// EnsureContext checks whether the given context.Context contains a Span. If
// not, it creates one using the provided Tracer and wraps it in the returned
// Span. The returned closure must be called after the request has been fully
// processed.
func EnsureContext(ctx context.Context, tracer opentracing.Tracer) (context.Context, func()) {
	_, _, funcName := caller.Lookup(1)
	if opentracing.SpanFromContext(ctx) == nil {
		sp := tracer.StartSpan(funcName)
		return opentracing.ContextWithSpan(ctx, sp), sp.Finish
	}
	return ctx, func() {}
}

// SpanFromContext returns the Span obtained from the context or, if none is
// found, a new one started through the tracer. Callers should call (or defer)
// the returned cleanup func as well to ensure that the span is Finish()ed, but
// callers should *not* attempt to call Finish directly -- in the case where the
// span was obtained from the context, it is not the caller's to Finish.
func SpanFromContext(opName string, tracer opentracing.Tracer, ctx context.Context) (opentracing.Span, func()) {
	sp := opentracing.SpanFromContext(ctx)
	if sp == nil {
		sp = tracer.StartSpan(opName)
		return sp, sp.Finish
	}
	return sp, func() {}
}

// JoinOrNew creates a new Span joined to the provided DelegatingCarrier or
// creates Span from the given tracer.
func JoinOrNew(tr opentracing.Tracer, carrier *Span, opName string) (opentracing.Span, error) {
	if carrier != nil {
		sp, err := tr.Join(opName, basictracer.Delegator, carrier)
		switch err {
		case nil:
			sp.LogEvent(opName)
			return sp, nil
		case opentracing.ErrTraceNotFound:
		default:
			return nil, err
		}
	}
	return tr.StartSpan(opName), nil
}

// InitSenderForLocalTestCluster initializes a TxnCoordSender that can be used
// with LocalTestCluster.
func InitSenderForLocalTestCluster(
	nodeDesc *roachpb.NodeDescriptor,
	tracer opentracing.Tracer,
	clock *hlc.Clock,
	latency time.Duration,
	stores client.Sender,
	stopper *stop.Stopper,
	gossip *gossip.Gossip,
) client.Sender {
	var rpcSend rpcSendFn = func(_ SendOptions, _ ReplicaSlice,
		args roachpb.BatchRequest, _ *rpc.Context) (*roachpb.BatchResponse, error) {
		if latency > 0 {
			time.Sleep(latency)
		}
		sp := tracer.StartSpan("node")
		defer sp.Finish()
		ctx := opentracing.ContextWithSpan(context.Background(), sp)
		log.Trace(ctx, args.String())
		br, pErr := stores.Send(ctx, args)
		if br == nil {
			br = &roachpb.BatchResponse{}
		}
		if br.Error != nil {
			panic(roachpb.ErrorUnexpectedlySet(stores, br))
		}
		br.Error = pErr
		if pErr != nil {
			log.Trace(ctx, "error: "+pErr.String())
		}
		return br, nil
	}
	retryOpts := GetDefaultDistSenderRetryOptions()
	retryOpts.Closer = stopper.ShouldDrain()
	distSender := NewDistSender(&DistSenderContext{
		Clock: clock,
		RangeDescriptorCacheSize: defaultRangeDescriptorCacheSize,
		RangeLookupMaxRanges:     defaultRangeLookupMaxRanges,
		LeaderCacheSize:          defaultLeaderCacheSize,
		RPCRetryOptions:          &retryOpts,
		nodeDescriptor:           nodeDesc,
		RPCSend:                  rpcSend,                    // defined above
		RangeDescriptorDB:        stores.(RangeDescriptorDB), // for descriptor lookup
	}, gossip)

	return NewTxnCoordSender(distSender, clock, false /* !linearizable */, tracer,
		stopper, NewTxnMetrics(metric.NewRegistry()))
}

func TestTracer(t *testing.T) {
	log.SetFlags(0)

	var tracer ot.Tracer
	tracer = &Tracer{}
	ot.InitGlobalTracer(tracer)

	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		serverSpan, err := tracer.Join(
			"serverSpan",
			ot.TextMap,
			ot.HTTPHeaderTextMapCarrier(r.Header))
		if err != nil {
			panic(err)
		}
		time.Sleep(time.Second * 1)
		serverSpan.Finish()
		fmt.Fprintln(w, "Hello, client")
	}))
	defer ts.Close()

	span, nctx := ot.StartSpanFromContext(context.TODO(), "main_test")
	defer span.Finish()

	foo(nctx, "bar", 0)

	httpClient := &http.Client{}
	httpReq, _ := http.NewRequest("GET", ts.URL, nil)

	// Transmit the span's TraceContext as HTTP headers on our
	// outbound request.
	tracer.Inject(
		span,
		ot.TextMap,
		ot.HTTPHeaderTextMapCarrier(httpReq.Header))

	if _, err := httpClient.Do(httpReq); err != nil {
		panic(err)
	}
}

// JoinOrNew creates a new Span joined to the provided DelegatingCarrier or
// creates Span from the given tracer.
func JoinOrNew(tr opentracing.Tracer, carrier *Span, opName string) (opentracing.Span, error) {
	if carrier != nil {
		wireContext, err := tr.Extract(basictracer.Delegator, carrier)
		switch err {
		case nil:
			sp := tr.StartSpan(opName, opentracing.FollowsFrom(wireContext))
			sp.LogEvent(opName)
			return sp, nil
		case opentracing.ErrSpanContextNotFound:
		default:
			return nil, err
		}
	}
	return tr.StartSpan(opName), nil
}

// JoinOrNew creates a new Span joined to the provided DelegatingCarrier or
// creates Span from the given tracer.
func JoinOrNew(
	tr opentracing.Tracer, carrier *SpanContextCarrier, opName string,
) (opentracing.Span, error) {
	if carrier != nil {
		wireContext, err := tr.Extract(basictracer.Delegator, carrier)
		switch err {
		case nil:
			sp := tr.StartSpan(opName, opentracing.FollowsFrom(wireContext))

			// Copy baggage items to tags so they show up in the Lightstep UI.
			sp.Context().ForeachBaggageItem(func(k, v string) bool { sp.SetTag(k, v); return true })

			sp.LogFields(otlog.String("event", opName))
			return sp, nil
		case opentracing.ErrSpanContextNotFound:
		default:
			return nil, err
		}
	}
	return tr.StartSpan(opName), nil
}

// Send implements the batch.Sender interface. If the request is part of a
// transaction, the TxnCoordSender adds the transaction to a map of active
// transactions and begins heartbeating it. Every subsequent request for the
// same transaction updates the lastUpdate timestamp to prevent live
// transactions from being considered abandoned and garbage collected.
// Read/write mutating requests have their key or key range added to the
// transaction's interval tree of key ranges for eventual cleanup via resolved
// write intents; they're tagged to an outgoing EndTransaction request, with
// the receiving replica in charge of resolving them.
func (tc *TxnCoordSender) Send(
	ctx context.Context, ba roachpb.BatchRequest,
) (*roachpb.BatchResponse, *roachpb.Error) {
	// Start new or pick up active trace. From here on, there's always an active
	// Trace, though its overhead is small unless it's sampled.
	sp := opentracing.SpanFromContext(ctx)
	var tracer opentracing.Tracer
	if sp == nil {
		tracer = tc.AmbientContext.Tracer
		sp = tracer.StartSpan(opTxnCoordSender)
		defer sp.Finish()
		ctx = opentracing.ContextWithSpan(ctx, sp)
	} else {
		tracer = sp.Tracer()
	}

	startNS := tc.clock.PhysicalNow()

	if ba.Txn != nil {
		// If this request is part of a transaction...
		if err := tc.maybeBeginTxn(&ba); err != nil {
			return nil, roachpb.NewError(err)
		}

		txnID := *ba.Txn.ID

		// Associate the txnID with the trace. We need to do this after the
		// maybeBeginTxn call. We set both a baggage item and a tag because only
		// tags show up in the LIghtstep UI.
		txnIDStr := txnID.String()
		sp.SetTag("txnID", txnIDStr)
		sp.SetBaggageItem("txnID", txnIDStr)

		var et *roachpb.EndTransactionRequest
		var hasET bool
		{
			var rArgs roachpb.Request
			rArgs, hasET = ba.GetArg(roachpb.EndTransaction)
			if hasET {
				et = rArgs.(*roachpb.EndTransactionRequest)
				if len(et.Key) != 0 {
					return nil, roachpb.NewErrorf("EndTransaction must not have a Key set")
				}
				et.Key = ba.Txn.Key
				if len(et.IntentSpans) > 0 {
					// TODO(tschottdorf): it may be useful to allow this later.
					// That would be part of a possible plan to allow txns which
					// write on multiple coordinators.
					return nil, roachpb.NewErrorf("client must not pass intents to EndTransaction")
				}
			}
		}

		if pErr := func() *roachpb.Error {
			tc.Lock()
			defer tc.Unlock()
			if pErr := tc.maybeRejectClientLocked(ctx, *ba.Txn); pErr != nil {
				return pErr
			}

			if !hasET {
				return nil
			}
			// Everything below is carried out only when trying to commit.

			// Populate et.IntentSpans, taking into account both any existing
			// and new writes, and taking care to perform proper deduplication.
			txnMeta := tc.txns[txnID]
			distinctSpans := true
			if txnMeta != nil {
				et.IntentSpans = txnMeta.keys
				// Defensively set distinctSpans to false if we had any previous
				// requests in this transaction. This effectively limits the distinct
				// spans optimization to 1pc transactions.
				distinctSpans = len(txnMeta.keys) == 0
			}
			// We can't pass in a batch response here to better limit the key
			// spans as we don't know what is going to be affected. This will
			// affect queries such as `DELETE FROM my.table LIMIT 10` when
			// executed as a 1PC transaction. e.g.: a (BeginTransaction,
			// DeleteRange, EndTransaction) batch.
			ba.IntentSpanIterate(nil, func(key, endKey roachpb.Key) {
				et.IntentSpans = append(et.IntentSpans, roachpb.Span{
					Key:    key,
					EndKey: endKey,
				})
			})
			// TODO(peter): Populate DistinctSpans on all batches, not just batches
			// which contain an EndTransactionRequest.
			var distinct bool
			// The request might already be used by an outgoing goroutine, so
//.........这里部分代码省略.........