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// Copyright 2012 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
// TODO( Remove this and spanify to fix the errors.
#pragma allow_unsafe_buffers
#include "net/base/mime_util.h"
#include <algorithm>
#include <iterator>
#include <map>
#include <string>
#include <string_view>
#include <unordered_set>
#include "base/base64.h"
#include "base/check_op.h"
#include "base/containers/span.h"
#include "base/lazy_instance.h"
#include "base/rand_util.h"
#include "base/strings/string_number_conversions.h"
#include "base/strings/string_split.h"
#include "base/strings/string_util.h"
#include "base/strings/utf_string_conversions.h"
#include "build/build_config.h"
#include "net/base/platform_mime_util.h"
#include "net/http/http_util.h"
using std::string;
namespace net {
// Singleton utility class for mime types.
class MimeUtil : public PlatformMimeUtil {
bool GetMimeTypeFromExtension(const base::FilePath::StringType& ext,
std::string* mime_type) const;
bool GetMimeTypeFromFile(const base::FilePath& file_path,
std::string* mime_type) const;
bool GetWellKnownMimeTypeFromExtension(const base::FilePath::StringType& ext,
std::string* mime_type) const;
bool GetPreferredExtensionForMimeType(
const std::string& mime_type,
base::FilePath::StringType* extension) const;
bool MatchesMimeType(const std::string& mime_type_pattern,
const std::string& mime_type) const;
bool ParseMimeTypeWithoutParameter(std::string_view type_string,
std::string* top_level_type,
std::string* subtype) const;
bool IsValidTopLevelMimeType(const std::string& type_string) const;
friend struct base::LazyInstanceTraitsBase<MimeUtil>;
bool GetMimeTypeFromExtensionHelper(const base::FilePath::StringType& ext,
bool include_platform_types,
std::string* mime_type) const;
}; // class MimeUtil
// This variable is Leaky because we need to access it from WorkerPool threads.
static base::LazyInstance<MimeUtil>::Leaky g_mime_util =
struct MimeInfo {
const char* const mime_type;
// Comma-separated list of possible extensions for the type. The first
// extension is considered preferred.
const char* const extensions;
// How to use the MIME maps
// ------------------------
// There are two hardcoded mappings from MIME types: kPrimaryMappings and
// kSecondaryMappings.
// kPrimaryMappings:
// Use this for mappings that are critical to the web platform. Mappings you
// add to this list take priority over the underlying platform when converting
// from file extension -> MIME type. Thus file extensions listed here will
// work consistently across platforms.
// kSecondaryMappings:
// Use this for mappings that must exist, but can be overridden by user
// preferences.
// The following applies to both lists:
// * The same extension can appear multiple times in the same list under
// different MIME types. Extensions that appear earlier take precedence over
// those that appear later.
// * A MIME type must not appear more than once in a single list. It is valid
// for the same MIME type to appear in kPrimaryMappings and
// kSecondaryMappings.
// The MIME maps are used for three types of lookups:
// 1) MIME type -> file extension. Implemented as
// GetPreferredExtensionForMimeType().
// Sources are consulted in the following order:
// a) As a special case application/octet-stream is mapped to nothing. Web
// sites are supposed to use this MIME type to indicate that the content
// is opaque and shouldn't be parsed as any specific type of content. It
// doesn't make sense to map this to anything.
// b) The underlying platform. If the operating system has a mapping from
// the MIME type to a file extension, then that takes priority. The
// platform is assumed to represent the user's preference.
// c) kPrimaryMappings. Order doesn't matter since there should only be at
// most one entry per MIME type.
// d) kSecondaryMappings. Again, order doesn't matter.
// 2) File extension -> MIME type. Implemented in GetMimeTypeFromExtension().
// Sources are considered in the following order:
// a) kPrimaryMappings. Order matters here since file extensions can appear
// multiple times on these lists. The first mapping in order of
// appearance in the list wins.
// b) Underlying platform.
// c) kSecondaryMappings. Again, the order matters.
// 3) File extension -> Well known MIME type. Implemented as
// GetWellKnownMimeTypeFromExtension().
// This is similar to 2), with the exception that b) is skipped. I.e. Only
// considers the hardcoded mappings in kPrimaryMappings and
// kSecondaryMappings.
// See comments above for details on how this list is used.
static const MimeInfo kPrimaryMappings[] = {
// Must precede audio/webm .
{"video/webm", "webm"},
// Must precede audio/mp3
{"audio/mpeg", "mp3"},
{"application/wasm", "wasm"},
{"application/x-chrome-extension", "crx"},
{"application/xhtml+xml", "xhtml,xht,xhtm"},
{"audio/flac", "flac"},
{"audio/mp3", "mp3"},
{"audio/ogg", "ogg,oga,opus"},
{"audio/wav", "wav"},
{"audio/webm", "webm"},
{"audio/x-m4a", "m4a"},
{"image/avif", "avif"},
{"image/gif", "gif"},
{"image/jpeg", "jpeg,jpg"},
{"image/png", "png"},
{"image/apng", "png,apng"},
{"image/svg+xml", "svg,svgz"},
{"image/webp", "webp"},
{"multipart/related", "mht,mhtml"},
{"text/css", "css"},
{"text/html", "html,htm,shtml,shtm"},
{"text/javascript", "js,mjs"},
{"text/xml", "xml"},
{"video/mp4", "mp4,m4v"},
{"video/ogg", "ogv,ogm"},
// This is a primary mapping (overrides the platform) rather than secondary
// to work around an issue when Excel is installed on Windows. Excel
// registers csv as application/ instead of text/csv from RFC
// 4180. See
{"text/csv", "csv"},
// See comments above for details on how this list is used.
static const MimeInfo kSecondaryMappings[] = {
// Must precede image/ .
{"image/x-icon", "ico"},
{"application/epub+zip", "epub"},
{"application/font-woff", "woff"},
{"application/gzip", "gz,tgz"},
{"application/javascript", "js"},
{"application/json", "json"}, // Per
{"application/msword", "doc,dot"},
{"application/octet-stream", "bin,exe,com"},
{"application/pdf", "pdf"},
{"application/pkcs7-mime", "p7m,p7c,p7z"},
{"application/pkcs7-signature", "p7s"},
{"application/postscript", "ps,eps,ai"},
{"application/rdf+xml", "rdf"},
{"application/rss+xml", "rss"},
{"application/rtf", "rtf"},
{"application/", "apk"},
{"application/vnd.mozilla.xul+xml", "xul"},
{"application/", "xls"},
{"application/", "ppt"},
{"application/x-gzip", "gz,tgz"},
{"application/x-mpegurl", "m3u8"},
{"application/x-shockwave-flash", "swf,swl"},
{"application/x-tar", "tar"},
{"application/x-x509-ca-cert", "cer,crt"},
{"application/zip", "zip"},
// This is the platform mapping on recent versions of Windows 10.
{"audio/webm", "weba"},
{"image/bmp", "bmp"},
{"image/jpeg", "jfif,pjpeg,pjp"},
{"image/tiff", "tiff,tif"},
{"image/", "ico"},
{"image/x-png", "png"},
{"image/x-xbitmap", "xbm"},
{"message/rfc822", "eml"},
{"text/calendar", "ics"},
{"text/html", "ehtml"},
{"text/plain", "txt,text"},
{"text/x-sh", "sh"},
{"text/xml", "xsl,xbl,xslt"},
{"video/mpeg", "mpeg,mpg"},
// Finds mime type of |ext| from |mappings|.
template <size_t num_mappings>
static const char* FindMimeType(const MimeInfo (&mappings)[num_mappings],
const std::string& ext) {
for (const auto& mapping : mappings) {
const char* extensions = mapping.extensions;
for (;;) {
size_t end_pos = strcspn(extensions, ",");
// The length check is required to prevent the std::string_view below from
// including uninitialized memory if ext is longer than extensions.
if (end_pos == ext.size() &&
std::string_view(extensions, ext.size()), ext)) {
return mapping.mime_type;
extensions += end_pos;
if (!*extensions)
extensions += 1; // skip over comma
return nullptr;
static base::FilePath::StringType StringToFilePathStringType(
std::string_view string_piece) {
return base::UTF8ToWide(string_piece);
return std::string(string_piece);
// Helper used in MimeUtil::GetPreferredExtensionForMimeType() to search
// preferred extension in MimeInfo arrays.
template <size_t num_mappings>
static bool FindPreferredExtension(const MimeInfo (&mappings)[num_mappings],
const std::string& mime_type,
base::FilePath::StringType* result) {
// There is no preferred extension for "application/octet-stream".
if (mime_type == "application/octet-stream")
return false;
for (const auto& mapping : mappings) {
if (mapping.mime_type == mime_type) {
const char* extensions = mapping.extensions;
const char* extension_end = strchr(extensions, ',');
size_t len =
extension_end ? extension_end - extensions : strlen(extensions);
*result = StringToFilePathStringType(std::string_view(extensions, len));
return true;
return false;
bool MimeUtil::GetMimeTypeFromExtension(const base::FilePath::StringType& ext,
string* result) const {
return GetMimeTypeFromExtensionHelper(ext, true, result);
bool MimeUtil::GetWellKnownMimeTypeFromExtension(
const base::FilePath::StringType& ext,
string* result) const {
return GetMimeTypeFromExtensionHelper(ext, false, result);
bool MimeUtil::GetPreferredExtensionForMimeType(
const std::string& mime_type,
base::FilePath::StringType* extension) const {
// Search the MIME type in the platform DB first, then in kPrimaryMappings and
// kSecondaryMappings.
return GetPlatformPreferredExtensionForMimeType(mime_type, extension) ||
FindPreferredExtension(kPrimaryMappings, mime_type, extension) ||
FindPreferredExtension(kSecondaryMappings, mime_type, extension);
bool MimeUtil::GetMimeTypeFromFile(const base::FilePath& file_path,
string* result) const {
base::FilePath::StringType file_name_str = file_path.Extension();
if (file_name_str.empty())
return false;
return GetMimeTypeFromExtension(file_name_str.substr(1), result);
bool MimeUtil::GetMimeTypeFromExtensionHelper(
const base::FilePath::StringType& ext,
bool include_platform_types,
string* result) const {
DCHECK(ext.empty() || ext[0] != '.')
<< "extension passed in must not include leading dot";
// Avoids crash when unable to handle a long file path. See
const unsigned kMaxFilePathSize = 65536;
if (ext.length() > kMaxFilePathSize)
return false;
// Reject a string which contains null character.
base::FilePath::StringType::size_type nul_pos =
if (nul_pos != base::FilePath::StringType::npos)
return false;
// We implement the same algorithm as Mozilla for mapping a file extension to
// a mime type. That is, we first check a hard-coded list (that cannot be
// overridden), and then if not found there, we defer to the system registry.
// Finally, we scan a secondary hard-coded list to catch types that we can
// deduce but that we also want to allow the OS to override.
base::FilePath path_ext(ext);
const string ext_narrow_str = path_ext.AsUTF8Unsafe();
const char* mime_type = FindMimeType(kPrimaryMappings, ext_narrow_str);
if (mime_type) {
*result = mime_type;
return true;
if (include_platform_types && GetPlatformMimeTypeFromExtension(ext, result))
return true;
mime_type = FindMimeType(kSecondaryMappings, ext_narrow_str);
if (mime_type) {
*result = mime_type;
return true;
return false;
MimeUtil::MimeUtil() = default;
// Tests for MIME parameter equality. Each parameter in the |mime_type_pattern|
// must be matched by a parameter in the |mime_type|. If there are no
// parameters in the pattern, the match is a success.
// According rfc2045 keys of parameters are case-insensitive, while values may
// or may not be case-sensitive, but they are usually case-sensitive. So, this
// function matches values in *case-sensitive* manner, however note that this
// may produce some false negatives.
bool MatchesMimeTypeParameters(const std::string& mime_type_pattern,
const std::string& mime_type) {
typedef std::map<std::string, std::string> StringPairMap;
const std::string::size_type semicolon = mime_type_pattern.find(';');
const std::string::size_type test_semicolon = mime_type.find(';');
if (semicolon != std::string::npos) {
if (test_semicolon == std::string::npos)
return false;
base::StringPairs pattern_parameters;
base::SplitStringIntoKeyValuePairs(mime_type_pattern.substr(semicolon + 1),
'=', ';', &pattern_parameters);
base::StringPairs test_parameters;
base::SplitStringIntoKeyValuePairs(mime_type.substr(test_semicolon + 1),
'=', ';', &test_parameters);
// Put the parameters to maps with the keys converted to lower case.
StringPairMap pattern_parameter_map;
for (const auto& pair : pattern_parameters) {
pattern_parameter_map[base::ToLowerASCII(pair.first)] = pair.second;
StringPairMap test_parameter_map;
for (const auto& pair : test_parameters) {
test_parameter_map[base::ToLowerASCII(pair.first)] = pair.second;
if (pattern_parameter_map.size() > test_parameter_map.size())
return false;
for (const auto& parameter_pair : pattern_parameter_map) {
const auto& test_parameter_pair_it =
if (test_parameter_pair_it == test_parameter_map.end())
return false;
if (parameter_pair.second != test_parameter_pair_it->second)
return false;
return true;
// This comparison handles absolute maching and also basic
// wildcards. The plugin mime types could be:
// application/x-foo
// application/*
// application/*+xml
// *
// Also tests mime parameters -- all parameters in the pattern must be present
// in the tested type for a match to succeed.
bool MimeUtil::MatchesMimeType(const std::string& mime_type_pattern,
const std::string& mime_type) const {
if (mime_type_pattern.empty())
return false;
std::string::size_type semicolon = mime_type_pattern.find(';');
const std::string base_pattern(mime_type_pattern.substr(0, semicolon));
semicolon = mime_type.find(';');
const std::string base_type(mime_type.substr(0, semicolon));
if (base_pattern == "*" || base_pattern == "*/*")
return MatchesMimeTypeParameters(mime_type_pattern, mime_type);
const std::string::size_type star = base_pattern.find('*');
if (star == std::string::npos) {
if (base::EqualsCaseInsensitiveASCII(base_pattern, base_type))
return MatchesMimeTypeParameters(mime_type_pattern, mime_type);
return false;
// Test length to prevent overlap between |left| and |right|.
if (base_type.length() < base_pattern.length() - 1)
return false;
std::string_view base_pattern_piece(base_pattern);
std::string_view left(base_pattern_piece.substr(0, star));
std::string_view right(base_pattern_piece.substr(star + 1));
if (!base::StartsWith(base_type, left, base::CompareCase::INSENSITIVE_ASCII))
return false;
if (!right.empty() &&
!base::EndsWith(base_type, right, base::CompareCase::INSENSITIVE_ASCII))
return false;
return MatchesMimeTypeParameters(mime_type_pattern, mime_type);
bool ParseMimeType(const std::string& type_str,
std::string* mime_type,
base::StringPairs* params) {
// Trim leading and trailing whitespace from type. We include '(' in
// the trailing trim set to catch media-type comments, which are not at all
// standard, but may occur in rare cases.
size_t type_val = type_str.find_first_not_of(HTTP_LWS);
type_val = std::min(type_val, type_str.length());
size_t type_end = type_str.find_first_of(HTTP_LWS ";(", type_val);
if (type_end == std::string::npos)
type_end = type_str.length();
// Reject a mime-type if it does not include a slash.
size_t slash_pos = type_str.find_first_of('/');
if (slash_pos == std::string::npos || slash_pos > type_end)
return false;
if (mime_type)
*mime_type = type_str.substr(type_val, type_end - type_val);
// Iterate over parameters. Can't split the string around semicolons
// preemptively because quoted strings may include semicolons. Mostly matches
// logic in Main differences: Does not
// validate characters are HTTP token code points / HTTP quoted-string token
// code points, and ignores spaces after "=" in parameters.
if (params)
std::string::size_type offset = type_str.find_first_of(';', type_end);
while (offset < type_str.size()) {
DCHECK_EQ(';', type_str[offset]);
// Trim off the semicolon.
// Trim off any following spaces.
offset = type_str.find_first_not_of(HTTP_LWS, offset);
std::string::size_type param_name_start = offset;
// Extend parameter name until run into a semicolon or equals sign. Per
// spec, trailing spaces are not removed.
offset = type_str.find_first_of(";=", offset);
// Nothing more to do if at end of string, or if there's no parameter
// value, since names without values aren't allowed.
if (offset == std::string::npos || type_str[offset] == ';')
auto param_name = base::MakeStringPiece(type_str.begin() + param_name_start,
type_str.begin() + offset);
// Now parse the value.
DCHECK_EQ('=', type_str[offset]);
// Trim off the '='.
// Remove leading spaces. This violates the spec, though it matches
// pre-existing behavior.
// TODO(mmenke): Consider doing this (only?) after parsing quotes, which
// seems to align more with the spec - not the content-type spec, but the
// GET spec's way of getting an encoding, and the spec for handling
// boundary values as well.
// See
offset = type_str.find_first_not_of(HTTP_LWS, offset);
std::string param_value;
if (offset == std::string::npos || type_str[offset] == ';') {
// Nothing to do here - an unquoted string of only whitespace should be
// skipped.
} else if (type_str[offset] != '"') {
// If the first character is not a quotation mark, copy data directly.
std::string::size_type value_start = offset;
offset = type_str.find_first_of(';', offset);
std::string::size_type value_end = offset;
// Remove terminal whitespace. If ran off the end of the string, have to
// update |value_end| first.
if (value_end == std::string::npos)
value_end = type_str.size();
while (value_end > value_start &&
HttpUtil::IsLWS(type_str[value_end - 1])) {
param_value = type_str.substr(value_start, value_end - value_start);
} else {
// Otherwise, append data, with special handling for backslashes, until
// a close quote. Do not trim whitespace for quoted-string.
// Skip open quote.
DCHECK_EQ('"', type_str[offset]);
while (offset < type_str.size() && type_str[offset] != '"') {
// Skip over backslash and append the next character, when not at
// the end of the string. Otherwise, copy the next character (Which may
// be a backslash).
if (type_str[offset] == '\\' && offset + 1 < type_str.size()) {
param_value += type_str[offset];
offset = type_str.find_first_of(';', offset);
if (params)
params->emplace_back(param_name, param_value);
return true;
bool MimeUtil::ParseMimeTypeWithoutParameter(std::string_view type_string,
std::string* top_level_type,
std::string* subtype) const {
std::vector<std::string_view> components = base::SplitStringPiece(
type_string, "/", base::KEEP_WHITESPACE, base::SPLIT_WANT_ALL);
if (components.size() != 2)
return false;
components[0] = TrimWhitespaceASCII(components[0], base::TRIM_LEADING);
components[1] = TrimWhitespaceASCII(components[1], base::TRIM_TRAILING);
if (!HttpUtil::IsToken(components[0]) || !HttpUtil::IsToken(components[1]))
return false;
if (top_level_type)
if (subtype)
return true;
// See
static const char* const kLegalTopLevelTypes[] = {
"application", "audio", "example", "font", "image",
"message", "model", "multipart", "text", "video",
bool MimeUtil::IsValidTopLevelMimeType(const std::string& type_string) const {
std::string lower_type = base::ToLowerASCII(type_string);
for (const char* const legal_type : kLegalTopLevelTypes) {
if ( == 0)
return true;
return type_string.size() > 2 &&
base::StartsWith(type_string, "x-",
// Wrappers for the singleton
bool GetMimeTypeFromExtension(const base::FilePath::StringType& ext,
std::string* mime_type) {
return g_mime_util.Get().GetMimeTypeFromExtension(ext, mime_type);
bool GetMimeTypeFromFile(const base::FilePath& file_path,
std::string* mime_type) {
return g_mime_util.Get().GetMimeTypeFromFile(file_path, mime_type);
bool GetWellKnownMimeTypeFromExtension(const base::FilePath::StringType& ext,
std::string* mime_type) {
return g_mime_util.Get().GetWellKnownMimeTypeFromExtension(ext, mime_type);
bool GetPreferredExtensionForMimeType(const std::string& mime_type,
base::FilePath::StringType* extension) {
return g_mime_util.Get().GetPreferredExtensionForMimeType(mime_type,
bool MatchesMimeType(const std::string& mime_type_pattern,
const std::string& mime_type) {
return g_mime_util.Get().MatchesMimeType(mime_type_pattern, mime_type);
bool ParseMimeTypeWithoutParameter(std::string_view type_string,
std::string* top_level_type,
std::string* subtype) {
return g_mime_util.Get().ParseMimeTypeWithoutParameter(
type_string, top_level_type, subtype);
bool IsValidTopLevelMimeType(const std::string& type_string) {
return g_mime_util.Get().IsValidTopLevelMimeType(type_string);
namespace {
// From and
static const char* const kStandardImageTypes[] = {"image/avif",
static const char* const kStandardAudioTypes[] = {
static const char* const kStandardFontTypes[] = {
"font/collection", "font/otf", "font/sfnt",
"font/ttf", "font/woff", "font/woff2",
static const char* const kStandardVideoTypes[] = {
struct StandardType {
const char* const leading_mime_type;
base::span<const char* const> standard_types;
static const StandardType kStandardTypes[] = {{"image/", kStandardImageTypes},
{"audio/", kStandardAudioTypes},
{"font/", kStandardFontTypes},
{"video/", kStandardVideoTypes},
{nullptr, {}}};
// GetExtensionsFromHardCodedMappings() adds file extensions (without a leading
// dot) to the set |extensions|, for all MIME types matching |mime_type|.
// The meaning of |mime_type| depends on the value of |prefix_match|:
// * If |prefix_match = false| then |mime_type| is an exact (case-insensitive)
// string such as "text/plain".
// * If |prefix_match = true| then |mime_type| is treated as the prefix for a
// (case-insensitive) string. For instance "Text/" would match "text/plain".
void GetExtensionsFromHardCodedMappings(
base::span<const MimeInfo> mappings,
const std::string& mime_type,
bool prefix_match,
std::unordered_set<base::FilePath::StringType>* extensions) {
for (const auto& mapping : mappings) {
std::string_view cur_mime_type(mapping.mime_type);
if (base::StartsWith(cur_mime_type, mime_type,
base::CompareCase::INSENSITIVE_ASCII) &&
(prefix_match || (cur_mime_type.length() == mime_type.length()))) {
for (std::string_view this_extension : base::SplitStringPiece(
mapping.extensions, ",", base::TRIM_WHITESPACE,
base::SPLIT_WANT_ALL)) {
void GetExtensionsHelper(
base::span<const char* const> standard_types,
const std::string& leading_mime_type,
std::unordered_set<base::FilePath::StringType>* extensions) {
for (auto* standard_type : standard_types) {
// Also look up the extensions from hard-coded mappings in case that some
// supported extensions are not registered in the system registry, like ogg.
GetExtensionsFromHardCodedMappings(kPrimaryMappings, leading_mime_type, true,
GetExtensionsFromHardCodedMappings(kSecondaryMappings, leading_mime_type,
true, extensions);
// Note that the elements in the source set will be appended to the target
// vector.
template <class T>
void UnorderedSetToVector(std::unordered_set<T>* source,
std::vector<T>* target) {
size_t old_target_size = target->size();
target->resize(old_target_size + source->size());
size_t i = 0;
for (auto iter = source->begin(); iter != source->end(); ++iter, ++i)
(*target)[old_target_size + i] = *iter;
// Characters to be used for mime multipart boundary.
// TODO(rsleevi): Follow the spec or fix the spec.
// The RFC 2046 spec says the alphanumeric characters plus the
// following characters are legal for boundaries: '()+_,-./:=?
// However the following characters, though legal, cause some sites
// to fail: (),./:=+
constexpr std::string_view kMimeBoundaryCharacters(
// Size of mime multipart boundary.
const size_t kMimeBoundarySize = 69;
} // namespace
void GetExtensionsForMimeType(
const std::string& unsafe_mime_type,
std::vector<base::FilePath::StringType>* extensions) {
if (unsafe_mime_type == "*/*" || unsafe_mime_type == "*")
const std::string mime_type = base::ToLowerASCII(unsafe_mime_type);
std::unordered_set<base::FilePath::StringType> unique_extensions;
if (base::EndsWith(mime_type, "/*", base::CompareCase::INSENSITIVE_ASCII)) {
std::string leading_mime_type = mime_type.substr(0, mime_type.length() - 1);
// Find the matching StandardType from within kStandardTypes, or fall
// through to the last (default) StandardType.
const StandardType* type = nullptr;
for (const StandardType& standard_type : kStandardTypes) {
type = &standard_type;
if (type->leading_mime_type &&
leading_mime_type == type->leading_mime_type) {
} else {
// Also look up the extensions from hard-coded mappings in case that some
// supported extensions are not registered in the system registry, like ogg.
GetExtensionsFromHardCodedMappings(kPrimaryMappings, mime_type, false,
GetExtensionsFromHardCodedMappings(kSecondaryMappings, mime_type, false,
UnorderedSetToVector(&unique_extensions, extensions);
NET_EXPORT std::string GenerateMimeMultipartBoundary() {
// Based on RFC 1341, section "7.2.1 Multipart: The common syntax":
// Because encapsulation boundaries must not appear in the body parts being
// encapsulated, a user agent must exercise care to choose a unique
// boundary. The boundary in the example above could have been the result of
// an algorithm designed to produce boundaries with a very low probability
// of already existing in the data to be encapsulated without having to
// prescan the data.
// [...]
// the boundary parameter [...] consists of 1 to 70 characters from a set of
// characters known to be very robust through email gateways, and NOT ending
// with white space.
// [...]
// boundary := 0*69<bchars> bcharsnospace
// bchars := bcharsnospace / " "
// bcharsnospace := DIGIT / ALPHA / "'" / "(" / ")" / "+" /
// "_" / "," / "-" / "." / "/" / ":" / "=" / "?"
std::string result;
while (result.size() < (kMimeBoundarySize - 4)) {
char c = kMimeBoundaryCharacters[base::RandInt(
0, kMimeBoundaryCharacters.size() - 1)];
// Not a strict requirement - documentation only.
DCHECK_EQ(kMimeBoundarySize, result.size());
return result;
void AddMultipartValueForUpload(const std::string& value_name,
const std::string& value,
const std::string& mime_boundary,
const std::string& content_type,
std::string* post_data) {
// First line is the boundary.
post_data->append("--" + mime_boundary + "\r\n");
// Next line is the Content-disposition.
post_data->append("Content-Disposition: form-data; name=\"" +
value_name + "\"\r\n");
if (!content_type.empty()) {
// If Content-type is specified, the next line is that.
post_data->append("Content-Type: " + content_type + "\r\n");
// Leave an empty line and append the value.
post_data->append("\r\n" + value + "\r\n");
void AddMultipartValueForUploadWithFileName(const std::string& value_name,
const std::string& file_name,
const std::string& value,
const std::string& mime_boundary,
const std::string& content_type,
std::string* post_data) {
// First line is the boundary.
post_data->append("--" + mime_boundary + "\r\n");
// Next line is the Content-disposition.
post_data->append("Content-Disposition: form-data; name=\"" + value_name +
"\"; filename=\"" + file_name + "\"\r\n");
if (!content_type.empty()) {
// If Content-type is specified, the next line is that.
post_data->append("Content-Type: " + content_type + "\r\n");
// Leave an empty line and append the value.
post_data->append("\r\n" + value + "\r\n");
void AddMultipartFinalDelimiterForUpload(const std::string& mime_boundary,
std::string* post_data) {
post_data->append("--" + mime_boundary + "--\r\n");
// TODO(toyoshim): We may prefer to implement a strict RFC2616 media-type
// ( parser.
std::optional<std::string> ExtractMimeTypeFromMediaType(
const std::string& type_string,
bool accept_comma_separated) {
std::string::size_type end = type_string.find(';');
if (accept_comma_separated) {
end = std::min(end, type_string.find(','));
std::string top_level_type;
std::string subtype;
if (ParseMimeTypeWithoutParameter(type_string.substr(0, end), &top_level_type,
&subtype)) {
return top_level_type + "/" + subtype;
return std::nullopt;
} // namespace net