session.go

package irmaclient

import (
	"encoding/json"
	"fmt"
	"sort"
	"strings"

	"math/big"

	"github.com/go-errors/errors"
	"github.com/mhe/gabi"
	"github.com/privacybydesign/irmago"
)

// This file contains the logic and state of performing IRMA sessions, communicates
// with IRMA API servers, and uses the calling Client to construct messages and replies
// in the IRMA protocol.

// PermissionHandler is a callback for providing permission for an IRMA session
// and specifying the attributes to be disclosed.
type PermissionHandler func(proceed bool, choice *irma.DisclosureChoice)

// PinHandler is used to provide the user's PIN code.
type PinHandler func(proceed bool, pin string)

// A Handler contains callbacks for communication to the user.
type Handler interface {
	StatusUpdate(action irma.Action, status irma.Status)
	Success(action irma.Action, result string)
	Cancelled(action irma.Action)
	Failure(action irma.Action, err *irma.SessionError)
	UnsatisfiableRequest(action irma.Action, ServerName string, missing irma.AttributeDisjunctionList)

	KeyshareBlocked(manager irma.SchemeManagerIdentifier, duration int)
	KeyshareEnrollmentIncomplete(manager irma.SchemeManagerIdentifier)
	KeyshareEnrollmentMissing(manager irma.SchemeManagerIdentifier)
	KeyshareEnrollmentDeleted(manager irma.SchemeManagerIdentifier)

	RequestIssuancePermission(request irma.IssuanceRequest, ServerName string, callback PermissionHandler)
	RequestVerificationPermission(request irma.DisclosureRequest, ServerName string, callback PermissionHandler)
	RequestSignaturePermission(request irma.SignatureRequest, ServerName string, callback PermissionHandler)
	RequestSchemeManagerPermission(manager *irma.SchemeManager, callback func(proceed bool))

	RequestPin(remainingAttempts int, callback PinHandler)
}

// SessionDismisser can dismiss the current IRMA session.
type SessionDismisser interface {
	Dismiss()
}

type session struct {
	Action  irma.Action
	Handler Handler
	Version *irma.ProtocolVersion

	choice  *irma.DisclosureChoice
	client  *Client
	request irma.SessionRequest
	done    bool

	// State for issuance protocol
	issuerProofNonce *big.Int
	builders         gabi.ProofBuilderList

	// These are empty on manual sessions
	ServerURL string
	transport *irma.HTTPTransport
}

// We implement the handler for the keyshare protocol
var _ keyshareSessionHandler = (*session)(nil)

// Supported protocol versions. Minor version numbers should be reverse sorted.
var supportedVersions = map[int][]int{
	2: {4, 3, 2, 1},
}

// Session constructors

// NewSession starts a new IRMA session, given (along with a handler to pass feedback to)
// either an irma.QR or *irma.QR; a string that contains a JSON-serialized irma.QR;
// or a string that contains a serialized *irma.SignatureRequest.
// In any other case it calls the Failure method of the specified Handler.
func (client *Client) NewSession(sessionrequest string, handler Handler) SessionDismisser {
	bts := []byte(sessionrequest)

	// Try to deserialize it as a Qr or SignatureRequest
	qr := &irma.Qr{}
	if err := irma.UnmarshalValidate(bts, qr); err == nil {
		return client.newQrSession(qr, handler)
	}

	sigrequest := &irma.SignatureRequest{}
	if err := irma.UnmarshalValidate(bts, sigrequest); err == nil {
		return client.newManualSession(sigrequest, handler)
	}

	handler.Failure(irma.ActionUnknown, &irma.SessionError{Err: errors.New("Session request could not be parsed")})
	return nil
}

// newManualSession starts a manual session, given a signature request in JSON and a handler to pass messages to
func (client *Client) newManualSession(sigrequest *irma.SignatureRequest, handler Handler) SessionDismisser {
	session := &session{
		Action:  irma.ActionSigning, // TODO hardcoded for now
		Handler: handler,
		client:  client,
		Version: irma.NewVersion(2, 0), // TODO hardcoded for now
		request: sigrequest,
	}

	sigrequest.RequestorName = "Email request"
	session.Handler.StatusUpdate(session.Action, irma.StatusManualStarted)
	session.processSessionInfo()
	return session
}

// newQrSession creates and starts a new interactive IRMA session
func (client *Client) newQrSession(qr *irma.Qr, handler Handler) SessionDismisser {
	session := &session{
		ServerURL: qr.URL,
		transport: irma.NewHTTPTransport(qr.URL),
		Action:    irma.Action(qr.Type),
		Handler:   handler,
		client:    client,
	}

	if session.Action == irma.ActionSchemeManager {
		go session.managerSession()
		return session
	}

	// Check if the action is one of the supported types
	switch session.Action {
	case irma.ActionDisclosing:
		session.request = &irma.DisclosureRequest{}
	case irma.ActionSigning:
		session.request = &irma.SignatureRequest{}
	case irma.ActionIssuing:
		session.request = &irma.IssuanceRequest{}
	case irma.ActionUnknown:
		fallthrough
	default:
		session.fail(&irma.SessionError{ErrorType: irma.ErrorUnknownAction, Info: string(session.Action)})
		return nil
	}

	version, err := calcVersion(qr)
	if err != nil {
		session.fail(&irma.SessionError{ErrorType: irma.ErrorProtocolVersionNotSupported, Err: err})
		return nil
	}
	session.Version = version
	session.transport.SetHeader("X-IRMA-ProtocolVersion", version.String())
	if !strings.HasSuffix(session.ServerURL, "/") {
		session.ServerURL += "/"
	}

	go session.getSessionInfo()
	return session
}

// Core session methods

// getSessionInfo retrieves the first message in the IRMA protocol (only in interactive sessions)
func (session *session) getSessionInfo() {
	defer session.recoverFromPanic()

	session.Handler.StatusUpdate(session.Action, irma.StatusCommunicating)

	// Get the first IRMA protocol message and parse it
	err := session.transport.Get("", session.request)
	if err != nil {
		session.fail(err.(*irma.SessionError))
		return
	}

	session.processSessionInfo()
}

// processSessionInfo continues the session after all session state has been received:
// it checks if the session can be performed and asks the user for consent.
func (session *session) processSessionInfo() {
	defer session.recoverFromPanic()

	if !session.checkAndUpateConfiguration() {
		return
	}

	confirmedProtocolVersion := session.request.GetVersion()
	if confirmedProtocolVersion != nil {
		session.Version = confirmedProtocolVersion
	} else {
		session.Version = irma.NewVersion(2, 0)
		session.request.SetVersion(session.Version)
	}

	if session.Action == irma.ActionIssuing {
		ir := session.request.(*irma.IssuanceRequest)
		_, err := ir.GetCredentialInfoList(session.client.Configuration, session.Version)
		if err != nil {
			session.fail(&irma.SessionError{ErrorType: irma.ErrorUnknownCredentialType, Err: err})
			return
		}

		// Calculate singleton credentials to be removed
		for _, credreq := range ir.Credentials {
			preexistingCredentials := session.client.attrs(*credreq.CredentialTypeID)
			if len(preexistingCredentials) != 0 && preexistingCredentials[0].IsValid() && preexistingCredentials[0].CredentialType().IsSingleton {
				ir.RemovalCredentialInfoList = append(ir.RemovalCredentialInfoList, preexistingCredentials[0].Info())
			}
		}
	}

	candidates, missing := session.client.CheckSatisfiability(session.request.ToDisclose())
	if len(missing) > 0 {
		session.Handler.UnsatisfiableRequest(session.Action, session.request.GetRequestorName(), missing)
		return
	}
	session.request.SetCandidates(candidates)

	// Ask for permission to execute the session
	callback := PermissionHandler(func(proceed bool, choice *irma.DisclosureChoice) {
		session.choice = choice
		session.request.SetDisclosureChoice(choice)
		go session.doSession(proceed)
	})
	session.Handler.StatusUpdate(session.Action, irma.StatusConnected)
	switch session.Action {
	case irma.ActionDisclosing:
		session.Handler.RequestVerificationPermission(
			*session.request.(*irma.DisclosureRequest), session.request.GetRequestorName(), callback)
	case irma.ActionSigning:
		session.Handler.RequestSignaturePermission(
			*session.request.(*irma.SignatureRequest), session.request.GetRequestorName(), callback)
	case irma.ActionIssuing:
		session.Handler.RequestIssuancePermission(
			*session.request.(*irma.IssuanceRequest), session.request.GetRequestorName(), callback)
	default:
		panic("Invalid session type") // does not happen, session.Action has been checked earlier
	}
}

// doSession performs the session: it computes all proofs of knowledge, constructs credentials in case of issuance,
// asks for the pin and performs the keyshare session, and finishes the session by either POSTing the result to the
// API server or returning it to the caller (in case of interactive and noninteractive sessions, respectively).
func (session *session) doSession(proceed bool) {
	defer session.recoverFromPanic()

	if !proceed {
		session.cancel()
		return
	}
	session.Handler.StatusUpdate(session.Action, irma.StatusCommunicating)

	if !session.Distributed() {
		message, err := session.getProof()
		if err != nil {
			session.fail(&irma.SessionError{ErrorType: irma.ErrorCrypto, Err: err})
			return
		}
		session.sendResponse(message)
	} else {
		var err error
		session.builders, session.issuerProofNonce, err = session.getBuilders()
		if err != nil {
			session.fail(&irma.SessionError{ErrorType: irma.ErrorCrypto, Err: err})
		}
		startKeyshareSession(
			session,
			session.Handler,
			session.builders,
			session.request,
			session.client.Configuration,
			session.client.keyshareServers,
			session.issuerProofNonce,
		)
	}
}

type disclosureResponse string

// sendResponse sends the proofs of knowledge of the hidden attributes and/or the secret key, or the constructed
// attribute-based signature, to the API server.
func (session *session) sendResponse(message interface{}) {
	var log *LogEntry
	var err error
	var messageJson []byte

	switch session.Action {
	case irma.ActionSigning:
		request, ok := session.request.(*irma.SignatureRequest)
		if !ok {
			session.fail(&irma.SessionError{ErrorType: irma.ErrorSerialization, Info: "Type assertion failed"})
			return
		}

		irmaSignature, err := request.SignatureFromMessage(message)
		if err != nil {
			session.fail(&irma.SessionError{ErrorType: irma.ErrorSerialization, Info: "Type assertion failed"})
			return
		}

		messageJson, err = json.Marshal(irmaSignature)
		if err != nil {
			session.fail(&irma.SessionError{ErrorType: irma.ErrorSerialization, Err: err})
			return
		}

		if session.IsInteractive() {
			var response disclosureResponse
			if err = session.transport.Post("proofs", &response, irmaSignature); err != nil {
				session.fail(err.(*irma.SessionError))
				return
			}
			if response != "VALID" {
				session.fail(&irma.SessionError{ErrorType: irma.ErrorRejected, Info: string(response)})
				return
			}
		}
		log, _ = session.createLogEntry(message.(gabi.ProofList)) // TODO err
	case irma.ActionDisclosing:
		var response disclosureResponse
		if err = session.transport.Post("proofs", &response, message); err != nil {
			session.fail(err.(*irma.SessionError))
			return
		}
		if response != "VALID" {
			session.fail(&irma.SessionError{ErrorType: irma.ErrorRejected, Info: string(response)})
			return
		}
		log, _ = session.createLogEntry(message.(gabi.ProofList)) // TODO err
	case irma.ActionIssuing:
		response := []*gabi.IssueSignatureMessage{}
		if err = session.transport.Post("commitments", &response, message); err != nil {
			session.fail(err.(*irma.SessionError))
			return
		}
		if err = session.client.ConstructCredentials(response, session.request.(*irma.IssuanceRequest), session.builders); err != nil {
			session.fail(&irma.SessionError{ErrorType: irma.ErrorCrypto, Err: err})
			return
		}
		log, _ = session.createLogEntry(message) // TODO err
	}

	_ = session.client.addLogEntry(log) // TODO err
	if session.Action == irma.ActionIssuing {
		session.client.handler.UpdateAttributes()
	}
	session.done = true
	session.Handler.Success(session.Action, string(messageJson))
}

// managerSession performs a "session" in which a new scheme manager is added (asking for permission first).
func (session *session) managerSession() {
	defer session.recoverFromPanic()

	// We have to download the scheme manager description.xml here before installing it,
	// because we need to show its contents (name, description, website) to the user
	// when asking installation permission.
	manager, err := irma.DownloadSchemeManager(session.ServerURL)
	if err != nil {
		session.Handler.Failure(session.Action, &irma.SessionError{ErrorType: irma.ErrorConfigurationDownload, Err: err})
		return
	}

	session.Handler.RequestSchemeManagerPermission(manager, func(proceed bool) {
		if !proceed {
			session.Handler.Cancelled(session.Action) // No need to DELETE session here
			return
		}
		if err := session.client.Configuration.InstallSchemeManager(manager); err != nil {
			session.Handler.Failure(session.Action, &irma.SessionError{ErrorType: irma.ErrorConfigurationDownload, Err: err})
			return
		}

		// Update state and inform user of success
		session.client.handler.UpdateConfiguration(
			&irma.IrmaIdentifierSet{
				SchemeManagers:  map[irma.SchemeManagerIdentifier]struct{}{manager.Identifier(): {}},
				Issuers:         map[irma.IssuerIdentifier]struct{}{},
				CredentialTypes: map[irma.CredentialTypeIdentifier]struct{}{},
			},
		)
		session.Handler.Success(session.Action, "")
	})
	return
}

// Response calculation methods

// getBuilders computes the builders for disclosure proofs or secretkey-knowledge proof (in case of disclosure/signing
// and issuing respectively).
func (session *session) getBuilders() (gabi.ProofBuilderList, *big.Int, error) {
	var builders gabi.ProofBuilderList
	var err error

	var issuerProofNonce *big.Int
	switch session.Action {
	case irma.ActionSigning:
		builders, err = session.client.ProofBuilders(session.choice, session.request, true)
	case irma.ActionDisclosing:
		builders, err = session.client.ProofBuilders(session.choice, session.request, false)
	case irma.ActionIssuing:
		builders, issuerProofNonce, err = session.client.IssuanceProofBuilders(session.request.(*irma.IssuanceRequest))
	}

	return builders, issuerProofNonce, err
}

// getProofs computes the disclosure proofs or secretkey-knowledge proof (in case of disclosure/signing
// and issuing respectively) to be sent to the server.
func (session *session) getProof() (interface{}, error) {
	var message interface{}
	var err error

	switch session.Action {
	case irma.ActionSigning:
		message, err = session.client.Proofs(session.choice, session.request, true)
	case irma.ActionDisclosing:
		message, err = session.client.Proofs(session.choice, session.request, false)
	case irma.ActionIssuing:
		message, session.builders, err = session.client.IssueCommitments(session.request.(*irma.IssuanceRequest))
	}

	return message, err
}

// Helper functions

func calcVersion(qr *irma.Qr) (*irma.ProtocolVersion, error) {
	// Iterate supportedVersions in reverse sorted order (i.e. biggest major number first)
	keys := make([]int, 0, len(supportedVersions))
	for k := range supportedVersions {
		keys = append(keys, k)
	}
	sort.Sort(sort.Reverse(sort.IntSlice(keys)))
	for _, major := range keys {
		for _, minor := range supportedVersions[major] {
			aboveMinimum := major > qr.ProtocolVersion.Major || (major == qr.ProtocolVersion.Major && minor >= qr.ProtocolVersion.Minor)
			underMaximum := major < qr.ProtocolMaxVersion.Major || (major == qr.ProtocolMaxVersion.Major && minor <= qr.ProtocolMaxVersion.Minor)
			if aboveMinimum && underMaximum {
				return irma.NewVersion(major, minor), nil
			}
		}
	}
	return nil, fmt.Errorf("No supported protocol version between %s and %s", qr.ProtocolVersion.String(), qr.ProtocolMaxVersion.String())
}

// checkKeyshareEnrollment checks if we are enrolled into all involved keyshare servers,
// and aborts the session if not
func (session *session) checkKeyshareEnrollment() bool {
	for id := range session.request.Identifiers().SchemeManagers {
		manager, ok := session.client.Configuration.SchemeManagers[id]
		if !ok {
			session.Handler.Failure(session.Action, &irma.SessionError{ErrorType: irma.ErrorUnknownSchemeManager, Info: id.String()})
			return false
		}
		distributed := manager.Distributed()
		_, enrolled := session.client.keyshareServers[id]
		if distributed && !enrolled {
			session.Handler.KeyshareEnrollmentMissing(id)
			return false
		}
	}
	return true
}

func (session *session) checkAndUpateConfiguration() bool {
	for id := range session.request.Identifiers().SchemeManagers {
		manager, contains := session.client.Configuration.SchemeManagers[id]
		if !contains {
			session.fail(&irma.SessionError{
				ErrorType: irma.ErrorUnknownSchemeManager,
				Info:      id.String(),
			})
			return false
		}
		if !manager.Valid {
			session.fail(&irma.SessionError{
				ErrorType: irma.ErrorInvalidSchemeManager,
				Info:      string(manager.Status),
			})
			return false
		}
	}

	// Check if we are enrolled into all involved keyshare servers
	if !session.checkKeyshareEnrollment() {
		return false
	}

	// Download missing credential types/issuers/public keys from the scheme manager
	downloaded, err := session.client.Configuration.Download(session.request)
	if err != nil {
		session.fail(&irma.SessionError{ErrorType: irma.ErrorConfigurationDownload, Err: err})
		return false
	}
	if downloaded != nil && !downloaded.Empty() {
		session.client.handler.UpdateConfiguration(downloaded)
	}
	return true
}

// IsInteractive returns whether this session uses an API server or not.
func (session *session) IsInteractive() bool {
	return session.ServerURL != ""
}

// Distributed returns whether or not this session involves a keyshare server.
func (session *session) Distributed() bool {
	var smi irma.SchemeManagerIdentifier
	if session.Action == irma.ActionIssuing {
		for _, credreq := range session.request.(*irma.IssuanceRequest).Credentials {
			smi = credreq.CredentialTypeID.IssuerIdentifier().SchemeManagerIdentifier()
			if session.client.Configuration.SchemeManagers[smi].Distributed() {
				return true
			}
		}
	}

	if session.choice == nil || session.choice.Attributes == nil {
		return false
	}

	for _, ai := range session.choice.Attributes {
		smi = ai.Type.CredentialTypeIdentifier().IssuerIdentifier().SchemeManagerIdentifier()
		if session.client.Configuration.SchemeManagers[smi].Distributed() {
			return true
		}
	}

	return false
}

// Session lifetime functions

func (session *session) recoverFromPanic() {
	if e := recover(); e != nil {
		if session.Handler != nil {
			session.Handler.Failure(session.Action, panicToError(e))
		}
	}
}

func panicToError(e interface{}) *irma.SessionError {
	var info string
	switch x := e.(type) {
	case string:
		info = x
	case error:
		info = x.Error()
	case fmt.Stringer:
		info = x.String()
	default: // nop
	}
	fmt.Println("Panic: " + info)
	return &irma.SessionError{ErrorType: irma.ErrorPanic, Info: info}
}

// Idempotently send DELETE to remote server, returning whether or not we did something
func (session *session) delete() bool {
	if !session.done {
		if session.IsInteractive() {
			session.transport.Delete()
		}
		session.done = true
		return true
	}
	return false
}

func (session *session) fail(err *irma.SessionError) {
	if session.delete() {
		err.Err = errors.Wrap(err.Err, 0)
		session.Handler.Failure(session.Action, err)
	}
}

func (session *session) cancel() {
	if session.delete() {
		session.Handler.Cancelled(session.Action)
	}
}

func (session *session) Dismiss() {
	session.cancel()
}

// Keyshare session handler methods

func (session *session) KeyshareDone(message interface{}) {
	session.sendResponse(message)
}

func (session *session) KeyshareCancelled() {
	session.cancel()
}

func (session *session) KeyshareEnrollmentIncomplete(manager irma.SchemeManagerIdentifier) {
	session.Handler.KeyshareEnrollmentIncomplete(manager)
}

func (session *session) KeyshareEnrollmentDeleted(manager irma.SchemeManagerIdentifier) {
	session.Handler.KeyshareEnrollmentDeleted(manager)
}

func (session *session) KeyshareBlocked(manager irma.SchemeManagerIdentifier, duration int) {
	session.Handler.KeyshareBlocked(manager, duration)
}

func (session *session) KeyshareError(manager *irma.SchemeManagerIdentifier, err error) {
	var serr *irma.SessionError
	var ok bool
	if serr, ok = err.(*irma.SessionError); !ok {
		serr = &irma.SessionError{ErrorType: irma.ErrorKeyshare, Err: err}
	} else {
		serr.ErrorType = irma.ErrorKeyshare
	}
	session.fail(serr)
}

func (session *session) KeysharePin() {
	session.Handler.StatusUpdate(session.Action, irma.StatusConnected)
}

func (session *session) KeysharePinOK() {
	session.Handler.StatusUpdate(session.Action, irma.StatusCommunicating)
}