brpc可通过多种方式访问用ub搭建的服务。

ubrpc (by protobuf)

r31687后，brpc支持通过protobuf访问ubrpc，不需要baidu-rpc-ub，也不依赖idl-compiler。（也可以让protobuf服务被ubrpc client访问，方法见使用ubrpc的服务）。

步骤：

用idl2proto把idl文件转化为proto文件，老版本idl2proto不会转化idl中的service，需要手动转化。

// Converted from echo.idl by brpc/tools/idl2proto
import "idl_options.proto";
option (idl_support) = true;
option cc_generic_services = true;
message EchoRequest {
  required string message = 1; 
}
message EchoResponse {
  required string message = 1; 
}
// 对于idl中多个request或response的方法，要建立一个包含所有request或response的消息。
// 这个例子中就是MultiRequests和MultiResponses。
message MultiRequests {
  required EchoRequest req1 = 1;
  required EchoRequest req2 = 2;
}
message MultiResponses {
  required EchoRequest res1 = 1;
  required EchoRequest res2 = 2;
}
service EchoService {
  // 对应idl中的void Echo(EchoRequest req, out EchoResponse res);
  rpc Echo(EchoRequest) returns (EchoResponse);
  // 对应idl中的uint32_t EchoWithMultiArgs(EchoRequest req1, EchoRequest req2, out EchoResponse res1, out EchoResponse res2);
  rpc EchoWithMultiArgs(MultiRequests) returns (MultiResponses);
}

原先的echo.idl文件：

struct EchoRequest {
    string message;
};
struct EchoResponse {
    string message;
};
service EchoService {
    void Echo(EchoRequest req, out EchoResponse res);
    uint32_t EchoWithMultiArgs(EchoRequest req1, EchoRequest req2, out EchoResponse res1, out EchoResponse res2);
};

插入如下片段以使用代码生成插件。

BRPC_PATH代表brpc产出的路径（包含bin include等目录），PROTOBUF_INCLUDE_PATH代表protobuf的包含路径。注意—mcpack_out要和—cpp_out一致。
```
protoc --plugin=protoc-gen-mcpack=$BRPC_PATH/bin/protoc-gen-mcpack --cpp_out=. --mcpack_out=. --proto_path=$BRPC_PATH/include --proto_path=PROTOBUF_INCLUDE_PATH
```

用channel发起访问。

idl不同于pb，允许有多个请求，我们先看只有一个请求的情况，和普通的pb访问基本上是一样的。

#include <brpc/channel.h>
#include "echo.pb.h"
...
brpc::Channel channel;
brpc::ChannelOptions opt;
opt.protocol = brpc::PROTOCOL_UBRPC_COMPACK; // or "ubrpc_compack";
if (channel.Init(..., &opt) != 0) {
    LOG(ERROR) << "Fail to init channel";
    return -1;
}
EchoService_Stub stub(&channel);
...
EchoRequest request;
EchoResponse response;
brpc::Controller cntl;
request.set_message("hello world");
stub.Echo(&cntl, &request, &response, NULL);
if (cntl.Failed()) {
    LOG(ERROR) << "Fail to send request, " << cntl.ErrorText();
    return;
}
// 取response中的字段
// [idl] void Echo(EchoRequest req, out EchoResponse res);
//                              ^ 
//                  response.message();

多个请求要设置一下set_idl_names。

#include <brpc/channel.h>
#include "echo.pb.h"
...
brpc::Channel channel;
brpc::ChannelOptions opt;
opt.protocol = brpc::PROTOCOL_UBRPC_COMPACK; // or "ubrpc_compack";
if (channel.Init(..., &opt) != 0) {
    LOG(ERROR) << "Fail to init channel";
    return -1;
}
EchoService_Stub stub(&channel);
...
MultiRequests multi_requests;
MultiResponses multi_responses;
brpc::Controller cntl;
multi_requests.mutable_req1()->set_message("hello");
multi_requests.mutable_req2()->set_message("world");
cntl.set_idl_names(brpc::idl_multi_req_multi_res);
stub.EchoWithMultiArgs(&cntl, &multi_requests, &multi_responses, NULL);
if (cntl.Failed()) {
    LOG(ERROR) << "Fail to send request, " << cntl.ErrorText();
    return;
}
// 取response中的字段
// [idl] uint32_t EchoWithMultiArgs(EchoRequest req1, EchoRequest req2,
//        ^                         out EchoResponse res1, out EchoResponse res2);
//        |                                           ^                      ^
//        |                          multi_responses.res1().message();       |
//        |                                                 multi_responses.res2().message();
// cntl.idl_result();

例子详见example/echo_c++_ubrpc_compack。

ubrpc (by baidu-rpc-ub)

server端由public/ubrpc搭建，request/response使用idl文件描述字段，序列化格式是compack或mcpack_v2。

步骤：

依赖public/baidu-rpc-ub模块，这个模块是brpc的扩展，不需要的用户不会依赖idl/mcpack/compack等模块。baidu-rpc-ub只包含扩展代码，brpc中的新特性会自动体现在这个模块中。

编写一个proto文件，其中定义了service，名字和idl中的相同，但请求类型必须是baidu.rpc.UBRequest，回复类型必须是baidu.rpc.UBResponse。这两个类型定义在brpc/ub.proto中，使用时得import。

import "brpc/ub.proto";              // UBRequest, UBResponse
option cc_generic_services = true;
// Define UB service. request/response must be UBRequest/UBResponse
service EchoService {
    rpc Echo(baidu.rpc.UBRequest) returns (baidu.rpc.UBResponse);
};

在COMAKE包含baidu-rpc-ub/src路径。

# brpc/ub.proto的包含路径
PROTOC(ENV.WorkRoot()+"third-64/protobuf/bin/protoc")
PROTOFLAGS("--proto_path=" + ENV.WorkRoot() + "public/baidu-rpc-ub/src/")

用法和访问其他协议类似：创建Channel，ChannelOptions.protocol为brpc::PROTOCOL_NSHEAD_CLIENT或**“nshead_client”**。request和response对象必须是baidu-rpc-ub提供的类型

#include <brpc/ub_call.h>
...
brpc::Channel channel;
brpc::ChannelOptions opt;
opt.protocol = brpc::PROTOCOL_NSHEAD_CLIENT; // or "nshead_client";
if (channel.Init(..., &opt) != 0) {
    LOG(ERROR) << "Fail to init channel";
    return -1;
}
EchoService_Stub stub(&channel);    
...
const int BUFSIZE = 1024 * 1024;  // 1M
char* buf_for_mempool = new char[BUFSIZE];
bsl::xmempool pool;
if (pool.create(buf_for_mempool, BUFSIZE) != 0) {
    LOG(FATAL) << "Fail to create bsl::xmempool";
    return -1;
}
// 构造UBRPC的request/response，idl结构体作为模块参数传入。为了构造idl结构，需要传入一个bsl::mempool
brpc::UBRPCCompackRequest<example::EchoService_Echo_params> request(&pool);
brpc::UBRPCCompackResponse<example::EchoService_Echo_response> response(&pool);
// 设置字段
request.mutable_req()->set_message("hello world");
// 发起RPC
brpc::Controller cntl;
stub.Echo(&cntl, &request, &response, NULL);
if (cntl.Failed()) {
    LOG(ERROR) << "Fail to Echo, " << cntl.ErrorText();
    return;
}
// 取回复中的字段
response.result_params().res().message();
...

具体example代码可以参考echo_c++_compack_ubrpc，类似的还有echo_c++_mcpack_ubrpc。

nshead+idl

server端是由public/ub搭建，通讯包组成为nshead+idl::compack/idl::mcpack(v2)

由于不需要指定service和method，无需编写proto文件，直接使用Channel.CallMethod方法发起RPC即可。请求包中的nshead可以填也可以不填，框架会补上正确的magic_num和body_len字段：

#include <brpc/ub_call.h>
...
brpc::Channel channel;
brpc::ChannelOptions opt;
opt.protocol = brpc::PROTOCOL_NSHEAD_CLIENT; // or "nshead_client";
if (channel.Init(..., &opt) != 0) {
    LOG(ERROR) << "Fail to init channel";
    return -1;
}
...
// 构造UB的request/response，完全类似构造原先idl结构，传入一个bsl::mempool（变量pool）
// 将类型作为模板传入，之后在使用上可以直接使用对应idl结构的接口
brpc::UBCompackRequest<example::EchoRequest> request(&pool);
brpc::UBCompackResponse<example::EchoResponse> response(&pool);
// Set `message' field of `EchoRequest'
request.set_message("hello world");
// Set fields of the request nshead struct if needed
request.mutable_nshead()->version = 99;
brpc::Controller cntl;
channel.CallMethod(NULL, &cntl, &request, &response, NULL);    // 假设channel已经通过之前所述方法Init成功
// Get `message' field of `EchoResponse'
response.message();

具体example代码可以参考echo_c++_mcpack_ub，compack情况类似，不再赘述

nshead+mcpack(非idl产生的)

server端是由public/ub搭建，通讯包组成为nshead+mcpack包，但不是idl编译器生成的，RPC前需要先构造RawBuffer将其传入，然后获取mc_pack_t并按之前手工填写mcpack的方式操作：

#include <brpc/ub_call.h>
...
brpc::Channel channel;
brpc::ChannelOptions opt;
opt.protocol = brpc::PROTOCOL_NSHEAD_CLIENT; // or "nshead_client";
if (channel.Init(..., &opt) != 0) {
    LOG(ERROR) << "Fail to init channel";
    return -1;
}
...
// 构造RawBuffer，一次RPC结束后RawBuffer可以复用，类似于bsl::mempool
const int BUFSIZE = 10 * 1024 * 1024;
brpc::RawBuffer req_buf(BUFSIZE);
brpc::RawBuffer res_buf(BUFSIZE);
// 传入RawBuffer来构造request和response
brpc::UBRawMcpackRequest request(&req_buf);
brpc::UBRawMcpackResponse response(&res_buf);
// Fetch mc_pack_t and fill in variables
mc_pack_t* req_pack = request.McpackHandle();
int ret = mc_pack_put_str(req_pack, "mystr", "hello world");
if (ret != 0) {
    LOG(FATAL) << "Failed to put string into mcpack: "
               << mc_pack_perror((long)req_pack) << (void*)req_pack;
    break;
}  
// Set fields of the request nshead struct if needed
request.mutable_nshead()->version = 99;
brpc::Controller cntl;
channel.CallMethod(NULL, &cntl, &request, &response, NULL);    // 假设channel已经通过之前所述方法Init成功
// Get response from response buffer
const mc_pack_t* res_pack = response.McpackHandle();
mc_pack_get_str(res_pack, "mystr");

具体example代码可以参考echo_c++_raw_mcpack。

nshead+blob

r32897后brpc直接支持用nshead+blob访问老server（而不用依赖baidu-rpc-ub）。example代码可以参考nshead_extension_c++。

#include <brpc/nshead_message.h>
...
brpc::Channel;
brpc::ChannelOptions opt;
opt.protocol = brpc::PROTOCOL_NSHEAD; // or "nshead"
if (channel.Init(..., &opt) != 0) {
    LOG(ERROR) << "Fail to init channel";
    return -1;
} 
...
brpc::NsheadMessage request;
brpc::NsheadMessage response;
// Append message to `request'
request.body.append("hello world");
// Set fields of the request nshead struct if needed
request.head.version = 99;
brpc::Controller cntl;
channel.CallMethod(NULL, &cntl, &request, &response, NULL);
if (cntl.Failed()) {
    LOG(ERROR) << "Fail to access the server: " << cntl.ErrorText();
    return -1;
}
// response.head and response.body contains nshead_t and blob respectively.

或者用户也可以使用baidu-rpc-ub中的UBRawBufferRequest和UBRawBufferResponse来访问。example代码可以参考echo_c++_raw_buffer。

brpc::Channel channel;
brpc::ChannelOptions opt;
opt.protocol = brpc::PROTOCOL_NSHEAD_CLIENT; // or "nshead_client"
if (channel.Init(..., &opt) != 0) {
    LOG(ERROR) << "Fail to init channel";
    return -1;
}
...
// 构造RawBuffer，一次RPC结束后RawBuffer可以复用，类似于bsl::mempool
const int BUFSIZE = 10 * 1024 * 1024;
brpc::RawBuffer req_buf(BUFSIZE);
brpc::RawBuffer res_buf(BUFSIZE);
// 传入RawBuffer来构造request和response
brpc::UBRawBufferRequest request(&req_buf);
brpc::UBRawBufferResponse response(&res_buf);
// Append message to `request'
request.append("hello world");
// Set fields of the request nshead struct if needed
request.mutable_nshead()->version = 99;
brpc::Controller cntl;
channel.CallMethod(NULL, &cntl, &request, &response, NULL);    // 假设channel已经通过之前所述方法Init成功
// Process response. response.data() is the buffer, response.size() is the length.

访问UB

ubrpc (by protobuf)

ubrpc (by baidu-rpc-ub)

nshead+idl

nshead+mcpack(非idl产生的)

nshead+blob