// NewBundlerFromPEM creates a new Bundler from PEM-encoded root certificates and
// intermediate certificates.
func NewBundlerFromPEM(caBundlePEM, intBundlePEM []byte) (*Bundler, error) {
	b := &Bundler{
		RootPool:         x509.NewCertPool(),
		IntermediatePool: x509.NewCertPool(),
		KnownIssuers:     map[string]bool{},
	}

	log.Debug("parsing root certificates from PEM")
	roots, err := helpers.ParseCertificatesPEM(caBundlePEM)
	if err != nil {
		log.Errorf("failed to parse root bundle: %v", err)
		return nil, errors.New(errors.RootError, errors.ParseFailed)
	}

	log.Debug("parse intermediate certificates from PEM")
	var intermediates []*x509.Certificate
	if intermediates, err = helpers.ParseCertificatesPEM(intBundlePEM); err != nil {
		log.Errorf("failed to parse intermediate bundle: %v", err)
		return nil, errors.New(errors.IntermediatesError, errors.ParseFailed)
	}

	log.Debug("building certificate pools")
	for _, c := range roots {
		b.RootPool.AddCert(c)
		b.KnownIssuers[string(c.Signature)] = true
	}

	for _, c := range intermediates {
		b.IntermediatePool.AddCert(c)
		b.KnownIssuers[string(c.Signature)] = true
	}

	log.Debug("bundler set up")
	return b, nil
}

// NewSourceFromFile reads the named file into an InMemorySource.
// The file read by this function must contain whitespace-separated OCSP
// responses. Each OCSP response must be in base64-encoded DER form (i.e.,
// PEM without headers or whitespace).  Invalid responses are ignored.
// This function pulls the entire file into an InMemorySource.
func NewSourceFromFile(responseFile string) (Source, error) {
	fileContents, err := ioutil.ReadFile(responseFile)
	if err != nil {
		return nil, err
	}

	responsesB64 := regexp.MustCompile("\\s").Split(string(fileContents), -1)
	src := InMemorySource{}
	for _, b64 := range responsesB64 {
		der, tmpErr := base64.StdEncoding.DecodeString(b64)
		if tmpErr != nil {
			log.Errorf("Base64 decode error on: %s", b64)
			continue
		}

		response, tmpErr := ocsp.ParseResponse(der, nil)
		if tmpErr != nil {
			log.Errorf("OCSP decode error on: %s", b64)
			continue
		}

		src[response.SerialNumber.String()] = der
	}

	log.Infof("Read %d OCSP responses", len(src))
	return src, nil
}

// NewBundler creates a new Bundler from the files passed in; these
// files should contain a list of valid root certificates and a list
// of valid intermediate certificates, respectively.
func NewBundler(caBundleFile, intBundleFile string) (*Bundler, error) {
	log.Debug("Loading CA bundle: ", caBundleFile)
	caBundlePEM, err := ioutil.ReadFile(caBundleFile)
	if err != nil {
		log.Errorf("root bundle failed to load: %v", err)
		return nil, errors.Wrap(errors.RootError, errors.ReadFailed, err)
	}

	log.Debug("Loading Intermediate bundle: ", intBundleFile)
	intBundlePEM, err := ioutil.ReadFile(intBundleFile)
	if err != nil {
		log.Errorf("intermediate bundle failed to load: %v", err)
		return nil, errors.Wrap(errors.IntermediatesError, errors.ReadFailed, err)
	}

	if _, err := os.Stat(IntermediateStash); err != nil && os.IsNotExist(err) {
		log.Infof("intermediate stash directory %s doesn't exist, creating", IntermediateStash)
		err = os.MkdirAll(IntermediateStash, 0755)
		if err != nil {
			log.Errorf("failed to create intermediate stash directory %s: %v",
				IntermediateStash, err)
			return nil, err
		}
		log.Infof("intermediate stash directory %s created", IntermediateStash)
	}
	return NewBundlerFromPEM(caBundlePEM, intBundlePEM)
}

// A Responder can process both GET and POST requests.  The mapping
// from an OCSP request to an OCSP response is done by the Source;
// the Responder simply decodes the request, and passes back whatever
// response is provided by the source.
func (rs Responder) ServeHTTP(response http.ResponseWriter, request *http.Request) {
	// Read response from request
	var requestBody []byte
	var err error
	switch request.Method {
	case "GET":
		re := regexp.MustCompile("^.*/")
		base64Request := re.ReplaceAllString(request.RequestURI, "")
		base64Request, err = url.QueryUnescape(base64Request)
		if err != nil {
			return
		}
		requestBody, err = base64.StdEncoding.DecodeString(base64Request)
		if err != nil {
			return
		}
	case "POST":
		requestBody, err = ioutil.ReadAll(request.Body)
		if err != nil {
			response.WriteHeader(http.StatusBadRequest)
			return
		}
	default:
		response.WriteHeader(http.StatusMethodNotAllowed)
		return
	}
	// TODO log request
	b64Body := base64.StdEncoding.EncodeToString(requestBody)
	log.Infof("Received OCSP request: %s", b64Body)

	// All responses after this point will be OCSP.
	// We could check for the content type of the request, but that
	// seems unnecessariliy restrictive.
	response.Header().Add("Content-Type", "application/ocsp-response")

	// Parse response as an OCSP request
	// XXX: This fails if the request contains the nonce extension.
	//      We don't intend to support nonces anyway, but maybe we
	//      should return unauthorizedRequest instead of malformed.
	ocspRequest, err := ocsp.ParseRequest(requestBody)
	if err != nil {
		log.Errorf("Error decoding request body: %s", b64Body)
		response.Write(malformedRequestErrorResponse)
		return
	}

	// Look up OCSP response from source
	ocspResponse, found := rs.Source.Response(ocspRequest)
	if !found {
		log.Errorf("No response found for request: %s", b64Body)
		response.Write(unauthorizedErrorResponse)
		return
	}

	// Write OCSP response to response
	response.WriteHeader(http.StatusOK)
	response.Write(ocspResponse)
}

// NewCertGeneratorHandler builds a new handler for generating
// certificates directly from certificate requests; the validator covers
// the certificate request and the CA's key and certificate are used to
// sign the generated request. If remote is not an empty string, the
// handler will send signature requests to the CFSSL instance contained
// in remote.
func NewCertGeneratorHandler(validator Validator, caFile, caKeyFile string, policy *config.Signing) (http.Handler, error) {
	var err error
	log.Info("setting up new generator / signer")
	cg := new(CertGeneratorHandler)

	if policy == nil {
		policy = &config.Signing{
			Default:  config.DefaultConfig(),
			Profiles: nil,
		}
	}

	root := universal.Root{
		Config: map[string]string{
			"ca-file":     caFile,
			"ca-key-file": caKeyFile,
		},
	}
	if cg.signer, err = universal.NewSigner(root, policy); err != nil {
		log.Errorf("setting up signer failed: %v", err)
		return nil, err
	}

	cg.generator = &csr.Generator{Validator: validator}

	return api.HTTPHandler{Handler: cg, Method: "POST"}, nil
}

// handleError is the centralised error handling and reporting.
func handleError(w http.ResponseWriter, err error) (code int) {
	if err == nil {
		return http.StatusOK
	}
	msg := err.Error()
	httpCode := http.StatusInternalServerError

	// If it is recognized as HttpError emitted from cf-ssl,
	// we rewrite the status code accordingly. If it is a
	// cf-ssl error, set the http status to StatusBadRequest
	switch err := err.(type) {
	case *errors.HTTPError:
		httpCode = err.StatusCode
		code = err.StatusCode
	case *errors.Error:
		httpCode = http.StatusBadRequest
		code = err.ErrorCode
		msg = err.Message
	}

	response := NewErrorResponse(msg, code)
	jsonMessage, err := json.Marshal(response)
	if err != nil {
		log.Errorf("Failed to marshal JSON: %v", err)
	} else {
		msg = string(jsonMessage)
	}
	http.Error(w, msg, httpCode)
	return code
}

// Generate creates a new CSR from a CertificateRequest structure and
// an existing key. The KeyRequest field is ignored.
func Generate(priv crypto.Signer, req *CertificateRequest) (csr []byte, err error) {
	sigAlgo := helpers.SignerAlgo(priv, crypto.SHA256)
	if sigAlgo == x509.UnknownSignatureAlgorithm {
		return nil, cferr.New(cferr.PrivateKeyError, cferr.Unavailable)
	}

	var tpl = x509.CertificateRequest{
		Subject:            req.Name(),
		SignatureAlgorithm: sigAlgo,
	}

	for i := range req.Hosts {
		if ip := net.ParseIP(req.Hosts[i]); ip != nil {
			tpl.IPAddresses = append(tpl.IPAddresses, ip)
		} else {
			tpl.DNSNames = append(tpl.DNSNames, req.Hosts[i])
		}
	}

	csr, err = x509.CreateCertificateRequest(rand.Reader, &tpl, priv)
	if err != nil {
		log.Errorf("failed to generate a CSR: %v", err)
		err = cferr.Wrap(cferr.CSRError, cferr.BadRequest, err)
		return
	}
	block := pem.Block{
		Type:  "CERTIFICATE REQUEST",
		Bytes: csr,
	}

	log.Info("encoded CSR")
	csr = pem.EncodeToMemory(&block)
	return
}

// New creates a new root certificate from the certificate request.
func New(req *csr.CertificateRequest) (cert, key []byte, err error) {
	if req.CA != nil {
		if req.CA.Expiry != "" {
			CAPolicy.Default.ExpiryString = req.CA.Expiry
			CAPolicy.Default.Expiry, err = time.ParseDuration(req.CA.Expiry)
		}

		if req.CA.PathLength != 0 {
			signer.MaxPathLen = req.CA.PathLength
		}
	}

	g := &csr.Generator{Validator: validator}
	csr, key, err := g.ProcessRequest(req)
	if err != nil {
		log.Errorf("failed to process request: %v", err)
		key = nil
		return
	}

	priv, err := helpers.ParsePrivateKeyPEM(key)
	if err != nil {
		log.Errorf("failed to parse private key: %v", err)
		return
	}

	s, err := local.NewSigner(priv, nil, signer.DefaultSigAlgo(priv), nil)
	if err != nil {
		log.Errorf("failed to create signer: %v", err)
		return
	}
	s.SetPolicy(CAPolicy)

	signReq := signer.SignRequest{Hosts: req.Hosts, Request: string(csr)}
	cert, err = s.Sign(signReq)

	return

}

// NewHandler generates a new Handler using the certificate
// authority private key and certficate to sign certificates. If remote
// is not an empty string, the handler will send signature requests to
// the CFSSL instance contained in remote by default.
func NewHandler(caFile, caKeyFile string, policy *config.Signing) (http.Handler, error) {
	root := universal.Root{
		Config: map[string]string{
			"cert-file": caFile,
			"key-file":  caKeyFile,
		},
	}
	s, err := universal.NewSigner(root, policy)
	if err != nil {
		log.Errorf("setting up signer failed: %v", err)
		return nil, err
	}

	return NewHandlerFromSigner(s)
}

func (b *Bundler) verifyChain(chain []*fetchedIntermediate) bool {
	// This process will verify if the root of the (partial) chain is in our root pool,
	// and will fail otherwise.
	log.Debugf("verifying chain")
	for vchain := chain[:]; len(vchain) > 0; vchain = vchain[1:] {
		cert := vchain[0]
		// If this is a certificate in one of the pools, skip it.
		if b.KnownIssuers[string(cert.Cert.Signature)] {
			log.Debugf("certificate is known")
			continue
		}

		_, err := cert.Cert.Verify(b.VerifyOptions())
		if err != nil {
			log.Debugf("certificate failed verification: %v", err)
			return false
		} else if len(chain) == len(vchain) && isChainRootNode(cert.Cert) {
			// The first certificate in the chain is a root; it shouldn't be stored.
			log.Debug("looking at root certificate, will not store")
			continue
		}

		// leaf cert has an empty name, don't store leaf cert.
		if cert.Name == "" {
			continue
		}

		log.Debug("add certificate to intermediate pool:", cert.Name)
		b.IntermediatePool.AddCert(cert.Cert)
		b.KnownIssuers[string(cert.Cert.Signature)] = true

		fileName := filepath.Join(IntermediateStash, cert.Name)

		var block = pem.Block{Type: "CERTIFICATE", Bytes: cert.Cert.Raw}

		log.Debugf("write intermediate to stash directory: %s", fileName)
		// If the write fails, verification should not fail.
		err = ioutil.WriteFile(fileName, pem.EncodeToMemory(&block), 0644)
		if err != nil {
			log.Errorf("failed to write new intermediate: %v", err)
		} else {
			log.Info("stashed new intermediate ", cert.Name)
		}
	}
	return true
}

// ParseRequest takes a certificate request and generates a key and
// CSR from it. It does no validation -- caveat emptor. It will,
// however, fail if the key request is not valid (i.e., an unsupported
// curve or RSA key size). The lack of validation was specifically
// chosen to allow the end user to define a policy and validate the
// request appropriately before calling this function.
func ParseRequest(req *CertificateRequest) (csr, key []byte, err error) {
	log.Info("received CSR")
	if req.KeyRequest == nil {
		req.KeyRequest = &KeyRequest{
			Algo: DefaultKeyRequest.Algo,
			Size: DefaultKeyRequest.Size,
		}
	}

	log.Infof("generating key: %s-%d", req.KeyRequest.Algo, req.KeyRequest.Size)
	priv, err := req.KeyRequest.Generate()
	if err != nil {
		err = cferr.Wrap(cferr.PrivateKeyError, cferr.GenerationFailed, err)
		return
	}

	switch priv := priv.(type) {
	case *rsa.PrivateKey:
		key = x509.MarshalPKCS1PrivateKey(priv)
		block := pem.Block{
			Type:  "RSA PRIVATE KEY",
			Bytes: key,
		}
		key = pem.EncodeToMemory(&block)
	case *ecdsa.PrivateKey:
		key, err = x509.MarshalECPrivateKey(priv)
		if err != nil {
			err = cferr.Wrap(cferr.PrivateKeyError, cferr.Unknown, err)
			return
		}
		block := pem.Block{
			Type:  "EC PRIVATE KEY",
			Bytes: key,
		}
		key = pem.EncodeToMemory(&block)
	default:
		panic("Generate should have failed to produce a valid key.")
	}

	var tpl = x509.CertificateRequest{
		Subject:            req.Name(),
		SignatureAlgorithm: req.KeyRequest.SigAlgo(),
		DNSNames:           req.Hosts,
	}
	csr, err = x509.CreateCertificateRequest(rand.Reader, &tpl, priv)
	if err != nil {
		log.Errorf("failed to generate a CSR: %v", err)
		// The use of CertificateError was a matter of some
		// debate; it is the one edge case in which a new
		// error category specifically for CSRs might be
		// useful, but it was deemed that one edge case did
		// not a new category justify.
		err = cferr.Wrap(cferr.CertificateError, cferr.BadRequest, err)
		return
	}
	block := pem.Block{
		Type:  "CERTIFICATE REQUEST",
		Bytes: csr,
	}

	log.Info("encoded CSR")
	csr = pem.EncodeToMemory(&block)
	return
}

// NewFromPEM creates a new root certificate from the key file passed in.
func NewFromPEM(req *csr.CertificateRequest, keyFile string) (cert []byte, err error) {
	if req.CA != nil {
		if req.CA.Expiry != "" {
			CAPolicy.Default.ExpiryString = req.CA.Expiry
			CAPolicy.Default.Expiry, err = time.ParseDuration(req.CA.Expiry)
		}

		if req.CA.PathLength != 0 {
			signer.MaxPathLen = req.CA.PathLength
		}
	}

	privData, err := ioutil.ReadFile(keyFile)
	if err != nil {
		return nil, err
	}

	priv, err := helpers.ParsePrivateKeyPEM(privData)
	if err != nil {
		return nil, err
	}

	var sigAlgo x509.SignatureAlgorithm
	switch priv := priv.(type) {
	case *rsa.PrivateKey:
		bitLength := priv.PublicKey.N.BitLen()
		switch {
		case bitLength >= 4096:
			sigAlgo = x509.SHA512WithRSA
		case bitLength >= 3072:
			sigAlgo = x509.SHA384WithRSA
		case bitLength >= 2048:
			sigAlgo = x509.SHA256WithRSA
		default:
			sigAlgo = x509.SHA1WithRSA
		}
	case *ecdsa.PrivateKey:
		switch priv.Curve {
		case elliptic.P521():
			sigAlgo = x509.ECDSAWithSHA512
		case elliptic.P384():
			sigAlgo = x509.ECDSAWithSHA384
		case elliptic.P256():
			sigAlgo = x509.ECDSAWithSHA256
		default:
			sigAlgo = x509.ECDSAWithSHA1
		}
	default:
		sigAlgo = x509.UnknownSignatureAlgorithm
	}

	var tpl = x509.CertificateRequest{
		Subject:            req.Name(),
		SignatureAlgorithm: sigAlgo,
		DNSNames:           req.Hosts,
	}

	certReq, err := x509.CreateCertificateRequest(rand.Reader, &tpl, priv)
	if err != nil {
		log.Errorf("failed to generate a CSR: %v", err)
		// The use of CertificateError was a matter of some
		// debate; it is the one edge case in which a new
		// error category specifically for CSRs might be
		// useful, but it was deemed that one edge case did
		// not a new category justify.
		err = cferr.Wrap(cferr.CertificateError, cferr.BadRequest, err)
		return
	}

	p := &pem.Block{
		Type:  "CERTIFICATE REQUEST",
		Bytes: certReq,
	}
	certReq = pem.EncodeToMemory(p)

	s, err := local.NewSigner(priv, nil, signer.DefaultSigAlgo(priv), nil)
	if err != nil {
		log.Errorf("failed to create signer: %v", err)
		return
	}
	s.SetPolicy(CAPolicy)

	signReq := signer.SignRequest{Request: string(certReq)}
	cert, err = s.Sign(signReq)
	return
}

// ParseRequest takes a certificate request and generates a key and
// CSR from it. It does no validation -- caveat emptor. It will,
// however, fail if the key request is not valid (i.e., an unsupported
// curve or RSA key size). The lack of validation was specifically
// chosen to allow the end user to define a policy and validate the
// request appropriately before calling this function.
func ParseRequest(req *CertificateRequest) (csr, key []byte, err error) {
	log.Info("received CSR")
	if req.KeyRequest == nil {
		req.KeyRequest = &KeyRequest{
			Algo: DefaultKeyRequest.Algo,
			Size: DefaultKeyRequest.Size,
		}
	}

	log.Infof("generating key: %s-%d", req.KeyRequest.Algo, req.KeyRequest.Size)
	priv, err := req.KeyRequest.Generate()
	if err != nil {
		err = cferr.Wrap(cferr.PrivateKeyError, cferr.GenerationFailed, err)
		return
	}

	switch priv := priv.(type) {
	case *rsa.PrivateKey:
		key = x509.MarshalPKCS1PrivateKey(priv)
		block := pem.Block{
			Type:  "RSA PRIVATE KEY",
			Bytes: key,
		}
		key = pem.EncodeToMemory(&block)
	case *ecdsa.PrivateKey:
		key, err = x509.MarshalECPrivateKey(priv)
		if err != nil {
			err = cferr.Wrap(cferr.PrivateKeyError, cferr.Unknown, err)
			return
		}
		block := pem.Block{
			Type:  "EC PRIVATE KEY",
			Bytes: key,
		}
		key = pem.EncodeToMemory(&block)
	default:
		panic("Generate should have failed to produce a valid key.")
	}

	var tpl = x509.CertificateRequest{
		Subject:            req.Name(),
		SignatureAlgorithm: req.KeyRequest.SigAlgo(),
	}

	for i := range req.Hosts {
		if ip := net.ParseIP(req.Hosts[i]); ip != nil {
			tpl.IPAddresses = append(tpl.IPAddresses, ip)
		} else {
			tpl.DNSNames = append(tpl.DNSNames, req.Hosts[i])
		}
	}

	csr, err = x509.CreateCertificateRequest(rand.Reader, &tpl, priv)
	if err != nil {
		log.Errorf("failed to generate a CSR: %v", err)
		err = cferr.Wrap(cferr.CSRError, cferr.BadRequest, err)
		return
	}
	block := pem.Block{
		Type:  "CERTIFICATE REQUEST",
		Bytes: csr,
	}

	log.Info("encoded CSR")
	csr = pem.EncodeToMemory(&block)
	return
}

func gencertMain(args []string, c cli.Config) (err error) {

	csrJSONFile, args, err := cli.PopFirstArgument(args)
	if err != nil {
		return
	}

	csrJSONFileBytes, err := cli.ReadStdin(csrJSONFile)
	if err != nil {
		return
	}

	var req csr.CertificateRequest
	err = json.Unmarshal(csrJSONFileBytes, &req)
	if err != nil {
		return
	}

	if c.IsCA {
		var key, cert []byte
		cert, err = initca.NewFromPEM(&req, c.CAKeyFile)
		if err != nil {
			log.Errorf("%v\n", err)
			log.Infof("generating a new CA key and certificate from CSR")
			cert, key, err = initca.New(&req)
			if err != nil {
				return
			}

		}
		cli.PrintCert(key, nil, cert)

	} else {
		if req.CA != nil {
			err = errors.New("ca section only permitted in initca")
			return
		}

		// Remote can be forced on the command line or in the config
		if c.Remote == "" && c.CFG == nil {
			if c.CAFile == "" {
				log.Error("need a CA certificate (provide one with -ca)")
				return
			}

			if c.CAKeyFile == "" {
				log.Error("need a CA key (provide one with -ca-key)")
				return
			}
		}

		var key, csrBytes []byte
		g := &csr.Generator{Validator: genkey.Validator}
		csrBytes, key, err = g.ProcessRequest(&req)
		if err != nil {
			key = nil
			return
		}

		s, err := sign.SignerFromConfig(c)
		if err != nil {
			return err
		}

		var cert []byte
		req := signer.SignRequest{
			Request: string(csrBytes),
			Hosts:   signer.SplitHosts(c.Hostname),
			Profile: c.Profile,
			Label:   c.Label,
		}

		cert, err = s.Sign(req)
		if err != nil {
			return err
		}

		cli.PrintCert(key, csrBytes, cert)
	}
	return nil
}

// Handle receives the incoming request, validates it, and processes it.
func (h *AuthHandler) Handle(w http.ResponseWriter, r *http.Request) error {
	log.Info("signature request received")

	body, err := ioutil.ReadAll(r.Body)
	if err != nil {
		log.Errorf("failed to read response body: %v", err)
		return err
	}
	r.Body.Close()

	var aReq auth.AuthenticatedRequest
	err = json.Unmarshal(body, &aReq)
	if err != nil {
		log.Errorf("failed to unmarshal authenticated request: %v", err)
		return errors.NewBadRequest(err)
	}

	var req jsonSignRequest
	err = json.Unmarshal(aReq.Request, &req)
	if err != nil {
		log.Errorf("failed to unmarshal request from authenticated request: %v", err)
		return errors.NewBadRequestString("Unable to parse authenticated sign request")
	}

	// Sanity checks to ensure that we have a valid policy. This
	// should have been checked in NewAuthHandler.
	policy := h.signer.Policy()
	if policy == nil {
		log.Critical("signer was initialised without a signing policy")
		return errors.NewBadRequestString("invalid policy")
	}
	profile := policy.Default

	if policy.Profiles != nil && req.Profile != "" {
		profile = policy.Profiles[req.Profile]
	}

	if profile == nil {
		log.Critical("signer was initialised without any valid profiles")
		return errors.NewBadRequestString("invalid profile")
	}

	if profile.Provider == nil {
		log.Error("profile has no authentication provider")
		return errors.NewBadRequestString("no authentication provider")
	}

	if !profile.Provider.Verify(&aReq) {
		log.Warning("received authenticated request with invalid token")
		return errors.NewBadRequestString("invalid token")
	}

	signReq := jsonReqToTrue(req)
	if signReq.Hosts == nil {
		return errors.NewBadRequestString("missing parameter 'hostname' or 'hosts'")
	}

	if signReq.Request == "" {
		return errors.NewBadRequestString("missing parameter 'certificate_request'")
	}

	cert, err := h.signer.Sign(signReq)
	if err != nil {
		log.Errorf("signature failed: %v", err)
		return err
	}

	result := map[string]string{"certificate": string(cert)}
	log.Info("wrote response")
	return api.SendResponse(w, result)
}

// fetchIntermediates goes through each of the URLs in the AIA "Issuing
// CA" extensions and fetches those certificates. If those
// certificates are not present in either the root pool or
// intermediate pool, the certificate is saved to file and added to
// the list of intermediates to be used for verification. This will
// not add any new certificates to the root pool; if the ultimate
// issuer is not trusted, fetching the certicate here will not change
// that.
func (b *Bundler) fetchIntermediates(certs []*x509.Certificate) (err error) {
	log.Debugf("searching intermediates")
	if _, err := os.Stat(IntermediateStash); err != nil && os.IsNotExist(err) {
		log.Infof("intermediate stash directory %s doesn't exist, creating", IntermediateStash)
		err = os.MkdirAll(IntermediateStash, 0755)
		if err != nil {
			log.Errorf("failed to create intermediate stash directory %s: %v", IntermediateStash, err)
			return err
		}
		log.Infof("intermediate stash directory %s created", IntermediateStash)
	}

	// stores URLs and certificate signatures that have been seen
	seen := map[string]bool{}
	var foundChains int

	// Construct a verify chain as a reversed partial bundle,
	// such that the certs are ordered by promxity to the root CAs.
	var chain []*fetchedIntermediate
	for i, cert := range certs {
		var name string

		// Only construct filenames for non-leaf intermediate certs
		// so they will be saved to disk if necessary.
		// Leaf cert gets a empty name and will be skipped.
		if i > 0 {
			name = constructCertFileName(cert)
		}

		chain = append([]*fetchedIntermediate{&fetchedIntermediate{cert, name}}, chain...)
		seen[string(cert.Signature)] = true
	}

	// Verify the chain and store valid intermediates in the chain.
	// If it doesn't verify, fetch the intermediates and extend the chain
	// in a DFS manner and verify each time we hit a root.
	for {
		if len(chain) == 0 {
			log.Debugf("search complete")
			if foundChains == 0 {
				return x509.UnknownAuthorityError{}
			}
			return nil
		}

		current := chain[0]
		var advanced bool
		if b.verifyChain(chain) {
			foundChains++
		}
		log.Debugf("walk AIA issuers")
		for _, url := range current.Cert.IssuingCertificateURL {
			if seen[url] {
				log.Debugf("url %s has been seen", url)
				continue
			}
			crt, err := fetchRemoteCertificate(url)
			if err != nil {
				continue
			} else if seen[string(crt.Cert.Signature)] {
				log.Debugf("fetched certificate is known")
				continue
			}
			seen[url] = true
			seen[string(crt.Cert.Signature)] = true
			chain = append([]*fetchedIntermediate{crt}, chain...)
			advanced = true
			break
		}

		if !advanced {
			log.Debugf("didn't advance, stepping back")
			chain = chain[1:]
		}
	}
}

// A Responder can process both GET and POST requests.  The mapping
// from an OCSP request to an OCSP response is done by the Source;
// the Responder simply decodes the request, and passes back whatever
// response is provided by the source.
// Note: The caller must use http.StripPrefix to strip any path components
// (including '/') on GET requests.
// Do not use this responder in conjunction with http.NewServeMux, because the
// default handler will try to canonicalize path components by changing any
// strings of repeated '/' into a single '/', which will break the base64
// encoding.
func (rs Responder) ServeHTTP(response http.ResponseWriter, request *http.Request) {
	// Read response from request
	var requestBody []byte
	var err error
	switch request.Method {
	case "GET":
		base64Request, err := url.QueryUnescape(request.URL.Path)
		if err != nil {
			log.Errorf("Error decoding URL: %s", request.URL.Path)
			response.WriteHeader(http.StatusBadRequest)
			return
		}
		// url.QueryUnescape not only unescapes %2B escaping, but it additionally
		// turns the resulting '+' into a space, which makes base64 decoding fail.
		// So we go back afterwards and turn ' ' back into '+'. This means we
		// accept some malformed input that includes ' ' or %20, but that's fine.
		base64RequestBytes := []byte(base64Request)
		for i := range base64RequestBytes {
			if base64RequestBytes[i] == ' ' {
				base64RequestBytes[i] = '+'
			}
		}
		requestBody, err = base64.StdEncoding.DecodeString(string(base64RequestBytes))
		if err != nil {
			log.Errorf("Error decoding base64 from URL: %s", base64Request)
			response.WriteHeader(http.StatusBadRequest)
			return
		}
	case "POST":
		requestBody, err = ioutil.ReadAll(request.Body)
		if err != nil {
			log.Errorf("Problem reading body of POST: %s", err)
			response.WriteHeader(http.StatusBadRequest)
			return
		}
	default:
		response.WriteHeader(http.StatusMethodNotAllowed)
		return
	}
	// TODO log request
	b64Body := base64.StdEncoding.EncodeToString(requestBody)
	log.Infof("Received OCSP request: %s", b64Body)

	// All responses after this point will be OCSP.
	// We could check for the content type of the request, but that
	// seems unnecessariliy restrictive.
	response.Header().Add("Content-Type", "application/ocsp-response")

	// Parse response as an OCSP request
	// XXX: This fails if the request contains the nonce extension.
	//      We don't intend to support nonces anyway, but maybe we
	//      should return unauthorizedRequest instead of malformed.
	ocspRequest, err := ocsp.ParseRequest(requestBody)
	if err != nil {
		log.Errorf("Error decoding request body: %s", b64Body)
		response.WriteHeader(http.StatusBadRequest)
		response.Write(malformedRequestErrorResponse)
		return
	}

	// Look up OCSP response from source
	ocspResponse, found := rs.Source.Response(ocspRequest)
	if !found {
		log.Errorf("No response found for request: %s", b64Body)
		response.Write(unauthorizedErrorResponse)
		return
	}

	parsedResponse, err := ocsp.ParseResponse(ocspResponse, nil)
	if err != nil {
		log.Errorf("Error parsing response: %s", err)
		response.Write(unauthorizedErrorResponse)
		return
	}

	// Write OCSP response to response
	response.Header().Add("Last-Modified", parsedResponse.ProducedAt.Format(time.RFC1123))
	response.Header().Add("Expires", parsedResponse.NextUpdate.Format(time.RFC1123))
	maxAge := int64(parsedResponse.NextUpdate.Sub(rs.clk.Now()) / time.Second)
	if maxAge > 0 {
		response.Header().Add("Cache-Control", fmt.Sprintf("max-age=%d", maxAge))
	}
	response.WriteHeader(http.StatusOK)
	response.Write(ocspResponse)
}

// registerHandlers instantiates various handlers and associate them to corresponding endpoints.
func registerHandlers(c cli.Config) error {
	log.Info("Setting up signer endpoint")
	s, err := sign.SignerFromConfig(c)
	if err != nil {
		log.Warningf("sign and authsign endpoints are disabled: %v", err)
	} else {
		if signHandler, err := apisign.NewHandlerFromSigner(s); err == nil {
			log.Info("Assigning handler to /sign")
			http.Handle("/api/v1/cfssl/sign", signHandler)
		} else {
			log.Warningf("endpoint '/api/v1/cfssl/sign' is disabled: %v", err)
		}

		if signHandler, err := apisign.NewAuthHandlerFromSigner(s); err == nil {
			log.Info("Assigning handler to /authsign")
			http.Handle("/api/v1/cfssl/authsign", signHandler)
		} else {
			log.Warningf("endpoint '/api/v1/cfssl/authsign' is disabled: %v", err)
		}
	}

	log.Info("Setting up info endpoint")
	infoHandler, err := info.NewHandler(s)
	if err != nil {
		log.Warningf("endpoint '/api/v1/cfssl/info' is disabled: %v", err)
	} else {
		http.Handle("/api/v1/cfssl/info", infoHandler)
	}

	log.Info("Setting up new cert endpoint")
	if err != nil {
		log.Errorf("endpoint '/api/v1/cfssl/newcert' is disabled")
	} else {
		newCertGenerator := generator.NewCertGeneratorHandlerFromSigner(generator.CSRValidate, s)
		http.Handle("/api/v1/cfssl/newcert", newCertGenerator)
	}

	log.Info("Setting up bundler endpoint")
	bundleHandler, err := bundle.NewHandler(c.CABundleFile, c.IntBundleFile)
	if err != nil {
		log.Warningf("endpoint '/api/v1/cfssl/bundle' is disabled: %v", err)
	} else {
		http.Handle("/api/v1/cfssl/bundle", bundleHandler)
	}

	log.Info("Setting up CSR endpoint")
	generatorHandler, err := generator.NewHandler(generator.CSRValidate)
	if err != nil {
		log.Errorf("Failed to set up CSR endpoint: %v", err)
		return err
	}
	http.Handle("/api/v1/cfssl/newkey", generatorHandler)

	log.Info("Setting up initial CA endpoint")
	http.Handle("/api/v1/cfssl/init_ca", initca.NewHandler())

	log.Info("Setting up scan endpoint")
	http.Handle("/api/v1/cfssl/scan", scan.NewHandler())

	log.Info("Setting up scaninfo endpoint")
	http.Handle("/api/v1/cfssl/scaninfo", scan.NewInfoHandler())

	log.Info("Handler set up complete.")
	return nil
}