.txt")
reader := bufio.NewReader(file)

for {
    line, err := reader.ReadString('\n')
    if err == io.EOF {
        break
    }
}

3. Streaming Data with io.Copy

One of the most powerful utilities in Go is io.Copy. It allows you to "pipe" data from a Reader directly into a Writer without loading the entire content into memory. This is essential for building high-performance proxies or file uploaders.

// Copies data from source into destination efficiently
io.Copy(destination, source)

4. Closing Resources

Always remember to close your readers/writers if they implement io.Closer (like files and network connections). As discussed in Module 6, the defer keyword is your best friend here.

Interview Pro-Tips: Why use interfaces for I/O?

If an interviewer asks why Go's I/O is designed this way:

• The Answer: It enables Composition. Because everything is a Reader or a Writer, you can "Chain" them. You can take a File (Reader), wrap it in a Gzip (Reader), and then wrap that in a Decryptor (Reader). Your code just sees a Reader, making it incredibly flexible and decoupled from the actual source of data.

Technical Summary

1. Reader/Writer: The "Atoms" of Go's I/O system.
2. bufio: Reduces system call overhead through memory buffering.
3. Streaming: Processing data as it arrives rather than loading it all at once.