org.springframework.web.servlet.resource.CssLinkResourceTransformer Maven / Gradle / Ivy
/*
* Copyright 2002-2021 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
*
* https://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.servlet.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.List;
import java.util.SortedSet;
import java.util.TreeSet;
import jakarta.servlet.http.HttpServletRequest;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.springframework.core.io.Resource;
import org.springframework.lang.Nullable;
import org.springframework.util.FileCopyUtils;
import org.springframework.util.StringUtils;
/**
* 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).
*
* 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 4.1
*/
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 linkParsers = new ArrayList<>(2);
public CssLinkResourceTransformer() {
this.linkParsers.add(new ImportStatementLinkParser());
this.linkParsers.add(new UrlFunctionLinkParser());
}
@SuppressWarnings("deprecation")
@Override
public Resource transform(HttpServletRequest request, Resource resource, ResourceTransformerChain transformerChain)
throws IOException {
resource = transformerChain.transform(request, resource);
String filename = resource.getFilename();
if (!"css".equals(StringUtils.getFilenameExtension(filename)) ||
resource instanceof EncodedResourceResolver.EncodedResource) {
return resource;
}
byte[] bytes = FileCopyUtils.copyToByteArray(resource.getInputStream());
String content = new String(bytes, DEFAULT_CHARSET);
SortedSet links = new TreeSet<>();
for (LinkParser parser : this.linkParsers) {
parser.parse(content, links);
}
if (links.isEmpty()) {
return resource;
}
int index = 0;
StringWriter writer = new StringWriter();
for (ContentChunkInfo linkContentChunkInfo : links) {
writer.write(content.substring(index, linkContentChunkInfo.getStart()));
String link = content.substring(linkContentChunkInfo.getStart(), linkContentChunkInfo.getEnd());
String newLink = null;
if (!hasScheme(link)) {
String absolutePath = toAbsolutePath(link, request);
newLink = resolveUrlPath(absolutePath, request, resource, transformerChain);
}
writer.write(newLink != null ? newLink : link);
index = linkContentChunkInfo.getEnd();
}
writer.write(content.substring(index));
return new TransformedResource(resource, writer.toString().getBytes(DEFAULT_CHARSET));
}
private boolean hasScheme(String link) {
int schemeIndex = link.indexOf(':');
return ((schemeIndex > 0 && !link.substring(0, schemeIndex).contains("/")) || link.indexOf("//") == 0);
}
/**
* Extract content chunks that represent links.
*/
@FunctionalInterface
protected interface LinkParser {
void parse(String content, SortedSet result);
}
/**
* Abstract base class for {@link LinkParser} implementations.
*/
protected abstract static class AbstractLinkParser implements LinkParser {
/** Return the keyword to use to search for links, e.g. "@import", "url(" */
protected abstract String getKeyword();
@Override
public void parse(String content, SortedSet result) {
int position = 0;
while (true) {
position = content.indexOf(getKeyword(), position);
if (position == -1) {
return;
}
position += getKeyword().length();
while (Character.isWhitespace(content.charAt(position))) {
position++;
}
if (content.charAt(position) == '\'') {
position = extractLink(position, "'", content, result);
}
else if (content.charAt(position) == '"') {
position = extractLink(position, "\"", content, result);
}
else {
position = extractLink(position, content, result);
}
}
}
protected int extractLink(int index, String endKey, String content, SortedSet linksToAdd) {
int start = index + 1;
int end = content.indexOf(endKey, start);
linksToAdd.add(new ContentChunkInfo(start, end));
return end + endKey.length();
}
/**
* Invoked after a keyword match, after whitespace has been removed, and when
* the next char is neither a single nor double quote.
*/
protected abstract int extractLink(int index, String content, SortedSet linksToAdd);
}
private static class ImportStatementLinkParser extends AbstractLinkParser {
@Override
protected String getKeyword() {
return "@import";
}
@Override
protected int extractLink(int index, String content, SortedSet linksToAdd) {
if (content.startsWith("url(", index)) {
// Ignore: UrlFunctionLinkParser will handle it.
}
else if (logger.isTraceEnabled()) {
logger.trace("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, SortedSet linksToAdd) {
// A url() function without unquoted
return extractLink(index - 1, ")", content, linksToAdd);
}
}
private static class ContentChunkInfo implements Comparable {
private final int start;
private final int end;
ContentChunkInfo(int start, int end) {
this.start = start;
this.end = end;
}
public int getStart() {
return this.start;
}
public int getEnd() {
return this.end;
}
@Override
public int compareTo(ContentChunkInfo other) {
return Integer.compare(this.start, other.start);
}
@Override
public boolean equals(@Nullable Object other) {
if (this == other) {
return true;
}
if (!(other instanceof ContentChunkInfo otherCci)) {
return false;
}
return (this.start == otherCci.start && this.end == otherCci.end);
}
@Override
public int hashCode() {
return this.start * 31 + this.end;
}
}
}