Ensures custom headers supplied to RemoveHopByHopHeadersFilter are compared case-insensitive

Fixes gh-2645

spring-cloud-gateway-server/src/main/java/org/springframework/cloud/gateway/filter/headers/RemoveHopByHopHeadersFilter.java

@@ -21,10 +21,12 @@ import java.util.HashSet;
 import java.util.List;
 import java.util.Map;
 import java.util.Set;
+import java.util.stream.Collectors;
 
 import org.springframework.boot.context.properties.ConfigurationProperties;
 import org.springframework.core.Ordered;
 import org.springframework.http.HttpHeaders;
+import org.springframework.util.Assert;
 import org.springframework.web.server.ServerWebExchange;
 
 @ConfigurationProperties("spring.cloud.gateway.filter.remove-hop-by-hop")
@@ -51,7 +53,8 @@ public class RemoveHopByHopHeadersFilter implements HttpHeadersFilter, Ordered {
 	}
 
 	public void setHeaders(Set<String> headers) {
-		this.headers = headers;
+		Assert.notNull(headers, "headers may not be null");
+		this.headers = headers.stream().map(String::toLowerCase).collect(Collectors.toSet());
 	}
 
 	@Override

spring-cloud-gateway-server/src/test/java/org/springframework/cloud/gateway/filter/headers/RemoveHopByHopHeadersFilterTests.java

@@ -18,6 +18,7 @@ package org.springframework.cloud.gateway.filter.headers;
 
 import java.util.Arrays;
 import java.util.HashSet;
+import java.util.LinkedHashSet;
 import java.util.Set;
 
 import org.junit.jupiter.api.Test;
@@ -25,6 +26,7 @@ import org.junit.jupiter.api.Test;
 import org.springframework.http.HttpHeaders;
 import org.springframework.mock.http.server.reactive.MockServerHttpRequest;
 import org.springframework.mock.web.server.MockServerWebExchange;
+import org.springframework.util.StringUtils;
 
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.springframework.cloud.gateway.filter.headers.RemoveHopByHopHeadersFilter.HEADERS_REMOVED_ON_REQUEST;
@@ -52,6 +54,23 @@ public class RemoveHopByHopHeadersFilterTests {
 		testFilter(MockServerWebExchange.from(builder));
 	}
 
+	@Test
+	public void caseInsensitiveCustom() {
+		MockServerHttpRequest.BaseBuilder<?> builder = MockServerHttpRequest.get("http://localhost/get");
+
+		HEADERS_REMOVED_ON_REQUEST
+				.forEach(header -> builder.header(StringUtils.capitalize(header.toLowerCase()), header + "1"));
+
+		LinkedHashSet<String> customHeaders = new LinkedHashSet<>();
+		HEADERS_REMOVED_ON_REQUEST.forEach(header -> {
+			String newHeader = header.charAt(0) + StringUtils.capitalize(header.substring(1));
+			customHeaders.add(newHeader);
+		});
+		RemoveHopByHopHeadersFilter filter = new RemoveHopByHopHeadersFilter();
+		filter.setHeaders(customHeaders);
+		testFilter(filter, MockServerWebExchange.from(builder));
+	}
+
 	@Test
 	public void removesHeadersListedInConnectionHeader() {
 		MockServerHttpRequest.BaseBuilder<?> builder = MockServerHttpRequest.get("http://localhost/get");
@@ -64,7 +83,11 @@ public class RemoveHopByHopHeadersFilterTests {
 	}
 
 	private void testFilter(MockServerWebExchange exchange, String... additionalHeaders) {
-		RemoveHopByHopHeadersFilter filter = new RemoveHopByHopHeadersFilter();
+		testFilter(new RemoveHopByHopHeadersFilter(), exchange, additionalHeaders);
+	}
+
+	private void testFilter(RemoveHopByHopHeadersFilter filter, MockServerWebExchange exchange,
+			String... additionalHeaders) {
 		HttpHeaders headers = filter.filter(exchange.getRequest().getHeaders(), exchange);
 
 		Set<String> toRemove = new HashSet<>(HEADERS_REMOVED_ON_REQUEST);