fix: article layout problem

Author: wufeng

Diff for: part3/group.md

@@ -10,7 +10,8 @@
 `group` 就是一个元数据。如果你为服务设置了设置`group`， 只有在这个`group`的客户端才能访问这些服务(这个限制是在路由的时候限制的， 当然你在客户端绕过这个限制)。
 
 
-```go server.go
+```go
+// server.go
 
 func main() {
 	flag.Parse()
@@ -38,25 +39,26 @@ func createServer2(addr, meta string) {
 
 如果在客户端你没有设置 `option.Group`, 客户端可以访问这些服务， 无论服务是否设置了组还是没设置。
 
-```go client.go
-	option := client.DefaultOption
-	option.Group = "test"
-	xclient := client.NewXClient("Arith", client.Failover, client.RoundRobin, d, option)
-	defer xclient.Close()
-
-	args := &example.Args{
-		A: 10,
-		B: 20,
-	}
-
-	for {
-		reply := &example.Reply{}
-		err := xclient.Call(context.Background(), "Mul", args, reply)
-		if err != nil {
-			log.Fatalf("failed to call: %v", err)
-		}
-
-		log.Printf("%d * %d = %d", args.A, args.B, reply.C)
-		time.Sleep(1e9)
-	}
+```go
+// client.go
+option := client.DefaultOption
+option.Group = "test"
+xclient := client.NewXClient("Arith", client.Failover, client.RoundRobin, d, option)
+defer xclient.Close()
+
+args := &example.Args{
+    A: 10,
+    B: 20,
+}
+
+for {
+    reply := &example.Reply{}
+    err := xclient.Call(context.Background(), "Mul", args, reply)
+    if err != nil {
+        log.Fatalf("failed to call: %v", err)
+    }
+
+    log.Printf("%d * %d = %d", args.A, args.B, reply.C)
+    time.Sleep(1e9)
+}
 ```

Diff for: part3/heartbeat.md

@@ -8,7 +8,7 @@ rpcx会自动处理心跳(事实上它直接就丢弃了心跳)。
 客户端需要启用心跳选项，并且设置心跳间隔：
 
 ```go
- 	option := client.DefaultOption
-	option.Heartbeat = true
-	option.HeartbeatInterval = time.Second
+option := client.DefaultOption
+option.Heartbeat = true
+option.HeartbeatInterval = time.Second
 ```

Diff for: part3/metadata.md

@@ -15,18 +15,20 @@
 
 如果你想在客户端读取客户端的数据， 你 **必须** 在上下文中设置 `share.ResMetaDataKey`。
 
-```go client.go
-	reply := &example.Reply{}
-	ctx := context.WithValue(context.Background(), share.ReqMetaDataKey, map[string]string{"aaa": "from client"})
-	ctx = context.WithValue(ctx, share.ResMetaDataKey, make(map[string]string))
-	err := xclient.Call(ctx, "Mul", args, reply)
+```go
+// client.go
+reply := &example.Reply{}
+ctx := context.WithValue(context.Background(), share.ReqMetaDataKey, map[string]string{"aaa": "from client"})
+ctx = context.WithValue(ctx, share.ResMetaDataKey, make(map[string]string))
+err := xclient.Call(ctx, "Mul", args, reply)
 ```
 
 ## Server
 
 服务器可以从上下文读取`share.ReqMetaDataKey` 和 `share.ResMetaDataKey`:
 
-```go server.go
-	reqMeta := ctx.Value(share.ReqMetaDataKey).(map[string]string)
-	resMeta := ctx.Value(share.ResMetaDataKey).(map[string]string)
+```go
+// server.go
+reqMeta := ctx.Value(share.ReqMetaDataKey).(map[string]string)
+resMeta := ctx.Value(share.ResMetaDataKey).(map[string]string)
 ```

Diff for: part3/state.md

@@ -8,8 +8,8 @@
 
 你可以通过 [rpcx-ui](https://github.com/smallnest/rpcx-ui))来时实现禁用和启用的功能。
 
-```go server.go
-
+```go
+// server.go
 func main() {
 	flag.Parse()
 
@@ -33,23 +33,24 @@ func createServer2(addr, meta string) {
 ```
 
 
-```go client.go
-	xclient := client.NewXClient("Arith", client.Failover, client.RoundRobin, d, client.DefaultOption)
-	defer xclient.Close()
+```go
+// client.go
+xclient := client.NewXClient("Arith", client.Failover, client.RoundRobin, d, client.DefaultOption)
+defer xclient.Close()
 
-	args := &example.Args{
-		A: 10,
-		B: 20,
-	}
+args := &example.Args{
+    A: 10,
+    B: 20,
+}
 
-	for {
-		reply := &example.Reply{}
-		err := xclient.Call(context.Background(), "Mul", args, reply)
-		if err != nil {
-			log.Fatalf("failed to call: %v", err)
-		}
+for {
+    reply := &example.Reply{}
+    err := xclient.Call(context.Background(), "Mul", args, reply)
+    if err != nil {
+        log.Fatalf("failed to call: %v", err)
+    }
 
-		log.Printf("%d * %d = %d", args.A, args.B, reply.C)
-		time.Sleep(1e9)
-	}
+    log.Printf("%d * %d = %d", args.A, args.B, reply.C)
+    time.Sleep(1e9)
+}
 ```

Diff for: part3/timeout.md

@@ -8,7 +8,7 @@
 
 你可以使用`OptionFn`设置服务器的 `readTimeout` 和 `writeTimeout`。
 
-```go server struct
+```go
 type Server struct {
 	……
 	readTimeout  time.Duration