How does Go's standard library use interface layering for I/O transformation?

The I/O stack in Go is built by wrapping interfaces. Each layer satisfies io.Reader or io.Writer and wraps the previous layer, adding one transformation: buffering, compression, encryption, counting. No layer modifies the others — they compose transparently.

// Layer by layer: file → gzip → bufio → hash → tee
f, err := os.Create("output.gz")
if err != nil { log.Fatal(err) }
defer f.Close()

// Layer 1: gzip compression on top of the file
gz := gzip.NewWriter(f)        // satisfies io.WriteCloser
defer gz.Close()

// Layer 2: buffering on top of gzip
buf := bufio.NewWriter(gz)     // satisfies io.Writer

// Layer 3: SHA-256 hash computation alongside writing
h := sha256.New()              // satisfies io.Writer
tee := io.MultiWriter(buf, h)  // writes to both buf and hash

// Write data — single Write call propagates through all layers
fmt.Fprintln(tee, "Hello, World!") // → buf → gz → f; also → h

buf.Flush()  // flush buffered data into gzip

sum := h.Sum(nil)
fmt.Printf("SHA-256: %x\n", sum)

// Reading side
f2, _   := os.Open("output.gz")
defer f2.Close()
gzr, _  := gzip.NewReader(f2)  // io.Reader that decompresses
buf2    := bufio.NewReader(gzr) // io.Reader that buffers
limited := io.LimitReader(buf2, 1024) // io.Reader that stops at 1 KB

data, _ := io.ReadAll(limited) // reads through all three layers
fmt.Println(string(data))

Each layer is oblivious to the others. gzip.NewReader doesn't know if it's wrapping a file or a network connection; bufio.NewReader doesn't know about compression. This is the Decorator pattern executed through Go interfaces: behaviours stack without modifying each other.

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