Derive media content types from file content, not the request #174
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| Original file line number | Diff line number | Diff line change |
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| /* | ||
| * Licensed to the Apache Software Foundation (ASF) under one or more | ||
| * contributor license agreements. The ASF licenses this file to You | ||
| * 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. For additional | ||
| * information regarding copyright in this work, please see the NOTICE | ||
| * file in the top level directory of this distribution. | ||
| */ | ||
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| package org.apache.roller.weblogger.util; | ||
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| import java.util.Arrays; | ||
| import java.util.Collections; | ||
| import java.util.HashSet; | ||
| import java.util.Locale; | ||
| import java.util.Set; | ||
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| import javax.servlet.http.HttpServletResponse; | ||
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| /** | ||
| * Decides what type an uploaded file is stored as, and how it is served back. | ||
| * | ||
| * <p>A client uploading a file states a type, but the stored type is derived | ||
| * from the file name. The declared value is a hint only, consulted where the | ||
| * name yields nothing, and it cannot introduce a type the browser would | ||
| * execute. | ||
| * | ||
| * <p>Serving applies the second half. Only a short list of formats that | ||
| * browsers render passively are sent inline; everything else is sent as an | ||
| * attachment, and {@code nosniff} accompanies every response so browsers do | ||
| * not substitute their own type guess. | ||
| */ | ||
| public final class MediaTypePolicy { | ||
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| private MediaTypePolicy() { | ||
| } | ||
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| public static final String DEFAULT_TYPE = "application/octet-stream"; | ||
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| /** | ||
| * Formats browsers render without executing anything the file carries. | ||
| * SVG is deliberately absent: it is an XML document that can carry script. | ||
| */ | ||
| private static final Set<String> INLINE_TYPES = Collections.unmodifiableSet( | ||
|
Contributor
There was a problem hiding this comment. Worth listing what this drops compared to |
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| new HashSet<>(Arrays.asList( | ||
| "image/jpeg", "image/pjpeg", "image/png", "image/gif", | ||
| "image/bmp", "image/x-ms-bmp", "image/webp", "image/tiff", | ||
| "image/x-icon", "image/vnd.microsoft.icon", | ||
| "application/pdf"))); | ||
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| /** Families served inline whatever the subtype. */ | ||
| private static final String[] INLINE_PREFIXES = {"audio/", "video/"}; | ||
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| /** | ||
| * Types a browser may execute, or that can carry something it will. These | ||
| * are never adopted from a client's declaration. | ||
| */ | ||
| private static final Set<String> ACTIVE_TYPES = Collections.unmodifiableSet( | ||
| new HashSet<>(Arrays.asList( | ||
| "text/html", "application/xhtml+xml", "application/xhtml", | ||
| "image/svg+xml", "text/xml", "application/xml", | ||
| "text/javascript", "application/javascript", | ||
| "application/ecmascript", "text/ecmascript", | ||
| "text/vbscript", "application/x-shockwave-flash", | ||
| "text/xsl", "application/xslt+xml"))); | ||
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| /** | ||
| * @param fileName the uploaded file's name | ||
| * @param declaredType the type the client said it was, may be null | ||
| * @return the type to store: derived from the name where that is | ||
| * conclusive, otherwise the declared type if it is not one a | ||
| * browser would act on, otherwise the generic binary type | ||
| */ | ||
| public static String storedTypeFor(String fileName, String declaredType) { | ||
|
Contributor
There was a problem hiding this comment. Because active declared types collapse to |
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| String derived = normalize(deriveFromName(fileName)); | ||
| if (isConclusive(derived)) { | ||
| return derived; | ||
| } | ||
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| String declared = normalize(declaredType); | ||
| if (isConclusive(declared) && !isActive(declared)) { | ||
| return declared; | ||
| } | ||
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| return DEFAULT_TYPE; | ||
| } | ||
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| /** @return true when browsers render this type without executing it */ | ||
| public static boolean isInlineSafe(String contentType) { | ||
|
Contributor
There was a problem hiding this comment.
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| String type = normalize(contentType); | ||
| if (type == null) { | ||
| return false; | ||
| } | ||
| if (INLINE_TYPES.contains(type)) { | ||
| return true; | ||
| } | ||
| for (String prefix : INLINE_PREFIXES) { | ||
| if (type.startsWith(prefix)) { | ||
| return true; | ||
| } | ||
| } | ||
| return false; | ||
| } | ||
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| /** @return true when a browser may execute this type, or script inside it */ | ||
| public static boolean isActive(String contentType) { | ||
| String type = normalize(contentType); | ||
| if (type == null) { | ||
| return false; | ||
| } | ||
| return ACTIVE_TYPES.contains(type) || type.endsWith("+xml"); | ||
| } | ||
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| /** | ||
| * Sets the type and the headers that govern how the response is treated. | ||
| * Anything outside the inline list is marked as an attachment. | ||
| */ | ||
| public static void applyResponseHeaders(HttpServletResponse response, | ||
| String contentType, String fileName) { | ||
| response.setHeader("X-Content-Type-Options", "nosniff"); | ||
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| String type = normalize(contentType); | ||
| if (type == null) { | ||
| type = DEFAULT_TYPE; | ||
| } | ||
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| if (isInlineSafe(type)) { | ||
| response.setContentType(type); | ||
| return; | ||
| } | ||
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| // Served as bytes to be saved rather than a document to be rendered. | ||
| response.setContentType(DEFAULT_TYPE); | ||
| response.setHeader("Content-Disposition", | ||
| "attachment; filename=\"" + headerSafe(fileName) + "\""); | ||
| } | ||
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| private static String deriveFromName(String fileName) { | ||
| if (fileName == null || fileName.trim().isEmpty()) { | ||
| return null; | ||
| } | ||
| try { | ||
| return Utilities.getContentTypeFromFileName(fileName); | ||
| } catch (Exception undetermined) { | ||
|
Contributor
There was a problem hiding this comment.
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| return null; | ||
| } | ||
| } | ||
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| /** @return the bare type in lower case, without parameters such as charset */ | ||
| private static String normalize(String contentType) { | ||
| if (contentType == null) { | ||
| return null; | ||
| } | ||
| String type = contentType.trim(); | ||
| int semicolon = type.indexOf(';'); | ||
| if (semicolon > -1) { | ||
| type = type.substring(0, semicolon).trim(); | ||
| } | ||
| return type.isEmpty() ? null : type.toLowerCase(Locale.ENGLISH); | ||
| } | ||
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| private static boolean isConclusive(String type) { | ||
| return type != null && !DEFAULT_TYPE.equals(type); | ||
| } | ||
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| /** | ||
| * @return the name with the characters that would end the quoted string or | ||
| * start another header removed, since it is placed in one | ||
| */ | ||
| private static String headerSafe(String fileName) { | ||
| if (fileName == null || fileName.trim().isEmpty()) { | ||
| return "download"; | ||
| } | ||
| String safe = fileName.replaceAll("[\\r\\n\"\\\\]", ""); | ||
| return safe.trim().isEmpty() ? "download" : safe; | ||
| } | ||
| } | ||
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context.getMimeType()returnsnullfor extensions not mapped inweb.xml/the container, andapplyResponseHeadersturnsnullinto an octet-stream attachment. On mastersetContentType(null)left the type unset and the browser could still display the file; now any unmapped (or uppercase, on a case-sensitive container) extension downloads in the theme preview.