Share link header parsing code between blink and content.

components/link_header_util/link_header_util.cc

+// 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 {
+ public:
+  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;
+  }
+
+ private:
+  // 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_ == ',')
+      ++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 == ',')
+          break;
+        if (c == '\'' || c == '"' || c == '<') {
+          in_quote = true;
+          quote_close_char = (c == '<' ? '>' : c);
+          quote_allows_escape = (c != '<');
+        }
+      }
+      ++token_end_;
+    }
+    return true;
+  }
+
+  std::string::const_iterator token_begin_;
+  std::string::const_iterator token_end_;
+  std::string::const_iterator end_;
+};
+
+// TODO(mek): Figure out if it makes sense to move this function to
+// net::HttpUtil, as it implements the "parmname" rule from
+// https://tools.ietf.org/html/rfc5987#section-3.2.1
+bool IsParameterName(std::string::const_iterator begin,
+                     std::string::const_iterator end) {
+  if (!net::HttpUtil::IsToken(begin, end))
+    return false;
+  for (auto it = begin; it != end; ++it) {
+    if (*it == '*' || *it == '\'' || *it == '%')
+      return false;
+  }
+  return true;
+}
+
+// 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;
+
+  ++begin;
+  *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.
+  ++*params_begin;
+
+  // 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()) {
+    values.push_back(
+        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, ';', net::HttpUtil::NameValuePairsIterator::VALUES_OPTIONAL,
+      net::HttpUtil::NameValuePairsIterator::STRICT_QUOTES);
+  while (params_iterator.GetNext()) {
+    if (!IsParameterName(params_iterator.name_begin(),
+                         params_iterator.name_end()))
+      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_t(0)));

[dcheng, 2016/04/20 04:41:06]

Just write base::nullopt here.

[Marijn Kruisselbrink, 2016/04/20 21:07:48]

Done. I initially wrote this against an older version of the base::optional
patch where base::nullopt didn't compile. But now that works of course.

+    else
+      params->insert(std::make_pair(name, params_iterator.value()));
+  }
+  return params_iterator.valid();
+}
+
+}  // namespace link_header_util