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naiveproxy/net/base/mime_sniffer.cc
klzgrad e45b4af2be Import chromium-68.0.3440.106
2018-08-11 05:35:24 +00:00

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// Copyright (c) 2012 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
// Detecting mime types is a tricky business because we need to balance
// compatibility concerns with security issues. Here is a survey of how other
// browsers behave and then a description of how we intend to behave.
//
// HTML payload, no Content-Type header:
// * IE 7: Render as HTML
// * Firefox 2: Render as HTML
// * Safari 3: Render as HTML
// * Opera 9: Render as HTML
//
// Here the choice seems clear:
// => Chrome: Render as HTML
//
// HTML payload, Content-Type: "text/plain":
// * IE 7: Render as HTML
// * Firefox 2: Render as text
// * Safari 3: Render as text (Note: Safari will Render as HTML if the URL
// has an HTML extension)
// * Opera 9: Render as text
//
// Here we choose to follow the majority (and break some compatibility with IE).
// Many folks dislike IE's behavior here.
// => Chrome: Render as text
// We generalize this as follows. If the Content-Type header is text/plain
// we won't detect dangerous mime types (those that can execute script).
//
// HTML payload, Content-Type: "application/octet-stream":
// * IE 7: Render as HTML
// * Firefox 2: Download as application/octet-stream
// * Safari 3: Render as HTML
// * Opera 9: Render as HTML
//
// We follow Firefox.
// => Chrome: Download as application/octet-stream
// One factor in this decision is that IIS 4 and 5 will send
// application/octet-stream for .xhtml files (because they don't recognize
// the extension). We did some experiments and it looks like this doesn't occur
// very often on the web. We choose the more secure option.
//
// GIF payload, no Content-Type header:
// * IE 7: Render as GIF
// * Firefox 2: Render as GIF
// * Safari 3: Download as Unknown (Note: Safari will Render as GIF if the
// URL has an GIF extension)
// * Opera 9: Render as GIF
//
// The choice is clear.
// => Chrome: Render as GIF
// Once we decide to render HTML without a Content-Type header, there isn't much
// reason not to render GIFs.
//
// GIF payload, Content-Type: "text/plain":
// * IE 7: Render as GIF
// * Firefox 2: Download as application/octet-stream (Note: Firefox will
// Download as GIF if the URL has an GIF extension)
// * Safari 3: Download as Unknown (Note: Safari will Render as GIF if the
// URL has an GIF extension)
// * Opera 9: Render as GIF
//
// Displaying as text/plain makes little sense as the content will look like
// gibberish. Here, we could change our minds and download.
// => Chrome: Render as GIF
//
// GIF payload, Content-Type: "application/octet-stream":
// * IE 7: Render as GIF
// * Firefox 2: Download as application/octet-stream (Note: Firefox will
// Download as GIF if the URL has an GIF extension)
// * Safari 3: Download as Unknown (Note: Safari will Render as GIF if the
// URL has an GIF extension)
// * Opera 9: Render as GIF
//
// We used to render as GIF here, but the problem is that some sites want to
// trigger downloads by sending application/octet-stream (even though they
// should be sending Content-Disposition: attachment). Although it is safe
// to render as GIF from a security perspective, we actually get better
// compatibility if we don't sniff from application/octet stream at all.
// => Chrome: Download as application/octet-stream
//
// Note that our definition of HTML payload is much stricter than IE's
// definition and roughly the same as Firefox's definition.
#include <stdint.h>
#include <string>
#include "net/base/mime_sniffer.h"
#include "base/containers/span.h"
#include "base/logging.h"
#include "base/stl_util.h"
#include "base/strings/string_util.h"
#include "url/gurl.h"
namespace net {
// The number of content bytes we need to use all our magic numbers. Feel free
// to increase this number if you add a longer magic number.
static const size_t kBytesRequiredForMagic = 42;
struct MagicNumber {
const char* mime_type;
const char* magic;
size_t magic_len;
bool is_string;
const char* mask; // if set, must have same length as |magic|
};
#define MAGIC_NUMBER(mime_type, magic) \
{ (mime_type), (magic), sizeof(magic)-1, false, NULL }
template <int MagicSize, int MaskSize>
class VerifySizes {
static_assert(MagicSize == MaskSize, "sizes must be equal");
public:
enum { SIZES = MagicSize };
};
#define verified_sizeof(magic, mask) \
VerifySizes<sizeof(magic), sizeof(mask)>::SIZES
#define MAGIC_MASK(mime_type, magic, mask) \
{ (mime_type), (magic), verified_sizeof(magic, mask)-1, false, (mask) }
// Magic strings are case insensitive and must not include '\0' characters
#define MAGIC_STRING(mime_type, magic) \
{ (mime_type), (magic), sizeof(magic)-1, true, NULL }
static const MagicNumber kMagicNumbers[] = {
// Source: HTML 5 specification
MAGIC_NUMBER("application/pdf", "%PDF-"),
MAGIC_NUMBER("application/postscript", "%!PS-Adobe-"),
MAGIC_NUMBER("image/gif", "GIF87a"),
MAGIC_NUMBER("image/gif", "GIF89a"),
MAGIC_NUMBER("image/png", "\x89" "PNG\x0D\x0A\x1A\x0A"),
MAGIC_NUMBER("image/jpeg", "\xFF\xD8\xFF"),
MAGIC_NUMBER("image/bmp", "BM"),
// Source: Mozilla
MAGIC_NUMBER("text/plain", "#!"), // Script
MAGIC_NUMBER("text/plain", "%!"), // Script, similar to PS
MAGIC_NUMBER("text/plain", "From"),
MAGIC_NUMBER("text/plain", ">From"),
// Chrome specific
MAGIC_NUMBER("application/x-gzip", "\x1F\x8B\x08"),
MAGIC_NUMBER("audio/x-pn-realaudio", "\x2E\x52\x4D\x46"),
MAGIC_NUMBER("video/x-ms-asf",
"\x30\x26\xB2\x75\x8E\x66\xCF\x11\xA6\xD9\x00\xAA\x00\x62\xCE\x6C"),
MAGIC_NUMBER("image/tiff", "I I"),
MAGIC_NUMBER("image/tiff", "II*"),
MAGIC_NUMBER("image/tiff", "MM\x00*"),
MAGIC_NUMBER("audio/mpeg", "ID3"),
MAGIC_NUMBER("image/webp", "RIFF....WEBPVP8 "),
MAGIC_NUMBER("video/webm", "\x1A\x45\xDF\xA3"),
MAGIC_NUMBER("application/zip", "PK\x03\x04"),
MAGIC_NUMBER("application/x-rar-compressed", "Rar!\x1A\x07\x00"),
MAGIC_NUMBER("application/x-msmetafile", "\xD7\xCD\xC6\x9A"),
MAGIC_NUMBER("application/octet-stream", "MZ"), // EXE
// Sniffing for Flash:
//
// MAGIC_NUMBER("application/x-shockwave-flash", "CWS"),
// MAGIC_NUMBER("application/x-shockwave-flash", "FLV"),
// MAGIC_NUMBER("application/x-shockwave-flash", "FWS"),
//
// Including these magic number for Flash is a trade off.
//
// Pros:
// * Flash is an important and popular file format
//
// Cons:
// * These patterns are fairly weak
// * If we mistakenly decide something is Flash, we will execute it
// in the origin of an unsuspecting site. This could be a security
// vulnerability if the site allows users to upload content.
//
// On balance, we do not include these patterns.
};
// The number of content bytes we need to use all our Microsoft Office magic
// numbers.
static const size_t kBytesRequiredForOfficeMagic = 8;
static const MagicNumber kOfficeMagicNumbers[] = {
MAGIC_NUMBER("CFB", "\xD0\xCF\x11\xE0\xA1\xB1\x1A\xE1"),
MAGIC_NUMBER("OOXML", "PK\x03\x04"),
};
enum OfficeDocType {
DOC_TYPE_WORD,
DOC_TYPE_EXCEL,
DOC_TYPE_POWERPOINT,
DOC_TYPE_NONE
};
struct OfficeExtensionType {
OfficeDocType doc_type;
const char* extension;
size_t extension_len;
};
#define OFFICE_EXTENSION(type, extension) \
{ (type), (extension), sizeof(extension) - 1 }
static const OfficeExtensionType kOfficeExtensionTypes[] = {
OFFICE_EXTENSION(DOC_TYPE_WORD, ".doc"),
OFFICE_EXTENSION(DOC_TYPE_EXCEL, ".xls"),
OFFICE_EXTENSION(DOC_TYPE_POWERPOINT, ".ppt"),
OFFICE_EXTENSION(DOC_TYPE_WORD, ".docx"),
OFFICE_EXTENSION(DOC_TYPE_EXCEL, ".xlsx"),
OFFICE_EXTENSION(DOC_TYPE_POWERPOINT, ".pptx"),
};
static const MagicNumber kExtraMagicNumbers[] = {
MAGIC_NUMBER("image/x-xbitmap", "#define"),
MAGIC_NUMBER("image/x-icon", "\x00\x00\x01\x00"),
MAGIC_NUMBER("image/svg+xml", "<?xml_version="),
MAGIC_NUMBER("audio/wav", "RIFF....WAVEfmt "),
MAGIC_NUMBER("video/avi", "RIFF....AVI LIST"),
MAGIC_NUMBER("audio/ogg", "OggS\0"),
MAGIC_MASK("video/mpeg", "\x00\x00\x01\xB0", "\xFF\xFF\xFF\xF0"),
MAGIC_MASK("audio/mpeg", "\xFF\xE0", "\xFF\xE0"),
MAGIC_NUMBER("video/3gpp", "....ftyp3g"),
MAGIC_NUMBER("video/3gpp", "....ftypavcl"),
MAGIC_NUMBER("video/mp4", "....ftyp"),
MAGIC_NUMBER("video/quicktime", "....moov"),
MAGIC_NUMBER("application/x-shockwave-flash", "CWS"),
MAGIC_NUMBER("application/x-shockwave-flash", "FWS"),
MAGIC_NUMBER("video/x-flv", "FLV"),
MAGIC_NUMBER("audio/x-flac", "fLaC"),
// RAW image types.
MAGIC_NUMBER("image/x-canon-cr2", "II\x2a\x00\x10\x00\x00\x00CR"),
MAGIC_NUMBER("image/x-canon-crw", "II\x1a\x00\x00\x00HEAPCCDR"),
MAGIC_NUMBER("image/x-minolta-mrw", "\x00MRM"),
MAGIC_NUMBER("image/x-olympus-orf", "MMOR"), // big-endian
MAGIC_NUMBER("image/x-olympus-orf", "IIRO"), // little-endian
MAGIC_NUMBER("image/x-olympus-orf", "IIRS"), // little-endian
MAGIC_NUMBER("image/x-fuji-raf", "FUJIFILMCCD-RAW "),
MAGIC_NUMBER("image/x-panasonic-raw",
"IIU\x00\x08\x00\x00\x00"), // Panasonic .raw
MAGIC_NUMBER("image/x-panasonic-raw",
"IIU\x00\x18\x00\x00\x00"), // Panasonic .rw2
MAGIC_NUMBER("image/x-phaseone-raw", "MMMMRaw"),
MAGIC_NUMBER("image/x-x3f", "FOVb"),
};
// Our HTML sniffer differs slightly from Mozilla. For example, Mozilla will
// decide that a document that begins "<!DOCTYPE SOAP-ENV:Envelope PUBLIC " is
// HTML, but we will not.
#define MAGIC_HTML_TAG(tag) \
MAGIC_STRING("text/html", "<" tag)
static const MagicNumber kSniffableTags[] = {
// XML processing directive. Although this is not an HTML mime type, we sniff
// for this in the HTML phase because text/xml is just as powerful as HTML and
// we want to leverage our white space skipping technology.
MAGIC_NUMBER("text/xml", "<?xml"), // Mozilla
// DOCTYPEs
MAGIC_HTML_TAG("!DOCTYPE html"), // HTML5 spec
// Sniffable tags, ordered by how often they occur in sniffable documents.
MAGIC_HTML_TAG("script"), // HTML5 spec, Mozilla
MAGIC_HTML_TAG("html"), // HTML5 spec, Mozilla
MAGIC_HTML_TAG("!--"),
MAGIC_HTML_TAG("head"), // HTML5 spec, Mozilla
MAGIC_HTML_TAG("iframe"), // Mozilla
MAGIC_HTML_TAG("h1"), // Mozilla
MAGIC_HTML_TAG("div"), // Mozilla
MAGIC_HTML_TAG("font"), // Mozilla
MAGIC_HTML_TAG("table"), // Mozilla
MAGIC_HTML_TAG("a"), // Mozilla
MAGIC_HTML_TAG("style"), // Mozilla
MAGIC_HTML_TAG("title"), // Mozilla
MAGIC_HTML_TAG("b"), // Mozilla
MAGIC_HTML_TAG("body"), // Mozilla
MAGIC_HTML_TAG("br"),
MAGIC_HTML_TAG("p"), // Mozilla
};
// Compare content header to a magic number where magic_entry can contain '.'
// for single character of anything, allowing some bytes to be skipped.
static bool MagicCmp(const char* magic_entry, const char* content, size_t len) {
while (len) {
if ((*magic_entry != '.') && (*magic_entry != *content))
return false;
++magic_entry;
++content;
--len;
}
return true;
}
// Like MagicCmp() except that it ANDs each byte with a mask before
// the comparison, because there are some bits we don't care about.
static bool MagicMaskCmp(const char* magic_entry,
const char* content,
size_t len,
const char* mask) {
while (len) {
if ((*magic_entry != '.') && (*magic_entry != (*mask & *content)))
return false;
++magic_entry;
++content;
++mask;
--len;
}
return true;
}
static bool MatchMagicNumber(const char* content,
size_t size,
const MagicNumber& magic_entry,
std::string* result) {
const size_t len = magic_entry.magic_len;
// Keep kBytesRequiredForMagic honest.
DCHECK_LE(len, kBytesRequiredForMagic);
// To compare with magic strings, we need to compute strlen(content), but
// content might not actually have a null terminator. In that case, we
// pretend the length is content_size.
const char* end = static_cast<const char*>(memchr(content, '\0', size));
const size_t content_strlen =
(end != NULL) ? static_cast<size_t>(end - content) : size;
bool match = false;
if (magic_entry.is_string) {
if (content_strlen >= len) {
// Do a case-insensitive prefix comparison.
DCHECK_EQ(strlen(magic_entry.magic), len);
match = base::EqualsCaseInsensitiveASCII(magic_entry.magic,
base::StringPiece(content, len));
}
} else {
if (size >= len) {
if (!magic_entry.mask) {
match = MagicCmp(magic_entry.magic, content, len);
} else {
match = MagicMaskCmp(magic_entry.magic, content, len, magic_entry.mask);
}
}
}
if (match) {
result->assign(magic_entry.mime_type);
return true;
}
return false;
}
static bool CheckForMagicNumbers(const char* content,
size_t size,
base::span<const MagicNumber> magic_numbers,
std::string* result) {
for (const MagicNumber& magic : magic_numbers) {
if (MatchMagicNumber(content, size, magic, result))
return true;
}
return false;
}
// Truncates |size| to |max_size| and returns true if |size| is at least
// |max_size|.
static bool TruncateSize(const size_t max_size, size_t* size) {
// Keep kMaxBytesToSniff honest.
DCHECK_LE(static_cast<int>(max_size), kMaxBytesToSniff);
if (*size >= max_size) {
*size = max_size;
return true;
}
return false;
}
// Returns true and sets result if the content appears to be HTML.
// Clears have_enough_content if more data could possibly change the result.
static bool SniffForHTML(const char* content,
size_t size,
bool* have_enough_content,
std::string* result) {
// For HTML, we are willing to consider up to 512 bytes. This may be overly
// conservative as IE only considers 256.
*have_enough_content &= TruncateSize(512, &size);
// We adopt a strategy similar to that used by Mozilla to sniff HTML tags,
// but with some modifications to better match the HTML5 spec.
const char* const end = content + size;
const char* pos;
for (pos = content; pos < end; ++pos) {
if (!base::IsAsciiWhitespace(*pos))
break;
}
// |pos| now points to first non-whitespace character (or at end).
return CheckForMagicNumbers(pos, end - pos, kSniffableTags, result);
}
// Returns true and sets result if the content matches any of kMagicNumbers.
// Clears have_enough_content if more data could possibly change the result.
static bool SniffForMagicNumbers(const char* content,
size_t size,
bool* have_enough_content,
std::string* result) {
*have_enough_content &= TruncateSize(kBytesRequiredForMagic, &size);
// Check our big table of Magic Numbers
return CheckForMagicNumbers(content, size, kMagicNumbers, result);
}
// Returns true and sets result if the content matches any of
// kOfficeMagicNumbers, and the URL has the proper extension.
// Clears |have_enough_content| if more data could possibly change the result.
static bool SniffForOfficeDocs(const char* content,
size_t size,
const GURL& url,
bool* have_enough_content,
std::string* result) {
*have_enough_content &= TruncateSize(kBytesRequiredForOfficeMagic, &size);
// Check our table of magic numbers for Office file types.
std::string office_version;
if (!CheckForMagicNumbers(content, size, kOfficeMagicNumbers,
&office_version))
return false;
OfficeDocType type = DOC_TYPE_NONE;
base::StringPiece url_path = url.path_piece();
for (const auto& office_extension : kOfficeExtensionTypes) {
if (url_path.length() < office_extension.extension_len)
continue;
base::StringPiece extension =
url_path.substr(url_path.length() - office_extension.extension_len);
if (base::EqualsCaseInsensitiveASCII(
extension, base::StringPiece(office_extension.extension,
office_extension.extension_len))) {
type = office_extension.doc_type;
break;
}
}
if (type == DOC_TYPE_NONE)
return false;
if (office_version == "CFB") {
switch (type) {
case DOC_TYPE_WORD:
*result = "application/msword";
return true;
case DOC_TYPE_EXCEL:
*result = "application/vnd.ms-excel";
return true;
case DOC_TYPE_POWERPOINT:
*result = "application/vnd.ms-powerpoint";
return true;
case DOC_TYPE_NONE:
NOTREACHED();
return false;
}
} else if (office_version == "OOXML") {
switch (type) {
case DOC_TYPE_WORD:
*result = "application/vnd.openxmlformats-officedocument."
"wordprocessingml.document";
return true;
case DOC_TYPE_EXCEL:
*result = "application/vnd.openxmlformats-officedocument."
"spreadsheetml.sheet";
return true;
case DOC_TYPE_POWERPOINT:
*result = "application/vnd.openxmlformats-officedocument."
"presentationml.presentation";
return true;
case DOC_TYPE_NONE:
NOTREACHED();
return false;
}
}
NOTREACHED();
return false;
}
static bool IsOfficeType(const std::string& type_hint) {
return (type_hint == "application/msword" ||
type_hint == "application/vnd.ms-excel" ||
type_hint == "application/vnd.ms-powerpoint" ||
type_hint == "application/vnd.openxmlformats-officedocument."
"wordprocessingml.document" ||
type_hint == "application/vnd.openxmlformats-officedocument."
"spreadsheetml.sheet" ||
type_hint == "application/vnd.openxmlformats-officedocument."
"presentationml.presentation" ||
type_hint == "application/vnd.ms-excel.sheet.macroenabled.12" ||
type_hint == "application/vnd.ms-word.document.macroenabled.12" ||
type_hint == "application/vnd.ms-powerpoint.presentation."
"macroenabled.12" ||
type_hint == "application/mspowerpoint" ||
type_hint == "application/msexcel" ||
type_hint == "application/vnd.ms-word" ||
type_hint == "application/vnd.ms-word.document.12" ||
type_hint == "application/vnd.msword");
}
// This function checks for files that have a Microsoft Office MIME type
// set, but are not actually Office files.
//
// If this is not actually an Office file, |*result| is set to
// "application/octet-stream", otherwise it is not modified.
//
// Returns false if additional data is required to determine the file type, or
// true if there is enough data to make a decision.
static bool SniffForInvalidOfficeDocs(const char* content,
size_t size,
const GURL& url,
std::string* result) {
if (!TruncateSize(kBytesRequiredForOfficeMagic, &size))
return false;
// Check our table of magic numbers for Office file types. If it does not
// match one, the MIME type was invalid. Set it instead to a safe value.
std::string office_version;
if (!CheckForMagicNumbers(content, size, kOfficeMagicNumbers,
&office_version)) {
*result = "application/octet-stream";
}
// We have enough information to determine if this was a Microsoft Office
// document or not, so sniffing is completed.
return true;
}
// Byte order marks
static const MagicNumber kMagicXML[] = {
MAGIC_STRING("application/atom+xml", "<feed"),
MAGIC_STRING("application/rss+xml", "<rss"), // UTF-8
};
// Returns true and sets result if the content appears to contain XHTML or a
// feed.
// Clears have_enough_content if more data could possibly change the result.
//
// TODO(evanm): this is similar but more conservative than what Safari does,
// while HTML5 has a different recommendation -- what should we do?
// TODO(evanm): this is incorrect for documents whose encoding isn't a superset
// of ASCII -- do we care?
static bool SniffXML(const char* content,
size_t size,
bool* have_enough_content,
std::string* result) {
// We allow at most 300 bytes of content before we expect the opening tag.
*have_enough_content &= TruncateSize(300, &size);
const char* pos = content;
const char* const end = content + size;
// This loop iterates through tag-looking offsets in the file.
// We want to skip XML processing instructions (of the form "<?xml ...")
// and stop at the first "plain" tag, then make a decision on the mime-type
// based on the name (or possibly attributes) of that tag.
const int kMaxTagIterations = 5;
for (int i = 0; i < kMaxTagIterations && pos < end; ++i) {
pos = reinterpret_cast<const char*>(memchr(pos, '<', end - pos));
if (!pos)
return false;
static constexpr base::StringPiece kXmlPrefix("<?xml");
static constexpr base::StringPiece kDocTypePrefix("<!DOCTYPE");
base::StringPiece current(pos, end - pos);
if (base::EqualsCaseInsensitiveASCII(current.substr(0, kXmlPrefix.size()),
kXmlPrefix)) {
// Skip XML declarations.
++pos;
continue;
}
if (base::EqualsCaseInsensitiveASCII(
current.substr(0, kDocTypePrefix.size()), kDocTypePrefix)) {
// Skip DOCTYPE declarations.
++pos;
continue;
}
if (CheckForMagicNumbers(pos, end - pos, kMagicXML, result))
return true;
// TODO(evanm): handle RSS 1.0, which is an RDF format and more difficult
// to identify.
// If we get here, we've hit an initial tag that hasn't matched one of the
// above tests. Abort.
return true;
}
// We iterated too far without finding a start tag.
// If we have more content to look at, we aren't going to change our mind by
// seeing more bytes from the network.
return pos < end;
}
// Byte order marks
static const MagicNumber kByteOrderMark[] = {
MAGIC_NUMBER("text/plain", "\xFE\xFF"), // UTF-16BE
MAGIC_NUMBER("text/plain", "\xFF\xFE"), // UTF-16LE
MAGIC_NUMBER("text/plain", "\xEF\xBB\xBF"), // UTF-8
};
// Returns true and sets result to "application/octet-stream" if the content
// appears to be binary data. Otherwise, returns false and sets "text/plain".
// Clears have_enough_content if more data could possibly change the result.
static bool SniffBinary(const char* content,
size_t size,
bool* have_enough_content,
std::string* result) {
// There is no concensus about exactly how to sniff for binary content.
// * IE 7: Don't sniff for binary looking bytes, but trust the file extension.
// * Firefox 3.5: Sniff first 4096 bytes for a binary looking byte.
// Here, we side with FF, but with a smaller buffer. This size was chosen
// because it is small enough to comfortably fit into a single packet (after
// allowing for headers) and yet large enough to account for binary formats
// that have a significant amount of ASCII at the beginning (crbug.com/15314).
const bool is_truncated = TruncateSize(kMaxBytesToSniff, &size);
// First, we look for a BOM.
std::string unused;
if (CheckForMagicNumbers(content, size, kByteOrderMark, &unused)) {
// If there is BOM, we think the buffer is not binary.
result->assign("text/plain");
return false;
}
// Next we look to see if any of the bytes "look binary."
if (LooksLikeBinary(content, size)) {
result->assign("application/octet-stream");
return true;
}
// No evidence either way. Default to non-binary and, if truncated, clear
// have_enough_content because there could be a binary looking byte in the
// truncated data.
*have_enough_content &= is_truncated;
result->assign("text/plain");
return false;
}
static bool IsUnknownMimeType(const std::string& mime_type) {
// TODO(tc): Maybe reuse some code in net/http/http_response_headers.* here.
// If we do, please be careful not to alter the semantics at all.
static const char* const kUnknownMimeTypes[] = {
// Empty mime types are as unknown as they get.
"",
// The unknown/unknown type is popular and uninformative
"unknown/unknown",
// The second most popular unknown mime type is application/unknown
"application/unknown",
// Firefox rejects a mime type if it is exactly */*
"*/*",
};
for (const char* const unknown_mime_type : kUnknownMimeTypes) {
if (mime_type == unknown_mime_type)
return true;
}
if (mime_type.find('/') == std::string::npos) {
// Firefox rejects a mime type if it does not contain a slash
return true;
}
return false;
}
// Returns true and sets result if the content appears to be a crx (Chrome
// extension) file.
// Clears have_enough_content if more data could possibly change the result.
static bool SniffCRX(const char* content,
size_t size,
const GURL& url,
const std::string& type_hint,
bool* have_enough_content,
std::string* result) {
// Technically, the crx magic number is just Cr24, but the bytes after that
// are a version number which changes infrequently. Including it in the
// sniffing gives us less room for error. If the version number ever changes,
// we can just add an entry to this list.
static const struct MagicNumber kCRXMagicNumbers[] = {
MAGIC_NUMBER("application/x-chrome-extension", "Cr24\x02\x00\x00\x00"),
MAGIC_NUMBER("application/x-chrome-extension", "Cr24\x03\x00\x00\x00")};
// Only consider files that have the extension ".crx".
if (!base::EndsWith(url.path_piece(), ".crx", base::CompareCase::SENSITIVE))
return false;
*have_enough_content &= TruncateSize(kBytesRequiredForMagic, &size);
return CheckForMagicNumbers(content, size, kCRXMagicNumbers, result);
}
bool ShouldSniffMimeType(const GURL& url, const std::string& mime_type) {
bool sniffable_scheme = url.is_empty() ||
url.SchemeIsHTTPOrHTTPS() ||
url.SchemeIs("ftp") ||
#if defined(OS_ANDROID)
url.SchemeIs("content") ||
#endif
url.SchemeIsFile() ||
url.SchemeIsFileSystem();
if (!sniffable_scheme)
return false;
static const char* const kSniffableTypes[] = {
// Many web servers are misconfigured to send text/plain for many
// different types of content.
"text/plain",
// We want to sniff application/octet-stream for
// application/x-chrome-extension, but nothing else.
"application/octet-stream",
// XHTML and Atom/RSS feeds are often served as plain xml instead of
// their more specific mime types.
"text/xml",
"application/xml",
// Check for false Microsoft Office MIME types.
"application/msword",
"application/vnd.ms-excel",
"application/vnd.ms-powerpoint",
"application/vnd.openxmlformats-officedocument.wordprocessingml.document",
"application/vnd.openxmlformats-officedocument.spreadsheetml.sheet",
"application/vnd.openxmlformats-officedocument.presentationml.presentation",
"application/vnd.ms-excel.sheet.macroenabled.12",
"application/vnd.ms-word.document.macroenabled.12",
"application/vnd.ms-powerpoint.presentation.macroenabled.12",
"application/mspowerpoint",
"application/msexcel",
"application/vnd.ms-word",
"application/vnd.ms-word.document.12",
"application/vnd.msword",
};
for (const char* const sniffable_type : kSniffableTypes) {
if (mime_type == sniffable_type)
return true;
}
if (IsUnknownMimeType(mime_type)) {
// The web server didn't specify a content type or specified a mime
// type that we ignore.
return true;
}
return false;
}
bool SniffMimeType(const char* content,
size_t content_size,
const GURL& url,
const std::string& type_hint,
ForceSniffFileUrlsForHtml force_sniff_file_url_for_html,
std::string* result) {
DCHECK_LT(content_size, 1000000U); // sanity check
DCHECK(content);
DCHECK(result);
// By default, we assume we have enough content.
// Each sniff routine may unset this if it wasn't provided enough content.
bool have_enough_content = true;
// By default, we'll return the type hint.
// Each sniff routine may modify this if it has a better guess..
result->assign(type_hint);
// If the file has a Microsoft Office MIME type, we should only check that it
// is a valid Office file. Because this is the only reason we sniff files
// with a Microsoft Office MIME type, we can return early.
if (IsOfficeType(type_hint))
return SniffForInvalidOfficeDocs(content, content_size, url, result);
// Cache information about the type_hint
bool hint_is_unknown_mime_type = IsUnknownMimeType(type_hint);
// First check for HTML, unless it's a file URL and
// |allow_sniffing_files_urls_as_html| is false.
if (hint_is_unknown_mime_type &&
(!url.SchemeIsFile() ||
force_sniff_file_url_for_html == ForceSniffFileUrlsForHtml::kEnabled)) {
// We're only willing to sniff HTML if the server has not supplied a mime
// type, or if the type it did supply indicates that it doesn't know what
// the type should be.
if (SniffForHTML(content, content_size, &have_enough_content, result))
return true; // We succeeded in sniffing HTML. No more content needed.
}
// We're only willing to sniff for binary in 3 cases:
// 1. The server has not supplied a mime type.
// 2. The type it did supply indicates that it doesn't know what the type
// should be.
// 3. The type is "text/plain" which is the default on some web servers and
// could be indicative of a mis-configuration that we shield the user from.
const bool hint_is_text_plain = (type_hint == "text/plain");
if (hint_is_unknown_mime_type || hint_is_text_plain) {
if (!SniffBinary(content, content_size, &have_enough_content, result)) {
// If the server said the content was text/plain and it doesn't appear
// to be binary, then we trust it.
if (hint_is_text_plain) {
return have_enough_content;
}
}
}
// If we have plain XML, sniff XML subtypes.
if (type_hint == "text/xml" || type_hint == "application/xml") {
// We're not interested in sniffing these types for images and the like.
// Instead, we're looking explicitly for a feed. If we don't find one
// we're done and return early.
if (SniffXML(content, content_size, &have_enough_content, result))
return true;
return have_enough_content;
}
// CRX files (Chrome extensions) have a special sniffing algorithm. It is
// tighter than the others because we don't have to match legacy behavior.
if (SniffCRX(content, content_size, url, type_hint,
&have_enough_content, result))
return true;
// Check the file extension and magic numbers to see if this is an Office
// document. This needs to be checked before the general magic numbers
// because zip files and Office documents (OOXML) have the same magic number.
if (SniffForOfficeDocs(content, content_size, url,
&have_enough_content, result))
return true; // We've matched a magic number. No more content needed.
// We're not interested in sniffing for magic numbers when the type_hint
// is application/octet-stream. Time to bail out.
if (type_hint == "application/octet-stream")
return have_enough_content;
// Now we look in our large table of magic numbers to see if we can find
// anything that matches the content.
if (SniffForMagicNumbers(content, content_size,
&have_enough_content, result))
return true; // We've matched a magic number. No more content needed.
return have_enough_content;
}
bool SniffMimeTypeFromLocalData(const char* content,
size_t size,
std::string* result) {
// First check the extra table.
if (CheckForMagicNumbers(content, size, kExtraMagicNumbers, result))
return true;
// Finally check the original table.
return CheckForMagicNumbers(content, size, kMagicNumbers, result);
}
bool LooksLikeBinary(const char* content, size_t size) {
// The definition of "binary bytes" is from the spec at
// https://mimesniff.spec.whatwg.org/#binary-data-byte
//
// The bytes which are considered to be "binary" are all < 0x20. Encode them
// one bit per byte, with 1 for a "binary" bit, and 0 for a "text" bit. The
// least-significant bit represents byte 0x00, the most-significant bit
// represents byte 0x1F.
const uint32_t kBinaryBits =
~(1u << '\t' | 1u << '\n' | 1u << '\r' | 1u << '\f' | 1u << '\x1b');
for (size_t i = 0; i < size; ++i) {
uint8_t byte = static_cast<uint8_t>(content[i]);
if (byte < 0x20 && (kBinaryBits & (1u << byte)))
return true;
}
return false;
}
} // namespace net
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