/*
* Copyright 2002-2017 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.web.reactive.resource;
import java.io.IOException;
import java.io.StringWriter;
import java.nio.charset.Charset;
import java.nio.charset.StandardCharsets;
import java.util.ArrayList;
import java.util.Collections;
import java.util.HashSet;
import java.util.List;
import java.util.Set;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import reactor.core.Exceptions;
import reactor.core.publisher.Flux;
import reactor.core.publisher.Mono;
import org.springframework.core.io.Resource;
import org.springframework.util.FileCopyUtils;
import org.springframework.util.StringUtils;
import org.springframework.web.server.ServerWebExchange;
/**
* A {@link ResourceTransformer} implementation that modifies links in a CSS
* file to match the public URL paths that should be exposed to clients (e.g.
* with an MD5 content-based hash inserted in the URL).
*
* <p>The implementation looks for links in CSS {@code @import} statements and
* also inside CSS {@code url()} functions. All links are then passed through the
* {@link ResourceResolverChain} and resolved relative to the location of the
* containing CSS file. If successfully resolved, the link is modified, otherwise
* the original link is preserved.
*
* @author Rossen Stoyanchev
* @since 5.0
*/
public class CssLinkResourceTransformer extends ResourceTransformerSupport {
private static final Charset DEFAULT_CHARSET = StandardCharsets.UTF_8;
private static final Log logger = LogFactory.getLog(CssLinkResourceTransformer.class);
private final List<LinkParser> linkParsers = new ArrayList<>(2);
public CssLinkResourceTransformer() {
this.linkParsers.add(new ImportLinkParser());
this.linkParsers.add(new UrlFunctionLinkParser());
}
@Override
public Mono<Resource> transform(ServerWebExchange exchange, Resource resource,
ResourceTransformerChain transformerChain) {
return transformerChain.transform(exchange, resource)
.flatMap(newResource -> {
String filename = newResource.getFilename();
if (!"css".equals(StringUtils.getFilenameExtension(filename)) ||
resource instanceof GzipResourceResolver.GzippedResource) {
return Mono.just(newResource);
}
if (logger.isTraceEnabled()) {
logger.trace("Transforming resource: " + newResource);
}
byte[] bytes = new byte[0];
try {
bytes = FileCopyUtils.copyToByteArray(newResource.getInputStream());
}
catch (IOException ex) {
return Mono.error(Exceptions.propagate(ex));
}
String fullContent = new String(bytes, DEFAULT_CHARSET);
List<Segment> segments = parseContent(fullContent);
if (segments.isEmpty()) {
if (logger.isTraceEnabled()) {
logger.trace("No links found.");
}
return Mono.just(newResource);
}
return Flux.fromIterable(segments)
.concatMap(segment -> {
String segmentContent = segment.getContent(fullContent);
if (segment.isLink() && !hasScheme(segmentContent)) {
String link = toAbsolutePath(segmentContent, exchange);
return resolveUrlPath(link, exchange, newResource, transformerChain)
.defaultIfEmpty(segmentContent);
}
else {
return Mono.just(segmentContent);
}
})
.reduce(new StringWriter(), (writer, chunk) -> {
writer.write(chunk);
return writer;
})
.flatMap(writer -> {
byte[] newContent = writer.toString().getBytes(DEFAULT_CHARSET);
return Mono.just(new TransformedResource(resource, newContent));
});
});
}
private List<Segment> parseContent(String fullContent) {
List<Segment> links = new ArrayList<>();
for (LinkParser parser : this.linkParsers) {
links.addAll(parser.parseLinks(fullContent));
}
if (links.isEmpty()) {
return Collections.emptyList();
}
Collections.sort(links);
int index = 0;
List<Segment> allSegments = new ArrayList<>(links);
for (Segment link : links) {
allSegments.add(new Segment(index, link.getStart(), false));
index = link.getEnd();
}
if (index < fullContent.length()) {
allSegments.add(new Segment(index, fullContent.length(), false));
}
Collections.sort(allSegments);
return allSegments;
}
private boolean hasScheme(String link) {
int schemeIndex = link.indexOf(":");
return (schemeIndex > 0 && !link.substring(0, schemeIndex).contains("/")) || link.indexOf("//") == 0;
}
@FunctionalInterface
protected interface LinkParser {
Set<Segment> parseLinks(String fullContent);
}
protected static abstract class AbstractLinkParser implements LinkParser {
/** Return the keyword to use to search for links. */
protected abstract String getKeyword();
@Override
public Set<Segment> parseLinks(String fullContent) {
Set<Segment> linksToAdd = new HashSet<>(8);
int index = 0;
do {
index = fullContent.indexOf(getKeyword(), index);
if (index == -1) {
break;
}
index = skipWhitespace(fullContent, index + getKeyword().length());
if (fullContent.charAt(index) == '\'') {
index = addLink(index, "'", fullContent, linksToAdd);
}
else if (fullContent.charAt(index) == '"') {
index = addLink(index, "\"", fullContent, linksToAdd);
}
else {
index = extractLink(index, fullContent, linksToAdd);
}
}
while (true);
return linksToAdd;
}
private int skipWhitespace(String content, int index) {
while (true) {
if (Character.isWhitespace(content.charAt(index))) {
index++;
continue;
}
return index;
}
}
protected int addLink(int index, String endKey, String content, Set<Segment> linksToAdd) {
int start = index + 1;
int end = content.indexOf(endKey, start);
linksToAdd.add(new Segment(start, end, true));
return end + endKey.length();
}
/**
* Invoked after a keyword match, after whitespaces removed, and when
* the next char is neither a single nor double quote.
*/
protected abstract int extractLink(int index, String content, Set<Segment> linksToAdd);
}
private static class ImportLinkParser extends AbstractLinkParser {
@Override
protected String getKeyword() {
return "@import";
}
@Override
protected int extractLink(int index, String content, Set<Segment> linksToAdd) {
if (content.substring(index, index + 4).equals("url(")) {
// Ignore, UrlLinkParser will take care
}
else if (logger.isErrorEnabled()) {
logger.error("Unexpected syntax for @import link at index " + index);
}
return index;
}
}
private static class UrlFunctionLinkParser extends AbstractLinkParser {
@Override
protected String getKeyword() {
return "url(";
}
@Override
protected int extractLink(int index, String content, Set<Segment> linksToAdd) {
// A url() function without unquoted
return addLink(index - 1, ")", content, linksToAdd);
}
}
private static class Segment implements Comparable<Segment> {
private final int start;
private final int end;
private final boolean link;
public Segment(int start, int end, boolean isLink) {
this.start = start;
this.end = end;
this.link = isLink;
}
public int getStart() {
return this.start;
}
public int getEnd() {
return this.end;
}
public boolean isLink() {
return this.link;
}
public String getContent(String fullContent) {
return fullContent.substring(this.start, this.end);
}
@Override
public int compareTo(Segment other) {
return (this.start < other.start ? -1 : (this.start == other.start ? 0 : 1));
}
@Override
public boolean equals(Object obj) {
if (this == obj) {
return true;
}
if (obj != null && obj instanceof Segment) {
Segment other = (Segment) obj;
return (this.start == other.start && this.end == other.end);
}
return false;
}
@Override
public int hashCode() {
return this.start * 31 + this.end;
}
}
}