安装

1. 安装protobuf 进入网站github.com/protocolbuffers/protobuf的release页面，点击下载protoc-3.10.1-linux-x86_64.zip文件

2. 安装protoc-gen-go和grpc

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$ go get -u github.com/golang/protobuf/protoc-gen-go@v1.3.2
$ go get -u google.golang.org/grpc
# -I指定import语句的包检索路径
$ protoc -I=$SRC_DIR --go_out=plugins=grpc:$DST_DIR $SRC_DIR/*.proto
# 或者
$ protoc -I=. --go_out=plugins=grpc:. --go_opt=paths=source_relative access-center/*.proto

使用gRPC发送rpc消息的时候，这些消息在http2上，究竟是怎样编码的。

注意，wireshark中，50051端口默认不会被识别为http2，所以需要手动设置“解码为HTTP/2” * 选中某个报文，右键->解码为->将TCP port:50051的当前值改为HTTP2

1. gRPC：支持多语言编程、基于HTTP/2通讯的中间件

                                     +----------------+
                .---<-Proto Request--|-+------------+ |
+--------------/-+                   |-> gRPC Stub  | |
| +-----------v+ |                   / +------------+ |
| | gRPC Server|-|->Proto Response>-`|  Ruby Client   |
| +-----------\+<--                  +----------------+
|              \ | \
|  c++ Service  \|  \                +-------------------+
+----------------\   -<ProtoRequest--|-+------------+    |
                  ------------------>->| gRPC Stub  |    |
                      ProtoResponse  | +------------+    |
                                     |Android-Java Client|
                                     +-------------------+

2. Protocol Buffers编码：消息结构

                    Message Struct 
   Field1    |  Field2    |  Field3    |
{Tag}{Value} |{Tag}{Value}|{Tag}{Value}|{} {} {}
  ^          |            |            |
  |
(field_number<<3)|wire_type

3. Wire Type

   Type	Meaning	Used For
   0	Varint	int32,int64,uint32,uint64,sint32,sint64,bool,enum
   1	64-bit	fixed64,sfixed64,double
   2	Length-delimited	string, bytes, embeded messages,packed repeated fields
   3	Start group	groups(deprecated)
   4	End group	groups(deprecated)
   5	32-bit	fixed32,sfixed32,float

4. 举例

Protocol Buffers
                           +------------------------------------------------------------+
field tag=1 type2(string)  |      length6  M   a  r  t  i  n                            |
 +-+-+-+-+-+-+-+-+         | +--+    +--+ +--+--+--+--+--+--+                           |
 |0 0 0 0 1|0 1 0|---------->|0a|    |06| |4d 61 72 74 69 6e|                           |
 +-+-+-+-+-+-+-+-+  0a     | +--+    +--+ +--+--+--+--+--+--+                           |
                           |                        1和0都表示序号，可以发现序号是逆序的   |
field tag=2 type0(varint)  |                         /                 /                |
 +-+-+-+-+-+-+-+-+         | +--+    +-----+        +-+-------------+ +-+-------------+ |
 |0 0 0 1 0|0 0 0|---------->|10|    |b9 0a|<-------|1|0 1 1 1 0 0 1| |0|0 0 0 1 0 1 0| |
 +-+-+-+-+-+-+-+-+  10     | +--+    +-----+        +-+-------------+ +-+-------------+ |
                           |                                                            |
field tag=3 type2(string)  |      length11  d  a  y  d  r  e  a  m  i  n  g             |
 +-+-+-+-+-+-+-+-+         | +--+    +--+ +--+--+--+--+--+--+--+--+--+--+--+            |
 |0 0 0 1 1|0 1 0|---------->|1a|    |0b| |64 61 79 64 72 65 61 6d 69 6e 67|            |
 +-+-+-+-+-+-+-+-+  1a     | +--+    +--+ +--+--+--+--+--+--+--+--+--+--+--+            |
                           +------------------------------------------------------------+

grpc的使用

1. package名必须和微服务名保持一致， grpc在调用的时候，路由规则是/package_name.service_name/method_name/

syntax = "proto3";

option go_package = "google.golang.org/grpc/examples/helloworld/helloworld";
option java_multiple_files = true; 
option java_package = "io.grpc.examples.helloworld";
option java_outer_classname = "HelloWorldProto";

package helloworld;

// The greeting service definition.
service Greeter {
  // Sends a greeting
  rpc SayHello (HelloRequest) returns (HelloReply) {}
} 

// The request message containing the user's name.
message HelloRequest {
  string name = 1;
} 

// The response message containing the greetings
message HelloReply {
  string message = 1;
} 

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