client: implement UnaryClientInterceptor chaining.

Add a WithChainUnaryClientInterceptor client option to allow
using more that one client call interceptor which will then
get chained and invoked in the order given.

This should allow us to implement opentelemetry instrumentation
as interceptors while allowing users to keep intercepting their
client calls for other reasons at the same time.

Signed-off-by: Krisztian Litkey <krisztian.litkey@intel.com>

client.go

@@ -71,6 +71,42 @@ func WithUnaryClientInterceptor(i UnaryClientInterceptor) ClientOpts {
 	}
 }
 
+// WithChainUnaryClientInterceptor sets the provided chain of client interceptors
+func WithChainUnaryClientInterceptor(interceptors ...UnaryClientInterceptor) ClientOpts {
+	return func(c *Client) {
+		if len(interceptors) == 0 {
+			return
+		}
+		if c.interceptor != nil {
+			interceptors = append([]UnaryClientInterceptor{c.interceptor}, interceptors...)
+		}
+		c.interceptor = func(
+			ctx context.Context,
+			req *Request,
+			reply *Response,
+			info *UnaryClientInfo,
+			final Invoker,
+		) error {
+			return interceptors[0](ctx, req, reply, info,
+				chainUnaryInterceptors(interceptors[1:], final, info))
+		}
+	}
+}
+
+func chainUnaryInterceptors(interceptors []UnaryClientInterceptor, final Invoker, info *UnaryClientInfo) Invoker {
+	if len(interceptors) == 0 {
+		return final
+	}
+	return func(
+		ctx context.Context,
+		req *Request,
+		reply *Response,
+	) error {
+		return interceptors[0](ctx, req, reply, info,
+			chainUnaryInterceptors(interceptors[1:], final, info))
+	}
+}
+
 // NewClient creates a new ttrpc client using the given connection
 func NewClient(conn net.Conn, opts ...ClientOpts) *Client {
 	ctx, cancel := context.WithCancel(context.Background())
@@ -85,13 +121,16 @@ func NewClient(conn net.Conn, opts ...ClientOpts) *Client {
 		ctx:             ctx,
 		userCloseFunc:   func() {},
 		userCloseWaitCh: make(chan struct{}),
-		interceptor:     defaultClientInterceptor,
 	}
 
 	for _, o := range opts {
 		o(c)
 	}
 
+	if c.interceptor == nil {
+		c.interceptor = defaultClientInterceptor
+	}
+
 	go c.run()
 	return c
 }

interceptor_test.go

@@ -0,0 +1,135 @@
+/*
+   Copyright The containerd Authors.
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+*/
+
+package ttrpc
+
+import (
+	"context"
+	"reflect"
+	"strings"
+	"testing"
+
+	"github.com/containerd/ttrpc/internal"
+)
+
+func TestUnaryClientInterceptor(t *testing.T) {
+	var (
+		intercepted = false
+		interceptor = func(ctx context.Context, req *Request, reply *Response, ci *UnaryClientInfo, i Invoker) error {
+			intercepted = true
+			return i(ctx, req, reply)
+		}
+
+		ctx             = context.Background()
+		server          = mustServer(t)(NewServer())
+		testImpl        = &testingServer{}
+		addr, listener  = newTestListener(t)
+		client, cleanup = newTestClient(t, addr, WithUnaryClientInterceptor(interceptor))
+		message         = strings.Repeat("a", 16)
+		reply           = strings.Repeat(message, 2)
+	)
+
+	defer listener.Close()
+	defer cleanup()
+
+	registerTestingService(server, testImpl)
+
+	go server.Serve(ctx, listener)
+	defer server.Shutdown(ctx)
+
+	request := &internal.TestPayload{
+		Foo: message,
+	}
+	response := &internal.TestPayload{}
+
+	if err := client.Call(ctx, serviceName, "Test", request, response); err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+
+	if !intercepted {
+		t.Fatalf("ttrpc client call not intercepted")
+	}
+
+	if response.Foo != reply {
+		t.Fatalf("unexpected test service reply: %q != %q", response.Foo, reply)
+	}
+}
+
+func TestChainUnaryClientInterceptor(t *testing.T) {
+	var (
+		orderIdx  = 0
+		recorded  = []string{}
+		intercept = func(idx int, tag string) UnaryClientInterceptor {
+			return func(ctx context.Context, req *Request, reply *Response, ci *UnaryClientInfo, i Invoker) error {
+				if idx != orderIdx {
+					t.Fatalf("unexpected interceptor invocation order (%d != %d)", orderIdx, idx)
+				}
+				recorded = append(recorded, tag)
+				orderIdx++
+				return i(ctx, req, reply)
+			}
+		}
+
+		ctx             = context.Background()
+		server          = mustServer(t)(NewServer())
+		testImpl        = &testingServer{}
+		addr, listener  = newTestListener(t)
+		client, cleanup = newTestClient(t, addr,
+			WithChainUnaryClientInterceptor(),
+			WithChainUnaryClientInterceptor(
+				intercept(0, "seen it"),
+				intercept(1, "been"),
+				intercept(2, "there"),
+				intercept(3, "done"),
+				intercept(4, "that"),
+			),
+		)
+		expected = []string{
+			"seen it",
+			"been",
+			"there",
+			"done",
+			"that",
+		}
+		message = strings.Repeat("a", 16)
+		reply   = strings.Repeat(message, 2)
+	)
+
+	defer listener.Close()
+	defer cleanup()
+
+	registerTestingService(server, testImpl)
+
+	go server.Serve(ctx, listener)
+	defer server.Shutdown(ctx)
+
+	request := &internal.TestPayload{
+		Foo: message,
+	}
+	response := &internal.TestPayload{}
+	if err := client.Call(ctx, serviceName, "Test", request, response); err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+
+	if !reflect.DeepEqual(recorded, expected) {
+		t.Fatalf("unexpected ttrpc chained client unary interceptor order (%s != %s)",
+			strings.Join(recorded, " "), strings.Join(expected, " "))
+	}
+
+	if response.Foo != reply {
+		t.Fatalf("unexpected test service reply: %q != %q", response.Foo, reply)
+	}
+}