tokidoki/storage/etag.go

package storage

import (
	"crypto/sha1"
	"encoding/base64"
	"hash"
	"io"
)

type ETagWriter struct {
	io.Writer
	output io.Writer
	csum   hash.Hash
}

// NewETagWriter creates a new io.Writer that pipes writes to the provided
// output while also calculating the contents ETag.
func NewETagWriter(output io.Writer) *ETagWriter {
	csum := sha1.New()
	return &ETagWriter{
		output: io.MultiWriter(output, csum),
		csum:   csum,
	}
}

func (e *ETagWriter) Write(p []byte) (n int, err error) {
	return e.output.Write(p)
}

func (e *ETagWriter) ETag() string {
	csum := e.csum.Sum(nil)
	return base64.StdEncoding.EncodeToString(csum[:])
}

type ETagReader struct {
	io.Reader
	input io.Reader
	csum  hash.Hash
}

// NewETagReader creates a new io.Reader that pipes reads from the provided
// input while also calculating the contents ETag.
func NewETagReader(input io.Reader) *ETagReader {
	csum := sha1.New()
	return &ETagReader{
		input: io.TeeReader(input, csum),
		csum:  csum,
	}
}

func (e *ETagReader) Read(p []byte) (n int, err error) {
	return e.input.Read(p)
}

func (e *ETagReader) ETag() string {
	csum := e.csum.Sum(nil)
	return base64.StdEncoding.EncodeToString(csum[:])
}