Provide simple way to create ServerRequest

This commit introduces support for creating a new `ServerRequest` from
an existing instance. This is especially useful when filtering requests
in a HandlerFilterFunction.

Issue: SPR-16707

spring-test/src/main/java/org/springframework/mock/web/reactive/function/server/MockServerRequest.java

@@ -40,6 +40,7 @@ import org.springframework.http.HttpMethod;
 import org.springframework.http.HttpRange;
 import org.springframework.http.HttpRequest;
 import org.springframework.http.MediaType;
+import org.springframework.http.codec.HttpMessageReader;
 import org.springframework.http.codec.multipart.Part;
 import org.springframework.http.server.PathContainer;
 import org.springframework.http.server.RequestPath;
@@ -50,7 +51,9 @@ import org.springframework.util.CollectionUtils;
 import org.springframework.util.LinkedMultiValueMap;
 import org.springframework.util.MultiValueMap;
 import org.springframework.web.reactive.function.BodyExtractor;
+import org.springframework.web.reactive.function.server.HandlerStrategies;
 import org.springframework.web.reactive.function.server.ServerRequest;
+import org.springframework.web.server.ServerWebExchange;
 import org.springframework.web.server.WebSession;
 import org.springframework.web.util.UriBuilder;
 import org.springframework.web.util.UriComponentsBuilder;
@@ -91,12 +94,18 @@ public class MockServerRequest implements ServerRequest {
 	@Nullable
 	private final InetSocketAddress remoteAddress;
 
+	private final List<HttpMessageReader<?>> messageReaders;
+
+	@Nullable
+	private final ServerWebExchange exchange;
+
 
 	private MockServerRequest(HttpMethod method, URI uri, String contextPath, MockHeaders headers,
 			MultiValueMap<String, HttpCookie> cookies, @Nullable Object body,
 			Map<String, Object> attributes, MultiValueMap<String, String> queryParams,
 			Map<String, String> pathVariables, @Nullable WebSession session, @Nullable Principal principal,
-			@Nullable InetSocketAddress remoteAddress) {
+			@Nullable InetSocketAddress remoteAddress, List<HttpMessageReader<?>> messageReaders,
+			@Nullable ServerWebExchange exchange) {
 
 		this.method = method;
 		this.uri = uri;
@@ -110,6 +119,8 @@ public class MockServerRequest implements ServerRequest {
 		this.session = session;
 		this.principal = principal;
 		this.remoteAddress = remoteAddress;
+		this.messageReaders = messageReaders;
+		this.exchange = exchange;
 	}
 
 
@@ -153,6 +164,11 @@ public class MockServerRequest implements ServerRequest {
 		return Optional.ofNullable(this.remoteAddress);
 	}
 
+	@Override
+	public List<HttpMessageReader<?>> messageReaders() {
+		return this.messageReaders;
+	}
+
 	@Override
 	@SuppressWarnings("unchecked")
 	public <S> S body(BodyExtractor<S, ? super ServerHttpRequest> extractor) {
@@ -220,7 +236,6 @@ public class MockServerRequest implements ServerRequest {
 		return Mono.justOrEmpty(this.principal);
 	}
 
-
 	@Override
 	@SuppressWarnings("unchecked")
 	public Mono<MultiValueMap<String, String>> formData() {
@@ -235,6 +250,12 @@ public class MockServerRequest implements ServerRequest {
 		return (Mono<MultiValueMap<String, Part>>) this.body;
 	}
 
+	@Override
+	public ServerWebExchange exchange() {
+		Assert.state(this.exchange != null, "No exchange");
+		return this.exchange;
+	}
+
 	public static Builder builder() {
 		return new BuilderImpl();
 	}
@@ -282,6 +303,10 @@ public class MockServerRequest implements ServerRequest {
 
 		Builder remoteAddress(InetSocketAddress remoteAddress);
 
+		Builder messageReaders(List<HttpMessageReader<?>> messageReaders);
+
+		Builder exchange(ServerWebExchange exchange);
+
 		MockServerRequest body(Object body);
 
 		MockServerRequest build();
@@ -318,6 +343,11 @@ public class MockServerRequest implements ServerRequest {
 		@Nullable
 		private InetSocketAddress remoteAddress;
 
+		private List<HttpMessageReader<?>> messageReaders = HandlerStrategies.withDefaults().messageReaders();
+
+		@Nullable
+		private ServerWebExchange exchange;
+
 		@Override
 		public Builder method(HttpMethod method) {
 			Assert.notNull(method, "'method' must not be null");
@@ -440,19 +470,35 @@ public class MockServerRequest implements ServerRequest {
 			return this;
 		}
 
+		@Override
+		public Builder messageReaders(List<HttpMessageReader<?>> messageReaders) {
+			Assert.notNull(messageReaders, "'messageReaders' must not be null");
+			this.messageReaders = messageReaders;
+			return this;
+		}
+
+		@Override
+		public Builder exchange(ServerWebExchange exchange) {
+			Assert.notNull(exchange, "'exchange' must not be null");
+			this.exchange = exchange;
+			return this;
+		}
+
 		@Override
 		public MockServerRequest body(Object body) {
 			this.body = body;
 			return new MockServerRequest(this.method, this.uri, this.contextPath, this.headers,
 					this.cookies, this.body, this.attributes, this.queryParams, this.pathVariables,
-					this.session, this.principal, this.remoteAddress);
+					this.session, this.principal, this.remoteAddress, this.messageReaders,
+					this.exchange);
 		}
 
 		@Override
 		public MockServerRequest build() {
 			return new MockServerRequest(this.method, this.uri, this.contextPath, this.headers,
 					this.cookies, null, this.attributes, this.queryParams, this.pathVariables,
-					this.session, this.principal, this.remoteAddress);
+					this.session, this.principal, this.remoteAddress, this.messageReaders,
+					this.exchange);
 		}
 	}