call.go

/*
 *
 * Copyright 2014, Google Inc.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are
 * met:
 *
 *     * Redistributions of source code must retain the above copyright
 * notice, this list of conditions and the following disclaimer.
 *     * Redistributions in binary form must reproduce the above
 * copyright notice, this list of conditions and the following disclaimer
 * in the documentation and/or other materials provided with the
 * distribution.
 *     * Neither the name of Google Inc. nor the names of its
 * contributors may be used to endorse or promote products derived from
 * this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 */

package grpc

import (
	"bytes"
	"io"
	"math"
	"time"

	"golang.org/x/net/context"
	"golang.org/x/net/trace"
	"google.golang.org/grpc/codes"
	"google.golang.org/grpc/peer"
	"google.golang.org/grpc/stats"
	"google.golang.org/grpc/transport"
)

// 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.
// TODO ctx is used for stats collection and processing. It is the context passed from the application.
func recvResponse(ctx context.Context, dopts dialOptions, t transport.ClientTransport, c *callInfo, stream *transport.Stream, reply interface{}) (err error) {
	// Try to acquire header metadata from the server if there is any.
	defer func() {
		if err != nil {
			if _, ok := err.(transport.ConnectionError); !ok {
				t.CloseStream(stream, err)
			}
		}
	}()
	c.headerMD, err = stream.Header()
	if err != nil {
		return
	}
	p := &parser{r: stream}
	var inPayload *stats.InPayload
	if dopts.copts.StatsHandler != nil {
		inPayload = &stats.InPayload{
			Client: true,
		}
	}
	for {
		if err = recv(p, dopts.codec, stream, dopts.dc, reply, math.MaxInt32, inPayload); err != nil {
			if err == io.EOF {
				break
			}
			return
		}
	}
	if inPayload != nil && err == io.EOF && stream.StatusCode() == codes.OK {
		// TODO in the current implementation, inTrailer may be handled before inPayload in some cases.
		// Fix the order if necessary.
		dopts.copts.StatsHandler.HandleRPC(ctx, inPayload)
	}
	c.trailerMD = stream.Trailer()
	if peer, ok := peer.FromContext(stream.Context()); ok {
		c.peer = peer
	}
	return nil
}

// sendRequest writes out various information of an RPC such as Context and Message.
func sendRequest(ctx context.Context, dopts dialOptions, compressor Compressor, callHdr *transport.CallHdr, t transport.ClientTransport, args interface{}, opts *transport.Options) (_ *transport.Stream, err error) {
	stream, err := t.NewStream(ctx, callHdr)
	if err != nil {
		return nil, err
	}
	defer func() {
		if err != nil {
			// If err is connection error, t will be closed, no need to close stream here.
			if _, ok := err.(transport.ConnectionError); !ok {
				t.CloseStream(stream, err)
			}
		}
	}()
	var (
		cbuf       *bytes.Buffer
		outPayload *stats.OutPayload
	)
	if compressor != nil {
		cbuf = new(bytes.Buffer)
	}
	if dopts.copts.StatsHandler != nil {
		outPayload = &stats.OutPayload{
			Client: true,
		}
	}
	outBuf, err := encode(dopts.codec, args, compressor, cbuf, outPayload)
	if err != nil {
		return nil, Errorf(codes.Internal, "grpc: %v", err)
	}
	err = t.Write(stream, outBuf, opts)
	if err == nil && outPayload != nil {
		outPayload.SentTime = time.Now()
		dopts.copts.StatsHandler.HandleRPC(ctx, outPayload)
	}
	// t.NewStream(...) could lead to an early rejection of the RPC (e.g., the service/method
	// does not exist.) so that t.Write could get io.EOF from wait(...). Leave the following
	// recvResponse to get the final status.
	if err != nil && err != io.EOF {
		return nil, err
	}
	// Sent successfully.
	return stream, nil
}

// Invoke sends the RPC request on the wire and returns after response is received.
// Invoke is called by generated code. Also users can call Invoke directly when it
// is really needed in their use cases.
func Invoke(ctx context.Context, method string, args, reply interface{}, cc *ClientConn, opts ...CallOption) error {
	//如果在dial的时候WithUnaryInterceptor  则会先调用拦截器（可以做一些传递数据，日志等等事情）
	if cc.dopts.unaryInt != nil {
		return cc.dopts.unaryInt(ctx, method, args, reply, cc, invoke, opts...)
	}
	return invoke(ctx, method, args, reply, cc, opts...)
}

func invoke(ctx context.Context, method string, args, reply interface{}, cc *ClientConn, opts ...CallOption) (e error) {
	c := defaultCallInfo //默认的callinfo配置
	if mc, ok := cc.getMethodConfig(method); ok {//获取methodConfig的配置
		c.failFast = !mc.WaitForReady
		if mc.Timeout > 0 {
			var cancel context.CancelFunc
			ctx, cancel = context.WithTimeout(ctx, mc.Timeout)
			defer cancel()
		}
	}
	for _, o := range opts {
		if err := o.before(&c); err != nil { //调用之前的处理
			return toRPCErr(err)
		}
	}
	defer func() {
		for _, o := range opts { //调用之后的处理
			o.after(&c)
		}
	}()
	if EnableTracing {
		c.traceInfo.tr = trace.New("grpc.Sent."+methodFamily(method), method)
		defer c.traceInfo.tr.Finish()
		c.traceInfo.firstLine.client = true
		if deadline, ok := ctx.Deadline(); ok {
			c.traceInfo.firstLine.deadline = deadline.Sub(time.Now())
		}
		c.traceInfo.tr.LazyLog(&c.traceInfo.firstLine, false)
		// TODO(dsymonds): Arrange for c.traceInfo.firstLine.remoteAddr to be set.
		defer func() {
			if e != nil {
				c.traceInfo.tr.LazyLog(&fmtStringer{"%v", []interface{}{e}}, true)
				c.traceInfo.tr.SetError()
			}
		}()
	}
	sh := cc.dopts.copts.StatsHandler//通过WithStatsHandler来设置的, 对调用前后的状态进行掌控
	if sh != nil {
		ctx = sh.TagRPC(ctx, &stats.RPCTagInfo{FullMethodName: method})//附加一些信息到ctx
		begin := &stats.Begin{
			Client:    true,
			BeginTime: time.Now(),
			FailFast:  c.failFast,
		}
		sh.HandleRPC(ctx, begin)
	}
	defer func() {
		if sh != nil {
			end := &stats.End{
				Client:  true,
				EndTime: time.Now(),
				Error:   e,
			}
			sh.HandleRPC(ctx, end)
		}
	}()
	topts := &transport.Options{
		Last:  true,
		Delay: false,
	}
	for {//进入循环
		var (
			err    error
			t      transport.ClientTransport
			stream *transport.Stream
			// Record the put handler from Balancer.Get(...). It is called once the
			// RPC has completed or failed.
			put func()
		)
		// TODO(zhaoq): Need a formal spec of fail-fast.
		callHdr := &transport.CallHdr{
			Host:   cc.authority,
			Method: method,
		}
		if cc.dopts.cp != nil {//发送的时候的数据压缩算法
			callHdr.SendCompress = cc.dopts.cp.Type()
		}

		gopts := BalancerGetOptions{
			BlockingWait: !c.failFast,// 默认failFast=true, 所以Balancer Get不到有效的地址的时候不会block
		}
		//获取一个连接
		t, put, err = cc.getTransport(ctx, gopts)
		if err != nil {
			// TODO(zhaoq): Probably revisit the error handling.
			if _, ok := err.(*rpcError); ok {
				return err
			}
			if err == errConnClosing || err == errConnUnavailable {
				if c.failFast {//默认是true
					return Errorf(codes.Unavailable, "%v", err)
				}
				continue
			}
			// All the other errors are treated as Internal errors.
			return Errorf(codes.Internal, "%v", err)
		}
		if c.traceInfo.tr != nil {
			c.traceInfo.tr.LazyLog(&payload{sent: true, msg: args}, true)
		}
		//发送请求
		stream, err = sendRequest(ctx, cc.dopts, cc.dopts.cp, callHdr, t, args, topts)
		if err != nil {
			if put != nil {
				put()
				put = nil
			}
			// Retry a non-failfast RPC when
			// i) there is a connection error; or
			// ii) the server started to drain before this RPC was initiated.
			if _, ok := err.(transport.ConnectionError); ok || err == transport.ErrStreamDrain {
				if c.failFast {//默认是true
					return toRPCErr(err)
				}
				continue
			}
			return toRPCErr(err)
		}
		//接受响应数据，里面是阻塞等待的
		err = recvResponse(ctx, cc.dopts, t, &c, stream, reply)
		if err != nil {
			if put != nil {
				put()
				put = nil
			}
			if _, ok := err.(transport.ConnectionError); ok || err == transport.ErrStreamDrain {
				if c.failFast {
					return toRPCErr(err)
				}
				continue
			}
			return toRPCErr(err)
		}
		if c.traceInfo.tr != nil {
			c.traceInfo.tr.LazyLog(&payload{sent: false, msg: reply}, true)
		}
		t.CloseStream(stream, nil)
		if put != nil {
			put()
			put = nil
		}
		return Errorf(stream.StatusCode(), "%s", stream.StatusDesc())
	}
}