朋友偶然问了一句，golang的grpc在接到请求后是如何调到对应的实现函数的？
当时对着代码讲了一通。后来想想觉得这是个好问题，写下来记录一下。
注册：
func main() {
listen, err := net.Listen("tcp", ":2008")
if err != nil {
fmt.Println("net.Listen tcp :2008 err", err)
return
}
s := grpc.NewServer()
hServer := xxx.Server{}
xxxxxx.RegisterXXXXXXServer(s, &hServer)
s.Serve(listen)
}
golang起grpc server的代码很简单，一个proto接口的实现 ：xxx.Server{}，然后register server，listen就可以了
func (s *Server) RegisterService(sd *ServiceDesc, ss interface{}) {
ht := reflect.TypeOf(sd.HandlerType).Elem()
st := reflect.TypeOf(ss)
if !st.Implements(ht) {
grpclog.Fatalf("grpc: Server.RegisterService found the handler of type %v that does not satisfy %v", st, ht)
}
s.register(sd, ss)
}
这是grpc server register的入口，首先对服务接口定义ServiceDesc和接口实现ss取type，判断ss是否实现了ServiceDesc中的接口
type service struct {
server interface{} // the server for service methods
md map[string]*MethodDesc
sd map[string]*StreamDesc
mdata interface{}
}
func (s *Server) register(sd *ServiceDesc, ss interface{}) {
s.mu.Lock()
defer s.mu.Unlock()
s.printf("RegisterService(%q)", sd.ServiceName)
if s.serve {
grpclog.Fatalf("grpc: Server.RegisterService after Server.Serve for %q", sd.ServiceName)
}
if _, ok := s.m[sd.ServiceName]; ok {
grpclog.Fatalf("grpc: Server.RegisterService found duplicate service registration for %q", sd.ServiceName)
}
srv := &service{
server: ss,
md: make(map[string]*MethodDesc),
sd: make(map[string]*StreamDesc),
mdata: sd.Metadata,
}
for i := range sd.Methods {
d := &sd.Methods[i]
srv.md[d.MethodName] = d
}
for i := range sd.Streams {
d := &sd.Streams[i]
srv.sd[d.StreamName] = d
}
s.m[sd.ServiceName] = srv
}
service 结构中的server就是实现了接口定义的实体，就是我们的响应服务。
md 保存了响应func的映射"MethodName -- func"
sd 保存了rpc流服务的映射"StreamName -- func"
mdata 保存了proto的位置
响应：
func (s *Server) Serve(lis net.Listener) error {
// ......
ls := &listenSocket{Listener: lis}
s.lis[ls] = true
// ......
var tempDelay time.Duration // how long to sleep on accept failure
for {
rawConn, err := lis.Accept()
if err != nil {
// ......
}
tempDelay = 0
// Start a new goroutine to deal with rawConn so we don't stall this Accept
// loop goroutine.
//
// Make sure we account for the goroutine so GracefulStop doesn't nil out
// s.conns before this conn can be added.
s.serveWG.Add(1)
go func() {
s.handleRawConn(rawConn)
s.serveWG.Done()
}()
}
}
func (s *Server) handleRawConn(rawConn net.Conn) {
rawConn.SetDeadline(time.Now().Add(s.opts.connectionTimeout))
conn, authInfo, err := s.useTransportAuthenticator(rawConn)
if err != nil {
// ......
return
}
s.mu.Lock()
if s.conns == nil {
s.mu.Unlock()
conn.Close()
return
}
s.mu.Unlock()
// Finish handshaking (HTTP2)
st := s.newHTTP2Transport(conn, authInfo)
if st == nil {
return
}
rawConn.SetDeadline(time.Time{})
if !s.addConn(st) {
return
}
go func() {
s.serveStreams(st)
s.removeConn(st)
}()
}
servers监听端口listenSocket，Accept到请求后起goroutine 处理。然后把 建立http2链接。这里的ServerTransport是指 所有gRPC服务器端传输的通用接口实现。
然后起goroutine 继续serveStreams
func (s *Server) serveStreams(st transport.ServerTransport) {
defer st.Close()
var wg sync.WaitGroup
st.HandleStreams(func(stream *transport.Stream) {
wg.Add(1)
go func() {
defer wg.Done()
s.handleStream(st, stream, s.traceInfo(st, stream))
}()
}, func(ctx context.Context, method string) context.Context {
if !EnableTracing {
return ctx
}
tr := trace.New("grpc.Recv."+methodFamily(method), method)
return trace.NewContext(ctx, tr)
})
wg.Wait()
}
func (t *http2Server) HandleStreams(handle func(*Stream), traceCtx func(context.Context, string) context.Context) {
defer close(t.readerDone)
for {
frame, err := t.framer.fr.ReadFrame()
atomic.StoreUint32(&t.activity, 1)
if err != nil {
if se, ok := err.(http2.StreamError); ok {
warningf("transport: http2Server.HandleStreams encountered http2.StreamError: %v", se)
t.mu.Lock()
s := t.activeStreams[se.StreamID]
t.mu.Unlock()
if s != nil {
t.closeStream(s, true, se.Code, false)
} else {
t.controlBuf.put(&cleanupStream{
streamID: se.StreamID,
rst: true,
rstCode: se.Code,
onWrite: func() {},
})
}
continue
}
if err == io.EOF || err == io.ErrUnexpectedEOF {
t.Close()
return
}
warningf("transport: http2Server.HandleStreams failed to read frame: %v", err)
t.Close()
return
}
switch frame := frame.(type) {
case *http2.MetaHeadersFrame:
if t.operateHeaders(frame, handle, traceCtx) {
t.Close()
break
}
case *http2.DataFrame:
t.handleData(frame)
case *http2.RSTStreamFrame:
t.handleRSTStream(frame)
case *http2.SettingsFrame:
t.handleSettings(frame)
case *http2.PingFrame:
t.handlePing(frame)
case *http2.WindowUpdateFrame:
t.handleWindowUpdate(frame)
case *http2.GoAwayFrame:
// TODO: Handle GoAway from the client appropriately.
default:
errorf("transport: http2Server.HandleStreams found unhandled frame type %v.", frame)
}
}
}
st.HandleStreams中解析了 ServerTransport中的frame，traceCtx将trace附加到ctx并返回新上下文，调用s.handleStream处理请求(s.handleStream中是真正调用服务响应函数地方)
func (s *Server) handleStream(t transport.ServerTransport, stream *transport.Stream, trInfo *traceInfo) {
sm := stream.Method()
if sm != "" && sm[0] == '/' {
sm = sm[1:]
}
pos := strings.LastIndex(sm, "/")
if pos == -1 {
if trInfo != nil {
trInfo.tr.LazyLog(&fmtStringer{"Malformed method name %q", []interface{}{sm}}, true)
trInfo.tr.SetError()
}
errDesc := fmt.Sprintf("malformed method name: %q", stream.Method())
if err := t.WriteStatus(stream, status.New(codes.ResourceExhausted, errDesc)); err != nil {
if trInfo != nil {
trInfo.tr.LazyLog(&fmtStringer{"%v", []interface{}{err}}, true)
trInfo.tr.SetError()
}
grpclog.Warningf("grpc: Server.handleStream failed to write status: %v", err)
}
if trInfo != nil {
trInfo.tr.Finish()
}
return
}
service := sm[:pos]
method := sm[pos+1:]
srv, knownService := s.m[service]
if knownService {
if md, ok := srv.md[method]; ok {
s.processUnaryRPC(t, stream, srv, md, trInfo)
return
}
if sd, ok := srv.sd[method]; ok {
s.processStreamingRPC(t, stream, srv, sd, trInfo)
return
}
}
// Unknown service, or known server unknown method.
if unknownDesc := s.opts.unknownStreamDesc; unknownDesc != nil {
s.processStreamingRPC(t, stream, nil, unknownDesc, trInfo)
return
}
var errDesc string
if !knownService {
errDesc = fmt.Sprintf("unknown service %v", service)
} else {
errDesc = fmt.Sprintf("unknown method %v for service %v", method, service)
}
if trInfo != nil {
trInfo.tr.LazyPrintf("%s", errDesc)
trInfo.tr.SetError()
}
if err := t.WriteStatus(stream, status.New(codes.Unimplemented, errDesc)); err != nil {
if trInfo != nil {
trInfo.tr.LazyLog(&fmtStringer{"%v", []interface{}{err}}, true)
trInfo.tr.SetError()
}
grpclog.Warningf("grpc: Server.handleStream failed to write status: %v", err)
}
if trInfo != nil {
trInfo.tr.Finish()
}
}
server.handleStream中根据ServerTransport中带来的server name, method name在最开始注册时记录的map中找到对应的handle func 执行processUnaryRPC(如果是流服务 那么会执行processStreamingRPC)。
func (s *Server) processUnaryRPC(t transport.ServerTransport, stream *transport.Stream, srv *service, md *MethodDesc, trInfo *traceInfo) (err error) {
//...
这里有一大段代码，都是在执行数据的comp/decomp操作
//..
ctx := NewContextWithServerTransportStream(stream.Context(), stream)
reply, appErr := md.Handler(srv.server, ctx, df, s.opts.unaryInt)
if appErr != nil {
appStatus, ok := status.FromError(appErr)
if !ok {
// Convert appErr if it is not a grpc status error.
appErr = status.Error(codes.Unknown, appErr.Error())
appStatus, _ = status.FromError(appErr)
}
if trInfo != nil {
trInfo.tr.LazyLog(stringer(appStatus.Message()), true)
trInfo.tr.SetError()
}
if e := t.WriteStatus(stream, appStatus); e != nil {
grpclog.Warningf("grpc: Server.processUnaryRPC failed to write status: %v", e)
}
if binlog != nil {
if h, _ := stream.Header(); h.Len() > 0 {
// Only log serverHeader if there was header. Otherwise it can
// be trailer only.
binlog.Log(&binarylog.ServerHeader{
Header: h,
})
}
binlog.Log(&binarylog.ServerTrailer{
Trailer: stream.Trailer(),
Err: appErr,
})
}
return appErr
}
if trInfo != nil {
trInfo.tr.LazyLog(stringer("OK"), false)
}
opts := &transport.Options{Last: true}
if err := s.sendResponse(t, stream, reply, cp, opts, comp); err != nil {
if err == io.EOF {
// The entire stream is done (for unary RPC only).
return err
}
if s, ok := status.FromError(err); ok {
if e := t.WriteStatus(stream, s); e != nil {
grpclog.Warningf("grpc: Server.processUnaryRPC failed to write status: %v", e)
}
} else {
switch st := err.(type) {
case transport.ConnectionError:
// Nothing to do here.
default:
panic(fmt.Sprintf("grpc: Unexpected error (%T) from sendResponse: %v", st, st))
}
}
if binlog != nil {
h, _ := stream.Header()
binlog.Log(&binarylog.ServerHeader{
Header: h,
})
binlog.Log(&binarylog.ServerTrailer{
Trailer: stream.Trailer(),
Err: appErr,
})
}
return err
}
if binlog != nil {
h, _ := stream.Header()
binlog.Log(&binarylog.ServerHeader{
Header: h,
})
binlog.Log(&binarylog.ServerMessage{
Message: reply,
})
}
if channelz.IsOn() {
t.IncrMsgSent()
}
if trInfo != nil {
trInfo.tr.LazyLog(&payload{sent: true, msg: reply}, true)
}
// TODO: Should we be logging if writing status failed here, like above?
// Should the logging be in WriteStatus? Should we ignore the WriteStatus
// error or allow the stats handler to see it?
err = t.WriteStatus(stream, status.New(codes.OK, ""))
if binlog != nil {
binlog.Log(&binarylog.ServerTrailer{
Trailer: stream.Trailer(),
Err: appErr,
})
}
return err
}
上面省略了一大段构造context，decomp的代码。
经过一系列context的构造，decomp 终于到了调请求对应实现方法的地方了：reply, appErr := md.Handler(srv.server, ctx, df, s.opts.unaryInt)，返回的reply就是给client的data。最下面WriteStatus codes.OK就是client _stub函数返回的status.ok()了。