doc: sync Stream Middleware (#1192)

content/en/docs/kitex/Tutorials/basic-feature/Kitex+StreamX+-+Stream+Middleware.md

@@ -0,0 +1,93 @@
+---
+title: "Stream Middleware"
+date: 2025-01-13
+weight: 1
+keywords: ["Stream Middleware"]
+description: ""
+---
+
+## Middleware Type
+
+### Stream Recv/Send Middleware
+
+**Trigger timing** : Called when streaming messages
+
+#### Type definition
+
+```go
+type StreamRecvEndpoint func(ctx context.Context, stream Stream, res any) (err error)
+type StreamSendEndpoint func(ctx context.Context, stream Stream, req any) (err error)
+
+type StreamRecvMiddleware func(next StreamRecvEndpoint) StreamRecvEndpoint
+type StreamSendMiddleware func(next StreamSendEndpoint) StreamSendEndpoint
+```
+
+**Parameter description** :
+
+- Directly obtain the current stream object
+- Res/req both represent real requests and responses.
+- Behavior before and after calling the Next function:
+
+| Middleware type      | Before calling Next                                                                                                    | After calling Next                                                                                 |
+| -------------------- | ---------------------------------------------------------------------------------------------------------------------- | -------------------------------------------------------------------------------------------------- |
+| StreamRecvMiddleware | - The data is not really collected, just called the stream. Recv () function.<br><br>- Res parameter is empty          | - Data received or encountered an error<br><br>- The res parameter has a real value                |
+| StreamSendMiddleware | - The data was not actually sent, just called the stream.Send () function<br><br>- The req parameter is a real request | - Data transmission completed or encountered an error<br><br>- The req parameter is a real request |
+
+#### Examples
+
+**Usage scenario** : Inject relevant business logic when the stream receives/sends messages.
+
+```go
+svr, err := xxx.NewServer(
+    //...
+    streamxserver.WithStreamRecvMiddleware(func(next streamx.StreamRecvEndpoint) streamx.StreamRecvEndpoint {
+        return func(ctx context.Context, stream streamx.Stream, res any) (err error) {
+            // ctx has user's token
+            token, ok := metainfo.GetPersistentValue(ctx, "user_token")
+            // check token balance
+            if !hasBalance(token) {
+                return fmt.Errorf("user dont have enough balance: token=%s", token)
+            }
+            return next(ctx, stream, res)
+        }
+    }),
+)
+```
+
+## Inject Middleware
+
+#### Inject Client Middleware
+
+```go
+cli, err := xxx.NewClient(
+    "a.b.c",
+    streamxclient.WithStreamRecvMiddleware(func(next streamx.StreamRecvEndpoint) streamx.StreamRecvEndpoint {
+        return func(ctx context.Context, stream streamx.Stream, res any) (err error) {
+           return next(ctx, stream, res)
+        }
+    }),
+    streamxclient.WithStreamSendMiddleware(func(next streamx.StreamSendEndpoint) streamx.StreamSendEndpoint {
+        return func(ctx context.Context, stream streamx.Stream, req any) (err error) {
+           return next(ctx, stream, req)
+        }
+    }),
+)
+```
+
+#### Inject Server Middleware
+
+```go
+server, err := xxx.NewServer(
+    // ....
+    streamxserver.WithStreamRecvMiddleware(func(next streamx.StreamRecvEndpoint) streamx.StreamRecvEndpoint {
+        return func(ctx context.Context, stream streamx.Stream, res any) (err error) {
+           return next(ctx, stream, res)
+        }
+    }),
+    streamxserver.WithStreamSendMiddleware(func(next streamx.StreamSendEndpoint) streamx.StreamSendEndpoint {
+        return func(ctx context.Context, stream streamx.Stream, req any) (err error) {
+           return next(ctx, stream, req)
+        }
+    }),
+)
+```