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// Copyright 2016 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.
#include "components/link_header_util/link_header_util.h"
#include "base/strings/string_util.h"
#include "net/http/http_util.h"
namespace link_header_util {
namespace {
// A variation of base::StringTokenizer and net::HttpUtil::ValuesIterator.
// Takes the parsing of StringTokenizer and adds support for quoted strings that
// are quoted by matching <> (and does not support escaping in those strings).
// Also has the behavior of ValuesIterator where it strips whitespace from all
// values and only outputs non-empty values.
// Only supports ',' as separator and supports "" and <> as quote chars.
class ValueTokenizer {
ValueTokenizer(std::string::const_iterator begin,
std::string::const_iterator end)
: token_begin_(begin), token_end_(begin), end_(end) {}
std::string::const_iterator token_begin() const { return token_begin_; }
std::string::const_iterator token_end() const { return token_end_; }
bool GetNext() {
while (GetNextInternal()) {
net::HttpUtil::TrimLWS(&token_begin_, &token_end_);
// Only return non-empty values.
if (token_begin_ != token_end_)
return true;
return false;
// Updates token_begin_ and token_end_ to point to the (possibly empty) next
// token. Returns false if end-of-string was reached first.
bool GetNextInternal() {
// First time this is called token_end_ points to the first character in the
// input. Every other time token_end_ points to the delimiter at the end of
// the last returned token (which could be the end of the string).
// End of string, return false.
if (token_end_ == end_)
return false;
// Skip past the delimiter.
if (*token_end_ == ',')
// Make token_begin_ point to the beginning of the next token, and search
// for the end of the token in token_end_.
token_begin_ = token_end_;
// Set to true if we're currently inside a quoted string.
bool in_quote = false;
// Set to true if we're currently inside a quoted string, and have just
// encountered an escape character. In this case a closing quote will be
// ignored.
bool in_escape = false;
// If currently in a quoted string, this is the character that (when not
// escaped) indicates the end of the string.
char quote_close_char = '\0';
// If currently in a quoted string, this is set to true if it is possible to
// escape the closing quote using '\'.
bool quote_allows_escape = false;
while (token_end_ != end_) {
char c = *token_end_;
if (in_quote) {
if (in_escape) {
in_escape = false;
} else if (quote_allows_escape && c == '\\') {
in_escape = true;
} else if (c == quote_close_char) {
in_quote = false;
} else {
if (c == ',')
if (c == '"' || c == '<') {
in_quote = true;
quote_close_char = (c == '<' ? '>' : c);
quote_allows_escape = (c != '<');
return true;
std::string::const_iterator token_begin_;
std::string::const_iterator token_end_;
std::string::const_iterator end_;
// Parses the URL part of a Link header. When successful |url_begin| points
// to the beginning of the url, |url_end| points to the end of the url and
// |params_begin| points to the first character after the '>' character at the
// end of the url.
bool ExtractURL(std::string::const_iterator begin,
std::string::const_iterator end,
std::string::const_iterator* url_begin,
std::string::const_iterator* url_end,
std::string::const_iterator* params_begin) {
// Extract the URL part (everything between '<' and first '>' character).
if (*begin != '<')
return false;
*url_begin = begin;
*url_end = std::find(begin, end, '>');
// Fail if we did not find a '>'.
if (*url_end == end)
return false;
*params_begin = *url_end;
// Skip the '>' at the end of the URL.
// Trim whitespace from the URL.
net::HttpUtil::TrimLWS(url_begin, url_end);
return true;
} // namespace
std::vector<StringIteratorPair> SplitLinkHeader(const std::string& header) {
std::vector<StringIteratorPair> values;
ValueTokenizer tokenizer(header.begin(), header.end());
while (tokenizer.GetNext()) {
StringIteratorPair(tokenizer.token_begin(), tokenizer.token_end()));
return values;
// Parses one link in a link header into its url and parameters.
// A link is of the form "<some-url>; param1=value1; param2=value2".
// Returns false if parsing the link failed, returns true on success. This
// method is more lenient than the RFC. It doesn't fail on things like invalid
// characters in the URL, and also doesn't verify that certain parameters should
// or shouldn't be quoted strings.
// If a parameter occurs more than once in the link, only the first value is
// returned in params as this is the required behavior for all attributes chrome
// currently cares about in link headers.
bool ParseLinkHeaderValue(
std::string::const_iterator begin,
std::string::const_iterator end,
std::string* url,
std::unordered_map<std::string, base::Optional<std::string>>* params) {
// Can't parse an empty string.
if (begin == end)
return false;
// Extract the URL part (everything between '<' and first '>' character).
std::string::const_iterator url_begin;
std::string::const_iterator url_end;
if (!ExtractURL(begin, end, &url_begin, &url_end, &begin))
return false;
*url = std::string(url_begin, url_end);
// Trim any remaining whitespace, and make sure there is a ';' separating
// parameters from the URL.
net::HttpUtil::TrimLWS(&begin, &end);
if (begin != end && *begin != ';')
return false;
// Parse all the parameters.
net::HttpUtil::NameValuePairsIterator params_iterator(
begin, end, ';',
while (params_iterator.GetNext()) {
if (!net::HttpUtil::IsParmName(params_iterator.name_begin(),
return false;
std::string name = base::ToLowerASCII(base::StringPiece(
params_iterator.name_begin(), params_iterator.name_end()));
if (!params_iterator.value_is_quoted() &&
params_iterator.value_begin() == params_iterator.value_end())
params->insert(std::make_pair(name, base::nullopt));
params->insert(std::make_pair(name, params_iterator.value()));
return params_iterator.valid();
} // namespace link_header_util