Integrate chat agent web interaction to api-gateway UI (#80)

## Purpose

+ Update gateway frontend to add chat-agent part.
+ Reactive web socket server in api-gateway.
+ Call by name for chat agent.
+ Spring cloud gateway route config for chat agent.
+ Make chat agent as Eureka client, because it will be called by spring
cloud gateway, which underlying uses load balancing.


![image](https://github.com/user-attachments/assets/324242bd-ef2d-4ecc-b11c-49a0659f3288)

## Does this introduce a breaking change?
<!-- Mark one with an "x". -->
```
[ ] Yes
[ ] No
```

## Pull Request Type
What kind of change does this Pull Request introduce?

<!-- Please check the one that applies to this PR using "x". -->
```
[ ] Bugfix
[ ] Feature
[ ] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no api changes)
[ ] Documentation content changes
[ ] Other... Please describe:
```

## How to Test
*  Get the code

```
git clone [repo-address]
cd [repo-name]
git checkout [branch-name]
npm install
```

* Test the code
<!-- Add steps to run the tests suite and/or manually test -->
```
```

## What to Check
Verify that the following are valid
* ...

## Other Information
<!-- Add any other helpful information that may be needed here. -->

---------

Co-authored-by: Hao Zhang <[email protected]>

src/spring-petclinic-api-gateway/pom.xml

@@ -90,6 +90,10 @@
             <groupId>io.opentelemetry</groupId>
             <artifactId>opentelemetry-exporter-zipkin</artifactId>
         </dependency>
+        <dependency>
+            <groupId>com.fasterxml.jackson.core</groupId>
+            <artifactId>jackson-databind</artifactId>
+        </dependency>
 
         <!-- Webjars -->
         <dependency>

src/spring-petclinic-api-gateway/src/main/java/org/springframework/samples/petclinic/api/application/ChatServiceClient.java

@@ -0,0 +1,35 @@
+/*
+ * Copyright 2002-2024 the original author or 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 org.springframework.samples.petclinic.api.application;
+
+import lombok.RequiredArgsConstructor;
+import org.springframework.stereotype.Component;
+import org.springframework.web.reactive.function.client.WebClient;
+import reactor.core.publisher.Mono;
+
+@Component
+@RequiredArgsConstructor
+public class ChatServiceClient {
+
+    private final WebClient.Builder webClientBuilder;
+
+    public Mono<String> chat(String sender, String message) {
+        return webClientBuilder.build().get()
+            .uri("http://chat-agent/chat/{sender}/{message}", sender, message)
+            .retrieve()
+            .bodyToMono(String.class);
+    }
+}

src/spring-petclinic-api-gateway/src/main/java/org/springframework/samples/petclinic/api/dto/ChatMessage.java

@@ -0,0 +1,45 @@
+/*
+ * Copyright 2002-2024 the original author or 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 org.springframework.samples.petclinic.api.dto;
+
+import lombok.*;
+
+/**
+ * Represents a chat message in the chat application.
+ */
+@Getter
+@Setter
+@AllArgsConstructor
+@NoArgsConstructor
+@Builder
+public class ChatMessage {
+
+	private String content;
+
+	private String sender;
+
+	private MessageType type;
+
+	/**
+	 * Enum representing the type of the chat message.
+	 */
+	public enum MessageType {
+
+		CHAT, LEAVE, JOIN
+
+	}
+
+}

src/spring-petclinic-api-gateway/src/main/java/org/springframework/samples/petclinic/api/websocket/ChatWebSocketHandler.java

@@ -0,0 +1,89 @@
+/*
+ * Copyright 2002-2024 the original author or 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 org.springframework.samples.petclinic.api.websocket;
+
+import com.fasterxml.jackson.databind.ObjectMapper;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.beans.factory.annotation.Value;
+import org.springframework.samples.petclinic.api.application.ChatServiceClient;
+import org.springframework.samples.petclinic.api.dto.ChatMessage;
+import org.springframework.stereotype.Component;
+import org.springframework.web.reactive.socket.WebSocketHandler;
+import org.springframework.web.reactive.socket.WebSocketMessage;
+import org.springframework.web.reactive.socket.WebSocketSession;
+import reactor.core.publisher.Mono;
+
+@Component
+public class ChatWebSocketHandler implements WebSocketHandler {
+
+    private final Logger logger = LoggerFactory.getLogger(ChatWebSocketHandler.class);
+
+    @Autowired
+    private ChatServiceClient chatServiceClient;
+
+    @Value("${petclinic.agent.name:petclinic agent}")
+    private String agentName;
+
+    @Override
+    public Mono<Void> handle(WebSocketSession session) {
+        return session.send(
+            session.receive()
+                .map(WebSocketMessage::getPayloadAsText)
+                .flatMap(
+                    payload -> processMessage(session, payload)
+                )
+        );
+    }
+
+    private Mono<WebSocketMessage> processMessage(WebSocketSession session, String payload) {
+        logger.info("received payload: {}", payload);
+
+        var objectMapper = new ObjectMapper();
+        ChatMessage receivedMessage = null;
+        try {
+            receivedMessage = objectMapper.readValue(payload, ChatMessage.class);
+        } catch (Exception e) {
+            logger.error("Exception thrown when deserializing client chat message: {}", payload);
+            return Mono.empty();
+        }
+
+        if (receivedMessage.getType() == ChatMessage.MessageType.JOIN) {
+            return Mono.just(session.textMessage(payload));
+        } else if (receivedMessage.getType() == ChatMessage.MessageType.CHAT) {
+            return chatServiceClient.chat(receivedMessage.getSender(), receivedMessage.getContent())
+                .flatMap(responseContent -> {
+                    ChatMessage responseMessage = new ChatMessage();
+                    responseMessage.setContent(responseContent);
+                    responseMessage.setSender(agentName);
+
+                    String responsePayload = null;
+                    try {
+                        responsePayload = objectMapper.writeValueAsString(responseMessage);
+                    } catch (Exception e) {
+                        logger.error("Exception thrown when serializing CHAT message: {}", responseMessage);
+                        return Mono.empty();
+                    }
+
+                    logger.info("response payload: {}", responsePayload);
+                    return Mono.just(session.textMessage(responsePayload));
+                });
+        }
+
+        return Mono.empty();
+    }
+}

src/spring-petclinic-api-gateway/src/main/java/org/springframework/samples/petclinic/api/websocket/WebSocketConfig.java

@@ -0,0 +1,47 @@
+/*
+ * Copyright 2002-2024 the original author or 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 org.springframework.samples.petclinic.api.websocket;
+
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+import org.springframework.web.reactive.HandlerMapping;
+import org.springframework.web.reactive.handler.SimpleUrlHandlerMapping;
+import org.springframework.web.reactive.socket.WebSocketHandler;
+import org.springframework.web.reactive.socket.server.support.WebSocketHandlerAdapter;
+
+import java.util.HashMap;
+import java.util.Map;
+
+@Configuration
+public class WebSocketConfig {
+
+    @Bean
+    public HandlerMapping webSocketMapping(ChatWebSocketHandler webSocketHandler) {
+        Map<String, WebSocketHandler> map = new HashMap<>();
+        map.put("/websocket", webSocketHandler);
+
+        SimpleUrlHandlerMapping mapping = new SimpleUrlHandlerMapping();
+        mapping.setUrlMap(map);
+        mapping.setOrder(-1); // give it higher precedence
+        return mapping;
+    }
+
+    // This bean is necessary for WebSocket support in WebFlux
+    @Bean
+    public WebSocketHandlerAdapter handlerAdapter() {
+        return new WebSocketHandlerAdapter();
+    }
+}

src/spring-petclinic-api-gateway/src/main/less/petclinic.less

@@ -84,6 +84,74 @@
   }
 }
 
+.form-control {
+  display: block;
+  width: 100%;
+  padding: 0.375rem 0.75rem;
+  font-size: 1rem;
+  font-weight: 400;
+  line-height: 1.5;
+  appearance: none;
+  background-clip: padding-box;
+}
+
+.no-marker {
+    list-style-type: none;
+}
+
+#chat-page {
+    .event-message {
+        width: 100%;
+        text-align: center;
+        clear: both;
+
+        p {
+            font-size: 14px;
+            word-wrap: break-word;
+        }
+    }
+
+    .own-message {
+        text-align: right;
+
+        i {
+            visibility: hidden !important;
+        }
+    }
+}
+
+.input-group {
+  position: relative;
+  display: flex;
+  flex-wrap: wrap;
+  align-items: stretch;
+  width: 100%;
+
+  > .form-control,
+  > .form-select,
+  > .form-floating {
+    position: relative;
+    flex: 1 1 auto;
+    width: 1%;
+    min-width: 0;
+  }
+
+  > .form-control:focus,
+  > .form-select:focus,
+  > .form-floating:focus-within {
+    z-index: 5;
+  }
+
+  .btn {
+    position: relative;
+    z-index: 2;
+
+    &:focus {
+      z-index: 5;
+    }
+  }
+}
+
 
 .container .text-muted {
   margin: 20px 0;

src/spring-petclinic-api-gateway/src/main/resources/application.yml

@@ -24,6 +24,12 @@ spring:
             - Path=/api/customer/**
           filters:
             - StripPrefix=2
+        - id: chat-agent
+          uri: lb://chat-agent
+          predicates:
+            - Path=/api/chat/**
+          filters:
+            - StripPrefix=2
 
 
 

src/spring-petclinic-api-gateway/src/main/resources/static/index.html

@@ -47,16 +47,18 @@
     <script src="/scripts/vet-list/vet-list.controller.js"></script>
     <script src="/scripts/vet-list/vet-list.component.js"></script>
 
+    <script src="/scripts/agent/agent.js"></script>
+    <script src="/scripts/agent/agent.component.js"></script>
+
     <script src="/scripts/infrastructure/infrastructure.js"></script>
     <script src="/scripts/infrastructure/httpErrorHandlingInterceptor.js"></script>
 </head>
 
 <body class="container">
 <layout-nav></layout-nav>
 <div class="container-fluid">
-    <div class="container xd-container">
-        <div ui-view=""></div>
-    </div>
+    <div class="row" style="height: 30px;"></div>
+    <div ui-view=""></div>
 </div>
 <layout-footer></layout-footer>
 </body>