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path: root/signer.go
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package acme

import (
	"crypto"
	"crypto/ecdsa"
	"crypto/rsa"
	"encoding/base64"
	"errors"
	"io/ioutil"
	"net/http"
	"strings"

	"github.com/square/go-jose"
)

// KeySize is a default RSA key size
const KeySize = 2048

var ErrNoNonces = errors.New("out of nonces")

type signer struct {
	jose.Signer
	nonces chan string
}

func Thumbnail(privKey crypto.PrivateKey) (string, error) {
	thumbnail := func(pubKey crypto.PublicKey) (string, error) {
		jwk := &jose.JsonWebKey{Key: pubKey}
		t, err := jwk.Thumbprint(crypto.SHA256)
		if err != nil {
			return "", err
		}
		return base64.RawURLEncoding.EncodeToString(t), nil
	}
	switch k := privKey.(type) {
	case *rsa.PrivateKey:
		return thumbnail(k.Public())
	case *ecdsa.PrivateKey:
		return thumbnail(k.Public())
	}
	return "", ErrKeyType
}

func newSigner(privKey crypto.PrivateKey) (*signer, error) {
	js := func(crypto.PrivateKey) (jose.Signer, error) {
		switch k := privKey.(type) {
		case *rsa.PrivateKey:
			return jose.NewSigner(jose.RS256, k)
		case *ecdsa.PrivateKey:
			return jose.NewSigner(jose.ES384, k)
		}
		return nil, ErrKeyType
	}
	s, err := js(privKey)
	if err != nil {
		return nil, err
	}
	sig := &signer{Signer: s, nonces: make(chan string, 100)}
	sig.SetNonceSource(sig)
	return sig, nil
}

// Nonce implements jose nonce provider
func (s signer) Nonce() (string, error) {
	select {
	case nonce := <-s.nonces:
		return nonce, nil
	default:
		return "", ErrNoNonces
	}
}

// RoundTrip extracts nonces from HTTP response
func (s signer) RoundTrip(req *http.Request) (*http.Response, error) {
	if req.Method == http.MethodPost {
		body, err := ioutil.ReadAll(req.Body)
		if err != nil {
			return nil, err
		}
		req.Body.Close()
		obj, err := s.Sign(body)
		if err != nil {
			return nil, err
		}
		signed := obj.FullSerialize()
		req.ContentLength = int64(len(signed))
		req.Body = ioutil.NopCloser(strings.NewReader(signed))
	}
	resp, err := http.DefaultTransport.RoundTrip(req)
	if err != nil {
		return nil, err
	}
	if nonce := resp.Header.Get("Replay-Nonce"); nonce != "" {
		select {
		case s.nonces <- nonce:
		default:
		}
	}
	return resp, nil
}