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package streamrpc
import (
"context"
"encoding/json"
"errors"
"fmt"
"net"
"time"
"google.golang.org/grpc"
"google.golang.org/grpc/metadata"
"google.golang.org/protobuf/proto"
)
var _ grpc.ServiceRegistrar = &Server{}
// Server handles network connections and routes them to StreamRPC handlers.
type Server struct {
methods map[string]*method
interceptor grpc.UnaryServerInterceptor
}
type method struct {
*grpc.MethodDesc
implementation interface{}
}
// ServerOption is an abstraction that lets you pass 0 or more server
// options to NewServer.
type ServerOption func(*Server)
// WithServerInterceptor adds a unary gRPC server interceptor.
func WithServerInterceptor(interceptor grpc.UnaryServerInterceptor) ServerOption {
return func(s *Server) { s.interceptor = interceptor }
}
// NewServer returns a new StreamRPC server. You can pass the result to
// grpc-go RegisterFooServer functions.
func NewServer(opts ...ServerOption) *Server {
s := &Server{
methods: make(map[string]*method),
}
for _, o := range opts {
o(s)
}
return s
}
// RegisterService implements grpc.ServiceRegistrar. It makes it possible
// to pass a *Server to grpc-go foopb.RegisterFooServer functions as the
// first argument.
func (s *Server) RegisterService(sd *grpc.ServiceDesc, impl interface{}) {
for i := range sd.Methods {
m := &sd.Methods[i]
s.methods["/"+sd.ServiceName+"/"+m.MethodName] = &method{
MethodDesc: m,
implementation: impl,
}
}
}
// Handle handles an incoming network connection with the StreamRPC
// protocol. It is intended to be called from a net.Listener.Accept loop
// (or something equivalent).
func (s *Server) Handle(c net.Conn) error {
defer c.Close()
deadline := time.Now().Add(defaultHandshakeTimeout)
req, err := recvFrame(c, deadline)
if err != nil {
return err
}
session := &serverSession{
c: c,
deadline: deadline,
}
if err := s.handleSession(session, req); err != nil {
return session.reject(err)
}
return nil
}
func (s *Server) handleSession(session *serverSession, reqBytes []byte) error {
req := &request{}
if err := json.Unmarshal(reqBytes, req); err != nil {
return err
}
method, ok := s.methods[req.Method]
if !ok {
return fmt.Errorf("method not found: %s", req.Method)
}
ctx, cancel := serverContext(session, req)
defer cancel()
if _, err := method.Handler(
method.implementation,
ctx,
func(msg interface{}) error { return proto.Unmarshal(req.Message, msg.(proto.Message)) },
s.interceptor,
); err != nil {
return err
}
return nil
}
func serverContext(session *serverSession, req *request) (context.Context, func()) {
ctx := context.Background()
ctx = context.WithValue(ctx, sessionKey{}, session)
ctx = metadata.NewIncomingContext(ctx, req.Metadata)
return context.WithCancel(ctx)
}
type sessionKey struct{}
// AcceptConnection completes the StreamRPC handshake on the server side.
// It notifies the client that the server has accepted the stream, and
// returns the connection.
func AcceptConnection(ctx context.Context) (net.Conn, error) {
session, ok := ctx.Value(sessionKey{}).(*serverSession)
if !ok {
return nil, errors.New("context has no serverSession")
}
return session.Accept()
}
// serverSession wraps an incoming connection whose handshake has not
// been completed yet.
type serverSession struct {
c net.Conn
accepted bool
deadline time.Time
}
// Accept completes the handshake on the connection wrapped by ss and
// unwraps the connection.
func (ss *serverSession) Accept() (net.Conn, error) {
if ss.accepted {
return nil, errors.New("connection already accepted")
}
ss.accepted = true
if err := sendFrame(ss.c, nil, ss.deadline); err != nil {
return nil, fmt.Errorf("accept session: %w", err)
}
return ss.c, nil
}
func (ss *serverSession) reject(err error) error {
if ss.accepted {
return nil
}
buf, err := json.Marshal(&response{Error: err.Error()})
if err != nil {
return fmt.Errorf("mashal response: %w", err)
}
return sendFrame(ss.c, buf, ss.deadline)
}
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