Redirect GraphiQL clients with servlet path

This commit ensures that both servlet context and servlet paths are
taken into account when generating URL paths to the GraphQL HTTP and WS
endpoints.

Fixes gh-402

Author: bclozel

spring-graphql/src/main/java/org/springframework/graphql/server/webmvc/GraphiQlHandler.java

@@ -78,23 +78,21 @@ public ServerResponse handleRequest(ServerRequest request) {
 	}
 
 	private URI getRedirectUrl(ServerRequest request) {
-		String contextPath = request.requestPath().contextPath().toString();
-		String path = request.requestPath().pathWithinApplication().toString();
-		UriBuilder builder = request.uriBuilder().replacePath(contextPath).path(path);
-
-		String pathQueryParam = applyContextPath(request, this.graphQlPath);
+		UriBuilder builder = request.uriBuilder();
+		String pathQueryParam = applyPathPrefix(request, this.graphQlPath);
 		builder.queryParam("path", pathQueryParam);
-
 		if (StringUtils.hasText(this.graphQlWsPath)) {
-			String wsPathQueryParam = applyContextPath(request, this.graphQlWsPath);
+			String wsPathQueryParam = applyPathPrefix(request, this.graphQlWsPath);
 			builder.queryParam("wsPath", wsPathQueryParam);
 		}
 		return builder.build();
 	}
 
-	private String applyContextPath(ServerRequest request, String path) {
-		String contextPath = request.requestPath().contextPath().toString();
-		return StringUtils.hasText(contextPath) ? contextPath + path : path;
+	private String applyPathPrefix(ServerRequest request, String path) {
+		String fullPath = request.requestPath().value();
+		String pathWithinApplication = request.requestPath().pathWithinApplication().toString();
+		int pathWithinApplicationIndex = fullPath.indexOf(pathWithinApplication);
+		return (pathWithinApplicationIndex != -1) ? fullPath.substring(0, pathWithinApplicationIndex) + path : path;
 	}
 
 }