// 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.

#include "net/http/http_vary_data.h"

#include <stdlib.h>

#include "base/pickle.h"
#include "base/strings/string_util.h"
#include "net/http/http_request_headers.h"
#include "net/http/http_request_info.h"
#include "net/http/http_response_headers.h"
#include "net/http/http_util.h"

namespace net {

HttpVaryData::HttpVaryData() : is_valid_(false) {
}

bool HttpVaryData::Init(const HttpRequestInfo& request_info,
                        const HttpResponseHeaders& response_headers) {
  base::MD5Context ctx;
  base::MD5Init(&ctx);

  is_valid_ = false;
  bool processed_header = false;

  // Feed the MD5 context in the order of the Vary header enumeration.  If the
  // Vary header repeats a header name, then that's OK.
  //
  // If the Vary header contains '*' then we should not construct any vary data
  // since it is all usurped by a '*'.  See section 13.6 of RFC 2616.
  //
  void* iter = NULL;
  std::string name = "vary", request_header;
  while (response_headers.EnumerateHeader(&iter, name, &request_header)) {
    if (request_header == "*")
      return false;
    AddField(request_info, request_header, &ctx);
    processed_header = true;
  }

  // Add an implicit 'Vary: cookie' header to any redirect to avoid redirect
  // loops which may result from redirects that are incorrectly marked as
  // cachable by the server.  Unfortunately, other browsers do not cache
  // redirects that result from requests containing a cookie header.  We are
  // treading on untested waters here, so we want to be extra careful to make
  // sure we do not end up with a redirect loop served from cache.
  //
  // If there is an explicit 'Vary: cookie' header, then we will just end up
  // digesting the cookie header twice.  Not a problem.
  //
  std::string location;
  if (response_headers.IsRedirect(&location)) {
    AddField(request_info, "cookie", &ctx);
    processed_header = true;
  }

  if (!processed_header)
    return false;

  base::MD5Final(&request_digest_, &ctx);
  return is_valid_ = true;
}

bool HttpVaryData::InitFromPickle(PickleIterator* iter) {
  is_valid_ = false;
  const char* data;
  if (iter->ReadBytes(&data, sizeof(request_digest_))) {
    memcpy(&request_digest_, data, sizeof(request_digest_));
    return is_valid_ = true;
  }
  return false;
}

void HttpVaryData::Persist(Pickle* pickle) const {
  DCHECK(is_valid());
  pickle->WriteBytes(&request_digest_, sizeof(request_digest_));
}

bool HttpVaryData::MatchesRequest(
    const HttpRequestInfo& request_info,
    const HttpResponseHeaders& cached_response_headers) const {
  HttpVaryData new_vary_data;
  if (!new_vary_data.Init(request_info, cached_response_headers)) {
    // This shouldn't happen provided the same response headers passed here
    // were also used when initializing |this|.
    NOTREACHED();
    return false;
  }
  return memcmp(&new_vary_data.request_digest_, &request_digest_,
                sizeof(request_digest_)) == 0;
}

// static
std::string HttpVaryData::GetRequestValue(
    const HttpRequestInfo& request_info,
    const std::string& request_header) {
  // Unfortunately, we do not have access to all of the request headers at this
  // point.  Most notably, we do not have access to an Authorization header if
  // one will be added to the request.

  std::string result;
  if (request_info.extra_headers.GetHeader(request_header, &result))
    return result;

  return std::string();
}

// static
void HttpVaryData::AddField(const HttpRequestInfo& request_info,
                            const std::string& request_header,
                            base::MD5Context* ctx) {
  std::string request_value = GetRequestValue(request_info, request_header);

  // Append a character that cannot appear in the request header line so that we
  // protect against case where the concatenation of two request headers could
  // look the same for a variety of values for the individual request headers.
  // For example, "foo: 12\nbar: 3" looks like "foo: 1\nbar: 23" otherwise.
  request_value.append(1, '\n');

  base::MD5Update(ctx, request_value);
}

}  // namespace net