// recvResponse receives and parses an RPC response.
// On error, it returns the error and indicates whether the call should be retried.
//
// TODO(zhaoq): Check whether the received message sequence is valid.
func recvResponse(codec Codec, t transport.ClientTransport, c *callInfo, stream *transport.Stream, reply interface{}) error {
// Try to acquire header metadata from the server if there is any.
var err error
c.headerMD, err = stream.Header()
if err != nil {
return err
}
p := &parser{s: stream}
for {
if err = recv(p, codec, reply); err != nil {
if err == io.EOF {
break
}
return err
}
}
c.trailerMD = stream.Trailer()
return nil
}
// Invoke is called by the generated code. It sends the RPC request on the
// wire and returns after response is received.
func Invoke(ctx context.Context, method string, args, reply interface{}, cc *ClientConn, opts ...CallOption) error {
var c callInfo
for _, o := range opts {
if err := o.before(&c); err != nil {
return toRPCErr(err)
}
}
defer func() {
for _, o := range opts {
o.after(&c)
}
}()
callHdr := &transport.CallHdr{
Host: cc.authority,
Method: method,
}
topts := &transport.Options{
Last: true,
Delay: false,
}
var (
ts int // track the transport sequence number
lastErr error // record the error that happened
)
for {
var (
err error
t transport.ClientTransport
stream *transport.Stream
)
// TODO(zhaoq): Need a formal spec of retry strategy for non-failfast rpcs.
if lastErr != nil && c.failFast {
return toRPCErr(lastErr)
}
t, ts, err = cc.wait(ctx, ts)
if err != nil {
if lastErr != nil {
// This was a retry; return the error from the last attempt.
return toRPCErr(lastErr)
}
return toRPCErr(err)
}
stream, err = sendRequest(ctx, cc.dopts.codec, callHdr, t, args, topts)
if err != nil {
if _, ok := err.(transport.ConnectionError); ok {
lastErr = err
continue
}
if lastErr != nil {
return toRPCErr(lastErr)
}
return toRPCErr(err)
}
// Receive the response
lastErr = recvResponse(cc.dopts.codec, t, &c, stream, reply)
if _, ok := lastErr.(transport.ConnectionError); ok {
continue
}
t.CloseStream(stream, lastErr)
if lastErr != nil {
return toRPCErr(lastErr)
}
return Errorf(stream.StatusCode(), stream.StatusDesc())
}
}