Customize the behavior of remote address resolver in spring-cloud-gateway sample

gateway/pom.xml

@@ -5,7 +5,7 @@
     <parent>
         <groupId>org.springframework.boot</groupId>
         <artifactId>spring-boot-starter-parent</artifactId>
-        <version>2.1.8.RELEASE</version>
+        <version>2.2.10.RELEASE</version>
         <relativePath/> <!-- lookup parent from repository -->
     </parent>
     <groupId>me.aboullaite</groupId>
@@ -16,7 +16,7 @@
 
     <properties>
         <java.version>1.8</java.version>
-        <spring-cloud.version>Greenwich.RELEASE</spring-cloud.version>
+        <spring-cloud.version>Hoxton.SR8</spring-cloud.version>
     </properties>
 
     <dependencies>

gateway/src/main/java/me/aboullaite/gateway/NettyReactiveWebServerConfig.java

@@ -0,0 +1,67 @@
+package me.aboullaite.gateway;
+
+import io.netty.handler.codec.http.HttpRequest;
+import org.springframework.boot.web.embedded.netty.NettyReactiveWebServerFactory;
+import org.springframework.boot.web.server.WebServerFactoryCustomizer;
+import org.springframework.context.annotation.Configuration;
+import org.springframework.http.server.reactive.ServerHttpRequest;
+import reactor.netty.http.server.ConnectionInfo;
+import reactor.netty.tcp.InetSocketAddressUtil;
+
+import java.net.InetSocketAddress;
+import java.util.function.BiFunction;
+
+/**
+ * This configuration customizes the behavior of remote address resolver. As a result,
+ * {@link ServerHttpRequest#getRemoteAddress} will return IP address that is extracted from X-Forwarded-For header
+ * by our {@link CustomizedHttpForwardedHeaderHandler}.
+ */
+@Configuration
+public class NettyReactiveWebServerConfig implements WebServerFactoryCustomizer<NettyReactiveWebServerFactory> {
+
+    @Override
+    public void customize(NettyReactiveWebServerFactory factory) {
+        factory.addServerCustomizers(httpServer -> httpServer.forwarded(new CustomizedHttpForwardedHeaderHandler()));
+    }
+
+    static class CustomizedHttpForwardedHeaderHandler
+            implements BiFunction<ConnectionInfo, HttpRequest, ConnectionInfo> {
+
+        static final String X_FORWARDED_IP_HEADER = "X-Forwarded-For";
+
+        /**
+         * Attempt to extract the last IP address from X-Forwarded-For header. If the header is present, create a
+         * ConnectionInfo instance with the extracted IP address and then return it. Otherwise, return the
+         * connectionInfo passed in. On the contrary, DefaultHttpForwardedHeaderHandler extracts the first IP
+         * address from the header when the header is present.
+         *
+         * @param connectionInfo
+         * @param request
+         * @return
+         */
+        @Override
+        public ConnectionInfo apply(ConnectionInfo connectionInfo, HttpRequest request) {
+            String ipHeader = request.headers().get(X_FORWARDED_IP_HEADER);
+
+            if (ipHeader != null) {
+                String[] ips = ipHeader.split(",");
+                String ip = ips[ips.length - 1].trim();
+
+                // If the IP address is internal, we will skip it and extract the previous one.
+                if (ips.length >= 2 && isInternal(ip)) {
+                    ip = ips[ips.length - 2].trim();
+                }
+
+                InetSocketAddress remoteAddress = InetSocketAddressUtil.parseAddress(ip,
+                        connectionInfo.getRemoteAddress().getPort());
+                connectionInfo = connectionInfo.withRemoteAddress(remoteAddress);
+            }
+
+            return connectionInfo;
+        }
+
+        private boolean isInternal(String ip) {
+            return ip.startsWith("10.");
+        }
+    }
+}

gateway/src/main/java/me/aboullaite/gateway/controller/RemoteAddressController.java

@@ -0,0 +1,27 @@
+package me.aboullaite.gateway.controller;
+
+import me.aboullaite.gateway.NettyReactiveWebServerConfig;
+import org.springframework.http.server.reactive.ServerHttpRequest;
+import org.springframework.web.bind.annotation.GetMapping;
+import org.springframework.web.bind.annotation.RestController;
+
+/**
+ * A demo controller that shows the customized behavior of {@link ServerHttpRequest#getRemoteAddress}. The
+ * customization class is CustomizedHttpForwardedHeaderHandler in {@link NettyReactiveWebServerConfig}.
+ */
+@RestController
+public class RemoteAddressController {
+
+    /**
+     * @param request
+     * @return Value of X-Forwarded-For header, as well as result of {@link ServerHttpRequest#getRemoteAddress}
+     */
+    @GetMapping("/remote_address")
+    public String getRemoteAddress(ServerHttpRequest request) {
+        return String.format("X-Forwarded-For: %s\n" +
+                        "getRemoteAddress() returns %s",
+                request.getHeaders().get("X-Forwarded-For"),
+                request.getRemoteAddress()
+        );
+    }
+}