Add gRPC client-side integration with golang.org/x/net/trace.

This will make client (outgoing) traces appear on /debug/requests.
There's some information lacking, but it's enough for now.

call.go

@@ -35,8 +35,10 @@ package grpc
 
 import (
 	"io"
+	"time"
 
 	"golang.org/x/net/context"
+	"golang.org/x/net/trace"
 	"google.golang.org/grpc/codes"
 	"google.golang.org/grpc/metadata"
 	"google.golang.org/grpc/transport"
@@ -97,11 +99,16 @@ type callInfo struct {
 	failFast  bool
 	headerMD  metadata.MD
 	trailerMD metadata.MD
+	traceInfo traceInfo // in trace.go
 }
 
+// EnableTracing controls whether to trace RPCs using the golang.org/x/net/trace package.
+// This should only be set before any RPCs are sent or received by this program.
+var EnableTracing = true
+
 // 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 {
+func Invoke(ctx context.Context, method string, args, reply interface{}, cc *ClientConn, opts ...CallOption) (err error) {
 	var c callInfo
 	for _, o := range opts {
 		if err := o.before(&c); err != nil {
@@ -113,6 +120,24 @@ func Invoke(ctx context.Context, method string, args, reply interface{}, cc *Cli
 			o.after(&c)
 		}
 	}()
+
+	if EnableTracing {
+		c.traceInfo.tr = trace.New("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 err != nil {
+				c.traceInfo.tr.LazyLog(&fmtStringer{"%v", []interface{}{err}}, true)
+				c.traceInfo.tr.SetError()
+			}
+		}()
+	}
+
 	callHdr := &transport.CallHdr{
 		Host:   cc.authority,
 		Method: method,
@@ -143,6 +168,9 @@ func Invoke(ctx context.Context, method string, args, reply interface{}, cc *Cli
 			}
 			return toRPCErr(err)
 		}
+		if EnableTracing {
+			c.traceInfo.tr.LazyLog(payload{args}, true)
+		}
 		stream, err = sendRequest(ctx, cc.dopts.codec, callHdr, t, args, topts)
 		if err != nil {
 			if _, ok := err.(transport.ConnectionError); ok {
@@ -159,6 +187,9 @@ func Invoke(ctx context.Context, method string, args, reply interface{}, cc *Cli
 		if _, ok := lastErr.(transport.ConnectionError); ok {
 			continue
 		}
+		if EnableTracing {
+			c.traceInfo.tr.LazyLog(payload{reply}, true)
+		}
 		t.CloseStream(stream, lastErr)
 		if lastErr != nil {
 			return toRPCErr(lastErr)

trace.go

@@ -0,0 +1,107 @@
+/*
+ *
+ * Copyright 2015, 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"
+	"fmt"
+	"io"
+	"net"
+	"strings"
+	"time"
+
+	"golang.org/x/net/trace"
+)
+
+// methodFamily returns the trace family for the given method.
+// It turns "/pkg.Service/GetFoo" into "pkg.Service".
+func methodFamily(m string) string {
+	m = strings.TrimPrefix(m, "/") // remove leading slash
+	if i := strings.Index(m, "/"); i >= 0 {
+		m = m[:i] // remove everything from second slash
+	}
+	if i := strings.LastIndex(m, "."); i >= 0 {
+		m = m[i+1:] // cut down to last dotted component
+	}
+	return m
+}
+
+// traceInfo contains tracing information for an RPC.
+type traceInfo struct {
+	tr        trace.Trace
+	firstLine firstLine
+}
+
+// firstLine is the first line of an RPC trace.
+type firstLine struct {
+	client     bool // whether this is a client (outgoing) RPC
+	remoteAddr net.Addr
+	deadline   time.Duration // may be zero
+}
+
+func (f *firstLine) String() string {
+	var line bytes.Buffer
+	io.WriteString(&line, "RPC: ")
+	if f.client {
+		io.WriteString(&line, "to")
+	} else {
+		io.WriteString(&line, "from")
+	}
+	fmt.Fprintf(&line, " %v deadline:", f.remoteAddr)
+	if f.deadline != 0 {
+		fmt.Fprint(&line, f.deadline)
+	} else {
+		io.WriteString(&line, "none")
+	}
+	return line.String()
+}
+
+// payload represents an RPC request or response payload.
+type payload struct {
+	m interface{} // e.g. a proto.Message
+	// TODO(dsymonds): add stringifying info to codec, and limit how much we hold here?
+}
+
+func (p payload) String() string {
+	return fmt.Sprint(p.m)
+}
+
+type fmtStringer struct {
+	format string
+	a      []interface{}
+}
+
+func (f *fmtStringer) String() string {
+	return fmt.Sprintf(f.format, f.a...)
+}