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package lsat
import (
"context"
"encoding/base64"
"fmt"
"regexp"
"sync"
"time"
"github.com/btcsuite/btcutil"
"github.com/lightninglabs/lndclient"
"github.com/lightningnetwork/lnd/lnrpc"
"github.com/lightningnetwork/lnd/lnwire"
"github.com/lightningnetwork/lnd/macaroons"
"github.com/lightningnetwork/lnd/zpay32"
"google.golang.org/grpc"
"google.golang.org/grpc/codes"
"google.golang.org/grpc/metadata"
"google.golang.org/grpc/status"
)
const (
// GRPCErrCode is the error code we receive from a gRPC call if the
// server expects a payment.
GRPCErrCode = codes.Internal
// GRPCErrMessage is the error message we receive from a gRPC call in
// conjunction with the GRPCErrCode to signal the client that a payment
// is required to access the service.
GRPCErrMessage = "payment required"
// AuthHeader is is the HTTP response header that contains the payment
// challenge.
AuthHeader = "WWW-Authenticate"
// DefaultMaxCostSats is the default maximum amount in satoshis that we
// are going to pay for an LSAT automatically. Does not include routing
// fees.
DefaultMaxCostSats = 1000
// DefaultMaxRoutingFeeSats is the default maximum routing fee in
// satoshis that we are going to pay to acquire an LSAT token.
DefaultMaxRoutingFeeSats = 10
// PaymentTimeout is the maximum time we allow a payment to take before
// we stop waiting for it.
PaymentTimeout = 60 * time.Second
// manualRetryHint is the error text we return to tell the user how a
// token payment can be retried if the payment fails.
manualRetryHint = "consider removing pending token file if error " +
"persists. use 'listauth' command to find out token file name"
)
var (
// authHeaderRegex is the regular expression the payment challenge must
// match for us to be able to parse the macaroon and invoice.
authHeaderRegex = regexp.MustCompile(
"LSAT macaroon=\"(.*?)\", invoice=\"(.*?)\"",
)
)
// Interceptor is a gRPC client interceptor that can handle LSAT authentication
// challenges with embedded payment requests. It uses a connection to lnd to
// automatically pay for an authentication token.
type Interceptor struct {
lnd *lndclient.LndServices
store Store
callTimeout time.Duration
maxCost btcutil.Amount
maxFee btcutil.Amount
lock sync.Mutex
}
// NewInterceptor creates a new gRPC client interceptor that uses the provided
// lnd connection to automatically acquire and pay for LSAT tokens, unless the
// indicated store already contains a usable token.
func NewInterceptor(lnd *lndclient.LndServices, store Store,
rpcCallTimeout time.Duration, maxCost,
maxFee btcutil.Amount) *Interceptor {
return &Interceptor{
lnd: lnd,
store: store,
callTimeout: rpcCallTimeout,
maxCost: maxCost,
maxFee: maxFee,
}
}
// interceptContext is a struct that contains all information about a call that
// is intercepted by the interceptor.
type interceptContext struct {
mainCtx context.Context
opts []grpc.CallOption
metadata *metadata.MD
token *Token
}
// UnaryInterceptor is an interceptor method that can be used directly by gRPC
// for unary calls. If the store contains a token, it is attached as credentials
// to every call before patching it through. The response error is also
// intercepted for every call. If there is an error returned and it is
// indicating a payment challenge, a token is acquired and paid for
// automatically. The original request is then repeated back to the server, now
// with the new token attached.
func (i *Interceptor) UnaryInterceptor(ctx context.Context, method string,
req, reply interface{}, cc *grpc.ClientConn, invoker grpc.UnaryInvoker,
opts ...grpc.CallOption) error {
// To avoid paying for a token twice if two parallel requests are
// happening, we require an exclusive lock here.
i.lock.Lock()
defer i.lock.Unlock()
// Create the context that we'll use to initiate the real request. This
// contains the means to extract response headers and possibly also an
// auth token, if we already have paid for one.
iCtx, err := i.newInterceptContext(ctx, opts)
if err != nil {
return err
}
// Try executing the call now. If anything goes wrong, we only handle
// the LSAT error message that comes in the form of a gRPC status error.
rpcCtx, cancel := context.WithTimeout(ctx, i.callTimeout)
defer cancel()
err = invoker(rpcCtx, method, req, reply, cc, iCtx.opts...)
if !isPaymentRequired(err) {
return err
}
// Find out if we need to pay for a new token or perhaps resume
// a previously aborted payment.
err = i.handlePayment(iCtx)
if err != nil {
return err
}
// Execute the same request again, now with the LSAT
// token added as an RPC credential.
rpcCtx2, cancel2 := context.WithTimeout(ctx, i.callTimeout)
defer cancel2()
return invoker(rpcCtx2, method, req, reply, cc, iCtx.opts...)
}
// StreamInterceptor is an interceptor method that can be used directly by gRPC
// for streaming calls. If the store contains a token, it is attached as
// credentials to every stream establishment call before patching it through.
// The response error is also intercepted for every initial stream initiation.
// If there is an error returned and it is indicating a payment challenge, a
// token is acquired and paid for automatically. The original request is then
// repeated back to the server, now with the new token attached.
func (i *Interceptor) StreamInterceptor(ctx context.Context,
desc *grpc.StreamDesc, cc *grpc.ClientConn, method string,
streamer grpc.Streamer, opts ...grpc.CallOption) (grpc.ClientStream,
error) {
// To avoid paying for a token twice if two parallel requests are
// happening, we require an exclusive lock here.
i.lock.Lock()
defer i.lock.Unlock()
// Create the context that we'll use to initiate the real request. This
// contains the means to extract response headers and possibly also an
// auth token, if we already have paid for one.
iCtx, err := i.newInterceptContext(ctx, opts)
if err != nil {
return nil, err
}
// Try establishing the stream now. If anything goes wrong, we only
// handle the LSAT error message that comes in the form of a gRPC status
// error. The context of a stream will be used for the whole lifetime of
// it, so we can't really clamp down on the initial call with a timeout.
stream, err := streamer(ctx, desc, cc, method, iCtx.opts...)
if !isPaymentRequired(err) {
return stream, err
}
// Find out if we need to pay for a new token or perhaps resume
// a previously aborted payment.
err = i.handlePayment(iCtx)
if err != nil {
return nil, err
}
// Execute the same request again, now with the LSAT token added
// as an RPC credential.
return streamer(ctx, desc, cc, method, iCtx.opts...)
}
// newInterceptContext creates the initial intercept context that can capture
// metadata from the server and sends the local token to the server if one
// already exists.
func (i *Interceptor) newInterceptContext(ctx context.Context,
opts []grpc.CallOption) (*interceptContext, error) {
iCtx := &interceptContext{
mainCtx: ctx,
opts: opts,
metadata: &metadata.MD{},
}
// Let's see if the store already contains a token and what state it
// might be in. If a previous call was aborted, we might have a pending
// token that needs to be handled separately.
var err error
iCtx.token, err = i.store.CurrentToken()
switch {
// If there is no token yet, nothing to do at this point.
case err == ErrNoToken:
// Some other error happened that we have to surface.
case err != nil:
log.Errorf("Failed to get token from store: %v", err)
return nil, fmt.Errorf("getting token from store failed: %v",
err)
// Only if we have a paid token append it. We don't resume a pending
// payment just yet, since we don't even know if a token is required for
// this call. We also never send a pending payment to the server since
// we know it's not valid.
case !iCtx.token.isPending():
if err = i.addLsatCredentials(iCtx); err != nil {
log.Errorf("Adding macaroon to request failed: %v", err)
return nil, fmt.Errorf("adding macaroon failed: %v",
err)
}
}
// We need a way to extract the response headers sent by the server.
// This can only be done through the experimental grpc.Trailer call
// option. We execute the request and inspect the error. If it's the
// LSAT specific payment required error, we might execute the same
// method again later with the paid LSAT token.
iCtx.opts = append(iCtx.opts, grpc.Trailer(iCtx.metadata))
return iCtx, nil
}
// handlePayment tries to obtain a valid token by either tracking the payment
// status of a pending token or paying for a new one.
func (i *Interceptor) handlePayment(iCtx *interceptContext) error {
switch {
// Resume/track a pending payment if it was interrupted for some reason.
case iCtx.token != nil && iCtx.token.isPending():
log.Infof("Payment of LSAT token is required, resuming/" +
"tracking previous payment from pending LSAT token")
err := i.trackPayment(iCtx.mainCtx, iCtx.token)
if err != nil {
return err
}
// We don't have a token yet, try to get a new one.
case iCtx.token == nil:
// We don't have a token yet, get a new one.
log.Infof("Payment of LSAT token is required, paying invoice")
var err error
iCtx.token, err = i.payLsatToken(iCtx.mainCtx, iCtx.metadata)
if err != nil {
return err
}
// We have a token and it's valid, nothing more to do here.
default:
log.Debugf("Found valid LSAT token to add to request")
}
if err := i.addLsatCredentials(iCtx); err != nil {
log.Errorf("Adding macaroon to request failed: %v", err)
return fmt.Errorf("adding macaroon failed: %v", err)
}
return nil
}
// addLsatCredentials adds an LSAT token to the given intercept context.
func (i *Interceptor) addLsatCredentials(iCtx *interceptContext) error {
if iCtx.token == nil {
return fmt.Errorf("cannot add nil token to context")
}
macaroon, err := iCtx.token.PaidMacaroon()
if err != nil {
return err
}
iCtx.opts = append(iCtx.opts, grpc.PerRPCCredentials(
macaroons.NewMacaroonCredential(macaroon),
))
return nil
}
// payLsatToken reads the payment challenge from the response metadata and tries
// to pay the invoice encoded in them, returning a paid LSAT token if
// successful.
func (i *Interceptor) payLsatToken(ctx context.Context, md *metadata.MD) (
*Token, error) {
// First parse the authentication header that was stored in the
// metadata.
authHeader := md.Get(AuthHeader)
if len(authHeader) == 0 {
return nil, fmt.Errorf("auth header not found in response")
}
matches := authHeaderRegex.FindStringSubmatch(authHeader[0])
if len(matches) != 3 {
return nil, fmt.Errorf("invalid auth header "+
"format: %s", authHeader[0])
}
// Decode the base64 macaroon and the invoice so we can store the
// information in our store later.
macBase64, invoiceStr := matches[1], matches[2]
macBytes, err := base64.StdEncoding.DecodeString(macBase64)
if err != nil {
return nil, fmt.Errorf("base64 decode of macaroon failed: "+
"%v", err)
}
invoice, err := zpay32.Decode(invoiceStr, i.lnd.ChainParams)
if err != nil {
return nil, fmt.Errorf("unable to decode invoice: %v", err)
}
// Check that the charged amount does not exceed our maximum cost.
maxCostMsat := lnwire.NewMSatFromSatoshis(i.maxCost)
if invoice.MilliSat != nil && *invoice.MilliSat > maxCostMsat {
return nil, fmt.Errorf("cannot pay for LSAT automatically, "+
"cost of %d msat exceeds configured max cost of %d "+
"msat", *invoice.MilliSat, maxCostMsat)
}
// Create and store the pending token so we can resume the payment in
// case the payment is interrupted somehow.
token, err := tokenFromChallenge(macBytes, invoice.PaymentHash)
if err != nil {
return nil, fmt.Errorf("unable to create token: %v", err)
}
err = i.store.StoreToken(token)
if err != nil {
return nil, fmt.Errorf("unable to store pending token: %v", err)
}
// Pay invoice now and wait for the result to arrive or the main context
// being canceled.
payCtx, cancel := context.WithTimeout(ctx, PaymentTimeout)
defer cancel()
respChan := i.lnd.Client.PayInvoice(
payCtx, invoiceStr, i.maxFee, nil,
)
select {
case result := <-respChan:
if result.Err != nil {
return nil, result.Err
}
token.Preimage = result.Preimage
token.AmountPaid = lnwire.NewMSatFromSatoshis(result.PaidAmt)
token.RoutingFeePaid = lnwire.NewMSatFromSatoshis(
result.PaidFee,
)
return token, i.store.StoreToken(token)
case <-payCtx.Done():
return nil, fmt.Errorf("payment timed out. try again to track "+
"payment. %s", manualRetryHint)
case <-ctx.Done():
return nil, fmt.Errorf("parent context canceled. try again to"+
"track payment. %s", manualRetryHint)
}
}
// trackPayment tries to resume a pending payment by tracking its state and
// waiting for a conclusive result.
func (i *Interceptor) trackPayment(ctx context.Context, token *Token) error {
// Lookup state of the payment.
paymentStateCtx, cancel := context.WithCancel(ctx)
defer cancel()
payStatusChan, payErrChan, err := i.lnd.Router.TrackPayment(
paymentStateCtx, token.PaymentHash,
)
if err != nil {
log.Errorf("Could not call TrackPayment on lnd: %v", err)
return fmt.Errorf("track payment call to lnd failed: %v", err)
}
// We can't wait forever, so we give the payment tracking the same
// timeout as the original payment.
payCtx, cancel := context.WithTimeout(ctx, PaymentTimeout)
defer cancel()
// We'll consume status updates until we reach a conclusive state or
// reach the timeout.
for {
select {
// If we receive a state without an error, the payment has been
// initiated. Loop until the payment
case result := <-payStatusChan:
switch result.State {
// If the payment was successful, we have all the
// information we need and we can return the fully paid
// token.
case lnrpc.Payment_SUCCEEDED:
extractPaymentDetails(token, result)
return i.store.StoreToken(token)
// The payment is still in transit, we'll give it more
// time to complete.
case lnrpc.Payment_IN_FLIGHT:
// Any other state means either error or timeout.
default:
return fmt.Errorf("payment tracking failed "+
"with state %s. %s",
result.State.String(), manualRetryHint)
}
// Abort the payment execution for any error.
case err := <-payErrChan:
return fmt.Errorf("payment tracking failed: %v. %s",
err, manualRetryHint)
case <-payCtx.Done():
return fmt.Errorf("payment tracking timed out. %s",
manualRetryHint)
}
}
}
// isPaymentRequired inspects an error to find out if it's the specific gRPC
// error returned by the server to indicate a payment is required to access the
// service.
func isPaymentRequired(err error) bool {
statusErr, ok := status.FromError(err)
return ok &&
statusErr.Message() == GRPCErrMessage &&
statusErr.Code() == GRPCErrCode
}
// extractPaymentDetails extracts the preimage and amounts paid for a payment
// from the payment status and stores them in the token.
func extractPaymentDetails(token *Token, status lndclient.PaymentStatus) {
token.Preimage = status.Preimage
token.AmountPaid = status.Value
token.RoutingFeePaid = status.Fee
}